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Most transported particles released from a catchment area are deposited and accumulated in the sediment layers of water reservoirs. Along with mineral particles, contaminants originating from human activity and natural processes are added to such aquatic systems (e.g., heavy metals). This is an especially important issue when a reservoir is being used as a source of drinking water. The main aim of this study was the environmental risk assessment of the sediment in the Dobczyce Reservoir and two of its tributaries (the Raba River and Wolni- ca Stream) during the years of 2004–2007 and 2016, 2017. Substantial variations in heavy metals were found due to the land use and catchment management. The potential ecological risk showed an uneven distribution, and the overall ecological risk level ranged from low to moderate.

Metale ciężkie w osadach dennych zbiorników rekreacyjnych na terenach zurbanizowanych i ocena ryzyka środowiskowegoWater reservoirs play important role in human environment, especially as a part of ecological networks in urban areas. Due to such localization they are subjected to the effects of the anthropogenic activities, introducing broad range of contaminants (e.g. heavy metals) through various pathways. The main aim of this study was to estimate heavy metal (Cd, Cr, Cu, Pb, Zn) contamination level in sediments of eight reservoirs in the Cracow urban area (Bagry, Nowohucki, Plaszowski, Dabski, Przylasek Rusiecki, Tyniec, Zakrzowek, and Zeslawice Reservoirs), and assess its potential environmental risk with use of various criteria (Igeo -geo-accumulation index, CF -contamination factor, PLI -pollution load index, TEC/PEC -threshold effect concentration/probable effect concentration). Furthermore, the role of reservoir catchment for sediment contamination (agricultural, industrial, and urbanized) was studied. Also, levels of metal contamination were compared with other recreational reservoirs in Poland (Jeziorsko, Barycz Dzierzno Duze, Pogoria III, Rusalka, and Sloneczne Reservoirs). The study revealed considerable variation in the chemical composition of bottom sediments, evidently depended on their localization. Results showed that the sediments of the Cracow area reservoirs and from the other urbanized catchments were moderately contaminated. Reservoirs from industrial catchments had a considerably higher content level, while water bodies localized in agricultural areas displayed low content of heavy metals. According to Igeo and CF sediments of Cracow area reservoirs were mostly Cd contaminated. However, Cd contents were relatively high in urban (Sloneczne) and industrial areas (Dzierzno Duze). The same situation was found in PEC values exceedances. In other cases, investigated heavy metals were mostly between the TEC and PEC values, which indicate moderate contamination of the sediments and moderate impact on biota. Therefore, further research and monitoring of sediments quality should be maintained in future seasons due to the use of water reservoirs throughout the year for recreational purposes.

Microplastics are ubiquitous in both marine and freshwater ecosystems, where they can act as a physical contaminant, as well as interact with chemicals present in the environment. It has been suggested that chemical contaminants can sorb to microplastics, such that microplastics act as a vector for chemicals into aquatic biota and enhance their negative effects. It has been repeatedly suggested that the main factors underpinning the binding of chemicals to microplastics are hydrophobic partitioning and the size of microplastic particles.Therefore, we used the hydrophobicity of chemicals, as log Kow, as well as the size of microplastic particles to conduct a quantitative analysis of published results to evaluate the influence of microplastics on chemical toxicity. We collated data from 39 laboratory studies that assessed the effects of microplastics, chemicals and their combination on several ecotoxicological responses of freshwater and marine organisms. Each chemical was assigned the relevant octanol / water partition coefficient (log KOW) as a measure of its hydrophobicity, and the mean size of microplastics particles used in each study was recorded. We found no effect of log KOW or the size of microplastic particles on the interaction between microplastics and chemicals with regards to any of the relevant ecotoxicological responses (behaviour, growth, survival and cellular) considered in this study. These findings are significant in showing that the effect of microplastics on the toxicity of chemicals is more complex than just considering hydrophobicity of chemicals and size of microplastics. We call for more mechanistic experiments to motivate a robust risk assessment and mitigation of microplastic toxicity in the environment.

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