**6. Conclusion**

The effects of chemical exposure on the auditory system have been studied by many authors. The findings suggest that chemicals such as solvents, pesticides and metals have both oto-and neuro-toxic properties. Studies conducted in animals have demonstrated that the outer hair cells are affected by solvents. The damage begins in the most external row of cochlear hair cells, and if the exposure continues the damage is spread to the middle and inner row of outer hair cells. A concomitant agent in many industries is noise exposure. Research conducted in animals and humans exposed to solvents and noise have found a synergism between these two agents. The ototoxicity induced by solvents appears to be different than the one induced by noise. Human studies in workers exposed to solvents have shown a higher prevalence of hearing loss among solvent-exposed workers when compared with non-exposed workers.

Additionally studies conducted in human populations exposed to pesticides have shown that these agents are associated with poorer hearing thresholds as well as with poorer performance for some central auditory functioning tests. Research conducted in human subjects exposed to metals such as lead and mercury also indicates that these agents relate to auditory dysfunction.

Current legislation in many countries establishes permissible exposure limits (PELs) for chemicals. These PELs are not based on the possible adverse auditory effects of chemicals.

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

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

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

The effects of chemical exposure on the auditory system have been studied by many authors. The findings suggest that chemicals such as solvents, pesticides and metals have both oto-and neuro-toxic properties. Studies conducted in animals have demonstrated that the outer hair cells are affected by solvents. The damage begins in the most external row of cochlear hair cells, and if the exposure continues the damage is spread to the middle and inner row of outer hair cells. A concomitant agent in many industries is noise exposure. Research conducted in animals and humans exposed to solvents and noise have found a synergism between these two agents. The ototoxicity induced by solvents appears to be different than the one induced by noise. Human studies in workers exposed to solvents have shown a higher prevalence of hearing loss among solvent-exposed workers when

Additionally studies conducted in human populations exposed to pesticides have shown that these agents are associated with poorer hearing thresholds as well as with poorer performance for some central auditory functioning tests. Research conducted in human subjects exposed to metals such as lead and mercury also indicates that these agents relate to

Current legislation in many countries establishes permissible exposure limits (PELs) for chemicals. These PELs are not based on the possible adverse auditory effects of chemicals.

taken into consideration when specifying occupational exposure limits.

resourced monitoring agencies (Amedofu & Fuente, 2008).

noise level.

**6. Conclusion** 

compared with non-exposed workers.

auditory dysfunction.

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 properties.

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.

#### **7. References**


Occupational Chemical-Induced Hearing Loss 187

Fuente, A. & McPherson, B. (2007). Central auditory processing effects induced by solvent

Fuente, A., McPherson, B. & Hickson, L. (2011). Central auditory dysfunction associated with exposure to a mixture of solvents. *International Journal of Audiology* (in press). Fuente, A., McPherson, B., Muñoz, V. & Espina, JP. (2006). Assessment of central auditory

Goelzer, B., Hansen, CH. & Sehrndt, GA. (2001). *Occupational exposure to noise: evaluation,* 

Dortmund, published on behalf of the World Health Organization, Geneva. Guida, HL., Morini, RG. & Vieir-Cardoso, AC. (2010). Audiological evaluation in workers

Harrel, M., Shea, JJ. & Emmet, JR. (1978). Bilateral sudden deafness following combined

Hirata, M., Ogawa Y., Okayama A. & Goto S. (1992). A cross- sectional study on the

Keith, RW. (2002). Alternatives for testing the central auditory system. In: *Best practices workshop: Combined effects of chemicals and noise on hearing*, Cincinnati. Laroche, C., Soli, S., Giguere, C., Lagace, J., Vaillancourt, V. & Fortin, M. (2003). An

Lasky, RE., Maier, MM., Snodgrass, EB., Hecox, KE. & Laughlin, NK. (1995). The effects of

Lataye, R. & Campo, P. (1997). Combined effects of a simultaneous exposure to noise and toluene on hearing function. *Neurotoxicology and Teratology*, Vol.19, pp. 373-382. Liu, Y., Rao, D. & Fechter. D. (1997). Correspondence between middle frequency auditory

Lataye, R., Campo, P. & Loquet, G. (2000). Combined effects of noise and styrene exposure

Lataye, R., Campo, P., Loquet, G. & Morel, G. (2005). Combined effects of noise and styrene

Lataye, R., Maguin, K. & Campo, P. (2007). Increase in cochlear microphonic potential after

Laukli, E. & Hansen, PW. (1995). An audiometric test battery for the evaluation of

on hearing function in the rat. *Hearing Research*, Vol.139, pp. 86-96.

toluene administration. *Hearing Research*, Vol.230, pp.34-42.

Gelfand, SA. (Ed.). (2001). *Essentials of Audiology* (2nd ed), Thieme, New York.

insecticide poisoning. *The Laryngoscope*, Vol. 88, pp. 1348-1351.

Vol.20, pp.271-279.

Vol.126, pp.1188-1194.

4, pp. 423-427.

*and Health*, 6, 17-37.

134-140.

pp. 49-64.

162-164.

*Hearing Research*, Vol.75, pp. 1-40.

Keith, RW. (2000). *Random Gap Detection Test*, Auditec, St. Louise.

*Neurotoxicology and Teratology*, Vol. 17, pp. 633-644.

exposure. *International Journal of Occupational Medicine and Environmental Health*,

processing in a group of workers exposed to solvents. *Acta Oto-Laryngologica*,

*prevention and control.* Federal Institute for Occupational Safety and Health,

exposed to noise and pesticide. *Brazilian Journal of Otorhinolaryngology*, Vol.76, No.

brainstem auditory evoked potential among workers exposed to carbon disulfide. *International Archives of Occupational and Environmental Health*, Vol.64, pp. 321-324. Johnson, AC. & Canlon, B. (1994). Progressive hair cell loss induced by toluene exposure.

approach to the development of hearing standards for hearing-critical jobs. *Noise* 

lead on otoacoustic emissions and auditory evoked potentials in monkeys.

loss in vivo and outer hair cell shortening in vitro. *Hearing Research*, Vol.112, pp.

on hearing: comparison between active and sedentary rats. *Noise & Health*, Vol.7,

occupational exposure to industrial solvents. *Acta Oto-laryngologica*, Vol.115, pp.


http://osha.europa.eu/en/publications/literature\_reviews/combined-exposureto-noise-and-ototoxic-substances


Ministério da Previdência e Assistência Social. (1999). *Decreto no 3048, de 12/05/1999-Aprova o* 

Campo, P., Lataye, R., Cossec. B. & Placidi, V. (1997). Toluene-induced hearing loss: A mid-

Campo, P., Maguin, K. & Lataye, R. (2007). Effects of aromatic solvents on acoustic reflexes mediated by central auditory pathways. *Toxicological Sciences*, Vol.99, pp. 582-590. Canadian Centre for Occupational Safety and Health. (2009). Chemicals and noise – a

Cappaert, NL., Klis, SF., Baretta, AB., Muijser, H. & Smoorenburg, GF. (2000). Ethyl

Deutsche Gesetzliche Unfallversicherung. (2006). *Position paper on ototoxic industrial* 

Draper, TH. & Bamiou, DE. (2009). Auditory neuropathy in a patient exposed to xylene: case

European Agency for Safety and Health at Work. (2009). *Combined exposure to noise and* 

European Parliament and the Council of the European Union. (2003). Directive 2003/10/EC

Fechter, LD., Liu, Y., Herr, DW. & Crofton, KM. (1998). Trichloroethylene ototoxicity: evidence for a cochlear origin. *Toxicological Sciences*, Vol.42, pp. 28-31. Food and Agriculture Organization of the United Nations. (2003). *International Code of* 

Fuente, A. (2008). *Auditory damage associated with solvent exposure: evidence from a crosssectional study*. Unpublished PhD thesis, The University of Hong Kong. Fuente, A. (2010). Central auditory dysfunction associated with solvent exposure. *Bulletin of* 

Fuente, A., Slade, MD., Taylor, T., Morata, TC., Keith, RW., Sparer, J. & Rabinowitz, PM.

*the American Auditory Society,* Vol.35, No.1, pp.55.

report. *Journal of Laryngology and Otology*, Vol.123, pp.462-465.

