Noise Exposure Discoveries: Correlations and Chemicals
Several sessions at AIHce 2017 focused on various aspects of noise exposure and had presenters sharing interesting insights.
Correlating Noise and Silica Exposures
Silica is a prominent occupational exposure hazard in many industries, including mining, stone processing, and construction. Exposure can result in lung diseases like silicosis and lung cancer, and increase the risk for tuberculosis. Silica exposure has also been linked to autoimmune diseases, like rheumatoid arthritis.
“So we imagined that in the stone processing industry, the actions that are causing high levels of noise are also probably the same actions that are causing the high level of silica, and that there might be a predictable level of covariance between the two exposures,” said Stephanie Sayler, a research area specialist senior in the Industrial Hygiene program at the University of Michigan, who studied stone processing workers in northern Thailand for three weeks in 2015 hoping to model or predict respirable silica levels using noise exposures. “Potentially, we could use the levels of noise in order to predict who is more likely to be overexposed to silica levels in order for them to be able to implement controls, according to either job category or noise exposure level.”
Noise has been used in the past to predict exposures such as toluene or vibration, but hasn’t been used for particulates. “The problem with silica sampling in low- and middle-income nations in small or medium sized industries is that it’s really expensive,” Sayler explained. “It can cost about $70 per sample. We’re hoping to put out a more affordable model for use in predicting levels of respirable silica exposure and overexposure, specifically.
“We were able to demonstrate that there was a relationship in this specific industry between noise and silica with differences between each of the job categories. We did have a significant degree of covariance between noise and silica exposure.” Referring to her data, Sayler said, “You can see this trend where we see that as the noise levels are being reduced, so are the silica levels.”
However, Sayler points to future research to learn even more about the noise-silica correlation, noting that her study was impacted by Thailand’s rainy season and a lack of measurable health outcomes.
Chemical Exposures and Hearing Loss
Of the thirty-six million Americans have hearing loss, one-third have Noise Induced Hearing Loss. NIHL is the third-most chronic health condition behind arthritis and heart disease. Hearing loss and tinnitus are the two most prevalent service-connected disabilities in the Department of Defense (DoD), greater than traumatic brain injuries.
Of the 31 million Americans exposed to dangerous noise levels, 9 million of those are also exposed to chemicals that damage hearing. Chemicals that are toxic to the auditory system may affect hearing or balance.
“Chemicals are believed to affect cochlear hair cells and inhibit the central nervous system,” said Lieutenant Commander Cody Schaal, PhD, CIH, CSP, an industrial hygiene officer in the U.S. Navy, at AIHce 2017. “This can occur from chemicals by themselves or in combination with noise and act in an additive or synergistic way. In most industrial environments, the average worker is not exposed to just noise; they’re not just exposed to lead. They’re exposed to a combination of stressors simultaneously, so it does warrant further investigation to determine the role that each has on hearing loss.
“One of the seminal studies actually identified a synergistic relationship with toluene and noise together, compared to a noise only group,” said Schaal, pointing to a review of literature on the topic. “Another study identified [that people] with exposures to high concentrations of metals and solvents in combination had nearly two-and-a-half times the odds of having a permanent threshold shift compared to a low-noise group.”
In his own investigation, Schaal wanted to explore the role of high concentrations of metals and solvents and noise together in various combinations on hearing loss. He focused on a population from a shipyard environment. “Lead, cadmium, arsenic, toluene, xylene and noise led to worse hearing in subjects than high noise alone,” Schaal said. “Multiple stressors may damage hearing more than noise alone, particularly toluene starting at greater than 25 ppm and xylene starting at 3 ppm.” But the permissible exposure limits are several times that: 200 ppm for toluene and 100 ppm for xylene. “So it’s possible that we’re going to see folks with worse hearing outcomes at concentrations well below the PEL and TLVs in some cases.”
Schaal concluded, “We should be targeting multiple stressors when it comes to implementing workplace interventions to reduce hearing loss from an occupational health perspective.”