A Systematic Uncertainty Analysis of an Evaluative Fate and Exposure Model

Abstract

Multimedia fate and exposure models are widely used to regulate the release of toxic chemicals, to set cleanup standards for contaminated sites, and to evaluate emissions in life-cycle assessment. CalTOX, one of these models, is used to calculate the potential dose, an outcome that is combined with the toxicity of the chemical to determine the Human Toxicity Potential (HTP), used to aggregate and compare emissions. The comprehensive assessment of the uncertainty in the potential dose calculation in this article serves to provide the information necessary to evaluate the reliability of decisions based on the HTP A framework for uncertainty analysis in multimedia risk assessment is proposed and evaluated with four types of uncertainty. Parameter uncertainty is assessed through Monte Carlo analysis. The variability in landscape parameters is assessed through a comparison of potential dose calculations for different regions in the United States. Decision rule uncertainty is explored through a comparison of the HTP values under open and closed system boundaries. Model uncertainty is evaluated through two case studies, one using alternative formulations for calculating the plant concentration and the other testing the steady state assumption for wet deposition. This investigation shows that steady state conditions for the removal of chemicals from the atmosphere are not appropriate and result in an underestimate of the potential dose for 25% of the 336 chemicals evaluated.

Uncertainty and variability in environmental life-cycle assessment

“…This may, however, be an important factor in the assessment of (metal) toxicity (Huijbregts et al, 2001a), aquatic eutrophication (Huijbregts and Seppälä, 2001) and photochemical ozone formation (Andersson-Sköld and Holmberg, 2000). Furthermore, the models used in the calculation of characterisation factors may suffer from significant uncertainties in their model structure (Hertwich et al, 2000;Huijbregts et al, 2000c;Ragas et al, 1999). In the context of our study, it was not feasible to assess the impact of these model uncertainties in our uncertainty analysis.…”

“…Model outcomes can be uncertain for several reasons, which have implications for the way the uncertainty is dealt with (Morgan and Henoion, 1990). A general distinction can be made between parameter uncertainty, model uncertainty and uncertainty due to choices (Hertwich et al, 2000;Huijbregts, 1998a). Parameter uncertainty is introduced by the empirical inaccuracy of input data.…”

Policies for Chemical Hazard and Risk Priority Setting: Can Persistence, Bioaccumulation, Toxicity, and Quantity Information Be Combined?

“…Multiple category cutoff criteria methods may be particularly susceptible to potentially high levels of type I and type II errors resulting in the misapplication of limited resources for the evaluation of substances that are of low potential risk while neglecting those substances that are of high potential risk. The main objective of this policy analysis is to evaluate the application of current knowledge used for chemical screening assessments to inform decisions and not to discover truth (15). Table 1 summarizes hazard and risk information and discrepancies between the existing methods and the holistic methods for four selected chemicals.…”

The whence, wherefore and whither of the new scientific discipline of environmental inquiry: Exposure Analysis The 2002 Wesolowski Lecture

“…Are we estimating the correct uncertainty magnitude when we estimate only parameter uncertainty? I believe we are not (Fayerweather et al, 1999;Hertwich et al, 2000;Moschandreas and Karuchit, 2002).…”