STP1007

    Application of a Risk Assessment Framework for Marine Disposal of Sewage Sludge at Midshelf and Offshelf Sites

    Published: Jan 1988


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    Abstract

    A risk assessment framework was developed for predicting impacts from midshelf and offshelf disposal of sewage sludge. In the application presented, only the impacts resulting from bioaccumulation of the contaminants were considered. Disposal sites were assumed to be characteristic of sites in the Middle Atlantic Bight. The contaminant transport model used assumed all contaminants were associated with particulates and calculated the flux through the water column and into the sediments. Since degradation losses and resuspension were not explicitly included in the model, results obtained represented upper-bound estimates of time-averaged contaminant flux to the sediments. Cross-shelf profiles of maximum concentrations in the sediment surface layer were calculated by using an expression that accounted for mixing in the bioturbated zone. By assuming that organisms reach equilibrium with the surrounding sediment, concentrations of neutral hydrophobic organic contaminants in infaunal organisms were computed by using a preference factor (PF) based upon the organic carbon content of the sediments and the lipid content of the organisms. Results indicated that body burdens may be at least a half-order of magnitude higher in organisms living in the vicinity of the midshelf site than those living offshelf. Predicted tissue residues were compared with the Food and Drug Administration (FDA) tolerance level for polychlorinated biphenyls (PCBs) and the action level for chlordane to determine potential impacts from bioaccumulation of these contaminants in the tissues of organisms. By using the U.S. Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS), the reference dose (RfD) for chlordane was obtained and used to evaluate the risk to humans based on a dose to man calculation. Carcinogenic risk estimates were made using estimated potency factors. Projected results indicated that tissue concentrations resulting from sludge disposal would be at least an order of magnitude lower than the FDA tolerance level for PCBs at both sites, even after 100 years of disposal. The simulated midshelf disposal for a 100-year period resulted in body burdens of 0.28 ppm chlordane compared to the FDA action level of 0.3 ppm. However, the calculated RfD for chlordane was exceeded after 70 years of midshelf disposal. Although higher noncarcinogenic risks were associated with midshelf disposal of chlordane after 100 years, higher carcinogenic risks were associated with midshelf disposal of PCBs. Because of large uncertainties in modeling the various processes affecting transport, fate, and contaminant uptake in the benthic food chain, the results are only intended to provide estimates of relative risks related to midshelf versus offshelf disposal options. Based on relative comparisons made in this analysis, higher human health risks would be associated with midshelf disposal than with offshelf disposal.

    Keywords:

    sewage sludge, benthic flux, risk assessment framework, preference factor, contaminant mass loading, Middle Atlantic Bight, ocean disposal, polychlorinated biphenyls, (PCBs), chlordane, aquatic toxicology


    Author Information:

    Nocito, JA
    Physical scientist, Science Applications International Corp., U.S. Environmental Protection Agency, Environmental Research Laboratory—Narragansett, Narragansett, RI

    Walker, HA
    Environmental scientist and branch chief, Exposure Assessment GroupU.S. Environmental Protection Agency, Environmental Research Laboratory—Narragansett, Narragansett, RI

    Paul, JF
    Environmental scientist and branch chief, Exposure Assessment GroupU.S. Environmental Protection Agency, Environmental Research Laboratory—Narragansett, Narragansett, RI

    Menzie, CA
    Senior scientist, Charles Menzie Associates, Westford, MA


    Paper ID: STP10284S

    Committee/Subcommittee: E47.01

    DOI: 10.1520/STP10284S


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