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Article

Heavy Metals in Leafy Vegetables and Soft Fruits from Allotment Gardens in the Warsaw Agglomeration: Health Risk Assessment

by
Jarosław Chmielewski
1,
Elżbieta Wszelaczyńska
2,*,
Jarosław Pobereżny
2,
Magdalena Florek-Łuszczki
3 and
Barbara Gworek
4
1
Department of Public Health, Academy of Medical Sciences of Applied and Holistic Sciences, 01-234 Warsaw, Poland
2
Department of Agronomy and Food Processing, Faculty of Agriculture and Biotechnology, University of Science and Technology, Prof. S. Kaliskiego 7, 85-796 Bydgoszcz, Poland
3
Department of Medical Anthropology, Institute of Rural Medicine, 20-090 Lublin, Poland
4
Department of Environmental Chemistry and Risk Assessment, The Institute of Environmental Protection—National Research Institute, 02-170 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(15), 6666; https://doi.org/10.3390/su17156666
Submission received: 15 May 2025 / Revised: 11 July 2025 / Accepted: 18 July 2025 / Published: 22 July 2025
(This article belongs to the Special Issue Soil Microorganisms, Plant Ecology and Sustainable Restoration)
Review Reports Versions Notes

Abstract

Vegetables and fruits grown in urban areas pose a potential threat to human health due to contamination with heavy metals (HMs). This study aimed to identify and quantify the concentrations of heavy metals (Fe, Mn, Zn, Cu, Pb, Cd) in tomatoes, leafy vegetables, and fruits collected from 16 allotment gardens (AGs) located in Warsaw. A total of 112 samples were analyzed (72 vegetable and 40 fruit samples). Vegetables from AGs accumulated significantly higher levels of HMs than fruits. Leafy vegetables, particularly those cultivated near high-traffic roads, exhibited markedly elevated levels of Pb, Cd, and Zn compared to those grown in peripheral areas. Lead concentrations exceeded permissible limits by six to twelve times, cadmium by one to thirteen times, and zinc by 0.7 to 2.4 times. Due to high levels of Pb and Cd, tomatoes should not be cultivated in urban environments. Regardless of location, only trace amounts of HMs were detected in fruits. The greatest health risk is associated with the consumption of leafy vegetables. Lettuce should be considered an indicator plant for assessing environmental contamination. The obtained Hazard Index (HI) values indicate that only the tested fruits are safe for consumption. Meanwhile, the values of the Hazard Quotient (HQ) indicate no health risk associated with the consumption of lettuce, cherries, and red currants. Among the analyzed elements, Pb showed a higher potential health risk than other metals. This study emphasizes the need for continuous monitoring of HM levels in urban soils and the establishment of baseline values for public health purposes. Remediation of contaminated soils and the implementation of safer agricultural practices are recommended to reduce the exposure of urban populations to the risks associated with the consumption of contaminated produce. In addition, the safety of fruits and vegetables grown in urban areas is influenced by the location of the AGs and the level of industrialization of the agglomeration. Therefore, the safety assessment of plant products derived from AGs should be monitored on a continuous basis, especially in vegetables.

