Method of establishing exposure limits for inhaled chamecal sustances

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For the purpose of improving the reliability of current exposure limits or to newly recommend limits for novel chemicals, following supecific problems were investigated. To make reasonable inter-species extrapolation from experimental animals to humans, it was shown that the differences of metabolism and toxicokinetic data between the both species are fundamental. This finding was obtained by model experiments using two organic solvents, m-xylene and chloroform.The toxicities of the transient metals generally differ according to the valency states.Mercury vapor and inoganic mercury compounds were shown to have different toxicity, and it was proposed that proper exposure limits should be set considering this difference. The hypersensitivity to chemicals poses a difficult problem when exposure limits for these chemicals ara considered. Cobalt, one of the sensitizing metals, is an example of this type of chemicals. The method of establishing exposure limits for cobalt was studied on cobalt-exposed workers in reference with several life style determinants. The exposure limits for such polular metal elements as lead and cadmium have been fairly well established, but the usefulness of biological monitoring by the use of blood, urine and other biological specimens has been morre recognized recently. Cohort observation on he workers exposed to these two metals clearly indicated that the biological monitoring is super to ambient air monitoring in accuracy of risk evaluation of individual workers.The neurotoxicity of organic solvents were investigated and the usefulness of glia markers as a sensitive toxicity parameter was made clear. The toxicity of the mixture of tolene and xylene was studied on the exposed workers and a proposal was made on the exposure limit for the mixture of these chemicals. Finally, a list of sensitizing chemicals wasmade as the supplement for the list of occupational exposure limits recommended by Japan Association of Occupational Health.