The Potential of the Vistula–Bug Interfluve Resources in the Context of the Sustainable Management of Non-Renewable Phosphorus Resources in Poland

Abstract

Phosphorus is one of the elements necessary for life and the proper growth of organisms, including humans, yet its natural resources are very limited. The bioavailability of phosphorus is especially critical during the initial phases of plant growth. A deficiency at this stage cannot be fully compensated for later, even despite increased phosphorous supplementation. Global reserves of phosphate rocks, the main source of phosphorus used in fertilizer production, are gradually being depleted. This situation prompts the need to search for alternative sources and to pay closer attention to the sustainable management of available resources. In this article, we focus on the Vistula–Bug interfluve in southeastern Poland, where relatively high phosphate concentrations have been documented. Our goal is to present geochemical and mineralogical data from bedrock in the areas richest in phosphorus and to discuss their significance in the context of domestic phosphorous management, with particular reference to southeastern Poland. We also discuss phosphate fertilizer production in Poland and its use in agriculture as well as phosphorus content in groundwater and surface water in the study area, with emphasis on the most readily assimilable forms, orthophosphates. Finally, we address the challenges of sustainable phosphorous management at both the local and global scale.

1. Introduction

Phosphorus (P) is an essential element for living organisms, agriculture and food security, and ecosystem functioning. As a structural component of RNA, DNA, ATP, and other vital biomolecules, it plays a crucial role in numerous biochemical processes that sustain life. The availability of P often limits primary production, i.e., the fixation of inorganic carbon into biomass by photosynthetic organisms [1], which forms the basis of terrestrial and aquatic food webs [2]. In agriculture and food security, P is frequently a limiting nutrient in many soils [3], and crop growth is restricted without its supplementation. As a consequence, P-rich fertilizers are critical for maintaining high yields [4]. However, imbalances in P availability affect ecosystems: deficiencies reduce soil fertility, while excess P inputs to water bodies drive eutrophication, one of the major environmental problems of recent decades [5].

Therefore, a comprehensive understanding of P sources, cycling in soil and aquatic systems, and interactions among geochemical and ecological processes is vital. Progress requires close cooperation between scientists and industry to improve phosphorus fertilization efficiency, identify alternative sources of phosphorus, and reduce anthropogenic phosphorus inputs into waters. The sustainable management of P natural resources will safeguard finite phosphate rock deposits and freshwater supplies for future generations.

The main sources of P range from natural to human-related. Among natural sources are mineral deposits (phosphate rocks), soil minerals, and organic matter, while fertilizers, animal manure and compost, detergent, and wastewaters constitute anthropogenic sources. The Earth’s crust contains approximately 1200 mg P kg⁻¹ of P, making it the 11th most abundant element [6]. Smaller amounts are also found in ocean reservoirs at about 88 ppb [6]. However, despite its relative abundance, not all forms of phosphorus are readily available for biological uptake.

The majority of naturally occurring P exists as phosphate, either as inorganic phosphates, such as phosphate minerals, or as organic phosphate esters (over 99%, [7]). In most mineral and organic compounds, P occurs in the +5 oxidation state, mainly as orthophosphate (PO₄³⁻). According to Fillipelli (2008) [8], the bioreactivity of P varies with its chemical form, increasing in the order of mineral, occluded, and organic phosphorus. Phosphate has a strong tendency to bind with positively charged cations or surfaces, which significantly limits its mobility in soils and aquatic systems. In soils, phosphorus commonly precipitates with calcium and magnesium under alkaline conditions or with iron and aluminum under acidic conditions [6,7,9,10]. Among these precipitated forms, calcium-bound phosphorus is generally more available for crop uptake [6,7]. For plants to absorb phosphorus, it should be present in solution as phosphate ions. The dominant form depends on soil pH: H₂PO₄⁻ is more prevalent under acidic environments, whereas HPO₄²⁻ is common in alkaline conditions [8].

Phosphate minerals occur as accessory components in many rocks of both acidic and alkaline character. Among them, apatites, highly insoluble Ca-phosphates, are the most common phosphate minerals in the lithosphere. The primary varieties are hydroxyapatite (Ca₅(PO₄)₃OH), fluorapatite (Ca₅(PO₄)₃F), and chlorapatite (Ca₅(PO₄)₃Cl) [11]. Although these formulas suggest a simple chemical composition, apatites are usually much more complex due to isomorphic substitutions involving Ca²⁺, Al³⁺, Fe²⁺, and Fe³⁺ as well as trace-element inclusions [12,13,14,15].

Phosphate rocks are primary natural reservoirs of mineral (inorganic) P. In Poland, they occur relatively frequently, scattered within sedimentary clastic and carbonate rocks of various ages, ranging from the Cambrian to the Eocene [16]. The two most important Polish phosphorite formations are (1) the Albian deposits located along the northern edge of the Holy Cross Mountains and (2) Eocene deposits in the northern area of the Lublin region.

Our research focuses on three regions within the Vistula–Bug interfluve (southeastern Poland), where both of these phosphorite formations are present:

• Annopol—situated at the easternmost part of the so-called Mesozoic Border of the Holy Cross Mountains);
• Bochotnica—western part of the Nałęczów Plateau, in the Lublin Upland;
• Niedźwiada and adjacent areas—located in the Lubartów Upland, Lublin Voivodeship.

In these regions, the mentioned bedrock has a relatively high phosphorus content as documented in Gąsiewicz (2020) [16]. Soils generally contain medium to high levels of available phosphorus (expressed as P₂O₅) [17]. Local high-purity spring waters, whose chemistry indicates minimal anthropogenic influence, also contain a significant amount of P compounds, particularly orthophosphates [18,19,20,21].

To better understand inorganic P sources in the chosen regions and to provide future directions for a sustainable management of its reserves, our research objectives are as follows:

(i)

Our objective is to briefly present the geological and petrological characteristics of phosphorites found in the Bug–Vistula interfluve area;

(ii)

Our objective is to provide a geochemical and mineralogical description of phosphorites from the study area;

(iii)

Our objective is to discuss the potential for exploitation and use of phosphorites from the study area in the context of sustainable phosphorus management in Poland. In addition, the issue of sustainable management of P non-renewable resources at both the local and global scale is discussed in this paper.

Phosphorites in Poland: Occurrence and Exploitation

The distribution of phosphorite deposits in Poland is shown in Figure 1. In English, phosphorites and phosphate rocks are often synonyms, where phosphate rock stands for a rock containing a high concentration of phosphate minerals. However, phosphate rocks can be of differing origins. According to Amar et al. (2022) [22] and references therein, five types of phosphate deposits can be distinguished: (1) sedimentary phosphate marine deposits; (2) igneous deposits; (3) metamorphic deposits; (4) weathered phosphate deposits; and (5) biogenic deposits. Among them, sedimentary deposits are the most abundant (approximately 75% [22]). In Polish, however, phosphorites are rocks that have a sedimentary origin [23]; therefore, we will use this term for Polish deposits here.

Polish sedimentary phosphorites mainly occur in the Albian belt (Lower Cretaceous) along the northeastern margin of the Holy Cross Mountains in the areas of Radom, Iłża, Annopol, Gościeradów, and Modliborzyce [24]. They are found also in the northern part of the Lublin region, where they are associated with Eocene deposits [16]. Other secondary P resources in Poland are phosphate rocks of various age. For instance, such rocks occur in the Holy Cross Mountains, where they include Paleozoic deposits (Cambrian, Ordovician, and Carboniferous). Additional occurrences are found on the southwestern margin of the Łódź region; in the condensed Albian sequence of the Carpathians; in Cenomanian and Turonian (late Cretaceous) deposits along the northern margin of the Holy Cross Mountains and the margin of the Miechów Trough; at the Uppermost Cretaceous–Paleocene boundary in the Carpathians and near Kazimierz and Wisłą; and in Paleogene deposits (Paleocene and Eocene) in the Bay of Puck region [24].

The phosphorites are present in various sediment types in the form of concretions rich in calcium phosphates. They occur usually in the form of various sizes concretions (from a few mm to several dozen cm), carbonate-rich fluorapatite (francolite), and much less frequently in the form of irregular and larger phosphate conglomerates. Phosphorite concentrations are locally very diverse and form more or less continuous horizons and beds [24]. The concretions mainly consist of phosphate minerals (up to 20–35%) and quartz (up to 30–40%), with a variable admixture of organic matter (locally up to 20%) and glauconite (<10%; e.g., [25]).

Despite the presence of phosphorite resources in Poland, they are not currently exploited for economic reasons. The country’s total P demand is met entirely through imports. While the majority of P is used in food production, it also serves important roles in the chemical, pharmaceutical, and metallurgical industries. Phosphoric acid, in particular, is used in agriculture and is a key ingredient in the production of soaps, detergents, and toothpaste. It is also widely used in the food industry as an acidulant in beverages and food as well as a preservative.

In recent years, especially since 2021, the global costs of importing phosphate ores has significantly risen. At the same time, many surface and groundwater bodies in Poland contain elevated levels of P compounds, especially easily assimilable orthophosphates, which contribute to eutrophication. As a consequence, proper identification of sources of P entering individual water bodies, together with measures to reduce the anthropogenic inputs, is paramount for the sustainable management of phosphorus resources.

