By Diana Holan, MS
Hearing loss is the #1 disability for military veterans, which is attributed to acute or chronic exposure to excessive noise.
However, studies from the last 20+ years have shown that working in excessive noise while inhaling toxic chemicals, including jet fuel, may be even more ototoxic than noise exposure alone. Such hearing loss may take 2-5 years post-exposure before manifesting.
In a 2011 rat study,Fechter et al. looked at two types of jet fuel: JP-8 (petroleum-based with hydrocarbons) and FT (Fischer-Tropsch synthesized) to test for the risk of hearing loss from only fuel exposure, versus inhalant exposure to varying doses of each jet fuel when combined with continuous or intermittent noise exposure. Results showed that exposure to either jet fuel alone or the FT synthetic fuel + noise did not cause hearing loss. However, the combination of JP-8 fuel + excessive noise exposure damaged the outer hair cells (OHCs) more than noise exposure alone, as measured by DPOAE testing.
In another rat experiment in 2012, Matti et al. showed that the degree of OHC damage increased in proportion to higher concentrations of the JP-8 inhalant exposure. In addition, “… the CAP response is disrupted more reliably than is the DPOAE response,” indicating there was damage to inner hair cells (IHCs) and other auditory structures necessary for auditory processing. Interestingly, the male rats were affected more, possibly due to their higher body fat levels that may have stored the JP-8 in their bodies for a longer period than for the lighter weight female rats.
It is difficult to measure these effects in humans, either retrospectively because of age and potential co-existing health issues, or longitudinally because of safety and ethical concerns. But the results of these tests may help determine safer exposure limits to excessive noise when combined with toxic chemicals, as well as guide further research to develop safer, synthetic fuels. This will benefit military personnel, as well as civilian employees in other fields where workers are exposed to hydrocarbon fuels and noise. And it is important information to have about patients with hearing loss that may be due to excessive noise exposure, especially if they are having auditory comprehension issues.
Diana Holan, MS, has been practicing audiology for over 20 years in Tucson and is committed to improving communication between patients and their families through the use of state-of-the-art hearing aid technology and various assistive techniques. She received a Bachelor’s of Science in Speech and Hearing and a Master’s of Science in Audiology from the University of Arizona