Fitting bioassay data and performing uncertainty analysis with BIOKMOD.

We have developed a computer code called BIOKMOD that we have applied to analyze several sources of uncertainties in the evaluation of internal exposures using bioassay data: (1) Multiple constant and random intakes in occupational exposures taking into account periods without intake (weekends, holidays, etc.) are evaluated, and they are compared with chronic intakes showing that the chronic approximation is not always good; (2) An analytical method to evaluate the statistical uncertainties associated with the biokinetic model is described; and (3) Non linear techniques are applied to estimate intakes using bioassay data, where not only the quantities taken in are assumed unknown but also other non linear parameters (AMAD, f1, etc). The methods described are accompanied with examples. Some of the most usual features of BIOKMOD can be run directly, using BIOKMODWEB, at the Web site: http://www3.enusa.es/webMathematica/Public/biokmod.html .