Emerging Contaminants in Coastal Landscape Park, South Baltic Sea Region: Year-Round Monitoring of Treated Wastewater Discharge into Czarna Wda River

Abstract

In response to the European Union’s revised Urban Wastewater Treatment Directive, which mandates enhanced monitoring and advanced treatment of micropollutants, this study was conducted. It took place within the Coastal Landscape Park (CLP), a Natura 2000 protected area in northern Poland. The focus was on the municipal wastewater treatment plant in Jastrzębia Góra, located in a region exposed to seasonal tourist pressure and discharging effluent into the Czarna Wda River. A total of 90 wastewater samples were collected during five monitoring campaigns (July, September 2021; February, May, July 2022) and analysed for 13 pharmaceuticals and personal care products (PPCPs) using ultra-high-performance liquid chromatography tandem mass spectrometry with electrospray ionisation (UHPLC-ESI-MS/MS). The monitoring included both untreated (UTWW) and treated wastewater (TWW) to assess the PPCP removal efficiency and persistence. The highest concentrations in the treated wastewater were observed for metoprolol (up to 472.9 ng/L), diclofenac (up to 3030 ng/L), trimethoprim (up to 603.6 ng/L) and carbamazepine (up to 2221 ng/L). A risk quotient (RQ) analysis identified diclofenac and LI-CBZ as priority substances for monitoring. Multivariate analyses (PCA, HCA) revealed co-occurrence patterns and seasonal trends. The results underline the need for advanced treatment solutions and targeted monitoring, especially in sensitive coastal catchments with variable micropollutant presence.

1. Introduction

The South Baltic region plays a vital ecological and economic role, with the region’s marine ecosystem diversity underpinning its economic relevance [1], particularly in the domains of fisheries and coastal tourism [2,3,4]. However, the discharge of treated wastewater containing pharmaceuticals and personal care products (PPCPs) threatens the integrity of these sensitive ecosystems [5], undermining their capacity to provide essential ecosystem services such as water purification, nutrient cycling and habitat provision [6,7,8]. A significant portion of these threats originates from municipal wastewater treatment plants, which remain the primary pathway for PPCP emissions into surface waters, especially in densely populated or tourist-heavy coastal areas. The semi-enclosed nature of the Baltic Sea exacerbates the situation, as limited water exchange can result in higher pollutant concentrations compared to more open marine systems [4,9,10].

The area of the Coastal Landscape Park, (the southern Baltic coast) is part of the Natura 2000 network and contains valuable marine habitats, such as underwater meadows of charophytes and eelgrass (Zostera marina). They serve as spawning grounds and shelters for numerous species of fish and invertebrates [1,11]. It is also an important refuge for marine mammals, such as the grey seal [12,13], as well as for many species of waterbirds associated with coastal habitats [14]. The park’s unique habitats are particularly vulnerable to pollution, making the presence of PPCPs in its waterways an urgent concern [15,16]. Maintaining the ecological balance of these ecosystems is essential for both effective environmental protection and the preservation of their tourism-related functions [17,18].

The PPCPs in aquatic environments represents a major environmental challenge [19,20,21]. These contaminants primarily enter aquatic environments via treated wastewater discharges, as most of these substances are not fully metabolised by humans and animals [22]. Conventional wastewater treatment plants are often ineffective in fully removing these compounds, resulting in their accumulation in natural water bodies [23]. This accumulation poses risks to aquatic organisms and may contribute to the development and spread of antibiotic-resistant bacteria, potentially impacting both ecosystems and human health [24,25,26].

In response to growing awareness of environmental pollution, the European Union has updated its guidelines, placing greater emphasis on the monitoring and mitigation of substances such as PPCPs [27]. The revised Urban Wastewater Treatment Directive now mandates the enhancement of treatment processes aimed at reducing the presence of micropollutants in wastewater [28]. These legislative changes highlight the need for comprehensive monitoring programs to assess and manage the environmental impact of such contaminants.

Point sources, in particular wastewater treatment plants, are the main contributors to PPCP emissions to the aquatic environment [29,30]. Healthcare-related wastewater, particularly from hospitals, poses a significant concern due to its typically elevated concentrations of pharmaceutical residues [31,32]. The following results highlight another critical issue: the increased concentration of micropollutants in discharged wastewater resulting from intensified tourism in ecologically sensitive areas [33,34]. Effectively addressing these emissions requires targeted strategies, such as the adoption of advanced treatment technologies and the application of enhanced water quality monitoring practices.

This study focuses specifically on wastewater effluents as the main vector of PPCP transport to the aquatic environment, assessing both contaminant levels and removal efficiency under real operating conditions. A selection of PPCPs was analysed, including UV filters (ethylhexyl methoxycinnamate, benzophenone-1 and benzophenone-3), β-blockers (metoprolol, propranolol and atenolol), antibiotics (sulfamethoxazole and trimethoprim), analgesics and anti-inflammatory drugs (paracetamol and diclofenac), as well as anticonvulsants and their metabolites (carbamazepine, carbamazepine 10,11-epoxide and licarbazepine). These substances were selected due to their documented persistence, widespread use, and in some cases their incomplete removal during conventional biological treatment, as well as frequent detection in treated wastewater and aquatic environments across Europe—particularly in hospital effluents, which are increasingly recognised as hotspots of pharmaceutical contamination [35]. Moreover, several of them, including benzophenone-3 and diclofenac, have been recognised by regulatory bodies such as the European Commission and HELCOM as contaminants of emerging concern due to their potential ecological risk [18,36,37]. Despite the well-documented environmental risks posed by PPCPs [38], there is a notable lack of large-scale, long-term studies addressing their seasonal variability in the South Baltic region [18,39,40]. This study seeks to fill this gap by implementing an extended monitoring program focused on PPCP concentrations in effluents discharged from wastewater treatment plants into the area of the Coastal Landscape Park (CLP). By examining seasonal fluctuations, this research provides novel insights into the occurrence, dynamics and potential ecological implications of PPCP contamination within this environmentally sensitive coastal zone.

