Evaluation of organic solvent ototoxicity by the upper limit of hearing

To clarify the effects of organic solvents on hearing, we measured the uppe r limit of hearing in 93 male workers exposed to organic solvents in 7 fact ories that produced plastic buttons or baths. Medical examinations, environ mental monitoring (i.e., concentration in breathing-zone air), and biologic al monitoring (i.e., concentration in urine) of the organic solvents were a lso done. Although the organic solvent concentrations in the environmental monitoring were lower than the occupational exposure limit, the upper limit of hearing was reduced in workers who were exposed for 5 y or more. This r eduction was dose-dependent and was related to styrene concentrations in br eathing-zone air and mandelic acid concentrations in urine. Even individual s who had normal medical examinations showed a reduced upper limit of heari ng. The upper limit of hearing may serve as an early detection indicator of health effects in workers constantly exposed to styrene.