2. Study Area: Vistula–Bug Interfluve

The study area is situated in southeastern Poland, in the Vistula–Bug interfluve. In the study area, Maastrichtian and Tertiary formations, including opokas, marls, chalk, gaizes, limestones, and sands (Dobrowolski et al., 2014 [26]) are characterized by relatively high phosphorus content [16]. On top of the carbonate Cretaceous formations, Paleogene deposits also occur. These include sandy gaizes with thin-bedded limestone interlayers of Paleocene age, as well as Eocene and Oligocene deposits that rest unconformably above them. At the base of these younger formations occur quartz sands with glauconite and silts containing phosphorite layers 1.0–2.0 m thick [27].

The relief of the Lublin Upland and Roztocze was formed during the early and middle Cenozoic stages of the morphogenesis of the Metacarpathian Ridge. The lithological variability of the Upper Cretaceous–Paleogene rock complex (and, in Roztocze, also Miocene deposits), which constitutes the primary substrate of the Quaternary cover, influenced subsequent morphogenetic processes such as denudation, glaciogenic, fluvial, and karst processes. The Maastrichtian and Paleocene rocks in this area display relatively limited variability in strength property. However, due to their “morphological hardness” [28], they can be divided into two groups: (1) limestone–silica rocks (opokas, gaizes) and (2) limestone and limestone–clay rocks (limestones, marls, chalk). The first group is more resistant to weathering and other destructive factors, while the second group is more prone to erosion and is responsible for the development of morphological depressions, often dominated by karst relief [26].

From a hydrogeological perspective, the Lublin Upland and Roztocze belong to the hydrogeological region of the Lublin Cretaceous. The main aquifer is hosted in Upper Cretaceous rocks, primarily opokas, gaizes, and marls, and locally also in Paleogene and Neogene limestones as well as Quaternary sands [29]. Natural underground outflows are quite common in both the Lublin Upland and Roztocze. The abundance and usually high efficiency of springs in this region result from a combination of factors: atmospheric recharge, terrain relief, and geological structure, including high permeability of near-surface layers and the large water capacity of the aeration and saturation zones [30,31]. This geological structure is of particular importance to our study.

Phosphorus in this area occurs mainly in three regions:

• Annopol—numerous phosphate nodules in Upper Cretaceous glauconite sandstones;
• Bochotnica—phosphate nodules associated with Danian glauconite sandstones;
• Niedźwiada—phosphate resources documented in recent years through detailed exploration of the Niedźwiada II glauconite-bearing sediment deposit, with an average P₂O₅ content of close to 23% [24].

The locations of these areas, together with all sampling points, are marked in Figure 2.

2.1. Annopol

The Annopol area, located on the eastern bank of the Vistula River (Figure 2), forms the easternmost part of the so-called Mesozoic Border of the Holy Cross Mountains [32]. The Cretaceous Annopol Anticline has been extensively studied [33,34,35,36,37,38] and is frequently cited in the literature for its abundant palaeontological finds [39,40,41,42,43,44].

Biogenic phosphates in the form of calcium-phosphate-rich concretions occur in shallow-marine Cretaceous sediments along the Radom–Iłża–Annopol–Gościeradów–Modliborzyce section (Mikulski et al. (2021) [45] and references therein). The depositional history of the area is as follows:

• Albian—sandstones and sands containing glauconite were deposited in the Annopol area.
• Cenomanian—sandy glauconitic marls were formed.
• Early Turonian—limestones with minor glauconite content were deposited with the Annopol area located on a submarine elevation.

Frequent interruption in sedimentation, combined with the accumulation of bones transported from the mainland and deposited in the marine environment, favored the formation of phosphate rocks. The main phosphate layer in the Annopol deposit was formed in the Albian, resulting from submarine erosion and the redeposition of previously formed phosphate rocks by marine currents [45]. Fossil assemblages in phosphorite accumulation zones typically include the teeth and bones of sharks, other vertebrates, and marine reptiles such as plesiosaurs and ichthyosaurs as well as turtle remains [46].

The most important information for our study comes from the Rachów-1 borehole, drilled to a depth of 1450.8 m in 1956–1957 [38]. Of particular interest are the Lower and Upper Cretaceous sediments, constituting a profile about 20 m thick and containing substantial phosphorite deposits. The profile of Cretaceous formations of the Annopol Anticline, down to 520 m depth, is presented in Figure 3.

The most recent stratigraphic interpretation of the phosphorite interval, based on lithological correlations, REE + Y signatures of phosphorites, age-diagnostic macrofossils, and sequence stratigraphic patterns, was proposed by Machalski et al. (2023) [39]. Earlier interpretations considered the phosphorite interval to be exclusively Albian. However, new macrofossil evidence indicates that the upper phosphorite levels at Annopol, the main target for phosphate mining, can be classified as Lower Cenomanian. According to the authors, lowstand reworking during the Albian–Cenomanian boundary played a significant role in concentrating phosphatic clasts and nodules into stratiform accumulations suitable for exploitation.

2.2. Bochotnica

The village of Bochotnica, located near Kazimierz Dolny on the Vistula River (Figure 2), lies within the Nałęczów Upland of the Lublin Synclinorium and administratively belongs to the Lublin Voivodeship. Maastrichtian and Danian deposits occur in this area [47,48,49,50]. The abandoned quarry in Bochotnica is located on the eastern side of the Vistula River, near the northern border of the village [51]. The quarry, which preserves approximately 200 m of passages and chambers, is now a protected site of the Kazimierz Landscape Park [52]. The entrances to the underground opoka mines remain visible below the hard opoka layer [49]. The Bochotnica documentation site is known as the “Krystyna and Władysław Pożaryski’s Wall”, named after the researchers who made significant contributions to the geological exploration of the Lublin region [47]. The profile of the Bochotnica quarry, showing the phosphorite horizon, is illustrated in Figure 4.

The Bochotnica outcrop, with its well-lithified, rain-washed walls, provides excellent opportunities to examine the details of the K-Pg interval in detail. Features visible on the quarry walls include the main burrowed surface with pseudobreccia, omission and post-omission Thalassinoides burrows, and the greensand with phosphatic nodules and fossils [49]. At this site, the Upper Maastrichtian opokas contain numerous fossils of marine invertebrates, vertebrates, and deposited terrestrial flora [53]. The Maastrichtian roof contains numerous marine invertebrate burrows filled with Danian glauconitic sandstone, phosphorite concretions, and numerous fossils. Its uneven top surface, about 0.5 m thick, includes channels filled with material derived from the overlaying quartz-glauconitic sandstone and is also commonly referred to as a phosphate layer due to the presence of phosphate concretions. These concretions often represent pseudomorphs after sponges and, occasionally, bivalves or brachiopods [54]. The glauconitic sandstone transitions into Danian gaizes and limestones [53]. As mentioned by Radwanek-Bąk and Bąk (2008) [54], this series is locally referred to as “siwak” due its gray color and has a thickness of about 40 m. A slight increase in iridium content has been observed in the fillings of burrows at the base of the Upper Cretaceous marine reservoir [54].

2.3. Niedźwiada and Adjacent Areas

The area of Niedźwiada and the nearby Górka Lubartowska and Leszkowice lies within the Lublin Voivodeship and hosts the largest and the best-documented deposits of Eocene quartz-glauconite sands in Poland (Niedźwiada and Brzeźnica Leśna Kolonia; Niedźwiada commune, Lubartów County) [55]. Phosphorite deposits in the Niedźwiada–Górka Lubartowska region have been documented in recent years thanks to detailed exploration of the Niedźwiada II glauconite-bearing sediment deposit. According to Słodkowska et al. (2022) [56], the Eocene deposits in northern Lublin are remnants of the eastern branch of the extensive epicontinental Proto-Northern Sea, which covered present-day Western, Central, and Eastern Europe. This sea reached its maximum extent in the Middle Eocene and was in a phase of regression during the Late Eocene, explaining the numerous amber occurrences in the Lublin region [57].

As reported by Karnkowski et al. (2024) [58], Baltic amber accumulations in the region are considered as “primary deposits”, representing initial, rich sedimentary accumulations associated with fine clastic, including clayey deposits of the Upper Eocene. The Paleogene amber-bearing association comprises sandy, silty, and clayey deposits with scattered amber fragments, typically containing glauconite. These amber-bearing formations occur at various depths, usually between 15 and 20 m (see Figure 5, [56]). Glauconitic sands usually occur in the upper layers of the profile, typically up to 15 m deep, which facilitates their exploitation. Lithological–stratigraphic sections of the Leszkowice, Górka Lubartowska, and Niedźwiada boreholes are presented in Figure 5.

The profiles of the Leszkowice, Górka Lubartowska, and Niedźwiada boreholes are dominated by sands, silts, and clays, often containing glauconite (Figure 5) (Słodkowska et al. (2022) [56]). The lowest part of the profiles contains marls and, sporadically, Upper Maastrichtian chalk. Above the Maastrichtian formations, Upper Eocene sediments are present (approx. 6 to 8 m thick, depending on the profile). The Eocene sediment series is tripartite: (1) a 2 m-thick layer of sandy glauconitic silts with amber grains, phosphates, and sandstone inclusions at the base; (2) a 4 m-thick glauconitic sands, and the top (3) 1.6 m-thick glauconitic silts. Overlying the Eocene deposits are Neogene silts or sands with carbonaceous matter, with thickness ranging from 3.4 to 4.3 m depending on the profile. Above the Neogene sediments lies a Pleistocene layer, varying in thickness from 8.3 m in Górka Lubartowska to 13.7 m in Niedźwiada, composed mainly of sands, locally mixed with fluvioglacial gravels. A closer examination of the Górka Lubartowska–Niedźwiada profile for the phosphate-bearing layer reveals that within the glauconite-rich sediments of the Lower Eocene, a transition zone about 20 cm thick contains small diagenetically altered glauconitic mud with pebbles and phosphate concretions. Above this, the profile includes a fine- to medium-grained glauconitic sand layer about 1.5 m thick, whereas a thin (0.05 m thick) lamina of quartz-glauconite sandstone occurs immediately below [55].

