Metal(loid)s in Bottom Sediments Ecological and Human Health Risk Assessment

The concentrations of metal(loid)s (Cd, Cr, Cu, Ni, Pb, Zn, and As) in bottom sediments from selected water reservoirs discussed in this article were sourced from a report published on the website of the Chief Inspectorate for Environmental Protection [18]. The report concerns monitoring river and lake bottom sediments in 2020–2021. Based on this data, we assessed the potential ecological and human health risks posed by selected metal(loid) in bottom sediments, which was the main aim of this study.

The water reservoir selection was based mainly on the functions they performed. Because our work is concerned with assessing potential ecological and health risks, we decided these would be recreational and tourist functions and water supply. Recreation and tourism are usually related to water sports, swimming, or fishing. However, sometimes they can be limited to, for example, walking or cycling, etc., around the reservoir (but despite this, people still break the prohibition). It happens when a water reservoir serves more specific functions, like water supply or flood control. In such a case, monitoring the characteristics and composition of bottom sediments is essential. This is because sediments in water ecosystems are a sink and a source of potentially toxic pollutants, like metal(loid)s [19, 20]. These pollutants can be released from sediments into the water under reducing conditions, such as a rapid decrease of pH, redox potential value (Eh), or oxygen content in water. In such a situation, secondary aquatic environment contamination with these pollutants may occur [20].

The study area encompasses three lakes and one dam reservoir, specifically:

A) Lake Gardno: located in the Pomeranian Voivodeship (Northern Poland), on the coast of the South Baltic Sea, within the Słowiński National Park and the boundaries of the Natura 2000 area (54°39′14″ N 17°06′43″E).

A distinguishing feature of the Lake Gardno catchment is its coastal location, lack of overland flow, and a large share of sea aerosols in the water cycle [21]. The frontal moraine hills surrounding Lake Gardno, from the west to the south, create a post-glacial landscape. Inside the moraine embankment on the lake's southern shore, a large area is covered by marsh and peat formations. The eastern coast of the lake is formed by the delta of the Łupawa River, and the northern shore is formed by the Gardzieńska Spit [22]. The structure of surface used in the Gardno Lake catchment area is characterized by a dominant share of forests (98.2%), a small share of surface waters (1.2%), and anthropogenic areas, i.e., roads and buildings (0.6%). The lake's catchment area is subject to low anthropogenic pressure, and the only local source of pollution is roads. During the colder period of the year, the environment may also be affected by pollution from the burning of fossil fuels in nearby towns [23]. Moreover, thanks to the mouth section of the River Łupawa, which connects Lake Gardno with the Baltic Sea, also sea waters may source various pollutants in this lake [21].

B) Lake Swarzędzkie: located in the Greater Poland Voivodeship (Western Poland), in the north-western part of the Swarzędz town (52°24′49″N 17°03′54″E). The lake is within the Natura 2000 area (Cybina Valley) of the Wrzesińska Plain.

Lake Swarzędzkie is surrounded by peat deposits, the largest of which is located at the Cybina tributary. To the south and southwest of the lake, there are sands, gravels, and kame silts. The areas east and west of the lake are covered with fluvioglacial sands and gravels from the Poznań phase of glaciation and older boulder clays and uncovered boulder clays from the Leszno phase of glaciation. The soil in question is of medium and poor quality. In the valuation structure of the discussed area, 75% are class III and IV soils [24]. The direct basin of Lake Swarzędzkie is covered by forest (45%), meadows and pastures (31.8%), built-up areas (21.7%), and farmland (1.3%) [25]. The waters feeding the Lake Swarzedzkie are significantly polluted with biogenic substances [26]. Moreover, until 1991, wastewater from Swarzędz was directly discharged into Lake Swarzędzkie [27].

C) Lake Szczutowskie: located in the Masovian Voivodeship (Eastern Poland), in the Szczutowo commune (52°56′30″N 19°34′45″E).

The catchment area of Lake Szczutowskie is located in the eastern part of the Chełmińsko-Dobrzyńskie Lakeland macroregion in the Urszulewska Plain mesoregion [28]. The landscape of this region is monotonous and plain. It comprises Pleistocene out-wash sands and gravels of the North Polish Glaciation, with numerous areas of Holocene sands, gravels, river muds, peats, and silts. There are also boulder clays, sands, and glacial gravels. It is characterized by fertile soil [29]. Based on the analysis of GIOŚ INSPIRE maps [30], it can be concluded that agricultural land use prevails in the Lake Szczutowskie catchment area. Forest areas also have a significant share in the land development structure. Residential buildings dominate on the lake's western shore; on the eastern coast, the number of buildings is much smaller.