In this article, we present the findings of a comprehensive seasonal monitoring campaign focused on the concentrations of selected PPCPs in wastewater treatment plant effluents. The study combines quantitative concentration data with multivariate statistical analyses, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), to assess patterns of co-occurrence and seasonal variability. Risk assessment was evaluated using the risk quotient (RQ) methodology. This integrated approach allowed for the recognition of key contaminants and evaluation of how conventional treatment performs under varying seasonal conditions, offering important insights into the factors affecting PPCP persistence and possible measures to reduce their discharge into vulnerable aquatic ecosystems.

2. Materials and Methods

2.1. Study Area and Sampling Details

2.1.1. Characteristics of the Chosen Research Object

The wastewater treatment plant in Jastrzębia Góra is located in the tourist region of northern Poland (Figure 1a). It serves the Władysławowo agglomeration, which includes the towns of Rozewie, Jastrzębia Góra, Tupadły, Ostrowo, Karwia, Mieroszyno, Kaczyniec and Czarny Młyn. Wastewater from Wastewater Treatment Plant (WWTP) Jastrzębia Góra is discharged into the Czarna Wda River, which, after a few kilometres, enters directly into the southern Baltic Sea.

The WWTP in Jastrzębia Góra serves a population of 4250, which increases to almost 50,000 during the summer due to tourism. Its designed capacity equals 517 m³/h, and its pollutant load corresponds to 62,000 PE (population equivalent). Due to the tourist character of the region, the maximum flow occurs only during the summer, while outside the tourist season, that is, most of the year, the flow does not exceed 15–20% of the maximum flow. Treatment technology includes a mechanical step and advanced biological step based on activated sludge with chemical precipitation to increase phosphorus removal. The technological scheme is shown in Figure 1b. Preliminary mechanical treatment of the wastewater is carried out in an interlocked unit—a screen-sandblaster. Biological treatment of the wastewater is carried out by a low-load, single-sediment multiphase activated sludge process in three integrated biological reactors for the simultaneous removal of carbon, nitrogen and phosphorus compounds according to the Bardenpho scheme with the Barnard modification. Then, the wastewater along with the sludge then flows into three final settling tanks, before which iron-based coagulant (PIX) dosing is provided for chemical support of phosphorus removal. Excess sludge and filtrate waters are returned to the treatment process, and stabilised sludge is sent to a mechanical sludge dewatering and hygienisation station equipped with a belt press [41].

2.1.2. Sampling

The study included five rounds of field campaigns at different times of the year: in July and September 2021 and in February, May and July 2022, during which 90 wastewater samples (inlet and outlet) were collected from the WWTP in Jastrzębia Góra. In the period between July and September, the WWTP is subjected to the seasonal population changes due to the tourist traffic. The samples were collected directly into plastic containers, which were then kept refrigerated during transportation to prevent degradation of the analytes. The samples were protected from exposure to sunlight, which is important for the stability of certain chemical compounds. After delivery to the laboratory, the samples were frozen until the micropollutants were analysed, which is standard practice to stop biological and chemical processes that can affect the composition of the samples.

2.2. Analytical Methods

2.2.1. Pharmaceuticals and Personal Care Products Determination

To determine the 13 selected PPCP concentrations, a Nexera XR ultra-high-performance liquid chromatography tandem mass spectrometer with electrospray ionisation (UHPLC-ESI-MS/MS) coupled with an LC/MS-8050 (Shimadzu Company, Kyoto, Japan) was used. The following micropollutants were selected: UV filters: benzophenone 1, 3 (BP-1, BP-3), ethylhexyl methoxycinnamate (EHMC); b-blockers: metoprolol (MET), propranolol (PROP), atenolol (ATE); analgesic and antipyretic drugs: diclofenac (DIC), acetaminophen (paracetamol) (APAP); anticonvulsants and their metabolites: carbamazepine (CBZ); carbamazepine-10,11-epoxide (CBZ-10,11 epoxide), licarbazepine (LI-CBZ); antibiotics: sulfamethoxazole (SMX); trimethoprim (TRI).

Analytical, isotopically labelled, and deuterated standards were purchased from DR Ehrenstorfer (LGC Standards, Wesel, Germany) and Sigma Aldrich (Merck, Darmstadt, Germany). Eluent additives (ammonium formate, formic acid) and acetonitrile were MS-grade (Merck, Darmstadt, Germany). MS-grade and ultrapure water were used for solution prep and glassware cleaning, respectively. Polytetrafluoroethylene (PTFE) syringe filters (0.2 µm, Chromafil^® Macherey-Nagel, Dueren, Germany) were used. Solvent evaporation was performed using a Turbovap LV (Biotage, Uppsala, Sweden) with an N₂ generator (PEAK Scientific, Scotland, UK).

Initially, 100 mL and 300 mL of the sample (untreated and treated wastewater, respectively) were used for analysis. Solid phase extraction (SPE) was applied as a sample preparation step, and no filtration step before the SPE was performed. Hydrophilic–Lipophilic Balanced (HLB), 500 mg (Oasis, Water Company, Pretoria, South Africa) was applied for the SPE. A shim-pack SP-C18, 2.1 × 150 mm, and 2.7 µm was used as an analytical column. All detailed chromatographic conditions are described in detail in our previous study [42]. The method detection limits (MDLs) and method quantification limits (MQLs) for the selected PPCPs are available in the Supplementary Material (Table S1).

2.2.2. Risk Assessment

A risk assessment was performed to evaluate potential adverse effects of the PPCPs on aquatic ecosystems. Risk quotients (RQs) were calculated to assess the potential risk associated with the detected concentrations of the selected PPCPs using the following Equation (1):

RQ = MEC/PNEC,

(1)

where MEC represents the measured environmental concentration, and PNEC denotes the predicted no-effect concentration [43]. RQs were calculated for the treated wastewater to assess its potential negative impact of it on the receiving aquatic environments. This approach made it possible to verify the risk related to wastewater discharge before dilution, which occurs into the recipient (Czarna Wda River), which is why the lowest PNEC values for freshwater obtained from the NORMAN Ecotoxicology Database were applied [44]. RQ thresholds were applied to classify the assessed risks as insignificant (0.01–0.1), low (0.1–1), moderate (1–10) and high (>10), as reported in previous studies [45,46].

