Superfund Research Program
Fish as Sentinels of Persistent Organic Pollutants
Polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) are highly persistent environmental contaminants. These compounds bioaccumulate and often biomagnify in food chains. Human exposure to these contaminants can result in dermal toxicity, immunotoxicity, carcinogenicity, and adverse effects on reproduction, development and endocrine function. In vertebrates, many toxicities of PCBs and PCDD/Fs are congener-specific. Thus, knowledge of the PCB and PCDD/F congener composition in environmental matrices can help in predicting and quantifying their toxicities. The Hudson River ecosystem exemplifies a site where such information would be valuable.
While only limited research has been conducted on PCDD/F contamination levels in sediments and biota of the Hudson River estuary, significant work has been done to determine the spatial distribution and temporal stability of PCBs in river sediments (see Research Brief 108), the water column, and selected biota along the main-stem Hudson River. Total body burdens of PCBs have been reported for several ecologically important fish species, but little information exists on the spatial patterns of total PCBs and individual congeners in any single species. Few, if any, studies have quantified total PCDD/Fs or characterized congener patterns in a single species throughout its distribution with the Hudson River estuary.
Dr. Isaac Wirgin at the New York University School of Medicine SBRP is examining PCB and PCDD/F totals and congener patterns in hepatic tissues young-of-the-year (YOY) and adult Atlantic tomcod collected from various sites in the main-stem Hudson River estuary. He and a team of researchers are investigating spatial and age-related variability in levels and patterns of PCBs and PCDD/Fs in tomcod from the area. This information may provide some insight into the dynamics and potential sources of these contaminants for Hudson River fishes. It may also help explain why tomcod from the Hudson River population are resistant to early life-stage toxicities and gene induction from exposure to these contaminants.
Over a 2 year period, the researchers collected adult and YOY tomcod at various points along the main-stem Hudson River, Hackensack River, and Newark Bay. Analysis of liver tissue samples led to several interesting findings:
Fifty miles upstream from the mouth of the river, detected total PCB body burdens were lower than those reported 20 years ago. This trend was not observed closer to the mouth of the river where sources such as sewage effluents may still be significant sources of PCBs to the ecosystem.
Adult male tomcod showed total hepatic PCB and PCDD/F burdens that were 2-5 times greater than females collected at the same location and time. This may be due, in part, to the female fish offloading organochlorine contaminants into eggs.
PCDD/F congener-specific analyses did not reveal distinctions between adult female and male tomcod or between YOY and adult tomcod collected at similar locations. The PCDD/F congener profile comparison between Newark/Hackensack and Hudson River revealed a distinct 2,3,7,8-TCDD source in the Newark/Hackensack location, which likely was due to the herbicide production facility that previously operated there.
Hepatic PCB congener composition differed dramatically between YOY and adult fish. The di- to tetrachlorinated biphenyls dominated the composition of PCB congeners in YOY tomcod, whereas the penta- to nonachlorinated biphenyls predominated in adults with particular prevalences of the 2,4,5-substituted diortho congeners, which are highly recalcitrant to biotransformation/elimination. Possible explanations for this pattern include (1) YOY and adult fish may have different diets; (2) adults are older and larger, thus they would have had more time/mass to bioaccumulate PCBs than YOY tomcod; or (3) it may be that the capacity of tomcod to metabolize and eliminate PCBs differs with life stage, and that older fish are less able to metabolize select higher-chlorinated PCB congeners than YOY tomcod. This suggests that either natural selection or a physiological acclimation response may reduce metabolism of PCBs and alter resulting congener profiles in older age groups of tomcod from highly polluted sites.
YOY tomcod exhibited significant spatial variation in total PCBs and PCDD/Fs. Levels of total PCDD/Fs detected in YOY tomcod from Newark Bay/Hackensack were among the highest ever reported in natural populations of any species. YOY tomcod presumably travel less than adults and may better represent the local contaminant levels where they were captured. The researchers were able to group YOY tomcod into congener-specific PCB pattern groups based on capture locations, providing additional support for the concept that YOY tomcod may be used to serve as site-specific indicators of the levels and congener-specific patterns of contaminants.
The researchers determined congener PCB patterns in the YOY tomcod in terms of compositions of Aroclor 1242, Aroclor 1254, and Aroclor 1260. For fish captured near the mouth of the river, the detected profiles were consistent with known PCB sources. But at ~ 80 miles upstream of the mouth of the river (RM 80), levels of A1242 declined unexpectedly. Dr. Wirgin's team determined that the shift occurs near a region of transition from brackish water to freshwater. Octanol-water partition coefficients for PCBs are lower in freshwater than in saltwater, which may impact the congener profile in two ways: (1) lower-chlorinated PCBs partition into freshwater from tissues to a greater extent than in saltwater and tomcod caught above RM 80 may have depurated a significant amount of the lower-chlorinated congeners which make up a large percentage of the A1242 upstream source (i.e., primarily tri- and tetrachlorinated biphenyls); or (2) the fish caught above RM80 animals may have assimilated a lesser amount of lower-chlorinated congeners due to the decreased partitioning of PCBs into lipid in freshwater versus saltwater.
These findings indicate that because of the spatial variation in PCB and PCDD/F patterns in YOY tomcod, this species may serve as an effective time-integrated biomonitor of site-specific organochlorine contamination.
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To learn more about this research, please refer to the following sources:
- Fernandez MP, Ikonomou MG, Courtenay SC, Wirgin II. 2004. Spatial variation in hepatic levels and patterns of PCBs and PCDD/Fs among young-of-the-year and adult Atlantic tomcod (Microgadus tomcod) in the Hudson River estuary. Environ Sci Technol 38(4):976-983. PMID:14998007
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