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BIOGEOCHEMISTRY OF CHLORINATED ORGANIC CONTAMINANTS IN AQUATIC ECOSYSTEMS
Citation:
Pruell, R J. AND B K. Taplin. BIOGEOCHEMISTRY OF CHLORINATED ORGANIC CONTAMINANTS IN AQUATIC ECOSYSTEMS. Presented at 224th National Meeting of the American Chemical Society, Boston. MA, August 18-22, 2002.
Description:
Over the last several years we have conducted both laboratory and field studies to develop a better understanding of the movement of chlorinated organic compounds through aquatic ecosystems, with special emphasis on the differential movement of these compounds due to physical/chemical properties or biological processes. This research has focussed primarily on polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in sediments and benthic biota.
Two laboratory experiments were designed to measure the bioaccumulation and trophic transfer of selected polychlorinated compounds by marine benthos exposed to environmentally contaminated sediments. In the first experiment, sandworms (Nereis virens), clams (Macoma nasuta) and grass shrimp (Palaemonetes pugio) were exposed to sediment collected from the Passaic River, New Jersey. Biota / sediment accumulation factors (BSAFs) were calculated ([organism/lipid] / [sediment/total organic carbon]) and used to compare results among species and compounds. Although final contaminant concentrations were highest in the sandworms, BSAFs were generally higher for the clams and shrimp and lower for the sandworms. Clams showed preferential accumulation of lower molecular weight PCB congeners, which may be due to the very low lipid content in this species. Sandworms and especially shrimp appeared to metabolize congeners 52, 101 and 151 which all contain vicinal hydrogens in the meta and para regions of the molecule.
In a second laboratory study we investigated the transfer of chlorinated organic contaminants from sandworms to a higher trophic level species, the American lobster, (Homarus americanus). Sandworms were exposed to Passaic River sediment for 70 days to allow steady-state concentrations to be reached and then these organisms were fed to the lobster.
Contaminant distributions were significantly altered as they passed from sediments to polychaetes and then to the lobster. PCB patterns in lobsters indicated that these organisms metabolized many of the PCB congeners. PCB congeners containing vicinal hydrogens in the meta-para region were preferentially eliminated which is consistent with cytochrome P450IIB-type metabolism.
The concentrations of non-ortho substituted PCBs (such as congeners 77 and 126) became enriched in the PCB mixtures of the polychaetes and especially the lobsters relative to the sediment, probably because these congeners were not metabolized. These congeners and the 2,3,7,8-TCDD toxicity equivalents of the PCB mixtures were enriched by a factor of about six in the lobsters relative to the sediment. Lobsters also significantly altered the ratios of chlordane and DDT series compounds relative to those in the sediments and polychaetes.
PCDDs and PCDFs containing four or five chlorines were accumulated by the polychaetes and lobster; however, the highly chlorinated congeners were not accumulated. Only the lesser chlorinated PCDDs and PCDFs (mostly tetra- and pentachlorinated congeners) were detected in the polychaetes and lobster.
Chlorinated hydrocarbons distributions were also measured in fish and sediments from the Woonasquatucket River, Rhode Island. The sediments of this urban, freshwater, river system contained high concentrations of a complex mixture of PCDDs and PCDFs; however, fish from this system predominantly contained only 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). The patterns of PCDDs in the sediments of the Woonasquatucket River indicate multiple input sources. However, the presence of 1,2,4,5,7,8-hexachloro(9-H)xanthene (HCX) and the concentration trends of 2,3,7,8-TCDD and HCX in the sediments of the river suggest that the production of hexachlorophene is the predominant source of 2,3,7,8-TCDD to this system.
In summary, laboratory and field studies have been used to study the bioaccumulation of chlorinated organic contaminants in aquatic ecosystems. Significant alterations occur in the distributions of contaminants as they are accumulated from sediments and move through aquatic food webs. These alterations have implications for the identification of contaminant sources and for conducting toxicological assessments.