Exposure to ototoxic substances can also cause hearing loss
Ototoxic substances are chemicals that can result in hearing loss.
When absorbed into the bloodstream, ototoxic substances may damage the cochlea (inner ear) and/or the auditory nerve pathways to the brain – which can lead to hearing loss and tinnitus.
Hearing loss is more likely if a worker is exposed to a combination of ototoxic substances, or a combination of the substance and noise.
There are three major classes of ototoxic substances:
1. Solvents e.g. butanol, carbon disulphide, ethanol
2. Heavy metals e.g. arsenic, lead, manganese
3. Asphyxiants e.g. acrylonitrile, carbon monoxide, hydrogen cyanide
The most common routes of entry for these ototoxic substances are via skin absorption, inhalation and, to a lesser extent, ingestion (mainly due to poor personal hygiene practices at work).
Work activities that commonly combine noise and ototoxic substances include:
- boat building
- furniture making
- fuelling vehicles and aircraft
- manufacturing, particularly of metal, leather and petroleum products
- weapons firing
Some medications have also been identified as ototoxic substances. These include some anti-cancer, anti-inflammatory, anti-thrombotic, anti-malarial, anti-rheumatic and antibiotic drugs.
Quinine and salicylic acids (such as aspirin) are also considered to be ototoxic substances.
Some ototoxins can be absorbed through the skin and are considered particularly hazardous. Exposure standards for chemicals and noise do not take account of the increased risk to hearing caused by ototoxic substances.
It is recommended that the noise exposure of workers (based on a daily shift) exposed to any ototoxic substances, be reduced to 80 dB(A) or below. They should also undergo audiometric testing and be given information on ototoxic substances.
Control measures such as substitution, isolation and local ventilation should be implemented to eliminate or reduce chemical exposures. Personal protective equipment should be used to prevent skin and respiratory absorption when other controls are insufficient.