Uncertainty and variability in risk from trophic transfer of contaminants in dredged sediments

The risks associated with bioaccumulative contaminants must be considered w hen evaluating dredged material disposal alternatives. The bioaccumulation of organochlorines and other contaminants by higher trophic level organisms represents one of the most significant sources of uncertainty in risk asse ssment. Both population variability (e.g. true population heterogeneity in body weight, lipid content, etc.) and uncertainty (e.g. measurement error) in trophic transfer can lead to large errors in predicted risk values for e cological receptors. This paper describes and quantitatively evaluates sour ces of uncertainty and variability in estimating the risk to an ecological receptor (osprey) from the trophic transfer of polychlorinated biphenyls (P CBs) in sediments from the New York-New Jersey (NY-NJ) Harbor. The distribu tion of toxicity quotients is obtained using a food chain model for the osp rey and specifying distributions for input parameters, which are disaggrega ted to represent either uncertainty or variability. PCB concentrations in s ediment and water are treated as predominantly uncertain, whereas lipid con tent in fish, feeding preferences, and fish weight are assumed to contribut e primarily to population variability in PCB accumulation. The analysis sho ws that point estimates of reasonable maximum exposure (RME) exceed the unc ertainty bounds on the 95th percentile of variability. The analysis also sh ows that uncertainties in the sediment and water contaminant concentrations contribute more to the range of risk estimates than does the variability i n the population exposure parameters. The separation of uncertainty and var iability in food chain models can help to support management decisions rega rding dredged material disposal by providing a quantitative expression of t he confidence in ecological risk estimates. A rationale is provided for the distinction between uncertain and variable parameters based on management goals and data availability. (C) 2001 Elsevier Science B.V. All rights rese nted.