A Model of the Environmental Fate of Chlorohydrocarbon Contaminants Associated with Sydney Sewage Discharges

Abstract

Bioconcentration and sediment sorption models were used with levels detected in the biota and sediments to calculate the ambient water concentrations of chlorohydrocarbon contaminants from a major outfall discharging sewage to the ocean near Malabar, in Sydney, Australia. The ambient water concentrations calculated using these models were in general agreement within a factor of about 2 in all but one case, and that was in agreement within an order of magnitude. A steady-state nonequilibrium fugacity model incorporating the oceanographic dimensions of the environment receiving the discharges was used to predict the environmental fate of a range of the chlorohydrocarbon contaminants. The model showed advection in water to be the dominant removal process, accounting for all except 1-2% of the contaminants discharged. With the exception of the more water soluble dieldrin, the major portion of contaminant present in the area was held in the sediments. The model was also used to estimate the rates of discharge of each of the contaminants. These were chlordane 83-640, DDT 150, dieldrin 1400-1500, hexachlorobenzene 360-400 and PCBs 55-96 g per day. Comparisons of the calculated ambient concentrations of each compound in the water and in fish in waters adjacent to the cliff-face outfall before and after its relocation to a deepwater outfall site indicated that relocation resulted in a reduction to about 2% of the previous levels.