Noise-induced hearing loss


Chronic Poisoning




Sensorineural hearing loss: NIHL


Presbycusis (sensorineural hearing loss in older people) results mainly from aging and noise exposure. Prevalence rates of presbycusis are 25% to 40% in people >65 and 40% to 66% in those >75. [Merck Manual, p. 781-3] Noise-induced hearing loss (NIHL) was listed in 1991 as one of the 64 sentinel health events that cause preventable disease and disability in workers. [Mullan, p. 782] In recent years, concern has been raised about the impact of organic solvents such as toluene and styrene on occupational hearing loss. See "Solvent-induced hearing loss." In a review published by IRSST, only four chemicals (lead, styrene, toluene, and trichloroethylene) were designated as "ototoxic substance." Of these four, only lead had "evidence of interaction" with noise. [www.irsst.qc.ca] In a review of "occupational exposure to chemicals and hearing impairment," the Nordic Expert Group found a blood lead NOAEL of 35ug/dl and a LOAEL of 55 ug/dl in long-term exposed monkeys. Interaction of lead poisoning with noise has not been studied in animals. "In humans, central auditory effects have been associated with current exposures and life-time weighted average blood lead concentrations of approximately 28-57 ug/dl." [Hyperlink] CDC statistics on blood lead reporting in 40 states showed a decline in the prevalence of blood leads >25 ug/dl from 14 per 100,000 employed adults in 1994 to 6.3 per 100,000 in 2009. [MMWR Weekly, July 1, 2011] The mean blood lead in the US has declined from about 15 ug/dl in the 1970s when leaded gasoline was used to the current level of <2 ug/dl. [Levy, p. 203] OSHA regulates noise exposures at or above an 8-hour time-weighted average of 85 dBA; [LaDou, p. 162] "Exposure to certain chemicals may also result in hearing loss. In settings where there may be exposures to noise and to carbon monoxide, lead, manganese, styrene, toluene, or xylene, periodic audiograms are advised and should be carefully examined." [ACGIH: TLVs and BEIs]


Audiogram: graphs the softest sounds that the subject can hear as a function of frequency; NIHL first affects hearing around 4000 Hz; After prolonged or severe exposure, the speech frequencies (500-3000 Hz) are affected; [LaDou, p. 160]

ICD-9 Code


Reference Link

Nordic Expert Group: Occupational exposure to chemicals and hearing impairment

Related Information in Haz-Map

Hazardous agents that cause the occupational disease: