Diagenetic fate of organic contaminants on the Palos Verdes Shelf, California

US Geological Survey, Box 25046, MS 407, Denver Federal Center, Lakewood, CO 80225, USA
Marine Chemistry (Impact Factor: 2.74). 06/2000; 70(4):289-315. DOI: 10.1016/S0304-4203(00)00034-7

ABSTRACT Municipal wastes discharged through deepwater submarine outfalls since 1937 have contaminated sediments of the Palos Verdes Shelf. A site approximately 6–8 km downcurrent from the outfall system was chosen for a study of the diagenetic fate of organic contaminants in the waste-impacted sediments. Concentrations of three classes of hydrophobic organic contaminants (DDT+metabolites, polychlorinated biphenyls (PCBs), and the long-chain alkylbenzenes) were determined in sediment cores collected at the study site in 1981 and 1992. Differences between the composition of effluent from the major source of DDT (Montrose Chemical) and that found in sediments suggests that parent DDT was transformed by hydrolytic dehydrochlorination during the earliest stages of diagenesis. As a result, p,p′-DDE is the dominant DDT metabolite found in shelf sediments, comprising 60–70% of ΣDDT. The p,p-DDE/p,p′-DDMU concentration ratio decreases with increasing sub-bottom depth in sediment cores, indicating that reductive dechlorination of p,p′-DDE is occurring. Approximately 9–23% of the DDE inventory in the sediments may have been converted to DDMU since DDT discharges began ca. 1953. At most, this is less than half of the decline in p,p′-DDE inventory that has been observed at the study site for the period 1981–1995. Most of the observed decrease is attributable to remobilization by processes such as sediment mixing coupled to resuspension, contaminant desorption, and current advection. Existing field data suggest that the in situ rate of DDE transformation is 102–103 times slower than rates determined in recent laboratory microcosm experiments (Quensen, J.F., Mueller, S.A., Jain, M.K., Tiedje, J.M., 1998. Reductive dechlorination of DDE to DDMU in marine sediment microcosms. Science, 280, 722–724.). This explains why the DDT composition (i.e. o,p′-, p,p′-isomers of DDE, DDD, DDT) of sediments from this site have not changed significantly since at least 1972. Congener-specific PCB compositions in shelf sediments are highly uniform and show no evidence of diagenetic transformation. Apparently, the agents/factors responsible for reductive dechlorination of DDE are not also effecting alteration of the PCBs. Two types of long-chain alkylbenzenes were found in the contaminated sediments. Comparison of chain length and isomer distributions of the linear alkylbenzenes in wastewater effluent and surficial sediment samples indicate that these compounds undergo biodegradation during sedimentation. Further degradation of the linear alkylbenzenes occurs after burial despite relatively invariant isomer compositions. The branched alkylbenzenes are much more persistent than the linear alkylbenzenes, presumably due to extensive branching of the alkyl side chain. Based on these results, p,p′-DDE, PCBs, and selected branched alkylbenzenes are sufficiently persistent for use in molecular stratigraphy. The linear alkylbenzenes may also provide information on depositional processes. However, their application as quantitative molecular tracers should be approached with caution.

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    • "The Southern California Bight is known to be the recipient of over 2400 metric tons of DDT manufacture wastes, among other contaminants, in process water discharged between 1940 and the early 1970s through the White Point sewage outfalls (Lee et al., 2002; Chen et al., 2012). Even after 40 years, the DDT that has accumulated in the coastal sediments is being constantly remobilized , either as DDT of any of its metabolites, to the overlaying seawater and the biota therein (Eganhouse et al., 2000; Zeng and Tran, 2002; Blasius and Goodmanlowe, 2008). Table 4 shows the trends observed in locations with 5 or more samplings for those sites listed above the national 85th percentile. "
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    Marine Pollution Bulletin 04/2014; 81(2). DOI:10.1016/j.marpolbul.2013.12.049 · 2.99 Impact Factor
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    • "Lowe, unpubl. data), where high levels of DDT have been measured (Eganhouse et al., 2000). However, the high DDT:PCB ratio may also be influenced by adult females feeding on coastal prey items such as California sea lions (Zalophus californius), harbor seals (Phoca vitulina richardsi), and juvenile northern elephant seals (Mirounga angustirostris) from southern and central California (Klimley et al., 1992). "
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    Marine environmental research 05/2013; 90. DOI:10.1016/j.marenvres.2013.05.009 · 2.76 Impact Factor
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    • "This consists to determine its half life and to estimate the time needed for the exportation of residues from an upstream watershed (Covaci et al., 2005). This aim can give information on the efficiency of a decision to ban pesticide use. 5. Estimating the fate of organic pollutants in sediment (Eganhouse et al., 2000; Devault et al., 2009). "
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