Bioaccumulation and health risk assessment of heavy metals in European eels taken from Lakes Köycegiz (Turkey) and Võrtsjärv (Estonia).

Monitoring heavy metal contaminants in fish is important for the assessment of environmental quality as well as food safety. In this study, European eel samples were collected from Lake Köycegiz and Lake Võrtsjärv in 2017 and 2018. The concentrations of Mn, Cd, Zn, Pb, and Cu metals were measured by using GF-AAS in four selected tissues of eel, including liver, gill, skin, and muscle in both lakes. The pollution index (Pi, MPI) values were calculated for both lakes and the health risk for consumers was assessed for both adults and children in Turkey and Estonia. The estimated weekly intake (EWI), hazard index (HI), and lifetime cancer risk values (CRs) for the metals were calculated for both lakes. According to the results of this study, a significant difference was determined between the metal concentrations (especially Cu, Cd, and Pb) in the tissues of the eel samples taken from the two lakes. These results show that besides the pollution levels in the aquatic environment, physiological needs and metabolic activities in different habitats have a significant effect on metal accumulation in eels. In addition, HI was found to be < 1 for both adult and child consumers in both lakes, which indicates that consumers would not experience non-carcinogenic health effects. However, the values of CR for Pb and Cd were found negligible in Lake Köycegiz, while the CR value for Pb was found to be very close to the danger limits in Lake Võrtsjärv.

Nitrate as a predictor of cyanobacteria biomass in eutrophic lakes in a climate change context.

We aimed to predict cyanobacteria biomass and nitrate (NO3-) concentrations in Lake Võrtsjärv, a large, shallow, and eutrophic lake in Estonia. We used a model chain based on the succession of a mechanistic (INCA-N) model and an empirical, generalized linear model. INCA-N model calibration and validation was performed with long term climate and catchment parameters. We constructed twelve scenarios as combinations of climate forcing from the Intergovernmental Panel on Climate Change (IPCC, 3 scenarios), land conversion (forest to agriculture, 2 scenarios), and fertilizer use (2 scenarios). Models predicted 46% of the variance of cyanobacteria biomass and 65% of that of NO3- concentrations. The model chain simulated that scenarios comprising both forest conversion to agricultural lands and a greater use of fertilizer per surface area unit would cause increases in lacustrine NO3- (up to twice the historical mean) and cyanobacteria biomass (up to a four-fold increase compared to the historical mean). The changes in NO3- concentrations and cyanobacteria biomass were more pronounced in low and moderate warming scenarios than in high warming scenarios because of increased denitrification rates in a warmer climate. Our findings show the importance of reducing anthropogenic pressures on lake catchments in order to reduce harmful pollutant and microalgae proliferation, and highlight the counterintuitive effects of multiple stressor interactions on lake functioning.