Distribution of hydrophobic organic contaminants in marine sediment fines-An alternative normalization strategy?

Abstract

The necessary normalization of contaminant concentrations, in order to be able to compare contaminant content in sediments with different sediment properties, is currently not standardized within environmental monitoring and assessment programs. Therefore, this study investigates an alternative normalization strategy for hydrophobic organic contaminants (HOCs) by removing the coarse and chemically inert sediment fraction using an improved, half-automated wet-sieving method. We compare the results to commonly used TOC normalization (2.5% total organic carbon [TOC], OSPAR). Simultaneously, the study provides a comprehensive overview of HOC concentrations in sediment fines (<63 µm) for the German Exclusive Economic Zone and therefore gathers information about the more bioavailable and mobile part of the sediment that particularly accumulates HOCs due to its high surface area. We analyzed bulk sediment samples and their corresponding fine grain fractions from 25 stations in the German Exclusive Economic Zone for 41 HOCs including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides. The results indicate that the wet-sieving procedure is capable of physically normalizing the concentrations of the investigated HOCs and is useful for the comparison of concentrations in different sediment types. The wet-sieving procedure is more time consuming than the normalization to the TOC content. However, it offers the possibility of lowering the detection limits (LODs) through the analytical sample preparation procedure used, as sieving concentrates the contaminants. Therefore, a higher number of results >LOD were detected in sediment fines, leading to more informative data sets. In contrast to the commonly used normalization to 2.5% TOC, the statistical analyses carried out (principal component analysis with subsequent cluster analysis) additionally indicate that physical normalization allows better differentiation of sampling sites by contaminant sources and geographic location rather than their sediment characteristics. Integr Environ Assess Manag 2023;19:1348-1360. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Keywords: Normalization of sediment data; North Sea sediments; Polychlorinated biphenyls; Polycyclic aromatic hydrocarbons; Sediment sieving.