**5. International legislation**

It is well documented that workplace noise exposure is a significant health hazard that leads to permanent, occupational noise-induced hearing loss. For this reason, many countries have developed national exposure standards for occupational noise, based on levels of exposure which are considered safe for human hearing. Likewise, exposure to chemicals in the workplace can lead to occupational chemical-induced hearing loss, as many of these chemicals have been internationally recognised as being hazardous to hearing. However, unlike noise exposure, standards for permissible levels of exposure to chemicals such as solvents in the US and other countries do not consider the adverse effects of chemicals on human hearing. This is because human exposure-response relationships remain unclear and thus chemical exposure standards have not been modified to reduce the risk of hearing impairment. Currently, recommended or mandatory workplace exposure limits (OELs) have been developed in many countries for airborne exposure to gases, vapours and particulates. The most widely used limits, threshold limit values (TLVs), are those issued in the USA by the American Conference of Governmental Industrial Hygienists (ACGIH). Table 5 shows the current US permissible exposure limits for some organic solvents according to different US organisations.

Taking into consideration the ototoxicity of many chemicals, some international bodies and governments have issued guidelines or recommendations regarding the ototoxicity of chemicals alone or when combined with noise. In the WHO Special Report "Occupational exposure to noise: evaluation, prevention and control" (Goelzer, Hansen & Sehrndt, 2001), the combined exposure to noise and other factors such as solvents, vibrations and metal dust is noted and it is suggested that more stringent criteria than those specified as being standard in the document should be applied. Ototoxic properties are acknowledged on the International Chemical Safety Cards (a joint programme of the International Labour Organization, WHO, and United Nations; Obadia, 2003) only for toluene, xylene and potassium bromate.

DPOAEs. No correlation of DPOAEs with blood lead level was found among the children. The group of adults had diminished DPOAEs which were consistent with noise-related

Murata et al. (1993) examined ABR and event-related potential (P300) recordings, along with non-audiological assessments in lead workers. The sample consisted of 22 gun metal foundry workers occupationally exposed to lead, zinc, and copper. Among the workers with higher blood lead concentrations, the latencies of P300 were significantly prolonged when compared with a gender- and age-matched control group. Both ABR and P300 latencies were significantly correlated with the indicators of lead absorption among these workers.

Discalzi et al. (1992) investigated the effects of industrial exposures to lead and mercury on the brainstem auditory pathway through ABR. The study included 22 workers exposed to lead, 8 workers exposed to mercury and 2 control groups of age- and gender-matched subjects never exposed to neurotoxic substances. The I-V IPL was examined. Results showed that both mercury and lead exposed workers had a significant delay for the I-V IPL. The researchers also found that those subjects with the highest level of lead in blood had a

It is well documented that workplace noise exposure is a significant health hazard that leads to permanent, occupational noise-induced hearing loss. For this reason, many countries have developed national exposure standards for occupational noise, based on levels of exposure which are considered safe for human hearing. Likewise, exposure to chemicals in the workplace can lead to occupational chemical-induced hearing loss, as many of these chemicals have been internationally recognised as being hazardous to hearing. However, unlike noise exposure, standards for permissible levels of exposure to chemicals such as solvents in the US and other countries do not consider the adverse effects of chemicals on human hearing. This is because human exposure-response relationships remain unclear and thus chemical exposure standards have not been modified to reduce the risk of hearing impairment. Currently, recommended or mandatory workplace exposure limits (OELs) have been developed in many countries for airborne exposure to gases, vapours and particulates. The most widely used limits, threshold limit values (TLVs), are those issued in the USA by the American Conference of Governmental Industrial Hygienists (ACGIH). Table 5 shows the current US permissible exposure limits for some organic solvents

Taking into consideration the ototoxicity of many chemicals, some international bodies and governments have issued guidelines or recommendations regarding the ototoxicity of chemicals alone or when combined with noise. In the WHO Special Report "Occupational exposure to noise: evaluation, prevention and control" (Goelzer, Hansen & Sehrndt, 2001), the combined exposure to noise and other factors such as solvents, vibrations and metal dust is noted and it is suggested that more stringent criteria than those specified as being standard in the document should be applied. Ototoxic properties are acknowledged on the International Chemical Safety Cards (a joint programme of the International Labour Organization, WHO, and United Nations; Obadia, 2003) only for toluene, xylene and

longer I-V IPL compared to workers with lower levels of lead in blood.

hearing loss.

**5. International legislation** 

according to different US organisations.

potassium bromate.


Table 5. Permissible exposure limits (PEL) to selected organic solvents according to different organisations in the U.S. PPM: parts per million; OSHA: Occupational Safety and Health Administration; NIOSH: National Institute for Occupational Safety and Health; ACGIH: American Conference of Industrial Hygienists.

In the United States of America, the American Conference of Industrial Governmental Hygienists (ACGIH, 2009) recommends that when exposure to noise and to carbon monoxide, lead, manganese, styrene, toluene, or xylene occurs, then periodic audiometry should be carried out and the results should be carefully reviewed. Also, the U.S. Army Fact Sheet 51-002-0903 on Occupational Ototoxins and Hearing Loss states that since the exposure threshold for ototoxic effects is not known, audiometric monitoring is necessary to determine whether the substance affects the hearing of exposed workers. It includes recommendations for annual audiometric assessment for workers whose chemical exposure (disregarding the use of respiratory protection) equals 50% of the most stringent criteria for occupational exposure limits, regardless of the noise level.

The Canadian Centre for Occupational Safety and Health (2009) has listed benzene, xylene, ethylbenze hydrogen cyanide, n-hexane, styrene, trichloroethylene, toluene, among others as chemicals associated with hearing loss.

