Influence of diffuse sources on levels and distribution of polychlorinated biphenyls in the Guadiana River estuary, Portugal

Particulate material was collected along the Guadiana River estuary at different river flow and tidal conditions: coarser material eroded by flood in January 2001 at one station in the river; fresh surface sediments after storm water runoff at 7 sites; 24 surface sediments at 10 cross sections in March 2001; one sediment core from the adjoining coastal area in the same period; 124 suspended particulate matter (SPM) samples at low- and high-tide of neap and spring tides in May and October 2001. Polychlorinated biphenyl (PCB) congeners were analysed in all materials. Interpretative parameters, like salinity and suspended particulate matter concentration, organic carbon, Al and Si were also determined. Low levels of PCB in sediments are in conformity with the absence of industrial activities in the drainage basin. Both coarser material and fresh surface sediments transported by the flood contained slightly higher PCB concentrations (0.8–1.8 ng g−1) than surface sediments (0.1–1.1 ng g−1). Furthermore, PCB concentrations were higher in suspended particulate matter transported by moderate river flows (October), particularly of upstream limit of salinity (0.4 to 30.1 ng g−1) than in May (0.8 and 8.2 ng g−1). Alterations were also recorded in PCB composition. Less chlorinated compounds (higher ratio between tri+tetra-CB and hexa-CB) were enriched in coarser and fresh surface sediments, as well as in a sediment layer of the core taken outside the estuary. This ratio increased also in suspended particulate matter of the upstream limit of salinity collected in October. Changes of PCB concentrations and proportions of congeners evidence the importance of storm water runoff to the PCB input into this low-contaminated estuarine system.