Priority assessment of toxic substances in life cycle assessment. Part II:assessing parameter uncertainty and human variability in the calculation of toxicity potentials

Toxicity potentials are standard values used in life cycle assessment (LCA) to enable a comparison of toxic impacts between substances. This paper pre sents the results of an uncertainty assessment of toxicity potentials that were calculated with the global nested multi-media fate, exposure and effec ts model USES-LCA. The variance in toxicity potentials resulting from input parameter uncertainties and human variability was quantified by means of M onte Carlo analysis with Latin Hypercube sampling (LHS). For Atrazine, 2,3, 7,8-TCDD and Lead, variation, expressed by the ratio of the 97.5%-ile and t he 2.5%-ile, ranges from about 1.5 to 6 orders of magnitude. The major part of this variation originates from a limited set of substance-specific inpu t parameters, i.e. parameters that describe transport mechanisms, substance degradation, indirect exposure routes and no-effect concentrations. Consid erable correlations were found between the toxicity potentials of one subst ance, in particular within one impact category. The uncertainties and corre lations reported in the present study may have a significant impact on the outcome of LCA case studies. (C) 2000 Elsevier Science Ltd. All rights rese rved.