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ARTICLES Table of Contents   
Year : 2002  |  Volume : 4  |  Issue : 14  |  Page : 41-48
NoiseChem : An European Commission research project on the effects of exposure to noise and industrial chemicals on hearing and balance

1 University College London, United Kingdom
2 National Institute for Occupational Safety and Health, USA
3 INRS, France
4 University of Oklahoma, USA
5 National Institute for Working Life, Sweden and Karolinska Institute, Sweden
6 Institute of Occupational Health, Denmark
7 Institute of Occupational Medicine and Environmental Health, Poland
8 Finnish Institute of Occupational Health, Finland
9 The NOFER Institute, Poland

Click here for correspondence address and email

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.

Keywords: Solvents, noise, multiple exposures, hearing and balance

How to cite this article:
Prasher D, Morata T, Campo P, Fechter L, Johnson AC, Lund SP, Pawlas K, Starck J, Sliwinska-Kowalska M, Sulkowski W. NoiseChem : An European Commission research project on the effects of exposure to noise and industrial chemicals on hearing and balance. Noise Health 2002;4:41-8

How to cite this URL:
Prasher D, Morata T, Campo P, Fechter L, Johnson AC, Lund SP, Pawlas K, Starck J, Sliwinska-Kowalska M, Sulkowski W. NoiseChem : An European Commission research project on the effects of exposure to noise and industrial chemicals on hearing and balance. Noise Health [serial online] 2002 [cited 2022 Sep 28];4:41-8. Available from: https://www.noiseandhealth.org/text.asp?2002/4/14/41/31810

  Introduction Top

The effect of combinations of environmental factors on workers' health requires much research attention as this reflects more closely the work conditions and little is known how individual toxic agents in mixed exposures interact to increase or modify the likelihood of adverse health effects. Most work environments consist of a myriad of physical and chemical agents that are potentially hazardous to health. Study results of isolated workplace hazards are often used to develop occupational safety criteria that may not be adequate for protecting workers in environments where simultaneous or sequential exposures to a variety of agents occur.

Around 30 million people in Europe work in noise environments that are hazardous to hearing, and an additional 10 million work with industrial chemicals considered to be ototoxic, such as solvents, heavy metals, and asphyxiants. A considerable number of these workplaces include both industrial chemicals and a noisy environment, thereby, enhancing the risk for hearing loss. The risk from noise exposure is well established, but from exposure to industrial chemicals is less well understood. Laboratory studies in animals (Johnson et al., 1988, Lataye and Campo, 1997; Lataye et al, 2000) and some occupational exposure studies (Morata et al., 1993; 1997a; Sliwinska-Kowalska et al., 2001) suggest that simultaneous exposures to noise and chemicals produce a hearing loss that is significantly greater than from either agent acting alone. In other words, there is an observed synergistic effect from having combined exposures to noise and chemicals. This means that individual noise and chemicals may be within exposure limits, but in combination they can still pose a risk. If this synergism were confirmed in humans, major changes would be required in the limitations set for occupational hazards to prevent occupational hearing loss. In addition to the synergistic effects on hearing, chemicals may also affect balance and auditory central nervous system function in a way not expected from noise exposure alone.

It is important, therefore, to examine the independent and combined effects of chemicals and noise on both the hearing and balance systems of exposed workers. In 1996, the U.S. National Institute for Occupational Safety and Health (NIOSH) developed the National Occupational Research Agenda (NORA) to redefine research priorities based on seven criteria:

  • seriousness of the hazard (based on death, injury, disease, disability, and economic impact)
  • number of workers affected
  • magnitude of risk, potential for risk reduction
  • expected trend in research area
  • insufficiency of existing research
  • probability that research would make a difference

NORA identified hearing loss due to noise and chemicals as a priority area. The need for research in this area is further heightened by the lack occupational guidelines or standards for combined exposures to chemicals and noise.

  Objectives Top

NoiseChem proposes to examine study designs, hearing assessment alternatives, and strategies for the analysis of combined effects. Moreover, on the basis of agreed protocols, NoiseChem's goal is to conduct epidemiological studies across eastern and western Europe.

