Ranking of potentially toxic pollutants and their impact on microbial communities in water bodies receiving wastewater discharges

Abstract

The contribution of urban sewage treatment plants to pollution with emerging contaminants is still underestimated and discharge zones are not always subject to adequate monitoring activities. In this study, we apply the combination of risk level ranking of a specific class of pollutants (potentially toxic elements) and assessment of the metabolic activity of sediment microbial communities. The ranking approach identifies the most harmful toxic elements in the local environment of the upper sub-catchment of the Iskar River, Bulgaria. The effect on microbial communities was assessed by the determination of the share of viable cells and the inhibition of their metabolic activity (fluorescent staining method with digital image analysis). The data showed that Hg and Cu came at the top of the list of concerns for the matrix of surface waters; Cu, Cd, and Pb pose the greatest risk in sediments. The microbial communities in the wastewater discharge area were affected by pollutants and by the high nutrients and organic content of the effluent. The applied approach has the potential to help us focus the future site-specific monitoring for pollution control in water bodies, receiving wastewater discharges, and contributes to a better understanding of the potential ecological risks from hazardous pollutants.