Vertical profiles of toxicity, organic carbon, and chemical contaminants in sediment cores from the palos verdes shelf and Santa Monica Bay, California

The toxicity of sediment to the amphipod Rhepoxynius abronius was determined in the laboratory for 5 cm vertical sections of sediment cores collected at two sites on the Palos Verdes Shelf near the Los Angeles County Sanitation Districts' municipal wastewater outfalls and at two reference sites in Santa Monica Bay, California. The vertical distribution of sediment toxicity near the outfalls was significantly correlated with profiles of total organic carbon and sediment chemical contamination (total oillgrease, p,p-DDE, PCBs [Aroclor 1242], di(2-ethylhexyl)phthalate, Cd, Cr, Pb). Dating of core horizons showed that sediment toxicity also was significantly correlated with the historic record of the mass emission rate of suspended solids from the outfalls. The vertical profile showed that toxicity of surficial sediments, increased after the initiation of the discharge in the 1950s, remained relatively high until the early 1970s, and then decreased after the implementation of source control and improved effluent treatment.