Of the seven input routes investigated (municipal wastewater, direct industrial discharge, vessel antifouling paints, harbor flushing, surface runoff, dry aerial fallout, and ocean current advection), during 1971-72 the largest quantities of DDTs and PCBs (the major residues observed) were carried via the submarine discharge of municipal wastewater. The inputs decreased sharply between 1971 and 1975 and dry aerial fallout became the predominant input route. Distributions of DDT residues in bottom sediments and organisms showed distinct gradients toward the predominant source, the Los Angeles County municipal wastewater outfalls, where concentrations exceeded control levels by factors of 100-1000. PCBs and chlorinated benzenes were found to be ubiquitous contaminants of the municipal wastewaters studies.