2.2.3. Statistical Analysis

Statistical computations were performed using the R programming language [47]. Data handling was performed using the Tidyverse package [48], whereas statistical visualisation was performed using the ggplot2 [49] and cowplot [50] libraries. The NADA and NADA2 packages were used for handling the left-censored values [51,52]. Clustering was performed with the cluster package [53], whereas for PCA analysis, the factoextra [54] library was utilised.

Statistical computations of sample characteristics, confidence intervals and statistical tests included information about left-censored values. For such cases, the regression on order statistics (ROS) was used [55]. In the case of the PCA, the left-censored values were substituted with half of the level of quantification (MQL) value.

The significance test of the difference between the mean values in two groups was performed using the logarithm of the data.

3. Results

3.1. Temporal Variation of Selected PPCPs

Figure 2 shows the seasonal fluctuations of selected PPCPs at the wastewater treatment plant based on the study of untreated (UTWW) and treated (TWW) wastewater samples collected during five monitoring campaigns between July 2021 and July 2022. Two types of graphs are presented for each compound: (a) illustrating changes in concentration over time and (b) comparing levels by wastewater type.

For most compounds, in particular UV filters (BP-1, BP-3), APAP and MET, strong reductions in concentration after treatment were observed, indicating the high efficiency of the biological treatment processes. However, the results also indicate limited removal of DIC, CBZ, its metabolites (CBZ-10,11-epoxide and LI-CBZ) and TRI, which were still present in relatively high concentrations in the treated effluent.

Seasonal patterns were observed for several compounds. The fluctuations in concentrations during the monitoring campaign suggest a link to changing patterns of pharmaceutical use and external factors such as tourist traffic or seasonal illness (Table S3). Antibiotics (SMX, TRI) and beta-blockers (MET, PROP, ATE) showed seasonal trends.

Compounds with high removal efficiency during biological treatment, such as APAP, MET, BP-1 and BP-3 (up to 99.9%; Table S2), showed consistently low concentrations in the effluent (TWW), with minimal variation between campaigns, indicating high efficiency, stability and predictability of the process. In contrast, substances with limited removal efficiency, such as TRI, DIC and CBZ, showed a wider range of concentrations and larger standard deviations (Figure 2(8ab,9ab,11ab)).

The statistical test for the means of logarithms of the pharmaceuticals concentrations was performed between the UTWW and TWW groups (Table S4). In most cases, the differences were determined to be statistically significant. However, in the case of SMX, TRI, DIC, CBZ and its analysed metabolites, the differences were not statistically significant. The p-values of the statistical tests are presented in

Table 1. p-values of significance tests between means of logarithms in TWW and UTWW groups.

PPCP	p-Value
BP-1	1.34 × 10−6
BP-3	8.81 × 10−6
EHMC	8.86 × 10−6
MET	1.73 × 10−7
PROP	8.52 × 10−4
ATE	1.09 × 10−4
SMX	0.0485
TRI	0.0695
DIC	0.8187
APAP	6.24 × 10−31
CBZ	0.2808
CBZ-10,11-epoxide	0.7583
LI-CBZ	0.0635

.

3.2. Multivariate Data Correlation

The PCA analysis of the scaled concentration data clearly shows two separate groups (Figure 3). These two groups mostly match the treated and untreated wastewater samples. We can also see two sets of variables that are strongly related to each other: (1) CBZ, CBZ10,11-epoxide and DIC; (2) BP-1, BP-3, EHMC, MET, PROP, ATE, SMX, APAP and LI-CBZ.

These two sets are not related to each other. Moreover, the TRI variable does not show any connection with either of the two groups.

The clustering dendrogram shows the three main clusters (Figure 4). One consists of two TWW points, samples 20 and 30 of July 2021. Then, two lower-level clusters are formed. One of them consists of three points of untreated wastewater. The middle main cluster contains the rest of the observations, which include both TWW and UTWW points.

Figure 5 presents correlation matrices for the PPCP concentrations in the untreated (UTWW) and treated wastewater (TWW). In the UTWW, the strongest positive correlation was observed between PROP and EHMC (r = 0.87), as well as CBZ and its metabolite CBZ-epoxide (r = 0.60). In the TWW, correlations were dominated by poorly biodegradable compounds such as DIC, APAP and CBZ (r = 0.45–0.54), with the strongest between CBZ and CBZ-epoxide (r = 0.76). Negative correlations (e.g., SMX–MET, r = –0.46) indicate divergent behaviour after treatment.

3.3. Risk Assessment Results

Table 2. Risk assessment—risk quotients (RQs) associated with treated wastewater.

Compound Class		UV Filters			b-Blockers			Antibiotic		Analgesic and Antipyretic Drugs		Anticonvulsants and It’s Metabolites
Compound name		BP-1	BP-3	EHMC	MET	PROP	ATE	SMX	TRI	DIC	APAP	CBZ	CBZ-epoxide	LI-CBZ
CAS No.		131-56-6	131-57-7	83834-59-7	51384-51-1	525-66-6	29122-68-7	15307-86-5	103-90-2	723-46-6	738-70-5	298-46-4	36507-30-9	35079-97-1
Lowest PNEC fresh-water	mgL−1	1.71	1.54	0.13	8.60	0.16	150.0	0.60	120.0	0.05	46.0	2.0	2.57	1.91
RQ for treated wastewater samples
value/risk
July 2021	Highest value TWW	<0.1	<0.1	1.3	<0.1	<0.1	<0.1	0.2	<0.1	58	<0.1	1.1	0.1	0.3
	Lowest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	8.6	<0.1	0.4	<0.1	0.1
	Average value TWW	<0.1	<0.1	0.2	<0.1	<0.1	<0.1	0.1	<0.1	24	<0.1	0.7	<0.1	0.2
September 2021	Highest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.1	<0.1	50	<0.1	0.7	<0.1	<0.1
	Lowest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	13	<0.1	0.3	<0.1	<0.1
	Average value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	29	<0.1	0.5	<0.1	<0.1
February 2022	Highest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	<0.1	36	<0.1	0.5	<0.1	0.1
	Lowest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	7.7	<0.1	<0.1	<0.1	<0.1
	Average value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	21	<0.1	0.2	<0.1	<0.1
May 2022	Highest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	<0.1	61	<0.1	0.7	0.2	<0.1
	Lowest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	17	<0.1	0.2	<0.1	<0.1
	Average value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	35	<0.1	0.5	<0.1	<0.1
July 2022	Highest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	<0.1	44	<0.1	0.9	<0.1	0.2
	Lowest value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	11	<0.1	0.2	<0.1	<0.1
	Average value TWW	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.2	<0.1	26	<0.1	0.6	<0.1	<0.1

