Effects of combined exposure to noise and toxic substances--critical review of the literature.

A number of studies have been conducted in recent years investigating the potential effects on various health endpoints of the combination of noise and a variety of different industrial substances. This review indicates that the information available in both animals and humans on this subject is limited particularly with respect to assessing occupational risk. Most studies have focused on auditory effects in animals, although investigations have been performed for other toxicological endpoints. For some substances, notably toluene, the information from animals studies does suggest an interaction but these were performed only at exposure levels to both noise and chemicals which were each individually ototoxic. Single simultaneous exposure to noise and styrene did not result in any enhancement of auditory impairment above that produced by noise or styrene alone. Single simultaneous exposure to noise and carbon monoxide (CO), however, showed some evidence of enhancement of ototoxicity beyond that produced by noise or carbon monoxide alone, although only at high atmospheric concentrations of CO. When 1,3-dinitrobenzene was administered parentally at neurotoxic dose levels with continuous noise exposure, there was an increased severity of effects in the brain stem. Combined exposure to noise and lead and/or cadmium resulted in histopathological heart lesions of undefined severity, a finding which was not observed for either of those agents in isolation. Dermal exposure to dimethylformamide and noise or inhalation exposure to xylene and noise resulted in some biochemical changes in cardiac muscle which were of doubtful toxicological significance. In developing mice, there was evidence that combined exposure to cadmium sulphate and noise caused an increased incidence of external and skeletal malformations but only at dose levels of cadmium which would have induced developmental effects. Overall, for each of these chemicals and endpoints observed there is a suggestion of some interaction with noise exposure. From the data that are currently available, however, inferences cannot be drawn on whether or not interactions would have occurred at lower, more occupationally relevant, levels of exposure. A number of studies have investigated human populations exposed to both noise and industrial chemicals. Due to confounding factors, however, it was concluded that these data were inadequate for assessing the combined effects of noise and chemical exposure on hearing.