“
“The number, diversity and complexity of synthetic chemicals produced

and released to the environment are overwhelming. As a consequence, we are rarely exposed to only one single contaminant, but typically to mixtures of numerous man-made-chemicals with varying constituents in varying concentrations and concentration ratios (Faust et al., 2003). However, in contrast to this exposure scenario, the present toxicological approach devotes 95% of its resources to the study of single chemicals (Groten, 2000) and provides threshold doses or concentrations of regulatory concern (such as acceptable daily intakes or predicted no effect concentrations) for individual chemicals, implying that exposures below these levels are to be considered safe. In addition, with a few exceptions, chemical risk selleck screening library assessment considers the effects of single Olaparib manufacturer substances in isolation, an approach that is only justified if the exposure to mixtures does not bear the risk of an increased toxicity. In fact, the behavior of chemicals in a mixture may not correspond to the one predicted from data obtained with the pure compounds (Altenburger et al., 2004). From the practical point of view, though, the

direct testing of all the potential combinations of contaminants is unfeasible, and thus we are confronted with the task of deriving valid predictions of multiple mixture toxicity from toxicity data on individual compounds (Faust et al., 2003). In a recent review on the state of the art on mixture toxicity (Kortenkamp et al., 2009) it was concluded that there is a deficit on mixtures studies in the area, amongst others, of neurotoxicity and that it is difficult to assess, based on experimentally published data, the type of combination effect. Furthermore, at present toxicity testing for hazard identification relies mostly on the use of animal models. This approach is costly and time-consuming, and is not practical for hazard identification of ID-8 the thousands of chemicals such as under the REACH directive or in the

high production volume program. Thus, even in the context of mixture toxicity, alternative approaches that have higher throughput capability and are predictive of in vivo effects are needed ( Coecke et al., 2007 and Lilienblum et al., 2008). From a toxicological point of view, in a mixture, chemicals may basically behave in two ways: they can have a joint action or they can interact (Plackett and Hewlett, 1952). In the first case they may act through concentration addition (CA) and independent action (IA) mechanisms also referred to as Loewe additivity and Bliss independence. CA is thought to be valid for mixtures where the components have similar sites and modes of action, while IA is currently held appropriate for mixtures where the components have different sites and dissimilar modes of action ( Greco et al., 1995 and McCarty and Borgert, 2006).