W5 PM Toxicity of Complex Mixtures
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 321-323

(VAN-1117-715614) New calculation rule for ecosystem toxicity of mixtures?

van de Meent, D.^{1, 2}, Posthuma, L.¹, de Zwart, D.¹, ¹ National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands² Radboud University, Nijmegen, The Netherlands

ABSTRACT- We propose a new procedure for calculating toxic pressure of mixtures on ecosystems. The inferred Fraction Affected (i.e. fraction of species exposed to significant concentrations of toxicants, ms-PAF), as proposed by Traas et al. (2002) is widely used as proxy for toxic pressure of (mixtures of) chemicals on ecosystems. Although that use is supported by some eco-epidemiological evidence, the procedure fails to explain one basic empirical observation: species differ less in sensitivity to complex mixtures than to single substances. Present toxic pressure metric predicts the widths of mixture SSDs to reflect the average width of the SSDs of the components of the mixture, whereas observations suggest that widths of SSDs decrease with increasing complexity of the mixture. We have explored alternate calculation rules for mixture toxicity that correctly reflect this observation. We hypothesize that single-species toxicity end points can be adequately modeled as a function of the metabolic sensitivity spectrum of the exposed biological species (multiple receptors within species) and the toxic activity spectrum of the chemical substance (multiple modes of action). Such calculation rules could explain that narrower SSDs are observed for mixtures with wider toxic activity spectra. We propose experimental strategies for testing the hypothesized new calculation rules.

Key words: mixture, toxic pressure, calculation rule, ecosystem