The NoiseChem study involves two research groups: (1) those working with animals to determine the mechanisms of ototoxic damage due to noise and chemical interactions through laboratory investigations; and (2) those examining the effects on human audio-vestibular systems using systematic, standardized procedures through epidemiological investigations on factory workers in Sweden, Finland, Poland, and the United Kingdom. A new partner will also be examining workers in France.

There are three work packages (WP) in the program. The objectives are as follows:

  • WP1: Develop standardized procedures for effective field evaluation of hearing and balance function.
  • WP2: Determine the effect of exposures to solvents at concentrations commonly found in industry and the interactive effects of solvents and noise on worker hearing and balance function.
  • WP3: Determine the mechanisms in laboratory animals for damage to hearing from solvents and their interaction with noise.

  Current Status Top

Chemicals - such as toluene, styrene, xylene, trichloroethylene, and carbon disulfide - and their mixtures are commonly used in industry and present a risk to hearing and balance. This risk is exacerbated by noise. Although organic solvents have been used in industry for over 150 years, serious consideration of their ototoxicity began only some 15 years ago. This lack of attention probably derives from the fact that substantial noise is often present in most occupational settings where solvent exposures occur and, as a consequence, hearing losses observed in these situations have often been attributed exclusively to noise exposure. Currently, occupational legislation does not consider environmental chemicals hazardous to hearing. Thus, there are many solvent-exposed workers whose needs concerning hearing conservation are unmet.

Recent studies have suggested that the risk to hearing may increase several-fold where the combination of noise and solvents exists. Particularly alarming are the prospects of noise and solvents that, when occurring alone, are within current exposure limits, but when combined, increase synergistically, thus, posing a greater risk to hearing. Therefore, it is important to determine the effects of combined exposures to noise and chemicals for the purposes of hearing conservation and exposure limit standards.

The ototoxicity of environmental agents - such as solvents, metals and asphyxiants - and their interactions with noise are issues just beginning to be addressed internationally; the group of researchers involved in this study have played a significant role in bringing this research to the fore. Balance dysfunction from solvents has largely been neglected due, in some extent, to the difficulties of testing for it in the field even though both ototoxic and neurotoxic agents can affect balance systems (Bhattacharya, 1999; Smith et al., 1997).

Organic solvents can produce permanent hearing impairment in both people and laboratory animals. The widespread use of these organic solvents and the specific nature of the hearing loss that has been reported pose a significant occupational health risk. Laboratory investigations appear to identify two distinct patterns of cochlear dysfunction and injury following solvent exposure. One pattern produced by toluene involves the impairment of outer hair cells, which normally encode middle frequency tones. These outer hair cells are located in the middle turns. The ototoxicity appears to stem from a preferential perturbation in motility of these cells and, thereby, of sensitivity to sound. Preferential dysmorphia in these cells and impaired regulation of free intracellular calcium levels can occur rapidly and at lower than predicted concentrations of toluene exposure to human brains. Because the outer hair cell alone shows rapid electromotility, a process that is sensitive to [Cai2+], it may be particularly vulnerable to ototoxic agents that disrupt intracellular calcium regulation. The second pattern produced by trichloroethylene, in contrast to toluene, preferentially impairs inner hair cell-spiral ganglion cell function. It is yet to be determined whether this reflects excitotoxic injury at this synapse.

The NoiseChem study will characterize the development of cochlear impairment to toluene and styrene using repeated-within-subject assessment of distortion product otoacoustic emissions and compound action potential. Comprehensive acute cochlear assessment of auditory nerve saturation, cochlear microphonic, and endocochlear potential measures will specify the target cells. Non-ototoxic solvents will be used as controls to identify selective mechanisms of ototoxicity. Toluene preferentially disrupts slow motility in outer hair cells, which encode middle frequency hearing, and elevates intracellular calcium by disrupting intracellular storage and/or release mechanisms. In vitro experiments will identify the specific calcium sequestration mechanism that is impaired by these ototoxic solvent and determine the relationship between changes in outer hair cell morphometry and in outer hair cell and spiral ganglion cell calcium homeostasis.

