Effect of floods on DNA damage of two cyprinid fish in the Sava River

Abstract

Freshwater ecosystems are constantly deteriorated due to the multitude of human activities, intensification of the industrial processes, wastewater discharge and agricultural chemicals. Besides, climate change provokes extreme weather and hydrological conditions leading to prolonged periods of droughts and floods. Floods can cause movements of polutants already present in the environment and introduce pathogenic bacteria in the flooded area. Many of the substances that reach environment could exhibit genotoxic potential on the genetic material of aquatic organisms, either alone or in complex mixtures of chemicals. Unfavorable hydrological conditions during 2014 resulted in extensive flooding in May in the Sava River basin. Obrenovac city was one of the most affected settlements on the river with esstimation that nearly 90% of town area was flooded. This led to evacuation of majority of inhabitants from the affected area. Our research was conducted from January to December 2014 on the Sava River, site Duboko, situated downstream of Obrenovac city. This is the area of intensive agricultural activity. Few km upstream the sampling site is the mouth of Kolubara river which is receiving untreated municipal wastewater of the town Obrenovac (50.000 inhabitants) and thermal power plant Nikola Tesla A with belonging ash fild. On monthly basis we have performed the measurements of basic phisico-chemical parameters, sampling water for microbiology analysis and fish tissue for the comet assay. Single Cell Gel Electrophoresis (SGCE) or Comet assay is widley accepted tool in ecogenotoxicology studies, in which DNA damage is measured on the level of a single eukaryotic cell. For the detection and quantification of E. coli and Enterococci we have used enzymathic methods and MPN approach. For comet assay analysis blood, liver and gill tissues were sampled from two cyprinid fishes. The highest water level was observed in May 2014, when flooding occured. Evacuation of inhabitants had led to exclusion of urban wastewater discharge which was refelcted through the lowest concentration of faecal pollution indicator bacteria, E. coli and Enterococci. With return of inhabitants in June their concentration in water started to increase gradually. In contrast, with withdrawl of water from the flooded agricultural land and ash disposal field high amounts of potentialy genotoxic substances were introduced into the Sava river, which was observed in sudden increase of DNA damage level in all three fish tissues during June. This study showed that flood occurence had major impact on the microbiological quality and genotoxic potential of the Sava River. Faecal pollution is mainly under the impact of urban wastewater discharge. On the other hand, genotoxic substances are most likely of industrial and agricultural origin. Acknowledgements This research was funded by project OI173045 „Fishes as water quality indicators in open waters of Serbia” (Ministry of Education, Science and Technological Development of the Republic of Serbia). This research was conducted in the Laboratory at the Chair of Microbiology, Center for genotoxicology and ecogenotoxicology, Faculty of Biology, University of Belgrade, and Institute for Multidisciplinary research, University of Belgrade.