Diagenetic fate of organic contaminants on the Palos Verdes Shelf, California
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.
- [Show abstract] [Hide abstract]
ABSTRACT: Organic molecules in reservoir sediments can be used as tracers of contaminant inputs into rivers. Vertical variations in the molecular records can be ascribed to pre-depositional alteration within the water column, or in situ post-depositional alteration. We report the molecular stratigraphy of four common riverine contaminant groups in sediment of the largest reservoir on the Danube River, the Iron Gate I Reservoir. Sediments were rapidly deposited, with little variation in texture and, as revealed by analytical pyrolysis, in the concentration and composition of natural sedimentary organic matter. However, a detailed molecular inspection did reveal differences in distribution and organic carbon (OC)-normalized concentrations of contaminants. The OC-normalized concentrations of nonylphenol increased by one order of magnitude with depth down the 70cm sediment core. There is a strong correlation between sediment depth and the ratio of nonylphenol to its precursor (nonylphenol monoethoxylate). This indicated that nonylphenol was produced in situ. While the relative proportions of C10-C14 linear alkylbenzenes remained constant with increasing depth, they exhibited variations in isomer distribution. These variations, which are due to different degrees of degradation, appear to have occurred within the water column prior to sedimentation of suspended solids. The distribution of 40 polycyclic aromatic hydrocarbons revealed origins from both pyrogenic and petrogenic sources. The differences in their compositions were not depth-related, but rather were associated with variations in the sorption capacities of texturally different sediments. Perylene showed slightly higher concentrations at greater depths, while the OC-normalized concentration of retene systematically increased with sediment depth. This is consistent with formation of retene and perylene via very early diagenetic transformation. The presence of petroleum biomarkers indicated minor contamination by fossil fuels.Science of The Total Environment 05/2013; 458-460C:90-100. · 3.26 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Organic contaminants were measured in young of the year (YOY) white sharks (Carcharodon carcharias) incidentally caught in southern California between 2005 and 2012 (n = 20) and were found to be unexpectedly high considering the young age and dietary preferences of young white sharks, suggesting these levels may be due to exposure in utero. To assess the potential contributions of dietary exposure to the observed levels, a five-parameter bioaccumulation model was used to estimate the total loads a newborn shark would potentially accumulate in one year from consuming contaminated prey from southern California. Maximum simulated dietary accumulation of DDTs and PCBs were 25.1 and 4.73 µg/g wet weight (ww) liver, respectively. Observed ΣDDT and ΣPCB concentrations (95±91 µg/g and 16±10 µg/g ww, respectively) in a majority of YOY sharks were substantially higher than the model predictions suggesting an additional source of contaminant exposure beyond foraging. Maternal offloading of organic contaminants during reproduction has been noted in other apex predators, but this is the first evidence of transfer in a matrotrophic shark. While there are signs of white shark population recovery in the eastern Pacific, the long-term physiological and population level consequences of biomagnification and maternal offloading of environmental contaminants in white sharks is unclear.PLoS ONE 01/2013; 8(4):e62886. · 3.73 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Organic contaminant and total mercury concentrations were compared in four species of lamniform sharks over several age classes to examine bioaccumulation patterns and gain insights into trophic ecology. Contaminants found in young of the year (YOY) sharks were assumed to be derived from maternal sources and used as a proxy to investigate factors that influence maternal offloading processes. YOY white (Carcharodon carcharias) and mako (Isurus oxyrinchus) sharks had comparable and significantly higher concentrations of PCBs, DDTs, pesticides, and mercury than YOY thresher (Alopias vulpinus) or salmon (Lamna ditropis) sharks. A significant positive relationship was found between YOY contaminant loads and maternal trophic position, suggesting that trophic ecology is one factor that plays an important role in maternal offloading. Differences in organic contaminant signatures and contaminant concentration magnitudes among species corroborated what is known about species habitat use and may be used to provide insights into the feeding ecology of these animals.Marine environmental research 05/2013; · 2.34 Impact Factor