Ocean monitoring off Palos Verdes, Southern California, 1970-1995

Treated wastewaters have been discharged to the ocean off Palos Verdes, via a submarine outfall system, since 1937. Currently, Los Angeles County Sanitation Districts serves the sewage treatment needs of 5 million people and the industries in 79 cities. Each day, 1.25×10⁶ meters³ (330 million gallons) of partial secondary effluent are discharged. From 1970, effluent emissions of suspended solids and contaminants declined substantially. Over 25 years of intensive marine ecological monitoring has documented remarkable environmental recovery. The areal extent of surface sediment organic enrichment and contamination decreased. Sediment dwelling invertebrates became more diverse and widely distributed. The depth and area of kelp beds expanded. Fish species returned to the outfall area; those which had been unusually abundant near the discharge declined. Dover sole fin erosion disappeared. The most significant environmental concerns on Palos Verdes relate to a historically discharged, partly buried sediment reservoir of bioavailable chlorinated hydrocarbons. Although tissue levels have declined, DDT and PCBs continue to pose potential health problems to marine organisms and their human consumers