Tidal creek and salt marsh sediments in South Carolina coastal estuaries: II. Distribution of organic contaminants

Twenty-eight tidal creeks along the South Carolina coast were sampled durin g the summer of 1995 to determine the levels of sediment contamination incl uding organic chemicals (i.e., polycyclic aromatic hydrocarbons [PAHs], pol ychlorinated biphenyls [PCBs], and DDT and its metabolites) associated with different types and varying levels of watershed development (i.e., industr ial/urban, suburban, forested, and salt marsh). Organic analysis utilized h igh-performance liquid chromatography (HPLC) with fluorescence detection an d capillary gas chromatography-ion trap mass spectrometry (GC-ITMS) for PAH s, and gas chromatography with electron capture detection (GC-ECD) for pest icides and PCBs. Results indicated that creeks with industrial/urban waters heds had significantly higher concentrations of PAHs, PCBs, and DDT compare d with creeks with suburban and forested (reference) watersheds. The suburb an watershed class of creeks had concentrations of half the PAH analytes an d the total PCBs which exceeded the concentrations found in the forested wa tershed class of creeks. The spatial distribution of organic contaminants w as evaluated in four of these tidal creek-salt marsh systems representing u rban/industrial, suburban, and forested watersheds, from, the creek channel . to the adjacent uplands. The distribution of organic contaminants within each representative creek was not concordant with the total organic carbon or the clay content of the sediment. The representative industrial/urban cr eek-marsh system, Diesel Creek, had the highest concentration of PAHs in th e creek channel and the highest concentration of PCBs and DDT on the marsh surface, primarily in the upper portion of the system, The representative s uburban creek-marsh system, Shem Creek, had elevated levels of both PAHs an d PCBs throughout the entire system. This system also had one site with a t otal PAH concentration of 324,000 ppb and a total DDT concentration that wa s 20-100 times higher than the other sites. One of the representative fores ted creek-marsh systems, Rathall Creek, had low levels of the three organic contaminants except for one sampling site that had PAH concentrations a fa ctor of 10 higher than the other sites. The other representative forested c reek-marsh system, Long Creek, bad low levels of PAHs and PCBs, but elevate d levels of DDT were observed, particularly in the upper portion on the mar sh surface. The results of this study suggest that (1) anthropogenic altera tion of the land cover in the watersheds of tidal creek-salt marsh systems may increase the organic contaminant loadings in the sediment, and (2) tida l creek-salt marsh sediments, particularly in the creek channel, are reposi tories and potentially conduits of organic contaminants from the upland env ironment to the deeper estuarine areas.