3. Materials and Methods

A preliminary estimate of phosphorus content in the bedrock in the study area was obtained using a Niton™ XL5 Plus handheld XRF analyzer (Thermo Scientific, Waltham, MA, USA). Following this initial assessment, only rocks with phosphorus content above 400 ppm were selected for further study. The collected samples were then prepared for geochemical, mineralogical, textural, and structural analyses. In this article, we present the results of analyses on samples representative of specific study areas within the Vistula–Bug river basins, characterized by relatively high phosphate content in the bedrock. These include phosphorites collected from the Annopol, Bochotnica, and Niedźwiada regions as well as the surrounding areas such as Górka Lubartowska and Leszkowice.

3.1. Petrography

Three thin sections of the studied samples were prepared to enable microscopic observations and the analysis of microfacies and other features. Microscopic examinations were performed using a DM2500P polarizing optical microscope (Leica, Wetzlar, Germany) with CCD camera at the Department of Geology, Soil Science, and Geoinformation, Maria Skłodowska-Curie University in Lublin, Poland. Microscopic observations in polarized, transmitted, and reflected light, together with their photographic documentation, were used to determine the mineralogical composition of the studied bedrocks as well as their structural and textural analyses. We especially targeted P-bearing minerals and glauconite. The additional observations before µ-XRF analysis were carried out using an Eclipse LV100POL polarizing microscope (Nikon, Tokio, Japan) at the Institute of Geological Sciences, Polish Academy of Sciences in Warsaw, Poland.

3.2. Morphology and Mineralogy

To obtain more detailed information about sample morphology and mineralogy, after microscopic observation, the polished thin-sections were analyzed using a SU6600 Scanning Electron Microscope (Hitachi, Tokio, Japan) with an EDS (Energy-dispersive X-ray spectroscopy) at the Department of Geology, Soil Science, and Geoinformation, Maria Skłodowska-Curie University in Lublin, Poland. The samples were examined under low vacuum conditions (approx. 4 Pa) using a 15 kV electron gun and a scanning spot width of 2 nm. The results were obtained after 60 s of exposure and then reported using the NSS 3 program.

To more precisely examine the qualitative composition of samples from the study area, the samples were analyzed at the Laboratory of Electron Microscopy, Microanalysis, and X-ray Diffraction, Faculty of Geology, University of Warsaw, using an X’Pert PRO MPD X-ray powder diffractometer (PANalytical B.V., Almelo, The Netherlands) using the Bragg–Brentano method. Samples were recorded in the 4–78° 2θ range, with a 0.026°2θ step. Powder samples were pressed with a sample rotation of 1 rpm/2 s, and CoKα radiation was filtered (Fe filter) with current parameters of 30 mA and 40 kV. Radiation detection was performed using a fast PIXcel linear detector. Total measurement time for a single sample was 4 h.

3.3. Geochemistry

Infrared spectra were recorded in the 4000–400 cm⁻¹ range with a resolution of 4 cm⁻¹ at ambient temperature, using a Nicolet 8700 FT-IR/NXR 9650 FT-Raman spectrometer system (Thermo Scientific, Waltham, MA, USA) equipped with a Smart Orbit™ diamond ATR attachment. Each spectrum was obtained by averaging 256 individual scans. The tested samples were previously ground using an agate mortar. The collected spectra were processed using OMNIC 8.1 software, including ATR correction, automatic baseline correction, and scaled normalization. The following publications were used for the interpretation of spectra and identification of minerals: Schmidt and Fröhlich, 2011 [59]; Antonakos et al., 2007 [60]; Bargar et al., 2004 [61]; and Chattoraj et al., 2017 [62]. These studies were performed at the Analytical Laboratory of the Faculty of Chemistry, Maria Skłodowska-Curie University in Lublin.

To complement petrographic observations, elemental maps of selected petrographic thin sections as well as selected areas within them were obtained using micro X-ray fluorescence (µ-XRF). The instrument used was a Bruker M4 Tornado tabletop spectrometer equipped with a rhodium (Rh) X-ray tube (50 W) and dual detectors for high-speed mapping. The analysis were performed at the Institute of Geography and Spatial Organization, Polish Academy of Sciences in Warsaw, Poland. Measurements were conducted under vacuum conditions (20 mbar) and with tube parameters of 50 kV and 300–500 µA (high voltage and anode current). Elemental maps were produced across the sample area with a typical pixel spacing of 30 microns and a dwell time of 10 ms per pixel. Higher-resolution maps were also produced on selected areas, especially targeting P-bearing minerals, P-rich areas, and glauconite phases, with pixel spacing down to 8 microns (overlapping) and a dwell time of 25 ms per pixel. The following elements were taken into considerations for mapping: Na, Mg, Al, Si, P, S, K, Ca, Ti, Mn, Fe, Cu, Sr, Ce, and Th. Spectral deconvolution was applied.

4. Results

The results of petrographic, geochemical, and mineralogical analyses are presented below, divided into three sections: (1) Annopol, (2) Bochotnica, and (3) Niedźwiada and adjacent areas (Górka Lubartowska and Leszkowice).

4.1. Annopol

Microphotographs of the analyzed phosphorites from Annopol are shown in Figure 6. Representative compositions dispersed fine apatite grains for the studied samples collected in Annopol area are shown in Figure 7.

The analyzed samples were mainly grayish-brown in color and exhibited a medium-grained, heterogeneous structure. The matrix was P and Ca rich while aggregates of glauconite were Fe and K rich (Figure 8). Microfacies contained various types and sizes of glauconite aggregates, highlighted in the elemental maps by their Fe and K enrichment (Figure 8B,C,E), usually accompanied by moderately rounded quartz extraclast, with quartzite lithoclasts occurring less frequently visible. The glauconite aggregates ranged in size from small, several tens of micrometers to several hundred micrometers, with some showing evidence of secondary modification.

The aggregates were often associated with hematite and francolite and occasionally with other minerals such as chalcedony or goethite. Francolite occurred as layered accumulations arranged in elongated, sometimes highly deformed fills that cemented grains and bioclasts within the concretions (Figure 6D,F). These accumulations may reach several millimeters in size and often form bean-shaped aggregates, imparting a spherical morphology to the concretions. Microscopic images reveal multilayered, deformed francolite accumulations and associated clasts, occasionally cemented with carbonates (calcite) admixture (Figure 6D). Small amounts of hematite and iron hydroxides are also observed, frequently concentrated around glauconite aggregates, particularly in redeposited clasts (Figure 6A,E).

Micro-scale analyses confirm the complex composition of these clasts: both francolite and glauconite form complex compounds with various admixtures, as shown in the representative EDS spectra (Figure 7), as well as an XRD pattern (Figure 9) and FTIR spectrum (Figure 10), discussed more detailed below.

In addition, the phosphorite samples contain various bioclasts. In the Annopol area, numerous and diverse macro remains are found, such as phosphatized sponge fragments, terebratulid brachiopods (with phosphatic or marly infilling), ammonites, bivalves, belemnites, nautilids, and gastropod phosphatic molds. Such findings have been frequently reported in the literature, among others, by Machalski et al., 2023 [39].

The XRD pattern of phosphorite concretion from Annopol is shown in Figure 9, while the Raman spectra of this sample are presented in Figure 10. The XRD analysis shows francolite, carbonate–fluorapatite, and fluorapatite as the main P-components, and minor but significant content of glauconite is also visible.

In the examined sample from Annopol (Figure 10), a mixture of minerals with a significant presence of phosphate was found. Phosphate presence was confirmed by the two most important sets of vibrations of the PO₄³⁻: at 1022 cm⁻¹ (ν3) the most important and usually the strongest peak, originating from asymmetric stretching bond P-O. It confirms the dominant presence of phosphates. The other is at 563 cm⁻¹ and 601 cm⁻¹ (ν4): a doublet in this range is indicative of a phosphate structure, resulting from bending vibrations of the O-P-O bonds. Additionally, a band at 1422 cm⁻¹ (ν3) was also detected: This is a strong, complex band in this range associated with the presence of carbonates in the mixture. This peak is very strong and irregular, which may indicate the presence of francolite (the phosphate part is also carbonate) and a free carbonate mineral. The 866 cm⁻¹ (ν2) band is e characteristic for the out-of-plane bending vibration of the CO₃²⁻. It occurs in both free carbonates and francolite. The 3366 cm⁻¹ (ν O-H) band in this range is typical of stretching vibrations of hydroxyl (OH) groups or adsorbed interlayer water present in hydrated and incompletely crystallized minerals. It may originate from glauconite, a clay mineral containing OH groups in octahedral layers of its structure.

