Monte Carlo Risk Assessment for Dioxin in Maine Fish: Using a Microexposure Approach to Evaluate the Need for Fish Advisories, 1993 Environmental Conference Proceedings

The presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in fish downstream of pulp and paper mills has prompted some regulatory agencies to issue fish consumption advisories on a number of rivers and streams throughout the United States. In many cases, the basis for these advisories is a screening level risk calculation using conservative values for the various parameters in the risk equation. In nearly all cases, predicted risks are substantially overestimated. In an effort to address this deficiency, we developed probability distributions for each of the critical exposure factors and incorporated these distributions into a MicroExposureTM Monte Carlo risk analysis.

Although the use of Monte Carlo analysis in exposure assessment is superior to using conservative point estimates, it tends to overestimate the intake of anglers at the higher consumption rates. This overestimation can lead to the incorrect conclusion that a small number of anglers may receive unacceptable risks. Using the MicroExposure model leads to a more accurate characterization of exposure through separate event modeling of the dose received during each fish meal consumed during an angler’s lifetime. Using the full distribution of fish consumption rates from the comprehensive Maine Angler Study (1) and the most recent TCDD monitoring data in fish downstream of Maine pulp mills (2-4), the MicroExposure model indicates that potential risks to all anglers are de minimis. Furthermore, the analysis indicates that previous estimates overstated actual risks by several orders of magnitude and that fish consumption advisories are no longer needed on rivers in Maine.