D) Wisła-Czarne dam Water Reservoir: located in the Silesian Voivodeship (Southern Poland), in the Wisła town (49°36′53″N 18°55′36″E). We considered an artificial dam reservoir instead of a natural lake in this region because the Silesian Voivodeship is more notable for its artificial reservoirs and mining subsidence lakes, which are critical in water supply, flood control, and recreation. Natural lakes are generally smaller and less well-known in this region [20].

The Wsisła-Czarny dam Reservoir was created below the junction of the Biała and Czarna Wisełka streams strands [31]. The reservoir's catchment area is located in the Beskid Śląski mesoregion, which belongs to the flysch Western Carpathians [28]. The city of Wisła is agricultural; as much as 92% of the commune's area is agricultural land, forest land, or wasteland. Urbanized areas constitute approximately 6% of the commune's area, and surface waters constitute approximately 2%. The areas along the banks of the Wisła-Czarne Reservoir are covered with forests. Near the reservoir, there are also numerous meadows and pastures with scattered single-family buildings and local roads [32]. Given the supply streams’ good quality, pollutants will likely enter the Wisła-Czarne Reservoir through dry and wet deposition or surface runoff. Moreover, in regions with a history of industrial development, like the Silesian Voivodeship, old contaminants may still be present in the sediments even if these activities have been reduced or ceased [20].

Figure 1 shows the locations of water reservoirs. The outlines of the lakes and one reservoir are from the web maps with ArcGIS Online, Esri's web-based mapping software [33], while the map of Europe marked Poland is from Google Maps [34]. The morphometric and hydrological parameters of considered water reservoirs are shown in Table 1.

Figure 1.

Location of water reservoirs [33, 34]. Where A) Lake Gardno; B) Lake Swarzędzkie; C) Lake Szczutowskie; D) Wisła-Czarne dam Reservoir

According to the report presented by the Chief Inspectorate for Environmental Protection [18], field research and sediment collection were conducted on PN-ISO 4364:2005 [38]. The number of samples collected depends on the reservoir area. In this study, the number of collected samples was from 1 to 3 per water reservoir. The location of the depths (at which samples were collected) was determined by GIOŚ based on available bathymetric data of the lakes, i.e., determined based on the Hydrographic Map of Poland at a scale of 1:50.000. A stainless Van Veen grab sampler obtained a 5-cm surface layer of bottom sediments. In the case of sampling from several depths, the material collected was averaged by transfer to 1 container and mix. The sediment samples were sieved through a nylon sieve with a mesh of 2 mm, placed in plastic containers, and adequately secured for transport by placing them in a closed cool-box container lined with bubble foil and ice inserts. This procedure was intended to protect the samples from damage and heating. The samples were delivered within approximately 24 hours of collection to the laboratory that performed the analyses [18].

Determining metal(loid)s in sediment samples was performed by accredited research units commissioned by the Chief Inspectorate for Environmental Protection. Bottom sediment analyses were conducted under the requirements of PN EN ISO/IEC 17025:2018-02 [39]. Sediment samples were dried to constant weight (at 60ºC), ground in a Retsch RM 200 grinder, and subjected to mineralization with aqua regia following the PN-EN 13657:2006 [40]. Metal(loid)s determinations were carried out using inductively coupled plasma atomic emission spectrometry ICP-OES on an Optima 5300 DV Perkin Elmer, according to PN-EN ISO 11885:2009 [41]. To convert the analysis results from mg·L⁻¹ into mg·kg⁻¹, the sediments were dried (in a separate procedure) at 105 ± 5°C to constant weight by PN-EN 12880:2004 [42]. Sediments were weighed using an analytical balance, Radwag.