Highlights: refers to the risk assessment level based on RQ: blue (RQ < 0.1)—insignificant risk; green (RQ: 0.1–1.0)—low risk; yellow (RQ:1.0–10)—moderate risk; red (RQ > 10)—high risk.

presents the risk assessment for selected micropollutants based on the risk quotient (RQ) values determined for the treated wastewater samples collected in the five seasonal campaigns. The results indicate compound-specific and seasonal variability. The risk assessment was performed using the highest, lowest and average MEC values observed within each sampling series, allowing for a more comprehensive evaluation of the variability. UV filters BP-1 and BP-3 consistently showed a low risk (RQ < 0.1), whereas EHMC exhibited elevated RQ values for the highest observed concentration of this UV filter. Among the β-blockers, metoprolol, propranolol and atenolol typically remained below the risk threshold (RQ < 0.1), with occasional exceedances for metoprolol. SMX reached RQ values up to 0.2, while TRI remained consistently below 0.1. Diclofenac (DIC) showed persistently high RQ values (up to 61). APAP presented an insignificant risk in all samples. For the anticonvulsants, CBZ and its epoxide metabolite showed moderate RQ values (0.1–1.1), while LI-CBZ exceeded the low-risk threshold in most samples, with maximum RQ values reaching 0.3.

4. Discussion

4.1. Temporal Variation of Selected PPCPs

In this article, we present the findings of a comprehensive seasonal monitoring campaign focused on the concentrations of selected PPCPs in WWTP influent and effluent. The results of this study provide information on the seasonal variability of selected PPCPs in the TWW and UTWW and demonstrate the varying effectiveness of conventional treatment processes. These results are important for understanding the environmental fate of micropollutants and identifying periods of increased environmental pressure. Long-term monitoring of this type is essential to support environmental risk assessment, guide the selection and optimisation of treatment technologies and generate robust data for informed decision-making under the revised Urban Wastewater Treatment Directive (2024/3019) [28]. Although only benzophenone-3 (BP-3) is currently included in the EU Watch List (5th update) [27], which is revised biennially, several other substances examined in this study—such as diclofenac, sulfamethoxazole or carbamazepine—are widely recognised in the scientific literature as contaminants of emerging concern. Their continued monitoring remains important for anticipating future regulatory developments and protecting aquatic environments.

4.1.1. UV Filters

In terms of the UV filter compounds analysed (Figure 2(1ab–3ab)), the highest concentrations in UTWW were recorded for EHMC, which reached levels of more than 2500 ng/L in July 2021. In the other campaigns—especially in winter and spring—its concentration did not exceed 300 ng/L, indicating a clear seasonal dependence (according to the compound categorisation and tentative external factor analysis shown in Table S3, Supplementary Materials). In TWW, EHMC was present at much lower levels, usually below 100 ng/L, indicating high, though incomplete, removal efficiency) in the range of 93.4–99.9% (Table S2). Although the removal efficiency was high, the residual presence of EHMC in treated effluents may be attributed to its partial biodegradability, as indicated by earlier research [56,57]. Similar observations were presented by Langford et al. [58], who reported EHMC concentrations below 5 ng/L in Norwegian wastewater and highlighted the risk of bioaccumulation of some UV filters despite their effective removal during biological treatment processes. These results highlight the importance of continuous monitoring of UV filters at the effluent discharge stage, especially during peak periods, in order to better assess their potential environmental impact and develop future regulatory actions.

Similar seasonal variability was observed for BP-1 and BP-3—their concentrations in the UTWW during the summer months reached 180–360 ng/L, while in the winter these values decreased below 33 ng/L. Both compounds were effectively removed from the TWW samples, and their average levels did not exceed the method quantification limit (<5 ng/L), confirming the high removal efficiency (up to 97.1%, Table S2) of biological treatment processes, as also reported by other researchers [59].

These trends are in line with the results of other investigations, which indicate an increase in the UV filter content of wastewater and surface water during summer. This is related to the more frequent use of sunscreen cosmetics and the seasonal overloading of treatment plants as a result of coastal tourism [60,61,62].

In relation to surface waters receiving treated wastewater, it was found that EHMC concentrations in the TWW samples were significantly higher than those recorded in the southern part of the South Baltic Sea, where researchers only recorded values below the limit of quantification [63,64,65]. BP-3 has been recorded in Baltic waters at concentrations up to 11.4 ng/L, while BP-1 was detected in much lower concentrations of 2.5 ng/L [63]. As regulatory frameworks continue to develop, ongoing monitoring of persistent compounds such as organic UV filters at WWTP discharge points remains essential to ensure environmental safety and compliance with EU directives.

4.1.2. β-Blockers

In the examined group of β-blockers (Figure 2(4ab–6ab)), the highest concentrations were recorded for MET, confirming its dominant presence in municipal wastewater. In the UTWW, the MET values averaged 3117 ± 1332 ng/L in summer (July, September 2021 and 2022) and reached the value of 5039 ng/L in spring (May 2022), while in winter the values decreased to 819.0 ng/L (February 2022). Such a clear seasonality may result from temporal patterns in drug consumption (seasonal population changes). PROP and ATE were present in the UTWW at much lower concentrations—usually below 30 ng/L—also showing a clear decrease in the winter season.

In the TWW, the MET concentrations also showed significant seasonal fluctuations. In July 2021, the average was 37.3 ± 24.2 ng/L, rising to 195.8 ± 138.3 ng/L in February 2022. The lowest values were recorded in May 2022 (average 20.9 ± 7.2 ng/L), which may suggest more effective removal during the warmer inter-seasonal period (removal efficacy increase from 42.3 to 99.7%, Table S2).

