R7 PM Uncertainty Analysis in Risk Assessment: Influences on Decision-making
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 327-329

(ROS-1117-728177) Assessing uncertainty when modeling fate, exposure and toxic effects of thousands of chemicals.

Rosenbaum, R¹, Pennington, D², Jolliet, O¹, ¹ Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland² European Commission - Joint Research Centre, Ispra, Italy

ABSTRACT- When assessing thousands of chemicals the scarcity of uncertainty distributions for substance properties as model input parameters demands practical solutions for assessing the uncertainty of toxicological effect indicators in (comparative) environmental risk assessment. An approach implemented in the IMPACT 2002 multimedia model provides uncertainty information related to impact characterization factors for aquatic ecosystems and human health. For fate and human exposure it relies on a practical method of adopting certainty values for the intake fraction per cluster of chemicals as a function of emission medium, dominating exposure pathway and model robustness towards the respective chemical. Multiplying and dividing the geometric mean point estimate by such a value provides an estimate of the upper and lower 95th percentile confidence interval bounds. These certainty values can be based on insights from techniques such as Monte Carlo simulations for representative chemicals, avoiding the need to repeat timely Monte Carlo calculations with every model run. Using expert judgment, the human health effect factor uncertainty is similarly defined and readily combined through addition with that of the intake fraction. The uncertainty for ecotoxicological effects is currently related to the number of aquatic species tested in the freshwater column. The more species test results available, the more robust the estimate of the ecotoxicological factor is assumed to be. The presented approach proved to be very transparent, robust while reflecting our current level of knowledge, quick to use, and is easily applied in practice to combine e.g. uncertainties of an emission inventory with those of the impact assessment in a comparative assessment study.

Key words: uncertainty, comparative, toxicity, risk