Variability and Uncertainty in Risk Estimation for Brownfields Redevelopment
Olsen, Arne Edward
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Various methods can be used to estimate the human health risk associated with exposure to contaminants at brownfields facilities. The deterministic method has been the standard practice, but the use of probabilistic methods is increasing. Contaminant data for non-carcinogens and carcinogens from 21 brownfields sites in Pennsylvania were collected and compiled. These were used to evaluate the performance of the deterministic and several probabilistic methods for assessing exposure and risk in relation to variability and uncertainty in the data set and input parameters. The probabilistic methods were based (a) entirely on Monte Carlo simulated input parameter distribution functions, (b) on a combination of some of these functions and fixed parameter values, or (c) on a parameter distribution function. These methods were used to generate contaminant intake doses, defined as the 90th, 95th, or 99.9th percentile of their estimated output distribution, for the principal human exposure routes. These values were then compared with the corresponding point values estimated by the deterministic method. For all exposure routes the probabilistic intake dose estimates, taken as the 90th and 95th percentiles of the output distribution, were not markedly different from the deterministic values or from each other. The opposite was generally the case for the estimates at the 99.9th cutoff percentile; especially for the Monte Carlo-based methods. Increasing standard deviation of the input contaminant concentration tended to produce higher intake dose estimates for all estimation methods. In pairwise comparisons with the deterministic estimates, this trend differed significantly only for the probabilistic intake doses estimated as the 99.9th percentile of the output distribution. Taken together, these results did not indicate clear and definitive advantages in using probabilistic methods over the deterministic method for exposure and risk assessment for brownfields redevelopment. They supported using the tired system for environmental risk assessment at any particular brownfields facility.
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