Organic pollutants in a large shallow lake, and the potential of the local quagga mussel population for their removal

Filter feeders, like mussels, can significantly lower the concentration of harmful substances in the water body. In the present study, we examined the distribution of organic pollutants (polycyclic aromatic hydrocarbons [PAHs], non-steroidal anti-inflammatory drugs [NSAIDs]) in Lake Balaton, the largest shallow lake of Central Europe. We also investigated the sensitivity of the invasive quagga mussel to these substances and its potential to reduce their concentration in the water column. Our findings show that organic pollutant levels in Lake Balaton were generally below concentrations known to harm mussels, as indicated by the stress gene activity patterns observed along the lake's longitudinal axis. However, in the most urbanized eastern part of the lake, especially in spring, we detected signs of environmental contamination from certain pollutants (e.g. diclofenac), highlighting potential risks to local ecosystems and communities. Removal capacity of the mussels for PAHs reached the maximum after four days of exposure to 5-10 % diluted water accommodated fraction of fuel-oil fraction #4 when the mussels (20 ind. L^-1) reduced the PAH level by 100-85 %. Mussels (50 ind. L^-1) removed 28 % and 21 % of ibuprofen and ketoprofen, respectively, from 1 µg L^-1 concentrated solutions within 24 h. Many of the stress response genes were activated in the quagga mussel after their exposure to PAHs. These results suggest a significant role of gregarious invasive bivalves in the removal of organic pollutants from lake water.