The present document, which describes recommended standardized procedures, aims to assist individual investigators plan a study on the effects of industrial chemicals on the auditory system, collect and analyze environmental and hearing sensitivity data that are accurate and comparable to data acquired by others. This draft document is currently being reviewed by the NoiseChem Research Group. In this peer review stage we are currently accepting critiques and suggestions to this proposal. Investigations on the aforementioned topic are necessary since there is strong evidence that occupational hearing loss may be caused not only by noise but also by exposure to certain chemicals in the work environment. Since some industrial chemicals are known to be ototoxic, it is plausible to expect that if these chemicals occurred in high enough concentrations in the workplace they could affect hearing. Laboratory studies have yielded a finding not expected, namely that when simultaneous exposure to noise and chemicals occur, the hearing loss observed was greater than the expected hearing loss from noise added to the expected hearing loss from the chemical. If this synergism is verified in humans, then changes will be required in the limits that are set for occupational hazards in order to prevent occupational hearing loss.

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The objective of this investigation was to study the effects of occupational exposure to organophosphates and pyrethroid insecticides on the central auditory system. The study group consisted of 98 workers exposed to insecticides and 54 non-exposed workers. Data on work history, medical history, present diseases, occupational and non-occupational exposure to noise or chemicals and lifestyle factors were obtained through an interview. Central auditory system functions were assessed through frequency patterns and duration patterns testing. Fifty-six percent of the exposed workers had hearing dysfunction at the central level and its relative risk was 7.58 for the group with exposure to insecticides (95% CI 2.9- 19.8) when compared to the non-exposed group. The group exposed to insecticides and noise had a relative risk for central disorders of 6.5 (95% CI 2.2-20.0) when compared to the non-exposed group and 9.8 (95% CI 1.4-64.5) when compared to the group exposed only to noise. The finding suggests that exposure to organophosphates and pyrethroid products can induce damage to central auditory system. Further research is needed on the ototoxic mechanisms of these chemicals, and on hearing loss prevention measurements that are applicable and adequate to such risks and populations.

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Exposure to multiple physical and chemical agents is common in occupational environments but workplace hazards and occupational safety criteria for combined exposures is lacking. NoiseChem is an European Commission research project examining the effects of exposure to noise and chemicals on hearing and balance. Partners in Sweden, Finland, France, Denmark, UK and Poland with expert guidance from partners in USA will examine workers and study the mechanisms of action in animals to determine the levels of risk associated with joint expo­sure to noise and solvents. This paper briefly outlines the project details.

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The damaging effects of noise on auditory function can be altered significantly by exposure to additional agents that may or may not by themselves be ototoxic. This chapter focuses on the ability of chemical asphyxiants present in both occupational settings and ambient environments to potentiate noise induced hearing loss in a laboratory animal model. Since the chemical agents under study do not produce permanent impairment of hearing by themselves, the finding of auditory impairment in excess of that which is produced by noise exposure alone can be defined as noise potentiation. This chapter focuses both on the exposure conditions that favour such potentiation and also on potential mechanisms for potentiation. The data show that low to moderate exposure levels of carbon monoxide (CO) and hydrogen cyanide can potentiate noise induced hearing loss (NIHL) and the relationship between such levels and those permitted in work environments is provided. Finally, evidence is presented that free oxygen radicals may be responsible for potentiation of NIHL by the chemical asphyxiants. First, the ability of a free radical spin trap agent, PBN, to prevent the adverse effects of CO is demonstrated. Then, in an additional experiment, electron paramagnetic spin resonance is used to demonstrate a high level of free radicals in the cochlea with combined exposure to CO + noise while individual exposures to CO and noise do not produce free radicals at levels detectable by this method.

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Styrene is an organic solvent employed in many manufacturing industries, as well as in other economic sectors. Recently, evidence is beginning to accumulate on the hazardous effects that styrene exposures have on the auditory system. In rats, a well-suited metabolic animal model for these studies, aromatic solvents seem to affect the auditory sensitivity mainly in the cochlear mid-frequency range. Outer hair cells are the primary targets within the organ of Corti, although the spiral ganglions are not spared. Therefore, styrene must be considered as an ototoxic chemical agent that can be potentially neurotoxic. Finally, noise-styrene exposures can have synergistic effects on the auditory system. The findings reported in both human and animal studies indicate that exposures to styrene, or to styrene associated to noise, may dramatically impact occupational hearing conservation practices and legislation. Human and animal studies will be summarized in discussing the effects of styrene alone or in combination with noise and other chemicals. Gaps in scientific knowledge are highlighted to assist future research.

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Solvents are commonly used in many industries and therefore exposure to multiple solvents is a common occupational hazard. A myriad of peripheral and central nervous system toxic effects can be produced by both acute and chronic low level exposures. Dizziness is often an early symptom of solvent exposure but has only in recent times been investigated specifically. The indications from the studies reviewed are that vestibular disturbances are common in workers exposed to solvents and dose-response relationships need to be established for early detection of vestibulo-toxicity.

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Knowledge of short term, task specific sources of exposure is becoming more important as, for many industries these represent the dominant source of exposure over the whole eight hour shift period. For solvents, workers can be exposed to very high peak or short term exposures, yet still be below the relevant occupational exposure limit. This article explains the importance of understanding short term exposures to solvents, and suggests that our appreciation of chronic ill health should go beyond total dose, and that any periods of high exposure should be controlled as far as reasonably practicable. It also shows that a better understaing of these exposures helps to target control measures and can reduce process running costs.

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A video-visualization technique, using a combination of a fast-response, direct-reading, personal gas monitor (photo-ionization detector) and synchronized video monitoring (with a standard camcorder), has been applied to assess exposure to solvents in various industries. The objective is to understand how short-term peaks occur and how they can be controlled to minimise both short-term exposure and their contribution to long-term exposure. The technique was employed to identify peaks associated with work activities and their contribution to total exposure arising from use of tetrachloroethene in a dry cleaning establishment. The exposure and video data are simultaneously displayed on computer and the information is disseminated on CD (and video), forming the basis of a detailed occupational hygiene assessment or training material.

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A brief outline of the role of solvents in surface coatings is given, to provide the background to the problems encountered in solvent substitution. The direct substitution of one solvent by another is relatively straightforward. Computer programs greatly simplify the process. However, the real challenge lies with the reduction in solvent use, through the development of low solvent coatings. While this is a process that has been going on for many years, there is no doubt that recent regulatory pressures regarding both occupational health and environmental standards have made it the single most important challenge for the industry. Examples are discussed of the development of high solids, low solvent industrial coatings as well as water borne industrial coatings. Although there has been rapid progress in recent years, there is no prospect in sight for the complete elimination of solvents. Good workplace hygiene must therefore remain a key element in the safe use of coatings.

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