1. Introduction

The term heavy metals (HMs) refers to chemical elements whose densities are greater than 4 g cm3 and are hazardous to organisms or even toxic at low concentrations [1,2].
Naturally occurring metallic elements are either components of the Earth’s crust or are introduced into the soil as a result of human activity. Both an excess and a deficiency of heavy metals (HMs), due to disruption in their environmental distribution, may lead to human health problems (2). Research indicates that exposure to heavy metals such as lead (Pb), cadmium (Cd), manganese (Mn), zinc (Zn), and copper (Cu) occurs through the respiratory system, skin contact, or the ingestion of contaminated food or drinking water [2,3,4,5,6]. The toxicity of Pb and Cd arises from their ability to form stable bonds with proteins, substituting essential metals (Cu, Fe) within their structure. This substitution is possible due to structural similarity between the elements [7]. Additionally, Pb and Cd inhibit certain enzymatic functions, leading to cellular dysfunction and poisoning of the organism [2,8]. In the human body, Pb and Cd may cause damage to the nervous and vascular systems, impair kidney and reproductive functions, and disturb the oxidative–antioxidative balance. Moreover, research findings [2,9,10,11,12] suggest that chronic exposure to Pb and Cd may be linked to various types of cancer. The Pb is especially dangerous for children and pregnant women, whereas Cd is among the most mobile elements in both soil and plants, enabling rapid absorption and transmission through the human food chain [3,5,6,13,14,15]. Zn poisoning—consumption above 40 mg per day—increases intestinal wall permeability, leads to metabolic disturbances, headaches, nausea, vomiting, diarrhea, and neurological changes in the form of anxiety disorders [2,16,17]. Exposure to Cu is associated with female infertility, cardiovascular diseases, and an increased risk of chronic kidney disease (CKD) [5,18]. Mn plays a significant positive role in brain function [19], but may be toxic due to its pro-oxidative properties [10,20]. Mn poisoning symptoms are similar to those observed in Parkinson’s disease [12,21]. Additionally, Mn impairs the functions of the kidneys, liver, pancreas, reproductive, and immune systems. Excessive inhalation of Mn may lead to manganese poisoning (manganism) [2,11,22]. Excess unabsorbed Fe causes gastritis and duodenitis, nausea, bloating, vomiting, indigestion, constipation, diarrhea, and abdominal pain, potentially contributing to the development of colorectal cancer (CRC) [2,16,23].
According to the authors [2,6,24], the most common source of consumer exposure to HMs is fruit and vegetables, which account for 90% of metal intake. The remaining 10% enters the body through skin contact and inhalation of contaminated air. The process of metal accumulation in plants involves three main stages: increased ion mobility, uptake, and transport to storage sites. Typically, metal accumulation in plants decreases in the following order: roots > stems > leaves > fruits and seeds [25].
In contrast, the most significant sources of vegetable and fruit contamination in urban environments include emissions from motor vehicles and the release of metallic particles from vehicular components, particularly brake and clutch systems, tire wear, and the corrosion of metal surfaces. The combustion of fossil fuels contributes significantly to the emission of elements such as lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), and mercury (Hg) into the environment [1,10,26,27]. The extent of soil contamination in urban settings is influenced by traffic intensity [26,27] and, notably, by the proximity of cultivated areas to roadways [26,28].
Nowadays, the risk of heavy metal contamination has increased through intensive economic development, industrialization, and urbanization [6,29]. Although industrialization and urbanization are increasing in Europe and beyond, leading to a decline in food self-sufficiency, “self-sufficient family farming remains the main livelihood in the 21st-century world” [30,31]. According to the research agency Kantar Polska S.A., nearly one in three Poles (30%) grow fruits and vegetables for personal use. In large cities with populations over 500,000, 17% of residents cultivate fruits and vegetables in allotment gardens (AGs), while in medium-sized cities (100,000–500,000) this number reaches 21%. According to Vávra et al. [30], over 30% of the population in Germany, the Czech Republic, and Scotland engage in food self-sufficiency using produce from AGs. This indicates that in Poland the potential for such production is not fully utilized, which may be due to differences in skills, motivation, and access to land [32].
Growing on AGs in urban areas contributes to social development [33], reduces carbon footprint and energy demand [34], contributes to job creation [35], and results in the development of the local economy and education [36]. All of this can make an important contribution to sustainable development and can benefit human health [37]. On the other hand, locating AGs on brownfield sites, currently used for horticultural purposes, can pose serious risks to human health [4,6,38,39]. Considering plant production in AGs, these areas should be located in zones free from air, soil, and groundwater pollution [4,38]. However, detailed and publicly available data on annual atmospheric deposition of heavy metals is often lacking for many cities, including Warsaw. Furthermore, few scientific studies address this issue. Therefore, precise monitoring of plants and soils in AGs for heavy metals is necessary. It is also essential to maintain optimal soil pH, use organic fertilization to limit metal bioavailability, implement phytoremediation, and cultivate in raised beds [40,41,42].
In addition, another problem faced by urban food production is the presence of HMs in the air and water, which ultimately leads to the contamination of vegetables and fruits grown on them with these metals. Food produced in the AGs consumed over a long period can lead to deterioration in the health of the local population. HMs do not decompose and do not degrade, so they can accumulate in the food chain of consumers. They therefore pose a threat to human health and even life [5,10,12,43]. Furthermore, there is no real monitoring of HM concentrations, especially in soil AGs as well as urban green public spaces. However, given the health benefits achieved by growing plants in urban areas, it is essential to properly manage these urban areas and monitor the yields obtained from them for the presence of contaminants, including HMs [2,4,35,44]. Therefore, it is reasonable to assess the risk posed by growing crops in urban areas to better understand the public health exposure of consumers of these agglomerations [2,4,43].
Please note that studies on the contamination of vegetables and fruits originating from allotment gardens (AGs) in urban agglomerations face a number of limitations that may affect their accuracy, representativeness, and interpretation of results. Major limitations include the variability of locations and environmental conditions, including the heterogeneity of gardens, differing wind directions within cities, and topography. The gardens located in depressions may accumulate more airborne particulate matter. In general, research is limited by the lack of uniform cultivation technologies, the use of different analytical methods and standardization. An additional challenge is the absence of long-term data on soil and plant contamination, as well as the lack of systematic monitoring of AGs. Often, there is also insufficient information on past industrial contamination of the studied AG areas, and previous use of plant protection products [45,46,47].
The research hypothesis assumes that fruits and vegetables grown in the AGs area of the city will be safe for the health of consumers. Cultivation in the AGs area is generally carried out without the use of mineral fertilization and chemical pesticides.
The study undertaken aimed to determine HM heavy metal contamination of leafy vegetables, tomatoes, and soft fruits grown in AGs in the capital city of Poland, together with a health risk assessment.
Additionally, a Health Risk Index (HRI) will be estimated to evaluate the impact of consuming fruits and vegetables contaminated with heavy metals on consumer health, based on HRI assessment (also known as THQ—Target Hazard Quotient).
Urban cultivation, through its positive impact on environmental protection and the health of local communities, can be an important element supporting the implementation of sustainable development goals.

