To: Allan Brouillet, Sue Kaelber-Matlock, and Brenda Brouillet (MDEQ)
From: Hector Galbraith (GES)
Date: July 16, 2004
Subject: GES comments on Entrix (2004) Wild Game Study Report
As requested by Allan Brouillet of Michigan DEQ, I have reviewed the report: Evaluation of PCDDs and PCDFs in Wild Game Taken From the Floodplain Along the Tittabawassee River (Entrix, 2004). This study reports organochlorine contaminant concentrations in wildlife game species collected on Tittabawassee River floodplain in the winter of 2003/2004. These data were collected to support the evaluation of risks posed to human health by the contaminants polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). However, the main objective of this review has been to evaluate the implications of the results in Entrix (2004) for the findings of two ecological risk assessments (ERA) already performed for the aquatic and terrestrial environments of the Tittabawassee River and its floodplain (GES 2003 and 2004, respectively), rather than to assess the utility of the results for any future human health risk assessment.
Specifically, this review focuses on two questions:
Section 1.1 of this memorandum outlines some important background information regarding existing risk assessment results, and against which the results reported in Entrix (2004) should be viewed. Section 2 explores the extent to which these new results affect the conclusions of the two previous ERAs at the site. Section 3 identifies some limitations of the results in Entrix (2004) for evaluating ecological risk (as distinct from human health risk) at the site. Section 4 presents a concise summary of the results of this evaluation, and Section 5 lists the references cited.
In 2003 and 2004 Galbraith Environmental Sciences (GES) performed two ERAs for the Michigan DEQ. The first of these (GES, 2003) focused on potential risks posed to piscivorous (fish-eating) wildlife by organochlorine contaminants in sediments and fish in the Tittabawassee River. The second (GES, 2004) focused on evaluating risks posed to terrestrial wildlife by the same contaminants in the Tittabawassee River floodplain soils. The data on which the aquatic ERA was based included sediment contaminant concentrations collected by Michigan DEQ, fish contaminant concentrations also collected by DEQ, contaminant concentrations in bird eggs (wood duck and hooded merganser) collected by DEQ and U.S. Fish and Wildlife Service, and data from the scientific literature. The data on which the terrestrial ERA was based comprised soil contaminant concentrations collected from the floodplain by Michigan DEQ, and data from the scientific literature. Because the terrestrial ERA, unlike the aquatic, did not include extensive contaminant data from biota on the floodplain, but instead modeled these body burdens, it was considered to be a screening level assessment.
The main result of the aquatic ERA was that the PCDDs and PCDFs in the sediments and fish in the Tittabawassee River exposed piscivorous wildlife to unacceptable risks (PCBs were relatively minor contributors to this risk). This prediction was confirmed by the extremely high concentrations of contaminants in the merganser and wood duck eggs. Using a food chain modeling approach, the terrestrial ERA predicted that the exposure of floodplain avian and mammalian predators (including foxes and birds of prey) to PCDDs/PCDFs through their food chains would also result in unacceptable risks. At the time of writing of the terrestrial ERA, no data (apart from some chicken eggs) were available to confirm that terrestrial food chains were being contaminated by the contaminants known to be present in the soils. This, however, was one of the main predictions of the terrestrial ERA. It was recognized by GES and by Michigan DEQ that it was important to test this prediction by collecting and analyzing terrestrial biota from the floodplain.
2. IMPLICATIONS OF ENTRIX (2004) RESULTS FOR EXISTING TITTABAWASSEE RIVER AND FLOODPLAIN ERA
Entrix (2004) reports the results of the collection and contaminant analysis of white-tailed deer (Odocoileus virginianus), wild turkeys (Melleagris gallopavo), and fox squirrels (Sciurus niger) from the floodplain of the Tittabawassee River (upriver and downriver of Midland) during the winter of 2003/2004. All three species are members of terrestrial food chains, the white-tailed deer being a browser that feeds on terrestrial grasses, forbs, shrubs, and tree saplings (Chapman and Feldhamer, 1982); the wild turkey feeding mainly on fruits, nuts, vegetation, and some invertebrates (Eaton, 1992); and the fox squirrel feeding mainly on acorns and other fruits and nuts (Chapman and Feldhamer, 1982). Thus, the species collected by Entrix (2004) can be expected to be potentially exposed to contaminants through terrestrial food chains, rather than aquatic pathways.
In the laboratory, the deer, turkey, and squirrel samples were analyzed for PCDD, PCDF, and PCB congeners.
The results reported in Entrix (2004) have a number of important implications for both the aquatic and terrestrial ERA already performed for the Tittabawassee River and its floodplain (GES, 2003 and 2004):
3. LIMITATIONS OF THE ENTRIX (2004) RESULTS IN EVALUATING ECOLOGICAL RISK
As discussed above, the main results of Entrix (2004) confirm predictions from two earlier MDEQ ERAs (GES, 2003 and 2004). However, the Entrix (2004) organism collection and analysis was intended to provide data that could be used to evaluate risks posed by organochlorine contaminants to human health, rather than to ecological receptors. This emphasis on human health necessitated collection and analysis techniques and procedures that limit the utility with which the results can be fully extrapolated to ecological risk. Also, apart from these "intentional" limitations, at least one unintended limitation occurred. These limitations are discussed below:
4. SUMMARY AND CONCLUSIONS
Review of the Entrix (2004) report has shown that the data contained therein support one of the major conclusions of the Michigan DEQ terrestrial ecological risk assessment (GES, 2004), that is that biota and food chains on the Tittabawassee River downriver of Midland are contaminated by PCDDs and PCDFs. A reasonable conclusion from this is that predators and scavengers at the tops of these food chains are likely to be even more exposed to these contaminants than the deer, squirrels, and turkeys sampled in the Entrix (2004) study.
However, the Entrix (2004) study was designed to generate data for an evaluation of risk to human health, rather than to ecological receptors. Because of this, design elements in the Entrix (2004) study, though perhaps appropriate for a human health risk analysis, result in an underestimation of the contaminant concentrations to which wildlife would be exposed and, hence, the magnitude of the risks incurred. These design elements comprise:
Braune, B.M., and R.J. Norstrom. 1989. Dynamics of organochlorine compounds in herring gulls: III. Tissue distribution and bioaccumulation in Lake Ontario gulls. Environ. Toxicol. Chem, 8:957-968.
Chapman, J.A. and G.A. Feldhamer. 1982. Wild Mammals of North America: Biology, Management, Economics. The Johns Hopkins University Press. Baltimore.
Eaton, S.W. 1992. Wild Turkey. In The Birds of North America, No. 22 (A. Poole, P. Stettenheim, and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, DC: The American Ornithologists’ Union.
Entrix. 2004. Evaluation of PCDDs and PCDFs in Wild Game Taken From the Floodplain Along the Tittabawassee River. Report to Dow Chemical Company, Midland, Michigan.
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MDEQ. 2003. Final Report. Phase II Tittabawassee/Saginaw River Dioxin Flood Plain Sampling Study. June 2003. Report issues by Michigan department of Environmental Quality, Bay City, Michigan.
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