DDTs and dumpsite in the Santa Monica Basin, California

Abstract

Sediment core samples from the Santa Monica (SM) Basin generally contain three times as much DDEs (o,p′ and p,p′ as DDTs. Total DDTs (Σ o,p′ -DDE, -DDD and -DDT and p,p′ -DDE, -DDD and -DDT) are relatively higher in some cores than in others in nearsurface horizons. Further, the ratios of o,p′ -DDT [1,1,1-trichloro-2(o-chlorophenyl)-2(p-chlorophenyl) ethane] to p,p′ -DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane] in some slope samples (0.43–0.87) and that of a tar cake (0.90) from Dumpsite II, San Pedro (SP) Basin are significantly higher than that observed in caustic waste from a DDT factory discharged into the southern California sewers or technical grade DDT (0.2–0.3). This observation and the fact that o,p′ -DDT metabolizes more readily than the p,p′ -isomer, suggest that at least part of the DDTs, in the sediments could not have originated from the above two sources. The unique DDT signature of the samples is probably characteristic of the acid wastes of the DDT factory discharged along with refinery wastes into the Dumpsites I and II. The discharged wastes could have entered SM and SP Basins from the dumpsites. Or, more likely, in the absence of precise records before 1961, industrial wastes could have been ‘short-dumped’ in nearshore regions. This could explain the unique DDT profiles from the slope sediments. In contrast, the central basin cores document the history of wastewater input. Thus o,p′p,p′ DDT ratio could potentially be diagnostic of their sources. Contaminants have apparently migrated in the sediment column by both upward and downward diffusion. The presence of the refractory metabolites in sediment trap particles suggests upward diffusion and resuspension.