2. Materials and Methods

Leafy vegetables (botanicals, lettuce, sorrel) and tomatoes, as well as soft fruits (cherries, gooseberries, red currants), were used in the study. The material for the study was collected from 16 AGs between 2022 and 2023. Samples were collected from plots where no micronutrient fertilization or composts of unknown origin were used. The primary soil samples were collected by means of a soil rod at a depth of 20 cm. The primary and final samples were prepared according to standard procedure [48]. To avoid the influence of mineral fertilization and the use of pesticides, a so-called mixed sample was analyzed, consisting of vegetables or fruit harvested at full maturity (consumption) from 5–7 sites. A total of 112 samples were analyzed, of which 72 were vegetables (beet greens—26, lettuce—33, sorrel—7, tomato—6) and 40 were fruits (gooseberries—14, red currants—11, cherries—15). As lettuce belongs to the group of vegetables with a high capacity to accumulate HM, for this purpose, three locations were sampled in the AGs, depending on the distance from the source of contamination. The first location is the plots lying along the street transect. The second location is a plot approximately 200 m from the edge of the road. The third location was plots in the central part of the gardens. Control samples of vegetables and fruit came from AGs located in agricultural areas 60 km from Warsaw. For the control samples, the gardens were selected, located on soils with similar physical and chemical properties compared to the soils on which the AGs in Warsaw were located. The control allotment garden was located on podzolic soils, classified within the granulometric group of light and loamy sands; in the upper part of the profile, dusty soils were present with a pH in KCl ranging from 6.8 to 7.0 and a humus content of 3.6%. The selected AGs in Warsaw were located on podzolic soils, a granulometric group—light and strong loamy sands, in the upper part of the profile, dusty soils with pH in KCl 7.2 and a humus content of 3.8%. The morphology of the soil profiles shows no significant transformation under the influence of horticultural cultivation about natural conditions, regardless of the location.
The collected fruit and vegetable samples were washed thoroughly and then ground in a Retsch 169 ZM 100 Ultra-Centrifuge blender (Retsch, Haan, Germany). The 0.1 kg of ground material was weighed onto porcelain plates and dried in a forced-air dryer (WAMED, model SUP-100, Warsaw, Poland) at 60 °C for 24 h. The temperature was then raised in the dryer to 105 °C, and the material was dried for a further 1.5 h. Drying at 105 °C enabled the acquisition of dry matter without loss of heavy metals during the drying process. After the drying process, the samples were cooled in desiccators to room temperature [49].
Dried vegetables and fruits were ground to powder (particle size 0.3–0.5 mm) using an Ultra-Centrifuge Retsch ZM 100 mill (Retsch, Germany). Samples were stored in the dark in airtight bags in desiccators and then ashed in a muffle furnace at 480 °C for 8 h. The ash was dissolved in concentrated hydrochloric acid (HCl—Chempur, Piekary Śląskie, Poland) and diluted with redistilled water in a ratio of 1:1. The entire ash mass was dissolved in 50 mL of hydrochloric acid. HMs were determined the day after mineralization. The mineralized solutions were stored at room temperature.
Metals in the resulting mineralizations were determined on an ICP–MS (Inductively Coupled Plasma–Mass Spectrometry) instrument, ELAN 6100 (PerkinElmer, Waltham, MA, USA), according to US EPA Method 6020B [50]. The analyses were conducted in an accredited laboratory of the Institute of Environmental Protection—National Research Institute in Warsaw. Laboratory tests were performed in duplicate. Certified reference materials—Montana soil and tobacco—were used for quality control.
Method detection limits:
HMLODUnits
Pb0.01–0.1µg L−1 lub µg kg−1 DM
Cd0.001–0.01µg L−1 lub µg kg−1 DM
Zn0.05–0.5µg L−1 lub µg kg−1 DM
Cu0.01–0.1µg L−1 lub µg kg−1 DM
For estimating exposure to heavy metals, the hazard quotient (HQ) is calculated.
D = C × K M C
where
  • D—dose taken;
  • C—concentration of the element in the sample of the vegetable/fruit (mg kg−1);
  • K—mass of the consumed vegetable/fruit (kg day−1) (The Statistical Yearbook of 2023);
  • MC—body weight of the exposed individual (assumed to be an adult—70 kg).
The health risk for an adult was estimated by calculating the exposure quotient, according to the following formula:
H Q = D R f D
where
  • HQ—hazard quotient;
  • RfD—reference dose.
The HI for the average daily consumption of vegetables and/or fruits was calculated as follows:
H I = ∑ i = 1 n H Q i
The analysis of cancer risk for human health resulting from exposure to substances with non-threshold effects, i.e., those with genotoxic or carcinogenic properties, is calculated using the following formula:
C R = D S F
where
  • D—the exposure dose to a substance is expressed in units of mg kg−1 day−1;
  • CR—cancer risk.
The results were statistically analyzed by calculating the arithmetic mean (x) and standard deviation (SD). The obtained results were analyzed using Statistica 13.1 software (StatSoft, Tulsa, OK, USA). The data were verified for normality of distribution using the Shapiro–Wilk test (they were transformed when required by either sqrt (x + 1) or ln (x + 1) and homogeneity of variance, and the average values obtained in individual groups were subjected to one-way ANOVA (analysis of variance) at a significance level of 0.05 using Tukey’s method.