The mechanisms that favour the interaction of chemicals and noise on auditory function, the possible targets for such effects, and the relationship between neurotoxicants and ototoxicants need to be addressed. While it is possible that any two agents may have interactive effects, it is not feasible to test all compounds, let alone all combinations of agents. A prominent problem of ototoxicity is that it is not clear which events lead to loss of auditory function.

A major objective of this research is to identify mechanisms by which chemicals disrupt hearing so that accurate predictions of these agents can be made. Once an ototoxicant is recognized, the probability for potentiation of noise-induced hearing loss by the agent must be assessed to allow accurate risk assessment.

Studies on workers in various fields are beginning to show that the combined occupational exposure to solvents and noise can result in greater hearing loss as, for example, in shipyard painters and paper mill workers, but the detailed exposure and effect relationships have not been identified. In a recent cross-sectional study of workers in a printing plant, the adjusted relative risk estimates for hearing loss were reported as four times greater for the noise group, eleven times greater for the noise and toluene group and five times greater for the solvent mixture group (Morata et al 1993; 1997a). Toluene and noise interactions are clearly indicated. Pure tone audiometric tests alone have been shown to be insufficient for describing the complete effects, as acoustic reflex findings suggest a retrocochlear element to the impairment. Thus, comprehensive evaluations of the peripheral and central auditory nervous system and the auditory efferent pathway are indicated for a complete exposure effects assessment.

Combined exposures to styrene and noise were tested in workers exposed to mixtures of polystyrene resin, methanol, and methyl acetate at concentrations below threshold limit values. The percentage of people lying outside the 90th percentile for the upper limit of hearing was 8.7% for the controls, 12.1% for noise group, and 33.3% for the solvents and noise group. However, these findings were not replicated by another study of workers in a glass-reinforced­plastics industry who were exposed to styrene and noise. No clear relationship was observed between cumulative noise and styrene exposure on audiometric thresholds.

Clearly consistency of exposure evaluation and effects assessment is required before studies can be compared.

   NoiseChem Study Top

A variety of study designs, which include case reports, case referents, and cross-sectional studies, indicate the multiplicity of objectives in the solvent exposure investigations. A wide variety of metrics and diverse approaches to the measurements of chemical exposures have been used to study auditory effects. These studies are not directly comparable, but provide a clear indication that industrial chemicals affect human hearing and may interact with noise, thus, further exacerbating the situation.

In this study a number of toxicants will be examined, namely - toluene, styrene, xylene, trichloroethylene, carbon disulfide, and solvent mixtures. All of these will be studied with and without simultaneous noise exposure to determine the interaction effects.

These proposed investigations will benefit from the following:

  • Detailed individual solvent and noise exposure evaluations.
  • Comprehensive study of the peripheral and central auditory and vestibular systems in populations exposed to solvents with and without noise.
  • Comprehensive individual risk factors analysis and their impact on effects.
  • Identification of possible susceptibility factors and individuals at most risk.
  • Large-scale, multi-centre European study of a range of solvents with and without noise and tested using a unified agreed set of protocols.
  • Hazard and risk assessments for the combinations of solvents and noise.
  • Detailed dose and response relationships for toluene, styrene, xylene, trichloroethylene, carbon disulfide and a combination of solvents with and without noise.
  • Estimation of solvent exposure variation across Europe.
  • Real-life mixed solvent exposure assessments and their effects on hearing and balance systems. Balance effects have largely been neglected, but need to be investigated for both ototoxic and neurotoxic agents.
  • Detailed investigation of balance disturbances from exposures to a large number of solvents, this being the first.

The implications of solvent ototoxicity to occupational health and especially hearing conservation are far reaching. Ultimately, they can be expected to widen the framework for analyses of the relationship between auditory function and working conditions. They may encourage a paradigm shift in hearing conservation, refocusing attention away from noise to hearing.

The following areas will be addressed by this group as the study progresses:

  • Appropriateness of the current threshold limits when certain hazards occur simultaneously in the workplace.
  • The adequacy of current hearing assessment and protection strategies.
  • Role of hearing assessment as applied to the early identification of those most susceptible to neurotoxic disorders.
  • Method for general risk assessment of interaction between two or more toxic agents, as such exposures are common in a majority of occupational settings.
  • Models for general risk assessment concerning interactions between chemicals and noise, which has never been proposed before now.
  • Further data on outcomes following specific exposure combinations as a basis for the generation of hypotheses concerning mechanisms that cause potentiation of auditory disorders.
  • Development of methods to estimate risks of common occupational exposures.

