Flooding modifies the genotoxic effects of pollution on a worm, a mussel and two fish species from the Sava River

Extreme hydrological events, such as water scarcity and flooding, can modify the effect of other stressors present in aquatic environment, which could result in the significant changes in the ecosystem functioning. Presence and interaction of various stressors (genotoxic pollutants) in the environment can influence the integrity of DNA molecules in aquatic organisms which can be negatively reflected on the individual, population and community levels. Therefore, in this study we have investigated the impact of flooding, in terms of genotoxicity, on organisms belonging to different trophic levels. The study was carried out on the site situated in the lower stretch of the Sava River which faced devastating effects of severe flooding in May 2014. The flooding occurred during our field experiment and this event provided a unique opportunity to assess its influence to the environment. The in situ effects of this specific situation were monitored by measuring physical, chemical and microbiological parameters of water, and by comparing the level of DNA damage in coelomocytes and haemocytes of freshwater worms Branchiura sowerbyi, haemocytes of freshwater mussels Unio tumidus and blood cells of freshwater fish Abramis bjoerkna/Abramis sapa, by means of the comet assay. Our study indicated that the flooding had a significant impact on water quality by decreasing the amount and discharge rate of urban wastewaters but simultaneously introducing contaminants from the nearby fly ash disposal field into river by runoff, which had diverse effects on the level of DNA damage in the studied organisms. This indicates that the assessment of genotoxic pollution in situ is strongly affected by the choice of the bioindicator organism.