3. Results and Discussion

The contents of all the HM metals tested in leafy vegetables and tomatoes were within very wide limits (Table 1), while in the fruits tested, the differences were not so significant (Table 2). Vegetables were shown to accumulate higher amounts of heavy metals compared to fruit. This is echoed by other authors [6,13,51,52] in studies where the HM content in vegetables was higher than in fruit. Liang et al. [13] report that vegetables, together with cereals, belong to the group of foods that can deliver the highest amounts of HMs to the consumer. This is due to the direct contact of the tested vegetables with the soil, which accumulates higher amounts of HMs compared to airborne contaminants [13,53]. In our research, the wide range of HM concentrations in plants may result from various soil physicochemical properties, such as soil type, pH, organic matter content, salinity, and carbonate levels. It may also be influenced by the proximity of busy roads to the sampling site [40,41,42]. In addition, leafy vegetables, compared to fruit, are characterized by significantly faster growth and development and a higher transpiration rate, which facilitates the absorption of heavy metals by the roots and their subsequent translocation from roots to leaves [6]. In addition, vegetables relative to fruit have a larger leaf surface area, facilitating the ingress of contaminants from precipitation and dust [54]. Furthermore, fruit plants store a large part of the absorbed HMs in parts other than their edible parts, mainly in the leaves [55].
It has been demonstrated that vegetables and fruits originating from areas distant from Warsaw (control sites) contain lower concentrations of heavy metals (HMs). These findings are consistent with the results reported by numerous authors, who indicate that in urban agglomerations, soil and air contamination with heavy metals and consequently, contamination of crops grown in such environments is significantly higher compared to rural areas (agrarian areas) [26,53,57,58].
The calculated mean concentrations (Table 1 and Table 2) indicate that the levels of heavy metals (HMs) in both the analyzed vegetables and fruits did not exceed the maximum permissible limits established by the European Union [6] for Zn, Cu, and Pb, except Cd, which was exceeded in lettuce and beet greens. The mean Cd concentrations in lettuce and beet greens were 1.36 and 1.03 mg kg−1 DM, respectively. Notably, some individual samples of lettuce and beet greens contained markedly elevated Cd levels, reaching up to 2.7 mg kg−1 DM and 2.4 mg kg−1 DM, respectively. Leaves have a large surface area, and HMs deposit directly on their surfaces. Unlike fruits or seeds, which are protected by tissue layers (peel, shells), leaves are directly exposed to air pollution with Cd and Pb, originating in urban areas from road traffic and industry. Moreover, to protect future generations, plants have developed mechanisms limiting the transport of heavy metals to generative organs [25,59,60]. Additionally, it was observed that in certain samples of lettuce and beet greens, the Zn content also exceeded the regulatory limits.
The concentration of iron (Fe) in the vegetables ranged from 92.0 to 1000 mg kg−1 DM, with an average of 320.0 mg kg−1 DM, and was higher across all vegetable samples compared to other HMs analyzed in this study. Based on average concentrations, the descending order of Fe accumulation in the tested vegetables was as follows: beet greens > lettuce > sorrel > tomato. This trend is consistent with the findings of Zhou et al. [61] and Huang et al. [62], who reported that leafy vegetables are generally more susceptible to the uptake of heavy metals compared to other vegetable types. According to Mahdavian and Somashekar [60,63], Fe concentrations in vegetables ranged from a minimum of 101.2 to a maximum of 279.5 mg kg−1 DM. Content in the studied beet greens and lettuce cultivated in Warsaw’s AGs exceeded the maximum permissible limit established by the FAO/WHO [56].
Furthermore, the results showed that fruits contribute, on average, approximately ten times less Fe to the diet compared to leafy vegetables, with Fe concentrations in fruits ranging from 27.0 to 84.0 mg kg−1 DM. These findings align with those reported by Mahdavian and Somashekar [63], whose study found an average Fe content of 167.4 mg kg−1 DM in fruits, about half that observed in vegetables.
The zinc (Zn) content in the analyzed leafy vegetables ranged from 13.0 to 254.0 mg kg−1 dry matter (DM), with a mean of 85.6 mg kg−1 DM, while in tomatoes, it ranged from 7.0 to 24.0 mg kg−1 DM, with a mean of 17.0 mg kg−1 DM (Table 1). Zou et al. [61] demonstrated that the Zn concentration in leafy vegetables (lettuce, spinach, cabbage) was 230.0, 400.0, and 120. Content in the studied beet greens and lettuce cultivated in Warsaw’s AGs exceeded the maximum permissible limit established by the FAO/WHO [56].
The manganese (Mn) content in the analyzed vegetables ranged from 9.0 to 154.0 mg kg−1 dry matter (DM), with an average of 40.5 mg kg−1 DM. The manganese concentration in the studied fruits was considerably lower, ranging from 4.0 to 19.0 mg kg−1 DM, with a mean value of 11.3 mg kg−1 DM (Table 2). According to Mahdavian and Somashekar [63], Mn levels in fruits ranged from 10.8 to 344.0 mg kg−1 DM (mean: 61.0 mg kg−1 DM), whereas in vegetables, these values were found to vary across a broader range, from 4.5 to 1109.6 mg kg−1 DM.
The Mn concentration in plants is influenced not only by the availability of bioaccessible forms of the element in the soil but also by the Fe content in the soil. The uptake of these elements by plants is antagonistic, meaning that the presence of one element in excess can inhibit the uptake of the other. The Fe-to-Mn ratio in plants can therefore be used to identify which element might be present in excess. The optimal Fe-to-Mn ratio in plants is considered to be between 1.5 and 2.5:1. Values below 1.5:1 are associated with symptoms of Mn toxicity and Fe deficiency, while ratios above 2.5:1 are indicative of excessive Fe, which is accompanied by Mn deficiency symptoms [64].
The observed Fe-to-Mn ratios in the vegetables (8.1:1) and fruits (4.8:1) in this study, based on the mean values, suggest that the analyzed vegetables and fruits contained an excess of Fe. This may be attributed to the alkaline pH of the soil in the AGs, as it is well established that in alkaline environments (pH > 7), Mn activity is significantly lower than that of Fe [65]. The influence of soil pH on heavy metal availability is also reported by Shen et al. [66], who found that, except for Hg and Pb, most heavy metals are significantly dependent on soil pH.
Furthermore, it was observed that the Mn concentrations in the vegetables and fruits from the AG in Warsaw did not exceed the permissible limit established by the FAO/WHO for this element [56].
The zinc (Zn) content in the analyzed leafy vegetables ranged from 13.0 to 254.0 mg kg−1 dry matter (DM), with a mean of 85.6 mg kg−1 DM, while in tomatoes, it ranged from 7.0 to 24.0 mg kg−1 DM, with a mean of 17.0 mg kg−1 DM (Table 1). Zou et al. [61] demonstrated that the Zn concentration in leafy vegetables (lettuce, spinach, cabbage) was 230.0, 400.0, and 120.0 mg kg−1 DM, respectively. In the study by Singh and Singh [67], the Zn content in spinach ranged from 56.0 to 73.0 mg kg−1 DM, and in cabbage, it ranged from 35.0 to 37.0 mg kg−1 DM. Śmiechowska and Florek [68] determined the average Zn content in root vegetables grown in AGs at 2.5 mg kg−1 DM. Mahdavian and Somashekar [63], in their analysis of the Zn content in edible parts of eighteen vegetable species, obtained values ranging from 2.3 to 52.6 mg kg−1 DM. For leafy vegetables, the mean Zn content was 14.5 mg kg−1 DM, while for tomatoes, it was 10.1 mg kg−1 DM, both lower than the values observed in our study. This suggests that the Zn content is largely dependent on the species of the vegetable.
