Distribution, sources and ecological risk assessment of polycyclic aromatic hydrocarbons in waters and sediments from Olt River dam reservoirs in Romania

This study provides important data on the distribution, sources and ecological risks of polycyclic aromatic hydrocarbons (PAHs), in surface waters and sediments collected from dam reservoirs on middle and lower course of the Olt River, the main tributary of the Danube, until the discharge into the Black Sea. A wide variation range of total PAHs concentrations in water (from 1.3 to 46.2 ng/L) and sediment (from 1.78 to 614.04 μg/kg) samples was emphasized by the results. The highest average PAHs concentration in water was recorded in the cold season and the lowest in the summer. In sediments, no differences were observed depending on the sampling period. Spatial distribution of PAHs in waters and sediments was correlated with the main anthropogenic activities along the river course. Regardless of the method used to attribute PAH sources (diagnostic ratios of specific PAHs, principal component analysis and hierarchical cluster analysis), it was confirmed that the potential anthropogenic sources of PAHs were both pyrogenic (incomplete combustion of biomass and coal) and pyrolytic (incomplete combustion of liquid fossil fuels and vehicle exhaust emissions), with a dominant pyrolytic input. Ecological risk assessment based on environmental quality standards, mean effect range-median quotient (m-ERM-Q), toxic equivalency factors (TEFs) and risk quotient (RQ) methods indicated potentially low ecological risks from PAHs. The ecological status of the Olt river waters poses no potential risk, and pollution of surface sediments can be classified as low polluted, except for two sites near industrial activities classified as moderately polluted. Therefore, a regular monitoring of PAHs concentration in the waters and sediments should be performed to prevent further contamination of PAHs in the studied area, especially in densely populated industrial areas.