4.2. Bochotnica

Microphotographs of the Bochotnica phosphorites are shown in Figure 11.

The analyzed rock samples are grayish-brown in color and contain small (1–2 cm) horizontal intercalations within the surrounding carbonate rocks. They display a medium-grained, heterogeneous structure and a porous, locally layered texture. The microphotographs show small, moderately rounded quartz extraclasts, accompanied by small, moderately rounded, isolated microcline clasts and occasional muscovite flakes. In addition, various glauconite aggregates are present, ranging from several tens to several hundred micrometers in size, some of which appear as redeposits. The samples also contain numerous bioclasts, represented by microfossils (mainly foraminifera) as well as fragments of mollusk and echinoderm calcite shells. Other bioclasts, such as rare sponge spicules, echinoderm fragments, foraminifera, and bryozoans, have also been reported in these deposits [49].

Microphotographs also show opal sponge spicules, sometimes secondarily filled with hematite. Hematite also occurs as small, isolated grains, imparting a brownish coloration to the rock. The matrix is composed of micritic carbonate silt, enriched in phosphates (Figure 11B–D). Dispersed apatite grains and, more often, monazites can also be found, as shown by the EDS analyses (Figure 12).

Some phosphate rock specimens exhibit distinct lamination, expressed by the directional arrangement of quartz clasts, glauconite aggregates, and small bioclasts (Figure 10). Within thin sections, P-rich accumulation is common, forming compact but still laminated clusters among the clastic minerals. These accumulations are sometimes filled with an admixture of fine micrite (calcite, Figure 13C,D). Accessory minerals, including zircon and monazite, occur locally, most often noted in thin interlayers at the boundary between the phosphorite nodules and their host rock. Small admixtures of clay minerals and silica are also found in the matrix. The EDS analysis confirms the presence of dispersed P-bearing phases, such as apatite and monazite, as well as phosphorus in a P-rich matrix (Figure 13C,D). The XRD pattern also shows various dispersed P-containing mineral phases as well as the presence of glauconite (Figure 14). Micro-scale studies revealed the complex interplay between the glauconite and phosphate phase, with iron oxides and hydroxides frequently detected in close association (Figure 13E,F).

The XRD pattern of phosphorite concretion from Bochotnica is shown in Figure 14, while the FTIR spectrum is presented in Figure 15. In the analyzed sample, the major components are quartz and calcite, with high content of P-bearing mineral phases, which were identified as francolite, fluorapatite, and carbonate–fluorapatite (Figure 14). The presence of minor but a still significant amount of glauconite was also reported.

In the case of the Bochotnica sample, the presence of a mixture involving phosphates was also indicated. Of particular interest is the 1032 cm⁻¹ (ν3) band, an asymmetric P-O stretching for phosphates. The slight shift compared to 1022 cm⁻¹ in the spectrum may result from differences in ionic substitution or overlap with the broad Si-O band of glauconite. Furthermore, characteristic bands of carbonate presence were also detected at 712 cm⁻¹ (ν4) and 873 cm⁻¹ (ν2). The 1425 cm⁻¹ (ν3) band, characteristic of the CO₃²⁻ group, is still present, indicating that it originates from carbonates or is incorporated into the structure of apatite or francolite. The 792 cm⁻¹ band indicates the presence of quartz in this sample. Furthermore, the 463 cm⁻¹ band (O-Si-O bending), originating from silicates, may be characteristic of quartz or glauconite. The 3626 cm⁻¹ band (O-H stretching) is characteristic of water embedded in silicate packets of clay minerals such as glauconite (Al-OH vibrations in an octahedral layer).

The absence of ν4 bending bands in the 560–610 cm⁻¹ range, a significant difference compared to the Annopol spectrum (where they were recorded), may suggest that they were very weak or broad and degraded, which may suggest a lower phosphate concentration or poorer crystallinity in this sample. The examined spectrum confirms the presence of all minerals identified by separate methods but suggests a change in proportions compared to the spectrum from Annopol, as phosphates are less distinct (a lack of ν4 peaks); although they are still present (ν3 peak at 1032 cm⁻¹), silicates are more dominant or more clearly crystallized (presence of the 792 cm⁻¹ peak), and the presence of carbonates and glauconite was also indicated.

4.3. Niedźwiada and Adjacent Area

Microphotographs of the samples collected in the Niedźwiada area (Leszkowice-Górka Lubartowska) are shown in Figure 15.

The samples collected from the area between Leszkowice and Górka Lubartowska are represented by glauconitic sandstone, grayish-green in color. The microscopic image shows numerous quartz grains. They are loosely arranged, not touching each other. These grains are rounded to varying degrees, but weak rounding predominates, some grains are elongated, and their size varies. Glauconite aggregates are present among the quartz. These aggregates include both fresh aggregates, exhibiting vibrant green colors in thin layers, and redeposited aggregates, often saturated with iron oxides and hydroxides to varying degrees (Figure 16C,D). The cement has the character of a rock matrix, filling the spaces between the grains. It is primarily chalcedony cement with admixtures of iron oxides and hydroxides, with opal occasionally visible. Secondary, decalcified chalcedony fillings in the rock are also visible, shaped like fossils. Some of the quartz grains contain inclusions of muscovite. This sandstone also contains bioclasts, usually mollusks (cockles-cardioidea sp., unpublished data by Prof. Barbara Studencka from the Polish Academy of Sciences, Museum of the Earth, Warsaw, Poland). These organisms are associated with a brackish environment with variable salinity. After sedimentation and lithification, these sediments were decalcified, and the fossil centers were filled with chalcedony and iron oxides and hydroxides. Similarly, oolites occur (Figure 16E) in the rocks under discussion, which were also replaced by silica [63]. Glauconite is common in these rocks (Figure 17B) and occurs as fresh or weathered, likely secondary redeposited. Under such variable conditions, phosphate minerals may occur as primary detrital grains (e.g., monazite, see Figure 16C,D and Figure 18) or as secondary dispersed mineralization formed through the oxidation of iron compounds. Small amounts of heavy minerals, such as zircon, are also locally observed.

The XRD pattern of glauconitic sandstone collected from the area between Leszkowice and Górka Lubartowska, nearby phosphorite-rich Niedźwiada, is shown in Figure 19, while the FTIR spectrum is presented in Figure 20. In the analyzed sample, the main components are quartz and glauconite, with minor content of pyrite and microcline (Figure 19).

The examined spectrum of the sample collected between the Leszkowice and Górka Lubartowska area indicates the presence of band characteristic for silicates, which indicates the presence of quartz and glauconite (781 cm⁻¹, 442 cm⁻¹, 693 cm⁻¹). Furthermore, the 1007 cm⁻¹ band, although located close to the ν3 phosphate band (1022–1032 cm⁻¹ in the previous spectra), in this case, its shift to 1007 cm⁻¹ suggests that it is dominated by a broad and intense asymmetric Si-O stretching vibration characteristic of glauconite (clay minerals have broad silicate bands in the range of 950–1050 cm⁻¹). A 3526 cm⁻¹ OH (Al-OH or Mg-OH) stretching band was also detected, which may indicate water presence in packet silicates in the glauconite structure. In clay minerals, this peak is key and lies within the typical range for these groups. Furthermore, a 1624 cm⁻¹ H-O-H bending band was detected, confirming the presence of water (adsorbed or interlayered), which is typical for glauconite and other clay minerals. The strong ν4 peaks (560–610 cm⁻¹), crucial for phosphates, are not clearly visible; only a slight broadening of the 1007 cm⁻¹ peak (ν3 band) may indicate their low presence in the sample.

5. Discussion

5.1. The Exploitation Potential of the Vistula–Bug Interfluve Phosphorite Resources

Poland possesses its own phosphorite resources, which occur, among other locations, in the Vistula–Bug interfluve region examined in this study (see Figure 1). The key quality parameters of eleven documented phosphorite deposits in Poland are shown in

Table 1. Key quality parameters of documented phosphorite deposits in Poland (compiled after [23,24], modified by the authors). The upper value from the economic geological resources column means ore resources; the lower value, in bold, means P₂O₅ resources. Resource definitions and categories used in the table are available online on the Polish Geological Institute—National Research Institute (PGI-NRI) website: [65,66].

Deposit	Economic Geological Resources [Thousand Tonnes]				Sub-Economic Resources [Thousand Tonnes]	Thickness [m]	Phosphorite Concretion Diameter [mm]	P2O5 Content [%]	Affluence of Phosphorite Concretions [kg/m2]	Affluence in Relation to Actual Limiting Parameters [%]
	Total	A + B	C1	C2
Annopol	7600 1030	4600 630	2980 400	-	-	0.3	>10	13.5	568	32
Burzenin	-	-	-	-	2740 490	0.7	>2	18.1	385	21
Chałupki	3170 440	150 20	3020 420	-	-	0.4	>10	14.9	354	21
Gościeradów	1420 210	-	-	1420 210	-	no data	>2	15.2	496	28
Iłża–Krzyżanowice	1860 390	-	-	1860 390	860 115	1.3	>2	18.6	791	44
Iłża–Chwałowice	620 140	-	-	620 140	625 90	0.4	>2	22.3	891	50
Iłża–Łęczany	10,230 1900	-	-	10,230 1900	1340 257	0.6	>2	18.6	654	36
Iłża–Walentynów	1690 330	-	-	1690 330	-	0.7	>2	19.9	470	26
Radom– Dąbrówka Warszawska	6760 1210	-	-	6760 1210	-	1.8	>2	16.5	upper series—317 lower series—460	upper series—18 lower series—26
Radom– Krogulcza	8470 1610	-	-	8470 1610	3114 592	0.5	>2	19.1	upper series—218 lower series—504	upper series—12 lower series—28
Radom– Wolanów	590 90	-	-	590 90	98 19	0.7	>2	15.4	upper series—170 lower series—447	upper series—9 lower series—25

. To support the following discussion, Figure 21 presents a comparison between the resource classification system used in Poland and the United Nations Framework Classification for Resources and Reserves (UNFC Update 2019) [64].

