We are all aware of the problem of noise in the workplace and how hearing can be irreparably damaged. But did you know that hearing can be damaged by certain chemicals in the workplace? Today and tomorrow we will explore findings concerning common workplace chemicals that are said to have the potential to damage hearing.
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The Occupational Safety and Health Administration (OSHA) requires that exposure to hazardous noise, i.e., noise exposure of 85 decibels (dB) or more over an 8-hour average be reduced or eliminated. In fact, when noise exposure reaches 85 dB or more over an 8-hour average, you are required to implement a hearing conservation program.
According to the National Institute for Occupational Safety and Health (NIOSH), occupational hearing loss (OHL) can occur when workers are exposed to loud (hazardous) noise, which is considered loud when it reaches 85 dB or higher, or if a person has to raise his/her voice to speak with someone 3 feet away. OHL can also occur from exposure to ototoxic chemicals, which refer to drugs or other substances that have a harmful effect on hearing and balance.
Examples of ototoxic chemicals in the workplace are:
- Organic solvents, such as styrene, trichloroethylene, toluene, and solvent mixtures;
- Heavy metals, such as mercury, lead, and trimethyltin; and
- Asphyxiants, such as carbon monoxide, hyrdrogen cyanide, and acrylonitrile.
NIOSH claims that about 10 million workers are exposed to solvents, and an unknown number are exposed to other ototoxicants.
In a collaboration with the Swedish Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals (NEG), NIOSH conducted research to evaluate occupational exposure to chemicals and hearing impairment. According to the resulting document, a 20-year study of 319 employees in a paper mill revealed that a large proportion of the workers in the chemical division showed a hearing loss severe enough to be regarded and compensated as a work-related hearing loss (23%) as compared to groups working in nonchemical environments (5%–8%). This was despite the lower noise levels in the chemical division.
Here’s a snapshot of some of the research findings for organic solvents commonly found in the workplace.
Findings for Organic Solvents
Styrene. In one study, the effects of styrene were investigated in male workers exposed in factories producing plastic buttons or bathtubs. Two investigations showed that hearing was reduced in workers exposed to styrene for 5 years or more, although both noise levels and styrene concentration in air were within limits recommended by several international agencies. Another study showed a significant positive correlation between the average work/life styrene concentration of 14 parts per million (ppm) and hearing loss.
Toluene. In one study, a group of rotogravure printers with normal hearing ability and exposed to an average of 97 ppm toluene for 12–14 years showed alterations of auditory-evoked brainstem responses. This led the researchers to conclude that auditory nervous system modifications were demonstrated before clinical signs of chronic exposure to toluene appeared. Another study investigated hearing loss among workers exposed to both toluene and noise in an adhesive material manufacturing plant. The results showed that hearing loss was 6 times higher for the toluene-plus-noise group compared to the noise-only group.
Carbon disulphide. Five studies of carbon disulfide and noise have been conducted in viscose rayon factories. In four of the studies, not only was the percentage of hearing loss higher among the workers exposed to both carbon disulphide and noise but also hearing losses were more serious and had an earlier onset than if the only environmental factor had been noise exposure.
Check tomorrow’s Advisor for findings concerning the relationship between metals and asphyxiants and occupational hearing loss.