*Journal of* the *Association for Research in Otolaryngology*, Vol.1, pp. 292-299. Cappaert, NL., Klis, SF., Muijser, H., de Groot, JC., Kulig, BM. & Smoorenburg, GF. (1999). The ototoxic effects of ethyl benzene in rats. *Hearing Research*, Vol.137, pp. 91-102. Crofton, KM., Lassiter, TL. & Rebert, CS. (1994). Solvent-induced ototoxicity in rats. An

Assistência Social, Brasilia.

Medicine available from

Luxembourg.

Rome.

*Union*, Vol.L42, 38-44.

*Medicine*,Vol.51, pp.1202-1211.

to-noise-and-ototoxic-substances

129-140.

ws

*regulamento da Previdência Social, e dá outras Providências*, Ministério da Previdência e

frequency location of the cochlear lesions. *Neurotoxicology and Teratology*, Vol.19, pp.

hazardous combination. *The Health and Safety Report*, Vol.7, No.10 available from http://www.ccohs.ca/newsletters/hsreport/issues/2009/10/ezine.html#inthene

benzene-induced ototoxicity in rats: a dose-dependent mid-frequency hearing loss.

atypical selective mid-frequency hearing deficit. *Hearing Research*, Vol.80, pp. 25-30.

*chemicals*. Deutsche Gesetzliche Unfallversicherung's Committee for Occupational

*ototoxic substances*, EU-OSHA European Agency for Safety and Health at Work,

on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise). *Official Journal of the European* 

*Conduct on the Distribution and Use of Pesticides*, Food and Agriculture Organization,

(2009). Peripheral and central auditory dysfunction induced by occupational exposure to organic solvents. *Journal of Occupational and Environmental* 

http://osha.europa.eu/en/publications/literature\_reviews/combined-exposure-


Occupational Chemical-Induced Hearing Loss 189

Nilsson, M., Soli, SD. & Sullivan, JA. (1994). Development of the Hearing In Noise Test for

Obadia, I. (2003). ILO activities in the area of chemical safety. *Toxicology*, Vol.190, pp. 105-

Ödkvist, LM., Arlinger, SD., Edling, C., Larsby, B. & Bergholtz, LM. (1987). Audiological

Ödkvist, LM., Moller, C. & Thuomas, KA. (1992). Otoneurologic disturbances caused by solvent pollution. *Otolaryngology and Head and Neck Surgery*, Vol.106, pp. 687-692. Pollastrini, L., Abramo, A., Cristalli, G., Baretti, F. & Greco, A. (1994). Early signs of

Pryor, GT., Rebert, CS. & Howd, RA. (1987). Hearing loss in rats caused by inhalation of mixed xylenes and styrene. *Journal of Applied Toxicology*, Vol.7, pp. 55-61. Queensland Government. (2004). *Noise Code of Practice 2004*. Workplace Health and Safety

http://www.deir.qld.gov.au/workplace/resources/pdfs/noise\_code2004.pdf Rebert CS., Boyes, WK., Pryor, GT., Svensgaard, DJ., Kassay, KM., Gordon, GR. & Shinsky,

trichloroethylene. *International Journal of Psychophysiology*, Vol.14, pp. 49-59. Rebert, CS., Schwartz, RW., Svendsgaard, DJ., Pryor, GT. & Boyes, WK. (1995). Combined

Safe Work Australia. (2010). Occupational noise-induced hearing loss in Australia:

Schäper, M., Demes, P., Zupanic, M., Blaszkewicz M. & Seeber, A. (2003). Occupational

Sliwinska-Kowalska, M., Zamyslowska-Szmytke, E., Szymczak, W., Kotylo, P., Fiszer, M.,

Sliwinska-Kowalska, M., Zamyslowska-Szmytke, E., Szymczak, W., Kotylo, P., Fiszer, M.,

N. (1993). Combined effects of solvents on the rat's auditory system: styrene and

effects of paired solvents on the rat's auditory system. *Toxicology*, Vol.105, pp. 345-

overcoming barriers to effective noise control and hearing loss prevention. Safe

http://safeworkaustralia.gov.au/AboutSafeWorkAustralia/WhatWeDo/Publicati ons/Documents/539/Occupational\_Noiseinduced\_Hearing\_Loss\_Australia\_2010.

toluene exposure and auditory function: results from a follow-up study. *Annals of* 