Propranolol and atenolol were found in the TWW at concentrations usually below 10 ng/L, although values ranging from 10 to 13 ng/L were observed in a few samples taken during warmer months. High values in single measurements may be due to fluctuations in the hydraulic load of the treatment plant and short-term system overload caused by intense wastewater inflow or high pollutant loads [66]. These observations are consistent with the findings of Kisielus et al. [39], who analysed treated effluents from WWTPs located in the Baltic Sea catchment. The study confirmed substantial variability in the removal efficiency of β-blockers in wastewater treatment plants using conventional activated sludge (CAS) processes, particularly for propranolol, where removal rates ranged from negative values to above 50%. This variability highlights the strong influence of local process configurations and supports the need for site-specific monitoring of pharmaceutical removal. Despite the 42.3–98.6% removal efficiency, MET was the most difficult to eliminate during winter, which is in line with earlier observations by Vieno et al. [67], who reported low biodegradability of MET and its persistence in the aquatic environment. These findings are also supported by Yi et al. [68], who emphasised that the removal rates of β-blockers, including MET and ATE, in WWTPs can vary significantly depending on treatment configuration, hydraulic retention time (HRT), sludge retention time (SRT) and seasonal temperature. Reported removal efficiencies ranged widely from <10% to >90%, highlighting the importance of operational conditions for effective elimination of these pharmaceuticals. The authors confirmed the presence of these compounds in treated wastewater and surface waters, with significant seasonal and local variations. Godoy et al. [69] emphasise that β-blockers are one of the most frequently detected pharmaceuticals in treated wastewater and the aquatic environment: In the Baltic Sea catchment area, MET and ATE concentrations reached up to 80 ng/L [70], but Nödler et al. [71] reported values of 10 ng/L and 13 ng/L, respectively.

Vieno et al. [67] observed concentration of 795 ng/L for ATE and 1060 ng/L for MET in UTWW, while the values decreased to 330 ng/L and 755 ng/L, respectively, in TWW. Even higher values of ATE for UTWW of 1260–7602 ng/L were observed by Kasprzyk-Horden et al. [30]. In the context of these data, our results for MET and ATE are lower, which may indicate lower local consumption alongside the more effective removal processes. This interpretation is also in line with the findings of Yi et al. [68], who reported that influent concentrations and pharmaceutical removal efficiencies are highly dependent on both regional drug consumption patterns and wastewater treatment plant design.

4.1.3. Antibiotics

In the UTWW and TWW, the concentrations of SMX and TRI showed significant seasonal variation and variable removal efficiency in the treatment processes (Figure 2(7ab,8ab)). In July and September 2021, the SMX concentrations in the UTWW averaged 136.6 ng/L and 184.0 ng/L, respectively, while in winter (February 2022), significantly lower values of 11.1 ng/L were observed. In spring (May 2022), the concentrations increased again to 77.3 ng/L. After treatment, SMX was present in the TWW in concentrations ranging from 13.4 to 148.8 ng/L, depending on the season. These seasonal differences may be related to cyclical increases in antibiotic consumption, especially during periods of increased morbidity [72].

The TRI concentrations in the UTWW also varied, ranging from 26.3 ng/L in May 2022 to 172.5 ng/L in September 2021. However, in the TWW, unusual increases in concentrations were observed in some months, including up to 603.6 ng/L in July 2022 and 412.3 ng/L in May 2022, which may indicate the possibility of desorption of the original form from activated sludge during the treatment processes or may be the result of recirculation in bioreactors [73,74]. In our study, the TRI values for some samples were higher in the TWW then in the UTWW. For comparison, the data presented in the MORPHEUS project Report [75] for SMX showed much higher concentrations in untreated wastewater from several German coastal WWTPs (430–4149 ng/L), with relatively high removal efficiencies ranging from 72% to 93%. In contrast, in our study, SMX levels were significantly lower both in raw and treated wastewater. Interestingly, the MORPHEUS dataset also included data from the same WWTP in Jastrzębia Góra, where SMX concentrations in treated effluents ranged from 125.3 to 296.6 ng/L, with removal efficiencies between 67.7% and 85.3%. These values align closely with our observations and highlight the importance of site-specific operational conditions, which may strongly influence antibiotic fate during wastewater treatment. The environmental persistence and moderate removal efficiency of SMX in conventional WWTPs have been confirmed by numerous studies, including large-scale monitoring by Zhou et al. [76], who reported high detection frequencies and risk levels exceeding environmental safety thresholds for this compound.

These results confirm that SMX and TRI are not removed sufficiently well in biological treatment processes. SMX, as a compound with high solubility and low sorption potential, is characterised by limited biodegradability [77], while TRI exhibits greater chemical stability, which favours its presence in TWW [37]. Our observations are consistent with earlier reports from the Baltic Sea region, where the presence of SMX and TRI has been confirmed in both treated wastewater and surface waters [18,34,39,71,78]. The potential impact of seasonal hydraulic overload associated with the tourist character of the region may also influence the variability of these antibiotics in studied TWW.

4.1.4. Analgesic and Antipyretic Drug

Of all the substances analysed, the highest concentrations were found for APAP, which in the UTWW ranged from 38,119 ng/L (February 2022) to 54,628 ng/L (May 2022), with very high values also recorded in the summer seasons, at 50,831 ng/L and 52,457 ng/L, respectively (Figure 2(10ab)). A significant reduction in concentrations was observed in TWW, although not complete—the average values ranged from 24.7 ng/L (May 2022) to 190.6 ng/L (July 2022). Such large fluctuations indicate variable treatment efficiency and potential hydraulic overloads of the system during periods of increased wastewater inflow. APAP, as an easily available and commonly used symptomatic treatment, is present in wastewater in large quantities regardless of the season, indicating intensive and constant use of this drug regardless of the season, with high concentrations occurring in both summer and winter. Similarly, high levels of APAP in municipal wastewater and its significant reduction during the treatment process were reported by Kasprzyk-Hordern et al., Björlenius et al. and Kot-Wasik et al. [30,70,78].