Our findings indicate that leafy vegetables exhibited higher Zn content compared to tomatoes. This is consistent with the results of Zhou et al. [61], where the concentrations of Zn in the edible parts of vegetables decreased in the following order: leafy vegetables > stem vegetables > root vegetables > solanaceous vegetables. In our study, the Zn levels in fruits ranged from 2.0 to 26.0 mg kg−1 DM, with a mean of 13.0 mg kg−1 DM. In the research by Mahdavian and Somashekar [63], Zn levels in ten fruit species ranged from 17.8 to 45.2 mg kg−1 DM, with an average concentration of 30.0 mg kg−1 DM. The Zn concentrations reported by these authors exceed those found in our study. However, it should be noted that Mahdavian and Somashekar [63] primarily examined citrus fruits, which were grown under different environmental conditions. These differences suggest that Zn concentrations in fruits are also influenced by genotype.
Furthermore, Tchounwou et al. [69] indicate that environmental conditions under which cultivation occurs can be a source of heavy metal contamination in vegetables and fruits. According to FAO/WHO guidelines, the recommended Zn content for vegetables and fruits is 50 mg kg−1 DM [56,63]. This suggests that, in our study, the Zn concentrations in the leaves of beet greens (mean 120 mg kg−1 DM) and lettuce (mean 100 mg kg−1 DM) exceeded the permissible limit. Additionally, it was observed that the allowable Zn content was exceeded in some samples of sorrel leaves, reaching up to 57.0 mg kg−1 DM. However, considering FAO/WHO standards, the Zn concentrations in fruits did not exceed the permissible level. It is important to note that Zn levels exceeding the permissible limit were observed in leafy vegetables. Leaves are metabolically active organs, explaining the higher Zn concentration. According to White et al. [70], leaves accumulate higher Zn concentrations than fruits, seeds, or tubers. Zn transport and distribution in the plant occur via the phloem, which, due to Zn’s limited mobility, may restrict its redistribution from leaves to fruits or seeds. Moreover, Zn accumulates in mesophyll cells, indicating that leaves serve not only as transport organs but also as Zn storage sites [70,71].
The copper (Cu) content in the analyzed leafy vegetables ranged from 1.4 to 87.4 mg kg−1 dry matter (DM), with an average of 15.1 mg kg−1 DM, while in tomatoes it ranged from 3.9 to 11.6 mg kg−1 DM, with a mean of 8.4 mg kg−1 DM (Table 1). In fruits, the concentration ranged from 2.8 to 28.0 mg kg−1 DM, with an average of 7.4 mg kg−1 DM (Table 2). Singh and Singh [67] reported that Cu concentrations in leafy vegetables (spinach and cabbage) were 21.7 mg kg−1 DM and trace amounts, respectively. The permissible Cu content in vegetables were established by the FAO/WHO [56,67]. Our study revealed considerable variability in Cu concentrations across all analyzed vegetables and fruits, with many samples exceeding the established limits, even though the average Cu content did not always reflect this (maximum Cu levels in vegetables and fruits are shown in Table 1 and Table 2). Furthermore, significant Cu contamination was found in the leaves of beet greens and lettuce. The Cu content in plants is influenced by soil pH, with Cu mobility increasing only when the pH falls below 5.0 [72]. Studies by other authors also indicate that Cu primarily accumulates in plant roots [73].
Cadmium (Cd) and lead (Pb) are elements that are entirely unnecessary for the human body [74]. Any amount of these elements ingested by humans poses a risk of adverse health effects [75]. According to the FAO/WHO [6,56], the maximum permissible levels of heavy metals in food products are as follows: Cd should not exceed 0.3 mg kg−1 DM in leafy vegetables and 0.1 mg kg−1 DM in other vegetables, while for small fruits, the permissible level is 0.2 mg kg−1 DM [56]. For Pb, the FAO/WHO and EU regulations [76] set the limits at 0.2 mg kg−1 DM for leafy vegetables, 0.01 mg kg−1 DM for stem vegetables, and 0.05 mg kg−1 DM for fruits. Our results showed that all vegetables grown in AGs were contaminated with both Cd and Pb, with concentrations exceeding the permissible levels only for lead. Among the analyzed vegetables, the highest Cd and Pb concentrations were found in leafy vegetables (lettuce and beet greens), while tomatoes contained the lowest levels. Additionally, the analyzed fruits, regardless of species, did not exceed the established limits, as they contained Cd and Pb at trace levels.
In our study, both vegetables and fruits grown far from urban agglomerations (control) did not exceed the established limits either. Mawari et al. [6] examined sixteen vegetable species and nine fruit species grown in urban areas and found that, in most cases, heavy metal concentrations were within the permissible levels defined by the FAO/WHO. Notably, the authors reported that no limits were exceeded in leafy vegetables, tomatoes, and all analyzed fruits. Kleiber et al. [74] reported Cd concentrations in tomatoes ranging from 0.38 to 0.41 mg kg−1 DM and Pb from 0.83 to 0.91 mg kg−1 DM, thus exceeding the limits, similar to our findings. However, Grochowska-Niedworok et al. [75], in their cultivation of different tomato varieties, did not exceed the established limits for Cd and Pb in both traditional tomato varieties and cherry tomatoes. It should be noted that these tomatoes were grown under organic farming conditions.
Vegetables can become contaminated with heavy metals not only as a result of mineral fertilizer use but also to a large extent due to the cultivation location. In urban areas, traffic emissions release pollutants primarily into the soil and the air directly above it, posing a threat to cultivated plants. Additionally, municipal pollution is another source of heavy metals [77]. It is also important to note that tomatoes are consumed frequently and in large quantities. Therefore, consumption of tomatoes containing trace amounts of Cd and Pb may pose a risk, as heavy metals accumulated in the body can lead to adverse health effects even after many years [75].
Certain types of vegetables tend to accumulate higher levels of contaminants responsible for foodborne poisoning. An example of this is lettuce, which exhibits a significantly greater ability to absorb heavy metals (HMs) [78,79,80]. Lettuce is a commonly cultivated vegetable due to its adaptive abilities, resistance to pests, and low production costs [11]. Therefore, lettuce, in particular, should be subjected to monitoring for contamination. The AGs located within urban agglomerations often border industrial infrastructure or municipal transportation routes. In the present study, an analysis of lettuce contamination was conducted using samples collected from various locations within the AGs, and the results are presented in Table 3.
It is also important to note that, regardless of the collection site, the heavy metal content in lettuce leaves exceeded the FAO/WHO permissible limits [6] for all analyzed elements, except for cadmium (Cd) in lettuce from plots located farthest from the streets. The highest exceedances of the permissible concentrations were recorded for lead (Pb) and cadmium (Cd), which were eighty and nine times higher than the permissible limits, respectively. Due to significant exceedances of Cd and Pb limits, the consumption of lettuce grown in urban AGs is not recommended.

