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

US Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192, USA; US Geological Survey, Box 25046, MS 407, Denver Federal Center, Lakewood, CO 80225, USA
Marine Chemistry (Impact Factor: 3). 01/2000; 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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    ABSTRACT: Sedimentproben aus Berliner Oberflächengewässern wurden mittels GC/MS qualitativ und quantitativ auf ihre Kontamination mit organischen Substanzen untersucht. Als die wichtigsten anthropogenen Kontaminanten konnten neben PAH und zinnorganischen Verbindungen chlorierte, bromierte und gemischthalogenierte Verbindungen und einige zugeordnete Metaboliten nachgewiesen werden. In der Gruppe der halogenierten Pestizide dominierten in allen untersuchten Proben die DDT-Metaboliten DDD, DDE, DDCN, DDMU und DDMS in ihrem räumlichen und quantitativen Auftreten. Das p,p′-DDD wurde als Hauptmetabolit in Konzentrationen bis zu 1230 μg/kg TS nachgewiesen. DDT selbst konnte nur noch in wenigen Proben nachgewiesen werden. Die Untersuchung ausgewählter DDT-Metaboliten auf ihre akute Cytotoxizität mit der Zellinie RTG-2 aus der Gonade der Regenbogenforelle (Oncorhynchus mykiss) zeigte eine hohe cytotoxische Wirkung. Der Test auf endokrine Wirksamkeit im Dot-Blot/RNase-Protection-Assay ergab ein östrogenes Potenzial in der Reihenfolge o,p′-DDT>p,p′-DDMS >p,p′-DDMU≥p,p′-DDCN. Die Untersuchungsergebnisse zeigen, dass ein chemisches Monitoring, das ausschließlich DDT, DDD und DDE berücksichtigt, das ökotoxikologische Schädigungspotenzial von DDT und seinen Metaboliten nicht ausreichend abzuschätzen vermag. Die Entwicklung einer Methode zur biotest-geleiteten Bewertung von DDX erscheint eine geeignete Strategie zur Lösung dieses Problems zu sein. Die nicht erforschte Kombinationswirkung, Unterschiede in der toxischen Wirkung zwischen verschiedenen Trophiestufen und in der Bioverfügbarkeit, sowie geringe Erkenntnisse über die Bildungsmechanismen von DDT-Metaboliten in situ und das enantioselektive Verhalten der meisten chiralen DDT-Metaboliten lassen weiteren Forschungsbedarf erkennen. Sediment samples from rivers and lakes of Berlin (Germany) were analysed for their contamination with organic compounds by means of qualitative and quantitative GC/MS analysis. The principal compounds detected were PAH, organotin derivates, several classes of chlorinated, brominated and mixed halogenated compounds and some of their related metabolites. The DDT metabolites DDD, DDE, DDCN, DDMU and DDMS were the most abundant compounds of halogenated pesticides in a wide range of samples. The main metabolite determined was p,p′-DDD, with concentrations up to 1230 μg/kg dw. The parent DDT compound was detected in only a few samples. The acute cytotoxicity of selected DDT-metabolites was determined with the permanent cell line RTG-2 from the gonads of the rainbow trout (Oncorhynchus mykiss). The results indicate a high cytotoxic potential of these metabolites. The oestrogenic potential was determined by the Dot-Blot/RNase-Protection-Assay an the order from o,p′-DDT>p,p′-DDMS>p,p′-DDMU≥p,p′-DDCN. Risk assessments based on chemical analysis of DDT, DDD and DDE alone is not able to estimate the real toxic potential of DDT and its metabolites. The development of a method for bioassay directed assessment seems to be an effective strategy to solve this problem. Especially scarce or not available data of combinatory effects, differences between different trophic levels and their availability to biota and low knowledge about the metabolism in situ as well as the enantioselective characteristics of most chiral DDT metabolites warrant future analyses.
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  • Clinical Neurophysiology - CLIN NEUROPHYSIOL. 01/2010; 121.
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    ABSTRACT: Particles from the Whites Point/JWPCP outfalls operated by the Los Angeles County Sanitation District (LACSD) have been discharged onto the Palos Verdes (PV) shelf, Southern California, since the late 1930s. Since the early 1950s, they have made a significant contribution to the sedimentary deposits on the shelf. In order to study the transport and diagenesis of organic carbon (OC) and associated trace metals, replicate sediment cores were collected during 1996 and 1997 at four different sites at the ∼60 m isobath on the PV shelf, and analyzed for OC, Ag, Al, Cd, Cr, Cu, Mn, Ni, Pb, and Zn. We conclude from these results that a significant fraction of OC and associated heavy metals were transported laterally on silt particles from shallower environments. Cross-shelf transport of sediments caused multiple peaks in measured profiles of OC and trace metals at site 6C, 2 km away from the outfall. The same mechanism is likely to contribute to a concentration decrease that is smaller than that expected from decreases from the Whites Point outfall emissions. Based on Pb/OC ratios in sediments, deposited in 1971, and comparisons to the outfall from the same year, we estimate that 50±10% of the OC deposited in the early 1970s, now buried at 30–50 cm depth, had oxidized since that time, implying a half-life of about 26 years for the outfall-OC, as an upper limit. The average OC oxidation rate at peak depth (about 2 mg C cm−2 year−1) is, however, only about 10% of the present-day OC accumulation rate (20 mg C cm−2 year−1), which itself is adding not much more than 1% per year to the post-1950s OC inventory (∼1500 mg cm−2). We furthermore estimate that the OC inventory in PV shelf sediments in 1971 was equivalent to about 35% of that emitted by the outfall. OC and trace metal inventories did not decrease in the period 1981 to 1997, contrary to those of other contaminants such as DDTs and PCBs.
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