The first phosphorite deposit in Poland, located in the Rachów–Annopol region (point no. 1 in Figure 2), was discovered by prof. Jan Samsonowicz in 1923 during a search for sandstone for road construction [23]. A year later, Samsonowicz [33,68] described numerous phosphate concretions in Upper Cretaceous glauconite sandstones. Shortly after the discovery, mining operations began in Annopol and nearby Chałupki (18 km to the northeast). Exploitation was first conducted in the form of open-cast mining, then replaced by subsurface mining [49]. The ore was used for fertilizer production by factories in Chorzów and Mościce [23]. In total, close to 950,000 tons of phosphate rock were extracted from the Annopol mine [49]. According to Mazurek et al., 2024 [23], the best method for refining Polish Cretaceous phosphorite deposits, such as those at Annopol and Chałupki, was a three-stage technology, including (1) hydrothermal separation, (2) phosphoric acid extraction from silicon phosphate, and (3) the production of concentrated phosphorus fertilizers from the phosphorite concentrate.

Current phosphorite processing methods are very similar to those described above, with various modifications depending on the type of the feed material [69]. In most processing plants, the simplest method is used: washing the extracted material, followed by the recovery of phosphorite nodules from the sludge. As noted by Mazurek et al., 2024 [23], this method allows ore containing 11.5–12% P₂O₅ to be upgraded into concentrate with up to 23% P₂O₅. When glauconite grains are present in the feed, the magnetic purification step is added to the processing scheme. In such cases, ore with 11–12% P₂O₅ and approximately 10% Fe₂O₃ can be processed into a concentrate containing about 26% P₂O₅. Glauconite grains occur, for example, in phosphorites from the Lublin region. In line with sustainable development requirements, further efforts are underway to minimize P losses during extraction and processing. For example, Lamghari et al. (2024) [70] proposed four new improvement scenarios, including an integrated approach that combines all solutions to obtain a comprehensive processing strategy.

For economic reasons, mining at the Chałupki deposit ceased in 1961 and at the Annopol mine in 1971 [23]. Further mining operations were deemed unprofitable, and since then, the total domestic demand for P has been met through import. After the mine’s closure and the withdrawal of state funding for geological research under the former socialist system, only preliminary exploration with shallow boreholes was conducted in the following years. Today, changes in the phosphate fertilizer market and the expansion of industrial infrastructure have led to a re-evaluation of previously adopted parameters.

As reported by Mazurek et al. (2024) [23], the following parameters were adopted for the evaluation of phosphorite resources: (i) the minable deposit interval < 2 m, as (ii) the ore should lie within this interval, which was to be extracted in its entirety, transported to the surface, and sieved using a 2 mm mesh; (iii) the average P₂O₅ content in the obtained concentrate >14 wt%; (iii) the average yield of >2 mm concentrate >14% (a condition set at that time by the Institute of Sulfuric Acid and Phosphate Fertilizers for products such as thermophosphates and superthomasine [71]). According to the guidelines, the deposits listed in Table 1 were documented for underground extraction. However, besides Annopol and Chałupki deposits, they were never developed [23].

Since 2014, phosphorites have been included on the list of critical raw materials in Poland, as well as in the European Union (EU). In Europe, phosphate rock is scarcely mined, with the exception of a small magmatic deposit in Finland. The main suppliers of phosphate rock to the EU are Morocco (27%), Russia (24%), Finland (17%), and Algeria (10%) [23]. The estimated average cost of P₂O₅ imports to Poland in 2022–2023 has doubled compared to the period 2010–2021. According to Mazurek et al., 2024 [23], relative to the highest prices of the import of P₂O₅-bearing phosphate rock, the assumed critical price for cost-effective domestic phosphate fertilizer production may be close to approximately 90% of that value. Several factors suggest the need to revise the existing parameters that define ore deposits and their boundaries for potential open-pit extraction in Poland. These include (i) the significant increase in global phosphate rock prices, related both to the depletion of natural deposits and the geopolitical situation; (ii) the scale of P imports to Poland; and (iii) the development of infrastructure for extraction, processing, and recovery of P from ore.

The economic feasibility of extracting phosphate from sediments with significantly lower P₂O₅ content has been considered in several countries in recent years. For example, in Canada’s Saguenay–Lac-St-Jean region of Quebec, mining ore containing approximately 6% P₂O₅ is under consideration [72]. Similarly, a low-grade phosphorite deposit with an average P₂O₅ content of 9.5% has been documented in Kazakhstan, while one of the most prospective deposits in Serbia (the Lisina deposit) contains an average of 9% P₂O₅ but is relatively high in iron oxide content (up to 5%) [23]. For phosphate rock resources in Poland designated for open-pit mining, a new proposal is being considered to verify the deposit abundance and the profitability of extraction and processing. The proposed threshold parameters are as follows: a minimum P₂O₅ content of 5%; a maximum cadmium content of 60 mg/Mg per metric ton of P₂O₅; a maximum strip ratio of 12:1; and a minimum deposit thickness of 1.5 m [23]. Additionally, about a decade ago, ideas emerged for utilizing domestic phosphate rock resources more efficiently. For example, it was proposed to produce phosphate rock meal from domestic deposits instead of highly processed commercial fertilizer [73].

According to the Regulation of the Minister of the Environment of 1 July 2015 on the geological documentation of a mineral deposit, excluding hydrocarbon deposit [74], the following limit values for defining phosphate deposits and their boundaries have been set in Poland: a maximum documentation depth of 400 m; a minimum average P₂O₅ content in phosphate concretions within the deposit profile of 15%; and a minimum abundance of phosphate concretions of 1800 kg/m². The documented domestic phosphorite deposits (Table 1) do not meet these criteria. Additionally, their high water content complicates exploitation, which resulted in their removal from the national resource balance in 2006. However, following detailed exploration of the glauconite-bearing sediments of Niedźwiada II deposit in recent years, phosphorites were documented as one of the accompanying raw materials in this formation, with recalculated resources approved in 2020 (see

Table 2. The list of phosphorite deposits in Poland as of 31 December 2024 [24].

Name of Deposit	The State of Development	Geological Resources in Place [Thousand Tonnes]						Economic Resources in Place as a Part of Anticipated Economic Resources	Output	Localization
		Anticipated Economic					Anticipated Sub-Economic
		Total	A + B	C1	C2	D
Total number of deposits: 1		8.04	-	8.04	-	-	-	-	-	Lublin Voivodeship, Lubartów County
Niedźwiada II	R	8.04	-	8.04	-	-	-	-	-	Lublin Voivodeship, Lubartów County

).

Phosphorites in Niedźwiada II deposits occur as gray-black, hard phosphate concretions with irregular surfaces, ranging in diameter from 2 to 30 mm. The deposit contains an average of 22.86% P₂O₅, and the phosphate phase has been identified as hydroxyapatite. This deposit is estimated to contain 7.33 thousand tons of economically recoverable resources; however, the deposit has not been exploited to date [24].

As reported by Karnkowski et al. (2024) [58], Baltic amber accumulations in the Lublin region are considered as “primary deposits” (initial, rich sedimentary accumulations) and are associated with fine clastic, including clayey, deposits of the Upper Eocene. The Paleogene amber-bearing association comprises sandy, silty, and clayey deposits with scattered amber fragments and is characterized by the presence of glauconite. Amber-bearing formations in the northern Lublin region occur at various depths, typically between 15 and 20 m (see Figure 5 [56]). Glauconitic sands occur in the upper layers of the profile, usually up to 15 m deep, which facilitates their exploitation. Phosphorites accompanying these amber deposits occur as hard, irregular-surfaced concretions, gray-black in color, with grain sizes ranging from 2 to 30 mm [58]. They are characterized by a high phosphorus content, with average P₂O₅ content of 22.86%, which exceeds the current quality criterion of 15% and is considered very satisfactory. The phosphate phase was identified by X-ray as hydroxyapatite [56]. In 2021, a concession was issued for the Niedźwiada II deposit; however, phosphate mining has not yet commenced.

In addition to their high P₂O₅ content, phosphorites from the study area are also enriched in rare earth elements (REEs). The majority of global REE reserves are focused in only a few countries, with China leading production at approximately 70% of the global total [75]. Alternative REE sources are being sought, and phosphorite deposits represent one such option, where REEs are present in lower concentrations but in larger volumes compared to primary REE ore deposits, which are increasingly targeted by the industry [75,76,77]. REEs are informally subdivided into light REEs (LREEs—La through Sm) and heavy REEs (HREEs—Eu through Lu and Y) [78]. REEEs, especially, play a critical role in high-tech industries [79].