Dudarewicz, A., Wesolowski, W., Pawlaczyk-Luszczynska, M. & Stolarek, R. (2001). Hearing loss among workers exposed to moderate concentrations of solvents. *Scandinavian Journal of Work, Environment & Health*, Vol.27, pp. 335-342. Sliwinska-Kowalska, M., Zamyslowska-Szmytke, E., Szymczak, W., Kotylo, P., Wesolowski,

W., Dudarewicz, A., Fiszer, M., Pawlaczyk-Luszczynska, M. Politanski, P., Kucharska, M. & Bilski, B. (2000). Assessment of hearing impairment in workers exposed to mixtures of organic solvents in the paint and lacquer industry.

Wesolowski, W., Wesolowski, W. & Pawlaczyk-Luszczynska, M. (2003). Ototoxic

solvents. *Acta Otorhinolaryngologica Italica*, Vol.14, pp. 503-512.

Queensland. Queensland Government available from

*Acoustical Society of America*, Vol.95, pp.1085-1099.

*Scandinavian Audiology*, Vol.16, pp. 75-81.

pp. 131-136.

115.

354.

pdf

Work Australia available from

*Occupational Hygiene*, Vol.47, pp. 493-502.

*Medycyna pracy*, Vol.51, pp. 1-10 [in Polish].

Relation to the diagnosis of toxic encephalopathy. *Scandinavian Audiology*, Vol.27,

the measurement of speech reception thresholds in quiet and in noise*. Journal of the* 

and vestibule-oculomotor findings in workers exposed to solvents and jet fuel.

occupational ototoxicity caused by inhalation of benzene derivative industrial


Loquet, G., Campo, P. & Lataye, R. (1999). Comparison of toluene-induced and styreneinduced hearing losses. *Neurotoxicology and Teratology*, Vol.21, pp. 689-697. Loquet, G., Campo, P., Lataye, R., Cossec, B. & Bonnet, P. (2000). Combined effects of

Mac Crawford, J., Hoppin, JA., Alavanja, MCR., Blair, A., Sandler, DP. & Kamel, F. (2008).

*Journal of Occupational and Environmental Medicine*, Vol.50, No 7, pp. 817-826. Makitie, AA., Pirvola U., Pyykko, I., Sakakibara, H., Riihimaki, V. & Ylikoski, J. (2003). The ototoxic interaction of styrene and noise. *Hearing Research*, Vol.179, pp. 9-20. Moen, BE., Riise, T. & Kyvik, KR. (1999). P300 brain potential among workers exposed to

McWilliams, ML., Chen, GD. & Fechter, LD. (2000). Low-level toluene disrupts auditory function in guinea pigs. *Toxicology and Applied Pharmacology*, Vol.15, pp. 18-29. Morata, TC. (1989). Study of the effects of simultaneous exposure to noise and carbon disulfide on workers hearing. *Scandinavian Audiology*, Vol.18, pp. 53-58. Morata, TC., Engel, T., Durao, A., Costa, TRS., Krieg, EF., Dunn, DE. & Lozano, MA. (1997).

Morata, TC., Johnson, AC., Nylen, P., Svensson, EB., Cheng, J., Krieg, EF., Lindblad, AC.,

Morata, TC & Lemasters, GK. (1995). Epidemiologic considerations in the evaluation of occupational hearing loss. *Occupational Medicine*, Vol.10, pp. 641-56. Morata, TC., Sliwinska-Kowalska, M., Johnson, AC., Starck, J., Pawlas, K., Zamyslowska-

Muijser, H., Hoogendijk, E. & Hooisma, J. (1988). The effects of occupational exposure to styrene on high-frequency hearing thresholds. *Toxicology*, Vol.49, pp. 331-340. Murata, K., Araki, S., Yokoyama, K., Uchida, E. & Fujimura, Y. (1993). Assessment of central,

Musiek, FE. (1983a). Assessment of central auditory dysfunction: The dichotic digit test

Musiek, FE. (1983b). Results of three dichotic speech tests on subjects with intracranial

Musiek, FE. (1994). Frequency (pitch) and duration patterns tests. *Journal of the American* 

National Occupational Health and Safety Commission. (1995). *Adopted National Exposure* 

*Standards for Atmospheric Contaminants in the Occupational Environment [NOHSC:1003 (1995)],* Australian Government Publishing Service, Canberra. Niklasson, M., Arlinger, S., Ledin, T., Müller, C., Ödkvist, L., Flodin, U. & Tham, R. (1998).

