Contamination of riverbed sediments by hazardous substances in the Mediterranean context: Influence of hydrological conditions

The aim of this study was to characterize spatial and temporal contamination by hazardous substances of the sediments of a Mediterranean river subject to significant hydrological variations. Four sediment sampling campaigns were undertaken along the Vène river under different hydrological conditions. Organotin compounds (OTCs), polychlorobiphenyls (PCBs), alkylphenols (APs) and polycyclic aromatic hydrocarbons (PAHs) in the sediments were analyzed. The results showed that the spatial pattern of contamination by OTCs differed with the hydrological conditions. During high flows, we observed a decrease in OTC concentrations to a background level (from 0.4–24 to 0.4–6.7 ng(Sn)/g dry weight; dw), showing that a large proportion of contaminated sediments were flushed out from the riverbed during the high flow period and transferred to the downstream environment. Concentrations of APs and PCBs were below the limits of quantification in all the sediments analyzed. Unlike OTCs, chemical analyses of PAHs showed that sewage effluents were the major source of contamination as sites located downstream from the discharge of sewage effluents were heavily contaminated (PAH concentrations ranged from 172 to 10,188 ng/g dw). Hydrological conditions also had an impact on the concentrations of PAH, since the highest concentrations (up to 10,188 ng/g dw) were measured downstream from the sewage effluent outlet during the period of high flow, probably due to urban runoff. Particulate transport of OTCs and PAHs after a rainy period was also evaluated using continuous flow centrifugation. High concentrations of OTCs (60.3 ng(Sn)/g dw) and PAHs (4193 ng/g dw) were observed in the exported suspended particulate matter.