Characterisation of the dynamics of organic contaminants ( n -alkanes, PAHs and PCBs) in a coastal area

The dynamics of three classes of organic contaminants, namely n-alkanes, polycyclic aromatic hydrocarbons and polychlorinated biphenyls, were evaluated from the settled suspended particulate matter (SPM) of two waste-water treatment plant outlets (O1 and O2) at the Marseille coast. We used a 1-m-high Plexiglas settling column filled with 7 L of seawater to determine the particles' settling rates, size distribution, and the extent of organic contaminants. Six classes of SPM (50–200 μm particles size) were obtained from 15 fractions of 500-mL successive filtering samples ranging from 30 s to 5 days, including those in the tube wall. The results of the experiment indicated that N 68% of the particles settled within 15 min, which highly correlated with the distribution of organic carbon and contaminant contents. Furthermore, we demonstrated that 9%–13% of the SPM, which contained 5%–11% of the organic contaminants, are non-settable even after 5 days. Extrapolating such behaviour in situ using molecular diagnostic indices for organic contaminant source apportionment indicated that these non-settable contaminant particles are exported to the sea.