Audiological disturbances caused by long-term exposure to industrial solvents.

revisited. Ear and Hearing. *Ear and Hearing*,Vol. 4, pp.79-83.

organic solvents. *Norsk Epidemiologi*, Vol.9, pp. 27-31.

*Scandinavian Audiology*, Vol.26, pp. 141-149.

*International Journal of Audiology* (in press).

lesions. *Ear and Hearing*, Vol.4, pp.318-323.

*Academy of Audiology*, Vol.5, pp.265-268.

Vol.44, pp. 806-814.

336.

*Research*, Vol.148, pp. 173-180.

exposure to styrene and ethanol on the auditory function in the rat. *Hearing* 

Hearing loss among licensed pesticide applicators in the agricultural health study.

Hearing loss from combined exposures among petroleum refinery workers.

Ernstgard, L. & Franks J. (2002). Audiometric findings in workers exposed to low levels of styrene and noise. *Journal of Occupational and Environmental Medicine*,

Szmytke, E., Nylen, P., Toppila, E., Krieg, E., Pawlas, N. & Prasher, D. (2011). A multicenter study on the audiometric findings of styrene-exposed workers.

peripheral, and autonomic nervous system functions in lead workers: neuroelectrophysiological studies. *Environmental Research*, Vol. 61, No. 2, pp. 323Relation to the diagnosis of toxic encephalopathy. *Scandinavian Audiology*, Vol.27, pp. 131-136.


http://www.deir.qld.gov.au/workplace/resources/pdfs/noise\_code2004.pdf


http://safeworkaustralia.gov.au/AboutSafeWorkAustralia/WhatWeDo/Publicati ons/Documents/539/Occupational\_Noiseinduced\_Hearing\_Loss\_Australia\_2010. pdf


**10** 

*Spain* 

**Exploration Databases** 

Juan Carlos Conte, Ana Isabel García, Emilio Rubio and Ana Isabel Domínguez

*C/ Domingo Miral, Zaragoza* 

**on Occupational Hearing Loss** 

*Catedra de Bioestadística, Facultad de Medicina, Universidad de Zaragoza,* 

Studies on occupational hearing loss have focused on noise as the primary cause. While the effect of this physical agent on hearing has been demonstrated, an analysis closer to the site of exposure confirms that the presence of other contaminants, such as chemicals, can interact with noise. This association may influence a temporal variability in the manifestation of an

In this respect, the term "working conditions" is too ambiguous (i.e., noise in the metal industry) as, in apparently similar conditions, several exposure environments can be identified: machining (noise+fluids, e.g. lathing), manufacture of structures (noise+fumes,

The European Agency for Safety and Health at Work recognises that noise-induced hearing loss is the most common occupational disorder in Europe. It advises that, in order to achieve greater efficiency in its prevention, more attention must be paid to the combined risk factors (multiple exposures) in workers exposed to high noise levels and chemical compounds

Similarly, recent studies conducted in the US (Agrawall et al., 2009) and New Zealand (Thorne et al., 2008) recognise noise-induced hearing loss as one of the most widespread occupational illnesses in these countries. Conclude that traditional noise monitoring and control methods have not achieved the expected results, identifying increasing prevalence in

This study aims to test the hypothesis of interaction between various physical and chemical pollutants and their influence on hearing. It obtains a complete temporal exposure model, based on survival analysis, which covers the entire working life of an individual between t=0 (start time) and t=50 years (maximum period). The study of multiple exposures using a qualitative variable allows the prevention cost associated with hygiene risk assessment (see 2.3.1. point 1) to be sufficiently reduced. This is also the methodology used in the study of other environment related illnesses caused by prolonged exposure to different

e.g. welding) and surface protection (noise+solvents, e.g. painting), among others.

the general working population, and particularly in young people.

**1. Introduction** 

occupational hearing pathology.

associated with their work.

agents.

effects of occupational exposure to styrene and co-exposure to styrene and noise. *Journal of Occupational and Environmental Medicine*, Vol.45, pp. 15-24.