Human Health Risk Assessment

The health risk analysis resulting from exposure to substances with threshold effects, i.e., those without genotoxic or carcinogenic properties, was based on a model recommended by the United States Environmental Protection Agency (US EPA). The amount of harmful substance ingested per day by an adult or child is determined as the dose taken, according to the US EPA methodology [81]. The HQ is an indicator that tells us whether something we consume, inhale, or come into contact with is safe for health. If HQ < 1—the risk is low. This means that the exposure level is lower than the reference dose considered safe. If HQ > 1—health risks may occur, as exposure exceeds the safe threshold, potentially increasing the likelihood of adverse health effects [6,47,53,82].
The RfD is the estimated daily amount of a chemical substance that does not cause adverse health effects over a lifetime of human exposure. In the case of elements such as Cd and Pb, which are toxic to the human body, the value of RfD is determined by various health safety organizations, including, among others, the United States Environmental Protection Agency (EPA) [83,84].
The measure of the potential risk of adverse health effects caused by a mixture of chemical constituents is the hazard index (HI). The HI (Hazard Index) is a metric used to assess the total health risk when exposed to multiple harmful substances simultaneously—for example, various pesticides in food or heavy metals in water. If HI < 1, the situation is considered safe; if HI > 1, there may be a health risk because the cumulative exposure exceeds safe limits [6,47,53,82].
The HQ index for an adult after consuming selected vegetables and fruits is presented in Table 4.
For the analyzed vegetables and fruits, the HQ value for all metals was below one. An exception was tomatoes, for which the calculated HQ value, considering Pb, was above four. For tomatoes, the estimated reference dose (RfD) for heavy metals, including Pb, is very low. According to the U.S. Environmental Protection Agency (EPA), the RfD for lead in tomatoes is as low as 0.0035 mg/kg/day. This implies that even small doses of lead may exceed this value, resulting in an HQ > 1. Furthermore, tomatoes are generally consumed in large quantities (raw, in sauces, and concentrates), contributing to a high Estimated Daily Intake (EDI) of lead. Pb in plant products is highly bioavailable, and the acidic environment of tomatoes further facilitates Pb release and absorption. Since the EDI is divided by the consumer’s body weight, tomato consumption poses a significantly higher health risk to children [85,86]. The HQ values followed the sequence below, depending on the established indicator value for lettuce (Pb > Cd > Zn > Cu); tomatoes (Pb > Cd > Cu > Zn); cherries (Cu > Zn); and red currant (Cu > Zn). The obtained HQ values indicate no risk to human health when consuming lettuce, cherries, and red currants at the defined metal concentration levels for these products. Among the analyzed elements, Pb posed a higher potential risk to human health than the other metals. It should be noted that the calculated HQ value (Pb) for tomatoes indicates the highest potential health risk for consumers of this vegetable from Warsaw’s AGs.
The study also determined the hazard index (HI) (Table 4) because the simultaneous intake of multiple heavy metals may increase the health risk for the body [6,53,82]. The calculated HI values indicate that only fruits can be consumed safely. However, tomatoes should not be consumed. The calculated HI for lettuce indicated that its consumption does not pose a health risk for humans. It should, however, be noted that considering the content, this relationship is reversed.
The CR index estimates the incremental probability of cancer development in an individual over their lifetime due to exposure to a potential carcinogenic factor. A risk value between 1 × 10−4 and 1 × 10−6 is generally considered acceptable, while a value exceeding 1 × 10−4 indicates a carcinogenic risk for the human body over a lifetime. The CR (Cancer Risk) indicates whether long-term exposure to a given substance may increase the risk of cancer [46,68,87,88].
The SF (Slope Factor) factor transforms the estimated daily intake of a toxin, averaged over a lifetime, into the incremental risk of developing cancer in an individual, according to USEPA 2011 [89]. The SF is a coefficient used in health risk assessment that refers to the slope factor applied in cancer risk modeling related to exposure to carcinogenic substances. It is an indicator used to estimate the risk of developing cancer due to exposure to a specific chemical substance. The SF is typically expressed as the number of cancer cases per unit of absorbed dose of the harmful substance (e.g., per mg kg/body weight/day), assuming the substance is carcinogenic, USEPA 2011 [66,68,89].
The calculated cancer risk in the present study for lettuce collected from AGs in Warsaw was as follows: for Cd, 2.6 × 10−6 and for Pb—1.54 × 10−5. The data suggest that the carcinogenic risk from environmental exposure to Cd and Pb can be considered negligible. However, this conclusion is not consistent with reports by other authors, whose studies demonstrated that the carcinogenic risk from Pb is within a tolerable range [90]. It should be noted, however, that these authors assessed potential environmental cancer risk for residents living near electronic waste landfill sites.