The DIC in the UTWW reached lower concentrations than APAP—from 672.5 ng/L (February 2022) to 2603 ng/L (September 2021) (Figure 2(9ab)). Its concentration ranged from 393.9 ng/L (February 2022) to 3030 ng/L (May 2022) in TWW, which indicates negligible treatment efficiency regardless of the season. These values are comparable to effluent data from other European countries (150–4100 ng/L) [73,79] and the Baltic Sea region (556.2–4001 ng/L) [18]. DIC is a substance with documented toxicity to aquatic organisms, which has been taken into account in the HELCOM [80] proposals for environmental indicators and numerous ecotoxicological studies [81,82]. Its persistence and low biodegradability mean that it can pose a long-term threat to surface waters, even after conventional treatment [36,83]. As noted by Vieno et al. [79], DIC is only moderately biodegradable, which limits its removal in conventional biological systems. Enhanced elimination may require advanced technologies such as membrane bioreactors, extended retention times or tertiary treatments based on oxidation or adsorption.

4.1.5. Anticonvulsants and Metabolites

Among the pharmaceuticals analysed, CBZ demonstrated exceptional persistence in the wastewater treatment system, as confirmed by both literature data and the results obtained in this study (Figure 2(11ab)). CBZ was present in the UTWW in all campaigns, with the highest concentration recorded in July 2021—2314 ng/L (the second sample from this campaign contained 788.3 ng/L), as well as in September 2021—1807 ng/L; May 2022—1686 ng/L; and July 2022—1204 ng/L. The lowest value was recorded in winter, in February 2022–389.3 ng/L. These results indicate the dominant nature of chronic CBZ use and its relatively stable presence in wastewater regardless of the season.

After wastewater treatment, CBZ was still present in a wide range of concentrations. In July 2021, they ranged from 880.1 to 2221 ng/L, and in February 2022, from 97.5 to 1016 ng/L. Such large differences may result from variations in the treatment plant load and possible secondary release of CBZ from recirculated wastewater sludge or the inflow of compounds previously retained in the wastewater system. The maximum values exceeding 1000 ng/L in several campaigns (Figure 2(11ab)) confirm the ineffectiveness of conventional treatment methods in eliminating this compound. Carbamazepine is known for its recalcitrance, and studies have shown that it is almost completely persistent during activated sludge treatment processes, contributing to its frequent detection in treated effluents [34]. Meyer et al. [84] reported CBZ concentrations in treated wastewater effluents ranging from 84 to 790 ng/L, and up to 370 ng/L in samples collected downstream from the discharge point. The antiepileptic drug carbamazepine also being one of the main compounds in the observed pattern showed concentrations up to 162 ng/L in the Oder river [85].

CBZ was also detected in the form of its metabolites—CBZ-10,11-epoxide and LI-CBZ (Figure 2(12ab,13ab)). The highest concentrations of CBZ-10,11-epoxide in the UTWW were observed during the summer months, reaching 303.6 ng/L and 268.7 ng/L. In the TWW, the compound was found at levels as high as 298.6 ng/L (July 2021) and 462.2 ng/L (May 2022). In the case of LI-CBZ, particularly high concentrations were recorded in a UTWW sample from July 2021 (5625 ng/L) and again in July 2022 (1819 ng/L). In the treated wastewater, the LI-CBZ levels reached 632.1 ng/L (July 2021) and 339.0 ng/L (July 2022), suggesting a significant role of transformation processes occurring during treatment.

These results are compatible with previous reports found in the literature, which repeatedly indicated the presence of CBZ in treated wastewater and its resistance to biodegradation. Ternes et al. [86] were among the first to propose CBZ as an indicator of anthropogenic pressure in the aquatic environment. Nödler et al. [87] and Kucharski et al. [82] emphasised its high chemical stability and widespread occurrence. Similar results of CBZ concentration levels were published by Björlenius et al., (UTWW: 86–1670 ng/L, TWW: 61–1805 ng/L) [70]. Moreover, Jelic et al. [88] indicated 400–1400 ng/L in TWW and Verlicchi et al. [36] observed concentrations in the range of 280–1910 ng/L.

In addition, Björlenius et al. [70] noted that the long half-life and accumulation potential of CBZ make it a suitable marker compound for tracing wastewater intrusions in aquatic ecosystems, especially in semi-enclosed basins such as the Baltic Sea. Archer et al. [89] reported the presence of CBZ in surface waters in the range of 157.1–279.5 ng/L. The fingerprint of CBZ was also visible in Baltic Sea sediments [90]. Moreover, the detection of CBZ in aquatic organisms, including marine waters, indicates a significant environmental risk due to its persistence and continuous presence in the environment [91,92].

4.2. Correlation and Compositional Analysis of PPCPs

PCA and HCA were performed to better understand the co-occurrence and similarities between the analysed pharmaceuticals. The PCA results showed that substances belonging to the same class and with similar physicochemical properties cluster in a similar component space, which may indicate their common origin, similar environmental behaviour and susceptibility to removal (Figure 3).

In particular, it was observed that the β-blockers (ATE, PROP, MET) grouped in a similar principal component space, reflecting their similar pharmacokinetic properties and similar resistance to biodegradation. This phenomenon is confirmed in the literature—the HELCOM report [18] indicates a strong representation of this group of drugs in the aquatic environment of the Baltic Sea, where they show homogeneous patterns of occurrence in both wastewater treatment plants and surface waters. ATE, MET and PROP are among the most frequently detected β-blockers in aquatic environments, with reported concentrations reaching several hundred μg/L. Their removal efficiency in WWTPs strongly depends on factors such as treatment configuration, biomass concentration, SRT and temperature, which explains the observed variation in elimination rates across different systems [68].

APAP and DIC did not form a distinct group in the PCA space. APAP showed similarity to β-blockers and selected UV filters, which may indicate similar patterns of presence and potential sources. DIC, on the other hand, clustered with carbamazepine and its metabolite, suggesting similar environmental persistence and limited susceptibility to removal in purification processes. In this study, the APAP concentrations in the TWW reached a maximum of 190.1 ng/L, and the DIC concentrations reached 3030 ng/L, confirming their presence also after treatment processes.