Various indices (methods) can be utilized to evaluate the potential adverse effects of metal(loid)s on the aquatic environment. In this paper, we used indices referring to one element or group of elements, so-called “single-element indices” and “multi-element indices”. Among the first group, we can distinguish the Geoaccumulation Index (I_geo) [12] and the Potential Ecological Risk Factor (ER) [13], while in the second, the Risk Index (RI) [13]. The I_geo index allows contamination assessment by comparing the current and pre-industrial concentrations of the elements in the relevant geochemical background [19]. In turn, the ER index provides a comprehensive method for assessing ecological risks posed by elements in aquatic environments by incorporating concentration, background levels, and toxicity. Meanwhile, RI refers to the sum of the ER of each considered element [43]. The indices mentioned above are recommended for determining the contaminating effect of metal(loid)s in sediments and the potential ecological risk associated with their toxicity [13]. The methodologies and formulas for these indices are shown in Table 2. Moreover, background values are essential for evaluating contamination levels and potential ecological risks [20]. In this study, the content of the metal(loid)s in the Earth’s crust was used as background values, as reported by Kabata-Pendias (2011) [44].

Bottom sediments can accumulate metal(loid)s over time, posing a potential risk to adults and children through various exposure pathways. In this study, the two most probable routes of exposure were considered: accidental oral ingestion and dermal (skin) contact [14]. Table 3 presents the methodology for estimating the average daily exposure doses (ADD_S) for ingestion and dermal contact.

The International Agency for Research on Cancer (IARC) (2012) [45] classifies cadmium, chromium, nickel, and arsenic as Group 1 carcinogens, while lead as Group 2A carcinogens. This indicates their significant risk to human health, particularly in terms of cancer, but not only [9, 43]. Given the above, this paper assessed the health risks associated with cadmium, chromium, nickel, lead, and arsenic in carcinogenic terms, in turn, copper and zinc were considered from a non-carcinogenic perspective. Such an approach provides a balanced view of the potential health risks. Table 4 shows the methods for health risk assessment.

The mean concentrations of considered metal(loid)s in bottom sediments show a clear pattern where Zn is consistently found in the highest concentration and Cd in the lowest across different water reservoirs. The concentration levels in considered sediments were as follows: Zn>Cr>Pb>Cu>Ni>As>Cd (Lake Gardno), Zn>Cu>Pb>Cr>Ni>As>Cd (Lake Swarzędzkie), Zn>Pb>Cu>Cr>As>Ni>Cd (Lake Szczutowskie) and Zn>Cu>Cr>Ni>Pb>As>Cd (Wisła-Czarne dam Reservoir). Considering the characteristics of their catchment area, the probable sources of metals and one metalloid in the discussed water reservoirs include municipal wastewater, runoff from agricultural areas, atmospheric deposition, and historical pollution. The concentrations of metal(loid)s in considered bottom sediments are presented in Figure 2.

Figure 2.

Metal(loid)s concentrations in bottom sediments

The data presented by the GIOŚ show that the concentrations of cadmium, chromium, nickel, and zinc in the bottom sediments of the Wisła-Czarne dam Reservoir are several to a dozen times higher than in the lakes in question. The exceptions were copper, arsenic, and lead. In the case of copper and arsenic, higher concentrations of these elements were recorded only in the sediments of Swarzędzkie and Szczutowskie Lakes, respectively. In turn, in the case of lead, its highest concentration was found in the sediments of Lake Szczutowskie. The lowest concentrations of metal(loid)s were indicated in the bottom sediments of Lake Gardno. It is located in a National Park, and the lake's catchment area is almost entirely forested, so the impact of anthropogenic pressure is negligible [48]. This proves that sediments from reservoirs in areas of limited human activity impact are less contaminated. As mentioned, generally, the highest concentrations of elements considered in this paper were recorded in the bottom sediments of a reservoir in Silesia Voivodeship. This region is known for its extensive industrial activities (hard coal mining, metallurgy, coking plants, electric power generation, chemical industries, and metal industries in the country), and it is the most industrialized region in Poland [20,49]. Research in this area confirmed that human activities influence the chemical composition of bottom sediments [8,49–50]. Even though the Wisła-Czarne Reservoir is situated several dozen kilometers from the central part of the Upper Silesian Industrial Region, it stands out from the other water reservoirs considered in this paper. For comparison, the concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the bottom sediments of water reservoirs in other regions of the country, like the Zemborzycki dam Reservoir located in Lublin Voivodeship (Eastern Poland) or Jutrosin Reservoir in Greater Poland (Western Poland), amounted to 0.5; 5.9; 7.1; 6.1; 54.2 and 43.1 mg·kg⁻¹ [51] and 0.2; 3.1; 3.5; 3.7; 6.2, and 23.1 mg·kg⁻¹ [52], respectively. It is highly probable, that the source of metal(loid)s in the bottom sediments of the Wisła-Czarne Reservoir is mainly the emission of metal-rich dust by smelters and also a high level of industrial dust that is carried by the wind from the main industrial zone in Silesia and together with atmospheric deposition (dry and wet), entered the aquatic environment. However, these pollutants partly may also be historical. Generally, the Silesian region is characterized by a higher concentration of metal(loid)s in bottom sediments than other regions. This statement was confirmed by various scientific research [49, 50, 53].