As shown by Machowiak et al. (2015) [46], the total REE content in the lower phosphorite horizon at Annopol was 165.5 ppm (LREE = 146.8; HREE = 18.8), while in the upper horizon, it was 144.3 ppm (LREE = 129.1; HREE = 15.2). The uranium content was 98.2 ppm and 35.3 ppm in the lower and upper horizons, respectively. More recent research by Machalski et al. (2023) [39] shows REE concentration ranging from 51.93 to 72.07 ppm and from 9.1 to 34.9 ppm for Y in the lower phosphorite horizon. In the upper horizon, total REE + Y concentration is 48.18–185.88 ppm for REE and 8.6–38.9 ppm for Y. Both francolite and monazite were identified as REE carriers [45]. In the nearby Chałupki deposit, REE content ranges from 177.37 to 354.18 ppm, with samples enriched in Ce and Sm-Gd, and francolite identified as a REE carrier [80]. Interest in phosphorites from Annopol and Chałupki has increased significantly in recent years due to their potential as a source of rare earth elements [45,77]. Detailed REE analyses have not yet been carried out for other phosphorite-rich areas of the Vistula–Bug interfluve; however, given that both phosphorites and REEs are currently considered critical raw materials for a domestic economy, such studies are likely to be undertaken in the near future.

Summarizing the results from the Vistula–Bug interfluve area, both phosphorites and glauconite are common, as evidenced by profiles, petrographic analyses, EDS and FTIR spectra, and XRD and µXRF analyses. The term “glauconite” is used both as a morphological term for greenish, sand-sized grains in sedimentary rocks and as the name of a specific mineral species—a hydrated, iron-rich, mica-like clay mineral [81]. Glauconite can be described as a hydrous phyllosilicate rich in iron and potassium, with the formula (K, Na) (Fe³⁺, Fe²⁺, Al, Mg)₂ 3[Si₃(Si,Al)O₁₀](OH)₂,4H₂O [82]. According to Kalinina et al. (2023) [83] and references therein, glauconite predominantly forms in a coastal-marine environments under conditions of sedimentary diagenesis. Glauconite-rich beds are present in the sedimentary sequence with phosphorites or, to a lesser extent, iron compounds in some basins. The mineral is particularly associated with marine transgressions [81], as is the case in the Lublin region. Although phosphorus is not a structural component of glauconite (see Figure 6C), it can be easily ‘bound’ by Fe and Al depending on ambient conditions (mainly pH). This can explain the relatively high P content of the matrix in samples containing glauconite.

In the study area, P primarily occurs in the form of francolite, the most common form of P in phosphorites [84]. Francolite is a structurally and chemically complex carbonate–fluorapatite [85], represented by the following formula: Ca_10−a–bNa_aMg_b(PO₄)_6−x(CO₃)_x-y-z(CO₃∙F)_y(SO₄)_zF₂. According to Godet et al. (2021) [85], substitutions occur at all crystallographic sites (i.e., Ca, PO₄, and F sites), allowing these sites to become enriched in economically relevant major and rare earth elements. The enrichment of REEs in the Annopol region may be related to the high francolite content in the deposits.

In addition to francolite, dispersed, usually fine apatite grains can be observed in the studied area of the Vistula–Bug interfluve, most often as hydroxy- and fluorapatite. In sites 2 and 3, monazite was also found as an accessory mineral. Monazite, generally described as (Ce, LREE, Th, U, Ca)PO₄, is common in magmatic, metamorphic, and ore-forming environments [86]. This phosphate mineral contains about 70% REE oxides, and based on the dominant REE, four monazite groups can be distinguished: monazite-(Ce), monazite-(La), monazite-(Nd), and monazite-(Sm), with monazite-(Ce) being the most common in nature [87]. The presence of monazite in ore deposits may suggests potential for enrichment with selected rare earth elements.

It is evident that new geological and quality parameters should be considered primarily for phosphorite deposits intended for open-pit exploitation. Such deposits must occur at shallow depths, as is the case with Eocene deposits in eastern Poland, represented in our study by No. 3, Niedźwiada, and adjacent areas (see Figure 2 and Figure 5). The phosphorite deposits in the Niedźwiada region lie below 30 m depth. Domestic Eocene phosphorite deposits occur in quartz–glauconitic sands, which are locally more calcareous and clayey, and are overlain by Neogene (Miocene) and Quaternary detrital sediments [23]. The thickness of the Quaternary and Neogene overburden ranges from less than 1 m to approximately 71 m, with a mean value of 28.9 m. Phosphate rocks in southeastern Poland are not yet well recognized, nor are they recognized in terms of REE content. According to Krzowski, 1995 [88], the P-bearing phase content associated with glauconitic sands in the Lublin region ranged from 0.07% to 1.36% of P₂O₅. Better recognition of deposits, especially Eocene ones, in the above-mentioned area of the Lublin region, along with verification of existing geological and quality parameters of deposits intended for open-pit exploitation, seems desirable in the coming years.

5.2. Phosphorite Resources from the Vistula–Bug Interfluve vs. Sustainable Management of P Resources in Poland

The main beneficiary of the phosphate mining industry is agriculture. In Poland, the demand for P for the mineral fertilizer production is currently fully met through imports. Domestic production of NPK fertilizers is well developed. On a global scale, Poland belongs to the group of countries with average fertilizer production, totaling 2.4 million tons of pure component, which constitutes 1.2% of global production, including 1.5% for nitrogen fertilizers [89]. However, in the European Union, Poland is one of the largest producers of fertilizers and a leader in the production of nitrogen and phosphorus fertilizers in terms of pure components. In 2022, Poland’s share of EU production was N—20.3%, P₂O₅—23.5%, and K₂O—9.6%. The majority of Polish NPK fertilizer exports in 2023 were directed to Ukraine (about 67%), while Ukraine accounted for 24.1% of N fertilizer exports and Germany for 26.3%. The production of mineral P fertilizers in Poland, in terms of pure component (P₂O₅), ranged from 442 to 475 thousand tons between 2015 and 2021 (Statistica Poland report, 2022 [90]). The commencement of extraction of Eocene phosphates from Niedźwiada II deposit and nearby areas, which are rich in glauconite sands accompanied by phosphorites, could alter the balance between imported phosphate ores, fertilizer production, and waste generation and recycling.

The consumption of phosphate fertilizer in Poland, according to Lewicka and Burkowicz, 2024 [91], taking the last ten years into account, was as follows: the majority of natural calcium phosphates were used to produce phosphorus and multi-component mineral fertilizers (90–95%) and to produce other phosphorus compounds and did not exceed 10%. The elemental phosphorus was used to produce phosphoric acid (food and feed industry) and phosphates (food, feed, and technical), mainly sodium tripolyphosphate (approx. 95%), while the production of other phosphorus compounds did not exceed 5%. The summarized data regarding the management of natural calcium phosphates and elemental phosphorus, as well as their values of trade and average unit values of natural calcium phosphates import to Poland in the years 2014–2023, is shown in

Table 3. Management of raw P materials in Poland in years 2014–2023 (after Lewicka and Burkowicz, 2024 [91]).

Management of Natural Calcium Phosphates in Poland [in 106 kg]
Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Import	1265.2	1249.7	1313.2	1213.1	1172.6	1324.6	1175	148.1	162.9	107.7
Export	0.6	1.6	0.3	0	0.1	0.6	1.5	0.4	0	0
Management of elemental phosphorus in Poland [in 106 kg]
Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Import	27.4	22.8	20.7	26.3	30.3	24.9	28	29.5	22.3	14.2
Export	9.3	8.2	8	9.8	9.9	9.9	8.4	10.8	10.4	5.9
Value of trade in natural calcium phosphates in Poland [in thousands of PLN *]
Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Import	1000	1225	575	25	32	110	301	29	55	1
Export	391,794	463,617	448,897	358,319	343,879	44,295	359,319	58,540	126,181	70,003
Value of trade in elemental phosphorus in Poland [in thousands of PLN *]
Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Import	99,041	104,360	96,354	113,623	104,445	113,173	100,055	132,101	243,133	122,575
Export	269,613	267,941	227,907	255,779	279,710	255,390	287,628	297,722	475,679	216,187
Average unit values of import of natural calcium phosphates to Poland [in PLN */t]
Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023
Natural calcium phosphates, unground	308	370	340	293	292	335	316	369	827	655
Natural calcium phosphates, ground	325	376	368	323	303	407	219	418	748	647

* 1 USD ~ 4.1 PLN, 1 EUR ~ 4.3 PLN according the average exchange rate in Poland in 2024.

.

If we look at data from the last decade, we see a sharp decline in imports of natural calcium phosphates from 1265.2 × 10⁶ kg in 2014 to 107.7 × 10⁶ kg in 2023 and elemental phosphorus from 27.4 × 10⁶ kg to 14.2 × 10⁶ kg in the same years. The several-fold decline in natural calcium phosphate imports was related to the COVID-19 pandemic and remains at a similar level today. At the same time, the average unit value of natural calcium phosphate imports into the country increased by more than double. It therefore seems prudent to verify both the abundance of potential phosphate rock deposits in Poland and the profitability of their extraction and processing, as also suggested by Mazurek et al., 2023 [23]. As a reminder, different criteria applied in previous years. For example, during the mining of the Annopol deposit, ore containing 14% P₂O₅ was mined until 1967, and from 1968—ore containing 8% P₂O₅ [92].

