Basic principles of toxicological evaluation of mixtures

The vast majority of toxicity studies and risk assessments deals with single chemicals. In reality, however, humans are exposed simultaneously to a large number of chemicals, indicating that exposure assessment and safety evaluation should focus on mixtures rather than on single chemicals. This review on the toxicology of chemical mixtures covers widely varying issues, ranging from the basic concepts and terminology of joint action and interaction of chemicals to different designs for studying the toxicity of mixtures. Literature data indicate that exposure to mixtures which contain low levels of chemicals, levels lower than their no observed adverse effect levels (NOAELs), can exert toxic effects whether their components have similar modes of action or not. Different approaches and examples of studies on priority real-life mixtures, strategy and guidelines for mixture risk assessment as well as challenges ahead are also presented