In the case of antibiotics, a clear spatial separation of SMX and TRI was observed in the PCA space—these substances were at opposite poles of the graph, which may indicate significant differences in their environmental behaviour or/and removal efficiency during treatment. Although SMX and TRI are often used together as a combined formulation, their different distribution may be due to differences in their chemical persistence, mobility or level of biodegradability. These observations are confirmed in the literature. The results of the project MORPHEUS project [75] clearly showed that in conventional activated sludge-based wastewater treatment plants, a removal efficiency of SMX in the range of 72–93% was achieved. In this study, TRI elimination was barely observed (Table S2). Similar conclusions are presented by Pérez et al. [93], indicating that TRI is more resistant to biodegradation. These differences may explain the different position of the two compounds in the PCA analysis and highlight the need to apply individual approaches to them in the context of monitoring and risk assessment.

The comparison with the MORPHEUS project [94] also reveals that conventional activated sludge systems, although widely used, are not equally effective for all pharmaceutical groups. The project results indicated that WWTPs that implemented additional treatment technologies, such as ozonation or adsorption on powdered activated carbon (PAC), achieved significantly higher removal efficiencies for compounds like diclofenac and carbamazepine—both classified as persistent and toxic to aquatic life. This highlights the technological gap between basic biological treatment and more advanced, targeted solutions and underscores the relevance of adapting treatment infrastructure to specific local pressures, particularly in sensitive areas or regions affected by seasonal overloading.

In the PCA (Figure 3), CBZ and its metabolite CBZ-10,11-epoxide occupied the most isolated position, which may reflect their high environmental persistence and characteristic presence profile in the samples. In contrast, LI-CBZ showed a different position, which may indicate a different mode of transformation, source of emission or a different susceptibility to removal during the treatment process. This interpretation is supported by literature data—e.g., Verlicchi et al. [36], Kasprzyk-Hordern et al. [37] and Sousa et al. [95]—which highlight that CBZ is among the pharmaceuticals most frequently detected in the aquatic environment and shows very low susceptibility to removal in conventional treatment processes.

The HCA dendrogram presents the results of the clustering of the wastewater samples based on the micropollutant concentration profiles (Figure 4). The analysis complements the PCA results by revealing similarity structures between the samples and showing a more complex picture. Although some clustering of TWW and UTWW samples is evident (e.g., July and September 2021 and February 2022), most samples, including both TWW and UTWW, were assigned to a common central cluster. This may indicate partial similarity in micropollutant concentration profiles between the selected raw and treated samples. In contrast, the two TWW samples (from 20 and 30 July 2021) formed a separate cluster, suggesting their different nature, possibly due to specific seasonal conditions or local anomalies.

The variation of samples within the dendrogram reflects the variability of wastewater composition over time and confirms the lack of a clear trend in micropollutant levels. This variability is consistent with earlier findings showing that PPCPs, especially those with low removal efficiency (e.g., CBZ, DIC, β-blockers), tend to fluctuate significantly under varying operational conditions and loading scenarios [88]. This analysis complements the PCA results by indicating the dynamic and non-linear nature of changes in PPCP concentrations, particularly for substances with varying treatment susceptibility (e.g., TRI, CBZ, DIC). In addition, the results of the correlation analysis (Figure 5) showed significant positive correlations between some of the compounds. In the UTWW (Figure 5a), a strong correlation was found between PROP and EHMCs (r = 0.87), which may suggest their similar behaviour during the wastewater treatment.

Strong positive correlations were also observed between SMX, TRI, DIC and APAP (r = 0.47–0.7), indicating their limited biodegradability and frequent co-occurrence in treated wastewater (Figure 5b). These conclusions are supported by HELCOM studies and Morpheus Project Report [75], which indicate that SMX and DIC are among the most frequently detected pharmaceutical compounds in municipal wastewater in the Baltic Sea region, and their concentrations are often correlated with the intensity of urbanisation and seasonality of consumption.

The negative correlations in the TWW are consistent with literature reports. As indicated by Gros et al. [73] and Verlicchi et al. [36], different groups of PPCPs are subject to different treatment mechanisms, leading to divergent patterns of presence in treated wastewater. Numerous studies confirm that removal efficiency of PPCPs is highly dependent on the applied treatment technology. While conventional activated sludge systems often fail to eliminate persistent compounds such as CBZ, TRI or DIC, advanced processes such as membrane bioreactors (MBRs), ozonation or activated carbon filtration demonstrate significantly better performance [36,79,96,97]. This highlights the importance of technology selection in achieving effective micropollutant reduction, especially in WWTPs discharging into sensitive environments. Moreover, Alygizakis et al. [98] demonstrated that the chemical profile of PPCPs in treated wastewater can be reshaped not only by the diversity of treatment technologies but also by complex transformation processes and biochemical interactions occurring during and after treatment.

The observed variability in PPCP concentrations, especially for substances with heterogeneous removal efficiencies (e.g., TRI, DIC, CBZ), highlights the need for continuous and adaptive monitoring strategies in wastewater treatment. As noted by La Cognata et al. [99], complementing traditional laboratory techniques, such as UHPLC-MS/MS, with real-time or in situ monitoring solutions can improve data resolution and enable earlier detection of treatment inefficiencies. Such an integrated approach is particularly valuable in coastal areas where there are seasonal fluctuations in both wastewater flow and pollutant loads.

The observed persistence of pharmaceuticals in wastewater, such as CBZ and SMX, is in line with previous results from large-scale studies in Europe. A comprehensive study by Loos et al. [34] confirmed that while state-of-the-art biological treatment methods are highly effective for readily biodegradable compounds such as ibuprofen (removal of around 90%), conventional wastewater treatment plants remain significantly less efficient for moderately persistent pharmaceuticals such as analgesic and antipyretic drugs or beta-blockers (removal of 20–80%). Interestingly, CBZ and SMX were found to be almost completely persistent during activated sludge treatment, confirming their role as markers of incomplete elimination and persistence in the environment. In addition, a comparison of effluent concentrations from 90 wastewater treatment plants across Europe with individual plant data showed that although median concentrations in the large-scale study were lower—probably due to the inclusion of industrial plants—maximum and mean values were similar to other regional reports, highlighting the widespread occurrence of these substances in European wastewater [34]. These results highlight the growing awareness in the EU of the need to upgrade tertiary treatment, including the introduction of ozonation or activated carbon systems, to improve the removal of PPCPs from municipal wastewater and reduce the environmental burden, particularly in light of the Wastewater Framework Directive [28] and increasing pressure on freshwater resources.

