Odor Mixtures

An additional problem in odor identification is that ambient odors are generally mixtures of compounds in different concentration levels. A comparison of the perceived intensity of two chemicals presented alone at a concentration and the two chemicals in a mixture at the same concentrations usually shows that the perceived intensity of either chemical in the mixture is lower than it is alone. This response is known as hypoadditivity. On the other hand, the CCS responses show that the perception of the odor is mainly additive, i.e., equal in the mixture to the perception of either chemical alone (Cometto-Muniz and Cain 1991).

Questions of safety with chemical mixtures are more successfully answered by experimentally determining the odor threshold of the mixture and then relating it to the chemical composition of the mixture. Some mixtures can contain a highly odorous but relatively nontoxic chemical together with a nonodorous but highly toxic chemical. The chemicals in a mixture can also disassociate through aging or different chemical processes, and the judgment of whether a toxic component is present can be incorrect if it is based solely on the detection of the odorous component. Assumptions about the relationship between odor and risk can only be made for specific cases for chemical mixtures.

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