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 o f 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 occupa tional risk. Most studies have focused on auditory effects in animals, although investigations have been performed for other toxicological e ndpoints. For some substances, notably toluene, the information from a nimals studies does suggest an interaction but these were performed on ly al exposure levels to both noise and chemicals which were each indi vidually ototoxic. Single simultaneous exposure to noise and styrene d id not result in any enhancement of auditory impairment above that pro duced by noise or styrene alone. Single simultaneous exposure to noise and carbon monoxide (GO), however, showed some evidence of enhancemen t of ototoxicity beyond that produced by noise or carbon monoxide alon e, although only at high atmospheric concentrations of CO. When 1,3-di nitrobenzene was administered parentally at neurotoxic dose levels wit h continuous noise exposure, there was an increased severity of effect s in the brain stem. Combined exposure to noise and lead and/or cadmiu m resulted in histopathological heart lesions of undefined severity, a finding which was not observed for either of those agents in isolatio n. Dermal exposure to dimethylformamide and noise or inhalation exposu re to xylene and noise resulted in some biochemical changes in cardiac muscle which were of doubtful toxicological significance. In developi ng mice, there was evidence that combined exposure to cadmium sulphate and noise caused an increased incidence of external and skeletal malf ormations but only at dose levels of cadmium which would have induced developmental effects. Overall, for each of these chemicals and endpoi nts observed there is a suggestion of some interaction with noise expo sure. 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 s tudies have investigated human populations exposed to both noise and i ndustrial chemicals. Due to confounding factors, however, it was concl uded that these data were inadequate for assessing the combined effect s of noise and chemical exposure on hearing. (C) 1997 British Occupati onal Hygiene Society. Published by Elsevier Science Ltd.