Fate of Trace Metals in Los Angeles County Wastewater Discharge

A chemical equilibrium model of the Los Angeles County sewage is presented which accounts for the chemical speciation of trace metals. Many metals are found in very insoluble sulfide (Zn, Hg, Ag, Cu, Cd, Pb) or oxide (Cr, Fe) forms, while some (Ni, Co, Mn) are relatively soluble. A study of the oxidation and dilution of the sewage by seawater demonstrates that most metals tend to be solubilized upon disposal in the ocean and that unmeasurable increments in the natural metal concentrations should result in the farfield. It is argued that the sewage particulate is not mobilized in the vicinity of the outfall and that the nearby sediments are a mixture of naturally occurring sediments and sewage particulate. About 0.5% of the sewage particulate— and its metal content—can be accounted for in the reduced area.