Risks from Combined Exposures to Different Chemicals

Abstract

Publisher Summary This chapter discusses the risks from combined exposures to different chemicals. The problem of mixtures of different chemicals in the environment is particularly important in surface water as the aquatic organisms are exposed to the joint action of the mixture. The chapter discusses a study for this problem in a series of experiments of fish. In the case of complex mixtures as in polluted surface water, the occasional occurrence of pairs of compounds with interaction (resulting in potentiation or antagonism) is not very important. What remains in the first place is simple similar action for compounds with the same site of action, as when more than one organophosphate is present. In the case of simple similar action, it is most convenient to refer to a fixed standard response level for both the single compounds and the mixture. In this case it was the LC50 for fish. In the second place, there is the independent action for mixtures of differently acting compounds, as for example with a mixture of dieldrin, parathion, and fluoroacetic acid. In the case of independent action of compounds in a mixture, two extreme possibilities may be distinguished. In the first possibility, the same fishes, which are more sensitive to one of the compounds, are also more sensitive to all the other compounds. If the sensitivity for the different compounds is random among the fishes, or rather if there is no correlation (r=O), than each component will contribute to the total toxicity of the mixture in accordance with its own probability of killing at its given concentration and toxicity. The probability of surviving the mixture can be calculated as the product of the probabilities of survival for each component.