Equilibrium sampling of HOCs in sediments and suspended particulate matter of the Elbe River

BACKGROUND: Chemical quality of sediment and suspended particulate matter (SPM) is usually assessed by total chemical concentrations (C(total)). However, the freely dissolved concentration (C(free)) is the ecologically more relevant parameter for bioavailability, diffusion and bioaccumulation. In recent studies, equilibrium sampling has been applied to determine C(free) of hydrophobic organic contaminants (HOCs) in the sediment pore water, whereas such data are missing for SPM. We applied solid-phase micro-extraction to measure and compare C(free) of PAHs and PCBs in pore water of sediments and SPM sampled along the German part of the river Elbe. Moreover, site-specific distribution ratios were evaluated and C(bio,lipid) was predicted using C(free). RESULTS: C(free) of PAHs remained largely constant while C(free) of PCBs varied along the Elbe River. The highest C(total) of PCBs and PAHs were found at Prossen (km 13) and Meißen (km 96). PCB C(total) even exceeded the environmental quality standard for sediment and SPM in Prossen. Site-specific distribution ratios (K(D)) revealed a stronger sorption for PAHs compared to PCBs, indicating a higher availability of PCBs. Equilibrium partitioning concentrations in lipids (C(lip↔sed)) showed a high correlation with actually measured lipid-normalised concentrations (C(bio,lipid)) in bream. This indicates that PCB bioaccumulation in this benthic fish species is closely linked to the sediment contamination. CONCLUSIONS: In rivers, SPM functions as a transportation vehicle for HOCs along the stream until it eventually deposits to the sediment. This study demonstrates that due to weaker sorption of PAHs and PCBs to the SPM this matrix poses a higher risk to the aquatic environment compared to the sediment. The prediction of C(bio,lipid) of PCBs was correct and shows that solid-phase micro-extraction is highly suited to predict lipid concentration, and thus a valuable tool for risk-assessment or sediment management. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12302-018-0159-8) contains supplementary material, which is available to authorized users.