4.3. Risk Assessment

Risk assessment based on risk quotient (RQ) values showed significant variation in the potential impact of individual PPCPs on the aquatic environment (Table 2). TWW was included in the analysis, with predicted no-effect concentrations (PNECs) selected for freshwaters (TWW recipient). This approach represents a worst-case scenario, assuming minimal dilution of PPCPs in the receiving aquatic environment, such as during low-flow or drought conditions. The highest RQ values (RQ > 10) were observed for DIC and the carbamazepine metabolite LI-CBZ, both before and after the treatment process. The persistence of such high risk levels even after treatment indicates the low efficiency of conventional processes in eliminating these substances and the need to implement more advanced technologies, such as ozonation or adsorption on activated carbon to reduce the impact on receiving waters [34,36]. CBZ and CBZ-epoxide also showed moderate-to-high RQ values, confirming their environmental persistence and limited biodegradability. This conclusion is reinforced by recent estimates by Björlenius et al. [70], who calculated a removal efficiency of only 17.3% per year for CBZ in the Baltic Sea environment. Such low removal rates, together with the long half-life of over 3.5 years and cumulative discharge from urban sources, support its classification as a high-risk compound in long-term aquatic exposure scenarios. The presence of CBZ in environmental waters and benthic organisms is also confirmed by Kucharski et al. [82] and Nödler et al. [87]. This is also consistent with previous studies showing that conventional biological treatment processes often fail to efficiently eliminate persistent pharmaceutical residues, resulting in their continuous presence in treated effluents and environmental waters [73].

Although APAP was detected at high concentrations in UTWW samples (up to 54,627 ng/L), the corresponding risk in the treated effluents remained low (<1.0), highlighting the efficiency of the treatment processes in removing this substance. This may be linked to seasonality—APAP, as an antipyretic and analgesic, showed an increased presence during the winter campaign (February 2022), which is in line with literature observations of an increase in the consumption of OTC (over-the-counter—non-prescription) drugs during seasons of increased morbidity [73,75].

EHMC showed intermediate risk levels (0.1 < RQ < 1.0) in selected summer campaigns, unlike BP-1 and BP-3, whose RQs remained below 0.1. This may reflect the seasonal increase in sunscreen use. Despite reduction during treatment, EHMC occasionally maintained RQs indicative of moderate risk.

Within the group of antibiotics, SMX exhibited higher RQ values than TRI, suggesting a greater potential for ecological impact. In contrast, TRI consistently showed a low risk profile (RQ < 0.1) across all samples. It is noteworthy that both compounds may pose higher risks under specific conditions, such as the presence of hospital wastewater or reduced denitrification efficiency [34].

Low ecological risk (RQ < 0.1) was observed for the β-blockers (MET, PROP, ATE) and UV filters (BP-1, BP-3), suggesting limited environmental pressure from these substances in the studied WWTP system.

These findings highlight the importance of implementing structured and evidence-based environmental risk assessments as an integral part of wastewater management strategies. This approach is in line with the requirements of the revised Urban Wastewater Treatment Directive (Directive (EU) 2024/3019) [28], which requires the use of advanced (quaternary) treatment technologies in large wastewater treatment plants (more than 105,000 PE). For medium-sized treatment plants (10,000–150,000 PE), the directive requires a site-specific risk assessment by 2045 to determine the need to implement additional treatment stages.

In this context, the interpretation of the quantitative and seasonal monitoring data presented in this study highlights the value of continuous surveillance to support the identification of priority pollutants and the assessment of their potential environmental impact. These data provide a sound basis for planning compliance measures and optimising treatment technologies, in line with the precautionary principle and the One Health concept [100]. Integrating these assessments into long-term monitoring programmes will be essential to minimise the ecological risks posed by persistent micropollutants and ensure effective protection of sensitive aquatic ecosystems.

5. Conclusions

The results clearly indicate that the occurrence of the tested PPCPs in both the raw and treated wastewater confirms the limited effectiveness of conventional treatment methods used in common municipal treatment plants. Substances such as carbamazepine, diclofenac, trimethoprim and carbamazepine metabolites were detected in significant concentrations even after the treatment process, indicating their environmental persistence and low biodegradability. This phenomenon highlights the need to implement quaternary treatment technologies, such as ozonation or adsorption on activated carbon, which could more effectively remove these types of compounds, especially to protect sensitive aquatic ecosystems.

In addition, the observed seasonal variation in concentrations of many PPCPs indicates both the influence of environmental factors and changes in consumer behaviour. Increases in concentrations in summer (e.g., EHMC, BP-3) may be related to tourism and the more frequent use of sunscreen cosmetics, while winter increases in paracetamol probably reflect a higher use of OTC drugs during the infection season. Such seasonal fluctuations are important for assessing the effectiveness of treatment and planning mitigation activities, especially in the context of protecting sensitive areas such as the Coastal Landscape Park, which is part of the Natura 2000 protected areas network. It is therefore necessary to implement regular and seasonally adjusted monitoring to better track changes and identify periods of increased environmental risk in a timely manner.

The use of statistical analyses, such as PCA and HCA, has enabled a better understanding of the co-occurrence of compounds and their behaviour in the treatment system. These analyses made it possible to distinguish groups of substances with similar origins or elimination mechanisms and to identify compounds with the highest persistence and environmental risk potential. The risk assessment showed that certain PPCPs—in particular diclofenac and LI-CBZ—should be prioritised in mitigation strategies and planning of protective actions. The joint interpretation of the quantitative, seasonal results and their inter-correlation highlights the need for an interdisciplinary approach to effluent quality management and surface water protection, which is in the line with the revised Urban Wastewater Treatment Directive recommendations.

In conclusion, the results obtained clearly indicate the need to integrate modern treatment technologies together with periodic environmental monitoring, which is particularly important in the context of surface water protection and counteracting long-term pharmaceutical pollution pressures.