The indices of potential ecological risk used in this paper have both advantages and disadvantages. In the first group, we can distinguish (1) the lack of additional costs associated with the risk evaluation. Risk assessment is based solely on the results of analyses performed as part of routine monitoring. Therefore, the indices constitute a free tool for assessing the quality of bottom sediments; (2) a broader view of the risk evaluation. For example, I_geo relates the element concentration in the sample to the background value. In contrast, ER and RI include the toxicity of a particular element; and (3) the universal character of the indices. Therefore, these indices can evaluate various environmental matrices, such as sediment, soil, sewage sludge, etc. The only disadvantage is the problem of choosing the proper background value concentrations for the particular element. The results of the ecological risk assessment are presented in Table 5.

The I_geo values indicate that although cadmium is the metal with the lowest content in the considered bottom sediments, it is still the main cause of their pollution, resulting in moderate and moderate to heavy contamination. At the same time, this also translates into a potential risk in the environmental dimension, which has not been noted about other elements. It should be emphasized here that although Cd occurs in the environment in low concentrations, it is also highly toxic to humans and animals (in excessive amounts), while less harmful to plants [54]. A trend similar to the one presented above was observed in other water reservoirs, where elements occurring in lower concentrations posed a greater risk in the ecological dimension than those with higher concentrations in bottom sediments. As an example, we can cite the results of research conducted for the Dzierżno Duże Reservoir (I_geo: Cd>Zn>Pb>As>Cu>Ni>Cr>Fe>Mn) [20] or the Rybnicki Reservoir (I_geo: Cu>Cd>Zn>Ni>Cr>Pb) [50], both located in the Silesian Voivodeship and also for the Rzeszów Reservoir (I_geo: Cd>Cr>Ni>Cu>Zn>Pb) [49], located in the Podkarpackie Voivodeship. The only water reservoir in which none of the discussed elements, present in bottom sediments posed a threat to the aquatic ecosystem was Lake Gardno, located in the Pomeranian Voivodeship. The lower levels of metal(loid) concentrations in the sediments of Lake Gardno and, therefore, no environmental risk is attributed to a lower degree of industrialization in this region, particularly of heavy industry, compared to other areas in the country.

The ER values reveal that cadmium is a primary element posing a risk among analyzed metal(loid)s (considerable to high risk). This is consistent with findings from the I_geo index. The only exception is arsenic in the bottom sediments of Lake Szczutowskie, for which a moderate risk was found. The ER index values for individual elements form the following series: As>Cd>Pb>Ni>Cu=Zn>Cr (Lake Gardno), Cd>As>Pb>Cu>Ni>Zn>Cr (Lake Swarzędzkie), Cd>As>Pb>Ni>Cu>Zn>Cr (Lake Szczutowskie) and Cd>As>Ni>Pb>Zn>Cu>Cr (Wisła-Czarne Reservoir). It is worth mentioning that among the elements considered, cadmium and arsenic have the highest toxicity coefficient, i.e. T=30 and T=10, respectively [13]. For comparison, in the case of the Bardowski Lagoon, the Kozłowa Góra Reservoir, and the Lake Bukwałd, located in the Masovian, Silesian, and Warmian-Masurian Voivodeships, respectively, the ER index values for individual elements formed the following series: Cd>Pb>Zn>Cu>Ni [55], Cd>Pb>Zn>Cu>Cr [56] and Cd>Ni>Pb>Cr>Cu>Zn [57]. The Gardno reservoir stands out as the only water reservoir where no ecological risk was identified due to analyzed metal(loid)s in its bottom sediments. This is perhaps related to the fact that Lake Gardno is located in a protected area of Słowiński National Park and the boundaries of the Natura 2000 area. Therefore, anthropogenic pressure on the environment has a negligible impact here.

Based on the values of the RI index, which expresses the total level of risk caused by a given group of elements, it was shown that the presence of the metal(loid)s in question in the bottom sediments of Lake Szczutowskie and the Wisła-Czarne Reservoir poses moderate ecological threats. No direct ecological risk was identified in the Gardno and Swarzędzkie Lakes case.