One of the main study objectives is to improve our understanding of the health risks of workers exposed to a mixture of solvents or combination of solvents and noise and, thereby, to reduce the harmful effects. Cooperation amongst the European noise specialists, engaged in research in their own countries, will be achieved by their coming together and jointly gaining from each other's experiences to improve the state of the art in industrial chemicals and noise-related effects research. The work plan is summarized in [Figure - 1], which sets out the environmental and health aspects to be studied in humans and animals, together with the objectives to be achieved, and the deliverables. [Figure - 2] provides the details of the chemicals to be studied, their usual applications in industry, and their monitoring in relation to NoiseChem targets.

Noise is a well recognised hazard to hearing but chemicals in the workplace and in the environment generally also pose a great hazard to hearing and particularly balance, yet most people remain unaware of this possibility. Chemical exposure which leads to problems of dizziness and imbalance can be disabling and lead the individual to be socially isolated. The social objective of NoiseChem project is to provide workers with the information on hazards of chemicals so that they can make informed choices and furthermore to allow decision makers to be armed with the most relevant scientific information to make appropriate decisions with regard to public health policy on chemical exposures particularly mixed exposures.

  Acknowledgement Top

The NoiseChem Project work is supported by a European Commission Grant (QLK4-CT-2000­00293). This paper is published jointly with the International Journal of Occupational Medicine and Environmental Health.[8]

  References Top

1.Bhattacharya A. (1999) Quantitative posturagraphy as an alternative noninvasive tool for alcohol/drug/chemical testing-preliminary thoughts. Drug Chem Toxicol; 22(1): 201-12  Back to cited text no. 1    
2.Johnson AC, Juntunen L, Nylen P, Borg E, Hoglund G. (1988)Effect of interaction between noise and toluene on auditory function in the rat. Acta Otolaryngol; 105(1-2):56-63.  Back to cited text no. 2    
3.Lataye R, Campo P. (1997) Combined effects of a simultaneous exposure to noise and toluene on hearing function. Neurotoxicol Teratol; 19(5): 373-82.  Back to cited text no. 3    
4.Lataye R, Campo P, Loquet G. (2000) Combined effects of noise and styrene exposure on hearing function in the rat. Hear Res; 139(1-2): 86-96.  Back to cited text no. 4    
5.Morata TC, Dunn DE, Kretschmer LW, Lemasters GK, Keith RW. (1993) Effects of occupational exposure to organic solvents and noise on hearing. Scand J Work Environ Health; 19(4): 245-54.  Back to cited text no. 5    
6.Morata TC, Fiorini AC, Fischer FM, Colacioppo S, Wallingford KM, Krieg EF, Dunn DE, Gozzoli L, Padrao MA, Cesar CL.(1997) Toluene-induced hearing loss among rotogravure printing workers. Scand J Work Environ Health; 23(4): 289-98.  Back to cited text no. 6    
7.Sliwinska-Kowalska M, Zamyslowska-Szmytke E, Szymczak W, Kotylo P, Fiszer M, Dudarewicz A, Wesolowski W, Pawlaczyk-Luszczynska M, Stolarek R. (2001) Hearing loss among workers exposed to moderate concentrations of solvents. Scand J Work Environ Health; 27(5):335-42  Back to cited text no. 7    
8.Smith LB, Bhattacharya A, Lemasters G, Succop P, Puhala E 2nd, Medvedovic M, Joyce J.(1997)Effect of chronic low-level exposure to jet fuel on postural balance of US Air Force personnel. J Occup Environ Med; 39(7): 623-32.  Back to cited text no. 8    

Correspondence Address:
Deepak Prasher
Institute of Laryngology and Otology, University College London, 330 Gray’s Inn Road, London WC1X 8EE
United Kingdom
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Source of Support: None, Conflict of Interest: None

PMID: 12678927

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