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(414) Mixture toxicity concepts and data revisited: useful for ecological risk assessment of contaminated soils? Mesman, Miranda1, Aldenberg, Tom1, Posthuma, Leo1, 1 ABSTRACT- Straightforward application of mixture toxicity concepts developed in the fields of toxicology and pharmacology in ecotoxicology is common, despite serious reasons for theoretical doubts and lack of validation. This situation has developed due to the urgent need of handling the presence of mixtures of toxic compounds in ecosystems, both terrestrial and aquatic, in risk assessment procedures. To address this problem a literature review was carried out on articles form 1992 till the first half of 2000. This contribution focuses on the methodological flaws in current practices, by reviewing existing concepts and the existing mixture toxicity data for soils. Furthermore, it introduces a new approach incorporating all issues relevant for assessing the risk of mixtures of toxic compounds for terrestrial ecosystems. In the studies Simple Similar Action and Independent Joint Action were most used as theoretical concepts to analyse experimental data, or to predict the net risk of a mixture. Experimental data do not show large deviations from either of the models predictions. However, the concepts only apply if there are "no interactions", which is evidently untrue when evaluating toxic stress in the environment. Interactions may e.g. occur in the soil or during uptake. To take this kind of methodological flaws into account, an alternative for predicting net mixture risk is proposed on the basis of the concept of Species Sensitivity Distributions. SSDs are commonly used for risk assessment on a per chemical basis. It can be extended to mixtures, and in this way, it seems possible to narrow the current conceptual gap between experimental toxicity data and their application for derivation of soil quality criteria and risk assessment. Key words: mixture toxicity, terrestrial, data & concepts, review |