Organic solvents such as toluene, xylenes, styrene, and trichloroethylene are considered as industrial ototoxic agents under Australian and New Zealand legislation (AS/NZS 1269.0:2005). Also, Australian government bodies such as Safe Work Australia and the Department of Commerce, have recognised solvents as ototoxic agents. Safe Work Australia (2010) indicated that some factors, such as ototoxic chemicals, may interact with noise to produce hearing loss that is greater than that associated with the effects of the individual causes. In addition, the presence of chemicals in the workplace has been suggested as being one of the possible factors leading to the maintained occurrence of noise-induced hearing loss (Safe Work Australia, 2010). In Australia (e.g., Queensland Government, 2004), it has been recommended, until revised standards are established, that the daily noise exposure of workers exposed to solvents be reduced to 80 dBA or below, and that regular audiometric testing should be carried out. Annual audiometry is highly recommended for Australian workers whose airborne exposures for some selected chemicals are at 50% or more of the exposure standards stated in the National Exposure Standards for Atmospheric

Occupational Chemical-Induced Hearing Loss 185

Therefore, guidelines in some developed countries have emerged to reduce the risk of hearing loss/auditory dysfunction in workers exposed to chemicals alone or to chemicals in combination with noise. There is an urgent need for further studies to establish dose/response relationships. With this information legislation around the world could be modified regarding the PELs for ototoxic agents such as solvents, metals and pesticides.

Health care professionals in the field of audition must be aware of the effects of chemicals on the auditory system and understand the complexity of such effects which relate to otoand neuro-toxic mechanisms. Chemical-exposed workers regardless of their noise exposure level should be routinely monitored with audiological procedures that investigate the peripheral and central auditory system. For these purposes, a test battery approach should be considered. There is still a lack of knowledge of the most sensitive audiological tests for the detection of chemical-induced auditory dysfunction. However, there is evidence that some tests can effectively detect some cases of central auditory dysfunction induced by solvent exposure. Such tests can be also used in populations of workers exposed to other chemicals that are known (or suspected) to have oto-and neurotoxic

Current industrial processes utilise massive quantities of chemicals that may jeopardise workers' hearing health. It is the role of audiologists, other hearing health care, and occupational health and safety professionals to prevent chemical-induced hearing loss/auditory dysfunction. To assist prevention, the scientific evidence regarding chemicalinduced hearing loss should be disseminated among workers, employers, health care professionals and legislators. Inside factories action to reduce exposure to these agents is essential to decrease the burden of occupational chemical-induced hearing loss. Industrybased initiatives should include the identification of populations at risk, the detection of early signs of chemical-induced hearing loss, and the delivery of hearing conservation

programmes to chemical-exposed workers regardless of their noise exposure levels.

*Occupational and Environmental Health*, Vol.64, pp. 389-392.

Nova Scientific Publishing, New York.

ed.), Thomson, Clifton Park, NY.

Vol.3, pp. 33-44.

Abbate, C., Giorgianni, C., Munao, F. & Brecciaroli R. (1993). Neurotoxicity induced by

ACGIH – American Conference of Governmental Industrial Hygienists. (2009). *Threshold Limit Values and Biological Exposure Indices*, ACGIH Publication, Cincinnati. Amedofu, G. & Fuente, A. (2008). Occupational hearing loss in developing countries. In: B.

Arnold, SA. (2000). The auditory brain stem response. In: R. J. Roeser, M. Valente, & H. Hosford-Dunn (Eds.). *Audiology. Diagnosis* (pp. 451-470), Thieme, New York. Bellis, TJ. (2003*). Assessment and Management of Central Auditory Processing Disorders*. (2nd

Brandt-Lassen, R., Lund, SP. & Jepsen, GB. (2000). Rats exposed to toluene and noise may

exposure to toluene. An electrophysiologic study. *International Archives of* 

McPherson & R. Brouillette (Eds.). *Audiology for Developing Countries* (pp. 189-222),

develop loss of auditory sensitivity due to synergistic interaction. *Noise & Health*,

properties.

**7. References** 

Contaminants in the Occupational Environment (NOHSC 1003, 1995), regardless of the noise level.

In Europe, the European Parliament published a noise directive (2003/10/EC), which has been adopted by all member countries since 2006. This directive calls on employers to consider the interaction of noise and work-related ototoxic substances on workers' health and safety. The European Agency for Safety and Health at Work (2009) has listed solvents such as toluene, styrene, p-xylene, among others as agents with "good evidence" about their adverse effects on hearing. In Germany, a position paper on ototoxic industrial chemicals was issued by the "Noise" and "Hazardous Substances" working groups of the Deutsche Gesetzliche Unfallversicherung (DGUV)'s committee for occupational medicine (Deutsche Gesetzliche Unfallversicherung's Occupational Medicine Committee, 2006). Among other recommendations, the position paper stated that public risk communication, including all points of contact, should be promoted, and that the ototoxicity of some chemicals should be taken into consideration when specifying occupational exposure limits.

Finally, in Brazil workers can claim compensation for hearing loss induced by occupational exposure to ototoxic chemicals, as a regulation issued in 1999 (Ministério da Previdência e Assistência Social, 1999) recognises the adverse effect of certain chemicals on hearing.

The scenario in most developing nations is very different. In many developing countries legislation is absent or under-enforced and local industrial workplace practices are performed without knowledge of the possible adverse health consequences of chemical agents. In these countries legislation requiring the safe usage of ototoxic chemicals used in industry and agriculture should be enacted, along with the establishment of adequately resourced monitoring agencies (Amedofu & Fuente, 2008).