4. Conclusions

The study emphasizes the need for continuous monitoring of heavy metal content in urban soils and the establishment of baseline values for long-term assessments of changes, which is crucial from a public health perspective. Vegetables, especially lettuce, beetroot, sorrel, and tomatoes, accumulate significantly more lead (Pb) and cadmium (Cd) than fruits, indicating their greater health risk for consumers. From a public health standpoint, the safest option is the cultivation of fruit trees and shrubs, while the cultivation of tomatoes in AGs should be considered unacceptable.
Lettuce grown near busy traffic routes contains significantly higher concentrations of Pb, Cd, and Zn than those grown in the center or on the outskirts of gardens, often exceeding the permissible limits multiple times. Due to its high capacity for heavy metal accumulation, lettuce can be an effective indicator plant for assessing the level of soil contamination.
Urban gardening holds potential in terms of food security; however, it requires the implementation of comprehensive measures (remediation, site selection, agricultural techniques) to reduce health risks associated with the presence of heavy metals. Further research is recommended on long-term methods for reducing the levels of toxic elements in the urban environment, including effective remediation and the implementation of safe agricultural practices. In urban AGs, to reduce the risk of HM contamination in crops, buffer zones of phytoremediation plants such as mustard, phacelia, or sunflower should be introduced. It is also advisable to cultivate safer crops with short growth cycles, such as zucchini, cucumbers, or leguminous plants in raised beds with clean soil. Regular soil pH monitoring, liming, and composting should also be performed. In addition, the safety of fruits and vegetables grown in urban areas is influenced by the location of the AGs and the level of industrialization of the agglomeration. Therefore, the safety assessment of plant products derived from AGs should be monitored on a continuous basis, especially in vegetables.
Our findings indicate that particular attention should be paid to monitoring the contamination of vegetables and fruits cultivated non-commercially in allotment gardens (AGs) located near major traffic arteries in Warsaw. It has been shown that, in order to better assess the variability of metal concentrations and identify factors contributing to contamination, long-term studies in various locations (plots) across Warsaw are necessary. The methods and results obtained in Warsaw may be adapted by other large cities, especially those with similar pollution levels and traffic intensity. The findings from Warsaw are valuable as a reference for European cities, as they can support the development of local public health protection strategies. Cities should consider prohibiting cultivation near major roads and implementing systematic monitoring of metal content in soil and plants.

