Anthropogenic activities have led to a global increase of metals in river sediments. Metals in freshwater are persistent pollutants that can be toxic at trace concentrations. One of the ways metals enter waterways is through direct or accidental discharge of mine tailings. The ecological consequences of long-term exposure on freshwater fisheries, and potential risks for human consumers, were evaluated by an empirical case study of the Tisza River in Central Europe. Fifteen years after catastrophic dam failures introduced over 240,000 m3 of mine tailings laced with cyanide and metals into the river, we evaluated bioaccumulation and trophic transfer of metals (Cd, Cu, Ni, Pb, Zn) by regressing δ15N against metals in fish from the Tisza River. Direct effects of metals on fish were modeled with a 6-month chronic exposure of channel catfish (Ictlurus punctatis) to environmentally relevant concentrations of Cd (2.5 and 25 µg/L). Human health risks were evaluated by surveying local consumption habits in comparison to recommended safety standards.
Results/Conclusions
The mine tailings disaster on the Tisza River caused extensive fish kills, and metals remaining in the system are bioaccumulating in fish at sublethal concentrations. Across species and sampling locations, metals in fish muscle (µg/g dry wt.) averaged: Zn (52.2) > Cu (0.64) > Pb (0.13) > Ni (0.26) > Cd (0.06). Cd, Ni, and Pb trended towards increased body burden with trophic position whereas Cu and Zn exhibited the opposite pattern. Chronic Cd exposure did not affect growth or body condition; however, Cd altered expression pattern of genes related to glucose metabolism, oxidative stress, and cortisol synthesis in channel catfish. Additionally, Consuming Tisza River fish generally poses moderate human health risks, with lead presenting the highest concern at nearly double the recommended daily allotment for an average adult. Although metals are elevated in the Tisza, they do not present a grave ecological or human health risk at this time. However, environmental changes that increase the bioavailability of metals in the system may present a challenge to freshwater fisheries and warrant further monitoring.