The problem of sustainable phosphorus management is global and has been studied by numerous researchers [93,94,95,96,97,98,99]. Several international meetings, conferences, and webinars have been organized around this issue, e.g., the European Sustainable Phosphorus, Monitoring Phosphorus in the Environment, Global Sustainable Phosphorus Summit, Water Protection Programme Against Pollution Caused by Phosphorus Compounds from Agricultural Sources, and Phosphorus—contemporary challenges for agriculture and the environment.

Recognizing that phosphorus is essential for agriculture, food security, and industry yet poses critical challenges for water quality and the environment, international programs such as the European Sustainable Phosphorus Platform (ESPP) have been launched. This platform brings together companies, scientists, and stakeholders engaged in sustainable phosphorus management and nutrient recycling.

Sustainable phosphorus management requires a thorough understanding of P cycles in various ecosystems, a reliable balance of gains and losses related to phosphorite mining and industry processing, and effective agricultural practices. Excessive use of phosphorus fertilizers can deplete the world’s non-renewable phosphate resources. Simultaneously, excess P introduced to soils can leach into groundwater and surface waters, contributing to anthropogenic eutrophication. Therefore, coordinated efforts between science, industry, and policymakers are paramount to protect both non-renewable phosphate reserves and water resources.

The sustainable management of phosphorus resources is also a key focus in Poland. According to Smol et al., 2023 [100], several projects are currently underway in the country aimed at P recovery, with support from various companies, including Jarocin Waterworks Company, Azoty Group “Fosfory”, and the Sewage Treatment Plant— Tarnowskie Wodociagi. Examples of these projects include (i) “Sustainable management of phosphorus in the Baltic region (InPhos)”, (ii) “Market ready technologies for P-recovery from municipal wastewater (PhosForce)”, (iii) “Towards Circular Economy in wastewater sector: Knowledge transfer and identification of the recovery potential for Phosphorus in Poland (CEPhosPOL)”, or (iiii) “Polish Fertilisers form Ash (PolFerAsh)”.

Several methods of phosphorus recovery from wastes were developed and implemented in Poland. For instance, PolFerAsh (Polish Fertilizers form Ash) proposed a new phosphorus recovery technology from Polish industrial sewage sludge ashes (SSAs) by using a wet method with mineral acid [101] or a wet method from SSAs with the use of nitric acid extraction [102]. In addition, the method of phosphorus recovery by acid extraction methods, developed by Cracow University of Technology, results in an efficiency of 80–96% of phosphorus recovery, and in this way, about 3000–4000 tons of phosphorus per year can be recycled and introduced back into the environment [103]. Thermochemical methods are the second type of methods commonly used to recover P from SSAs [103], with P recovery efficiency > 95% [104]. According to Witek-Krowiak et al. (2022) [104], combining biological, chemical, and physical methods with thermal treatment is the most effective way for phosphorus recovery from wastewater sludge. In turn, for animal by-products and other biological waste, the most optimal solution for P recovery appears to be chemical methods, with a recovery rate over 96%. Nutrient-rich waste, such as sewage sludge or sewage sludge ash, can be treated to recover nutrients and further use in the production of mineral fertilizers, a solution strongly recommended by the European Commission in the frame of the ‘Farm to Fork’ strategy, which is an integral part of the European Green Deal [104].

It should be noted that proper phosphorus management begins at the stage of ore extracting and processing. The sustainable use of phosphorus fertilizers in agriculture is just as important. Soil phosphorus has a direct influence on major sustainability outcomes, such as crop yields, water quality, and carbon sequestration, which was emphasized by Helfenstein et al., 2024 [105]. Phosphorus in soils is present mainly in organic forms or is associated with soil minerals [12,106,107]. The cycle of this element is divided into two subcycles, a geochemical subcycle and biological, where the central point in the overall cycle consists of the inorganic solution P pool. Both plants and soil microorganisms need orthophosphates from this pool of inorganic P [12]. In soil solutions, soil pH is considered the “master variable” of soil chemistry [10]. To be available to plants, P first must be dissolved into the solution, which also means that at the same time, it can potentially be lost through leaching or run-off. Therefore, soil pH management is crucial for both agronomic and environmental management. Aluminum is most active to phosphate precipitation at a pH of 5.0 to 5.5, Fe at pH < 4, whereas Ca is responsible for phosphate precipitation in alkaline soils, especially at pH around 8 [9]. As indicated Penn and Camberato, 2019 [10], phosphorus uptake by plants and desorption by soil occur at a lower optimum pH than the near neutral pH, as usually estimated. Furthermore, microorganisms play a key role in phosphorus bioavailability.

Microbiota are of key importance in the plant rhizosphere, contributing to the circulation of phosphorus in various ways, primarily by facilitating the solubilization and uptake through the secretion of enzymes and organic acids [108,109]. Rhizosphere-associated microorganisms are responsible for receiving and interpretating signals produced by themselves, other microbes, and plants, and they can influence the host plant by releasing signaling molecules. This communication is mainly related to the induction of plant immunity, stress tolerance, overall growth, health, nutrient acquisition, and the maintenance of the associated rhizosphere microbiome [110]. Ectomycorrhizal fungi constitute of a similarly significant component of forest soil microbiomes, forming association with approximately 60% of trees globally [111]. According to Yan et al. (2025) [112] and references therein, these fungi influence phosphorus availability in the rhizosphere and help host plants efficiently obtain soil nutrients and water, while also interacting with soil saprotrophic microbes to regulate soil carbon decomposition and nutrient cycling.

However, plants absorb only a small dose of P from fertilizers (about 10–20%, Ogwu et al. (2025) [107]), leading to significant inefficiencies and negative environmental consequences. As mentioned by Samreen and Kausar (2019) [113], P fertilizers used worldwide are produced from acid- or heat-treated phosphate rock to break the apatite bond and increase the water-soluble P content. Many commercially available phosphorus fertilizers include phosphate rock, phosphoric acid, calcium orthophosphates, and various phosphates compounds [113]. According to Annis (2016) [114], phosphorus is applied as ammonium phosphates or superphosphate, and phosphorus fertilizers are often characterized by their (N–P–K, nitrogen–phosphorus–potassium) composition. Common phosphate fertilizers include liquid ammonium polyphosphate (10–34–0), dry mono- or diammonium phosphate (11–48–0, 16–48–0, or 18–46–0), superphosphate (0–20–0), or concentrated superphosphate (0–45–0). When incorporated into the soil, phosphorus in fertilizers is converted to water-soluble inorganic phosphate as orthophosphate ions within hours after application [115]. When fertilizer reaches the soil, available soil moisture begins to dissolve its particles, increasing the concentration of inorganic phosphate in solution, and diffuses at a short distance from the fertilizer particles. Inorganic phosphorus is negatively charged and readily reacts with iron (Fe³⁺), aluminum (Al³⁺), and calcium (Ca²⁺) ions to form a relatively insoluble complex, unavailable for crop uptake [115]. Phosphorus is usually quickly precipitated in soil, both in acid and alkaline pH (in acid environments, P is precipitated by iron and aluminum, in alkaline—by calcium); however, phosphorus is relatively more available to crops when it is precipitated by Ca, which is important when estimating phosphorus fertilization.

In the research area of Vistula–Bug interfluve, the agricultural land in the Lublin region covers approximately 1.6 million ha, of which 80% is arable land and 20% is grassland [116]. According to Rutkowska and Kopiński (2022) [17], based on the results of agrochemical studies conducted in Poland over recent decades, a systematic increase in soil phosphorus content can be observed. According to the same authors, between 1955 and 2019, the share of soils with very low and low available P content decreased from 56% to 30%. Monitoring studies conducted in 2008–2016 show that the average content of available phosphorus in Polish soils was 16.9 mg P₂O₅ per 100 g of soil [117]. In the Lublin voivodeship, the average content of available P was very similar, at 16.8 mg per 100 g of soil [117]. Of nearly 135,000 soil samples collected from the Lublin Voivodeship between 2016 and 2019, the content of available phosphorus P₂O₅, was as follows (in % of samples tested): very low—8%, low—26%, medium—28%, high—18%, and very high—20% [17].

In Poland, according to data from the period 2010–2013 [118], about 43% of soils were acidic and very acidic, approximately 33% were slightly acidic, and approximately 24% were neutral and alkaline. In Lublin Voivodeship, the percentage of acidic, neutral, and alkaline soils in the total soil pool of this area is as follows: 17% of soils with pH < 4.5, 27%—pH 4.6–5.5, 25%—pH 5.6–6.5, 15%—pH 6.6–7.2, and 16% of soils with pH > 7.2. These data indicate that limiting is needed or recommended for about 53% of the soils in the Lublin region.

