ABSTRACT
Environmental xenobiotics usually occur as complex mixtures as a result of being released into the environment as a mixture, combining with chemicals present in the environment, and/or transformations due to interactions with physical and/or chemical factors in the environment. The overall effects of complex mixtures on biological organisms results from interactions between the chemicals in the mixture and processes within the organism. Each phase in the pharmacokinetic and pharmacodynamic processes for an individual xenobiotic can be altered by other chemicals in the mixture. For instance, the toxicity of a xenobiotic can be increased (potentiated or synergized) by another chemical that increases its absorption or decreases its metabolism into a less toxic form. Alternatively, the toxicity of a xenobiotic can be decreased (antagonized) by another chemical that reduces its absorption or reduces its activation to a more toxic metabolite. The effects of mixtures of environmental xenobiotics on biological organisms is dependant on the scenario of exposure (route, concentration and duration (acute versus chronic)). Examples of each of these interactions on various exposure scenarios are included in this chapter.