Author Contributions

Conceptualization, J.C., M.F.-Ł. and B.G.; methodology, J.C., M.F.-Ł., B.G., J.P. and E.W.; validation, J.C., M.F.-Ł., B.G., J.P. and E.W.; formal analysis, J.C., M.F.-Ł., B.G., J.P. and E.W.; investigation, J.C., M.F.-Ł., B.G., J.P. and E.W.; resources, J.C., M.F.-Ł., B.G., J.P. and E.W.; data curation, J.C., M.F.-Ł., B.G., J.P. and E.W.; writing—original draft preparation, J.C., M.F.-Ł., B.G., J.P. and E.W.; writing—review and editing, J.C., M.F.-Ł., B.G., J.P. and E.W.; visualization, J.C., M.F.-Ł., B.G., J.P. and E.W.; project administration, J.C., M.F.-Ł., B.G., J.P. and E.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Table 1. Content of heavy metals (mg kg−1 dry matter (DM)) in leafy vegetables from AGs of Warsaw.
Table 1. Content of heavy metals (mg kg−1 dry matter (DM)) in leafy vegetables from AGs of Warsaw.
PlantnStatistical ParametersFeMnZnCuPbCd
Beet greens26min.25028609.901.00.10
max.100011325487.418.02.40
average400 b67 b120 a22.5 a10.0 a1.03 b
SD174296316.44.40.71
Lettuce33min.26825237.901.00.10
max.98015420134.121.02.70
average528 a67 b100 b13.3 b11.1 a1.36 a
SD30330395.404.90.82
Sorrel7min.22210131.401.00.10
max.360365718.2210.80
average284 c18c37 c9.40 c7.0 b0.18 c
SD5612207.904.00.13
Tomatoes6min.92973.900.10.01
max.109122411.67.00.20
average100 de10c17 d8.40 c2.5 c0.15 c
SD6183.662.20.05
Control12min.13060303.500.2LOD
max.180140505.300.3
average155 d100 a40 c4.40 d0.2 d
SD141831.251.5
Acceptable limit (WHO/FAO) *
(mg kg−1 DM)		450.00500.0050.0010.000.300.20
Acceptable limit (EU Standard) **
(mg kg−1 DM)		 - - 200.0100.060.01.0
* According to Sultana et al. [56]; ** according to Mawari et al. [6]; means sharing the same letter in a column are not significantly different (significance level of 0.05 using Tukey’s method). Significant values are in (bold).
Table 2. Heavy metal content (mg kg−1 DM) in fruits from AGs in Warsaw.
Table 2. Heavy metal content (mg kg−1 DM) in fruits from AGs in Warsaw.
PlantnStatistical ParametersFeMnZnCuPbCd
Cherries15min.27668.10LODLOD
max.60131518.10
average44 c8 b10 b5.90 b
SD8124.00
Gooseberries14min.46723.20LODLOD
max.84192428.00
average65 a13a15a10.70 a
SD12357.00
Red currant11min.38462.80LODLOD
max.82182612.40
average53 b13 a14 a5.70 b
SD15452.90
Control9min.15120.20LODLOD
max.10650.50
average12.5 d3.5 c4.0 c0.35 c
SD3230.05
Acceptable limit (WHO/FAO) *
(mg kg−1 DM)		450.00500.0050.0010.000.300.20
Acceptable limit (EU Standard) **
(mg kg−1 DM)		 - - 200.0100.060.01.0
* According to Sultana et al. [56]; ** according to Mawari et al. [6]; means sharing the same letter in a column are not significantly different (significance level of 0.05 using Tukey’s method). Significant values are in (bold).
Table 3. Heavy metal content (mg kg−1 DM) in lettuce leaves from different areas of AGs in Warsaw.
Table 3. Heavy metal content (mg kg−1 DM) in lettuce leaves from different areas of AGs in Warsaw.
Sampling LocationFeZnCuPbCd
Crops located along the street (n = 22)666 ± 171 a140 ± 48.6 a17.9 ± 0.51 a16.0 ± 4.43 a2.81 ± 0.72 a
Crops located in the central part of the AGs (n = 16)531 ± 163a b85 ± 31.2 b11.5 ± 2.54 b10.1 ± 2.42 b1.03 ± 0.45 b
Crops located furthest from the street (n = 15)387 ± 76.3 b74 ± 39.1 b10.5 ± 3.52 b7.3 ± 3.32 c0.25 ± 0.15 c
Mean52810013.311.11.36
Means sharing the different letter in column are significantly different from each other (Tukey’s significant difference test, p < 0.05).
Table 4. Calculated HQ and HI indices for an adult for selected heavy metals in vegetables and fruits.
Table 4. Calculated HQ and HI indices for an adult for selected heavy metals in vegetables and fruits.
Vegetables/FruitsHQHI
CdPbCuZn
Lettuce0.03240.31630.000160.001330.3502
Tomatoes0.21434.46430.0600.000304.7389
Cherries--0.0180.000240.0182
Red currant--0.000450.00000170.000045
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Chmielewski, J.; Wszelaczyńska, E.; Pobereżny, J.; Florek-Łuszczki, M.; Gworek, B. Heavy Metals in Leafy Vegetables and Soft Fruits from Allotment Gardens in the Warsaw Agglomeration: Health Risk Assessment. Sustainability 2025, 17, 6666. https://doi.org/10.3390/su17156666

AMA Style

Chmielewski J, Wszelaczyńska E, Pobereżny J, Florek-Łuszczki M, Gworek B. Heavy Metals in Leafy Vegetables and Soft Fruits from Allotment Gardens in the Warsaw Agglomeration: Health Risk Assessment. Sustainability. 2025; 17(15):6666. https://doi.org/10.3390/su17156666

Chicago/Turabian Style

Chmielewski, Jarosław, Elżbieta Wszelaczyńska, Jarosław Pobereżny, Magdalena Florek-Łuszczki, and Barbara Gworek. 2025. "Heavy Metals in Leafy Vegetables and Soft Fruits from Allotment Gardens in the Warsaw Agglomeration: Health Risk Assessment" Sustainability 17, no. 15: 6666. https://doi.org/10.3390/su17156666

APA Style

Chmielewski, J., Wszelaczyńska, E., Pobereżny, J., Florek-Łuszczki, M., & Gworek, B. (2025). Heavy Metals in Leafy Vegetables and Soft Fruits from Allotment Gardens in the Warsaw Agglomeration: Health Risk Assessment. Sustainability, 17(15), 6666. https://doi.org/10.3390/su17156666

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