The basic natural source of phosphorus in the soil is the parent rock and the phosphorus minerals contained therein, the most important of which are, of course, fluorapatite and hydroxyapatite [119,120]. For example, as reported by Sapek (2014) [120], the phosphorus content of rendzina formed from travertine is about 0.2 g·kg^–1, while that of rendzina formed from the Devonian formation is 2.8 g·kg^–1. This shows how the type of parent rock influences soil P content. The recommended balance factor resulting from soil phosphorus content, which was 1.019 between 2016 and 2019, will remain similar in 2030 (projected value: 1.020; according to calculations conducted by the Institute of Soil Science and Plant Cultivation—State Research Institute in Puławy) [17]. Data from the previously mentioned institute show that changes in the available phosphorus content in P-rich soils occur very slowly. In fact, according to Tujaka and Gosek (2009) [121], the lack of phosphorus fertilization over a period of three years had no significant effect on either crop yield or the total uptake of P by plants. The supply of phosphorus to plants is largely determined by the topsoil layer (0–30 cm), which contain more than half of the total soil phosphorus. Therefore, in such soils, even if P fertilization is omitted, long-term use is possible without negative production consequences. This leads to the conclusion that in soils with high and very high phosphorus content, it is not only possible but also necessary to reduce phosphorus fertilization to avoid introducing excessive amounts of this element into the soil. This is crucial because, as we have mentioned earlier, soluble and mobile forms of phosphorus accumulated in the soil can be released into the soil solution and eventually migrate into groundwater, nearby streams, and other surface waters, ultimately leading to eutrophication.

In the Annopol area, groundwater resources occur within the Upper and Lower Cretaceous as well as Upper Jurassic formations, and also within Quaternary sediments. Of these, the Upper Cretaceous and, locally, the Quaternary aquifers are of practical importance. According to Nowak (2006) [122], the thickness of the aquifer is from 40 to 80 m, and the free water table occurs at a depth < 5 m in river valleys, 5–15 m in valley slope zones, and 60–80 m in the plateau area in the watershed zone. The groundwater is extracted through wells drilled primarily from the Upper Cretaceous aquifer and in the Rachów and Annopol, as well as from the Lower Cretaceous and Upper Jurassic aquifers, with potential flow rates typically ranging from 10 to 50 m³/h.

Groundwater contamination threat depends on: (a) the degree of isolation of the aquifers by Quaternary clays and loess; (b) the depth of the water table; or (c) the presence of contamination points. In the case of the discussed region, the highest level of contamination threat exists for both the Quaternary and Upper Cretaceous horizons in the Vistula River Valley. Nearby facilities, such as sewage treatment plants, municipal landfills, gas stations, transportation routes, and fertilizers and pesticides leached from the soil, can introduce pollutants into waters, significantly degrading water quality.

Only the ore rich in P₂O₅ and that meets the appropriate requirements for heavy metal content and other components in the ore, such as arsenic and especially cadmium, and other mineral compounds (such as quartz, calcite, iron oxides, clay minerals, etc.) can be used to produce phosphate fertilizers. Additionally, on the one hand, phosphate ions can be easily retained in the soil solution, bound by various cations (Ca, Fe, Al), depending on the soil pH, and their excess can be leached into groundwater, resulting in a deterioration of its quality. Therefore, in the last decade, glauconite, a rich source of potassium that also contains REEs and other nutrients, has been increasingly mentioned as an alternative and so-called green fertilizer. Green fertilizers are needed to restore soil fertility and improve environmental conditions [123] and promote sustainable agriculture. Glauconite is common in large quantities in the Niedźwiada II area, where documented deposits of glauconitic sands are accompanied by phosphorite deposits. These deposits appear to have the greatest potential because they are shallow, facilitating their extraction, and can contribute to improving soil quality while also being a more ecological solution than phosphate fertilizers. Bearing in mind that the bedrock will constitute a natural source of phosphorus in soils and nearby waters, special emphasis must be placed on the optimal use of phosphate fertilizers in agriculture. At the same time, it is important to emphasize the need to seek alternative sources of phosphorus and develop methods for its recovery, which will not only minimize the extraction of finite, non-renewable phosphorus resources but also protect the environment and water resources.

In urbanized and agricultural areas where P fertilization is used and the bedrock is rich in phosphorus, special emphasis should be placed to the proper management of this element and to reducing anthropogenic sources of phosphorus released into the environment. The hydrological situation described above, using the example of Annopol, generally applies to the Vistula and Bug interfluve. In this area, despite the classification of spring waters as high purity, whose chemistry confirms the negligible contribution of anthropogenic influence, high P compound contents, particularly orthophosphates, have been reported numerous times [18,19,20,21]. For example, for selected springs in the Lublin Upland and Roztocze regions, the average concentration of orthophosphates in spring waters ranges from 0.2 to 1.1 mg/dm³, a similarly high orthophosphate concentration in riverine waters from the study area was observed, average 0.4 mg/dm³ [21]. On the one hand, considering the abundance of phosphate rock in the Lublin and Roztocze regions, it is important to emphasize their essential, irreplaceable role in agriculture. Due primarily to economic factors, the profitability of phosphorite mining will most likely be reassessed in the coming years, also due to the co-occurring REE resources in the deposits. On the other hand, excessive amounts of P introduced into the environment by humans not only constantly deplete limited phosphate rock resources but also lead to contamination of groundwater and surface waters, and consequently, eutrophication, which also has negative environmental effects.

Sustainable phosphorus resource management allows for the highest yields with only the necessary amount of phosphorus introduced into the soil by humans. Optimizing food production costs is particularly important for less developed regions of the world, where hunger and malnutrition affect a significant part of the population. It should be remembered that naturally occurring phosphate rock deposits are gradually being depleted, and excessive amounts introduced into the soil not only fail to increase crop yields but also leach into water, causing eutrophication. Sustainable phosphorus management also leads to the protection of water resources. Current methods for recovering phosphorus from various types of waste allow for some of this phosphorus to be reintroduced into the environment, but this recycling requires additional financial resources that could be allocated to other purposes through more sustainable P resource management. In summary, the sustainable management of non-renewable phosphorus resources is crucial both locally and globally.

6. Conclusions

Phosphorus is an essential and irreplaceable element for life, and its main source, such as phosphate rock, may soon become depleted. Excess phosphorus introduced into the pedosphere is not fully utilized by plants and can leach from soils and rocks into groundwater and surface waters, causing eutrophication. Not all forms of phosphorus are bioavailable, highlighting the need to increase the efficiency of P supplementation in agriculture and to minimize losses during phosphate ore mining and processing. The proper management of non-renewable phosphorus resources will help secure both phosphate rock resources and drinking water supplies for future generations.

Sedimentary phosphate rocks occur in Poland, especially in the Vistula–Bug interfluve. Of the most important Polish phosphorite formations, the first, Albian deposits located along the northern edge of the Holy Cross Mountains, is represented in our study by Annopol and Bochotnica deposits (sites no. 1 and no. 2), while the second, Eocene deposits in the northern area of the Lublin region, is represented by the deposits from Niedźwiada and the adjacent areas (site no. 3).

In the case of Annopol deposits, the main phosphate layer was formed in the Albian, resulting from submarine erosion and redeposition by marine currents of previously formed phosphate rocks. In turn, in Bochotnica, the main phosphorite layer was found in a glauconitic sandstone layer formed in lower Danian. In contrast, in the Niedźwiada region, including nearby Leszkowice and Górka Lubartowska, Eocene phosphorites can be found at shallow depths as deposits accompanying glauconitic sands. In the case of Albian deposits, the high phosphorus content is associated with the ubiquitous presence of francolite (a mixture of various forms of phosphate minerals) in phosphate nodules; although less numerous, scattered grains of apatite and monazite can also be observed. In the Niedźwiada region, phosphorites accompany glauconite sand deposits, and their average content is nearly 23%.

Samples collected in Bochotnica indicate that the area is rich in phosphorites, and that monazite, a rare earth element carrier, is also relatively common. These results suggest considering further exploration for phosphorite deposits in the area close to Bochotnica. The phosphorite concretions collected in the Annopol area have relatively high P₂O₅ concentration and are enriched in some rare earth elements. Currently, the deposits would be suitable only for underground mining; however, they do not meet current mining economic criteria, and therefore no mining is being carried out.

Among the studied deposits, the most promising seems to be the shallow-lying phosphorites (<30 m deep) in the Niedźwiada region. This documented deposit contains 7.33 thousand tons of economic resources and is not exploited yet. The glauconitic sands associated with these above-mentioned phosphorites are a valuable source of potassium, nutrients, and REEs and can be considered a so-called green fertilizer, offering a more environmental friendly alternative to commonly used phosphate fertilizers.

Currently, no phosphate ore is mined in Poland, and domestic demand is entirely covered by import. However, due to the dramatic increase in global phosphate rock prices and the ongoing depletion of these resources by major producers, alternative phosphorus sources are being sought, and new criteria for evaluating domestic phosphorite deposits are under consideration. The currently unexploited phosphate deposits in the Lublin region can be considered as prospective not only because the domestic phosphorus demand could be partially met by local mining, but also because these deposits contain REEs, which are themselves critical raw material. At the same time, further research should be carried out to improve the efficiency of P recovery from various types of P-rich waste.

High concentrations of orthophosphate in some studied waters in the Vistula–Bug interfluve, primarily in spring waters, for which chemical test results exclude a significant anthropogenic influence and whose parent rocks are carbonate formation relatively enriched in phosphate minerals, may indicate that the primary source of orthophosphate in these waters in the leaching of phosphates from the bedrock. The primary natural source of phosphorus in the soil is the parent rock and the phosphorus minerals contained therein. Additional supplementation with phosphate fertilizers should be carried out only in those areas where it is actually required; otherwise, excess P will leach into groundwater. Reducing the impact of anthropogenic sources of phosphorus, such as municipal and industrial wastewater, on groundwater and surface water should be particularly important, especially in areas with P-rich bedrocks.