Risk Indexes for Mixtures of Hazardous Substances

4 Risk Index for Mixtures of Hazardous Substances. For the purpose of developing a comprehensive and risk-based hazardous waste classification system, a simple method of calculating the risk posed by mixtures of radionuclides and hazardous chemicals is needed. The method should account for the linear, nonthreshold dose-response relationships for radionuclides and chemical carcinogens (stochastic effects) and the threshold dose-response relationships for noncarcinogenic hazardous chemicals (deterministic effects). 

NCRP believes that a conceptually simple composite risk index for mixtures of hazardous substances can be developed that provides an adequate representation of risk for the purpose of waste classification. The composite risk index is written in terms of separate risk indexes for substances that induce stochastic (s) and deterministic (d) effects as  

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Limits on amounts of hazardous substances in each waste class would be calculated based on values of the so-called risk index for each hazardous substance in the waste and the composite risk index for mixtures of hazardous substances. For the purpose of describing the recommended framework for a risk-based hazardous waste classification system, the risk index is generally defined as ... 

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