n-Hexane exposure in the California vehicle repair industry: Risk assessment and policy analysis

This study was conducted to address exposure and policy-related questions pertaining to the first reported cases of n-hexane-induced peripheral neuropathy in the vehicle repair industry. The study included a solvent exposure assessment among vehicle repair technicians; a risk characterization for n-hexane-induced peripheral neuropathy; and an analysis of the public policies that resulted in the use of hexane in the California vehicle repair industry. Real-time total solvent exposure measurements showed a breathing zone (BZ) "pulse" that reached 394 mg/m3 (arithmetic mean; 95% CI = 337, 452) during the first four minutes of solvent spraying in each of 26 tasks. A mean BZ air exchange rate of 0.83 exchanges per minute (range = 0.61--1.2) was calculated from the BZ solvent decay rate. Air velocity measurements (n = 720) in two shops showed a geometric mean of only 17 ft/min (GSD = 3.2 ft/min). Monte Carlo modeling of task-based BZ charcoal tube samples (n = 23) from nine technicians in three shops (using 25--35% hexane) showed a shift-length, time-weighted [arithmetic] average exposure concentration for n-hexane of 17.8 mg/m3 (SD = 6.4), well below the California Permissible Exposure Limit (PEL) of 180 mg/m3. All other solvents well also well below California PEL values. An epidemiological health risk model produced an estimate of 129 per 1,000 technicians at risk of peripheral neuropathy at the California n-hexane PEL. A survey of the solvent industry (response rate = 74%, n = 17) and interviews with solvent industry officials (n = 13), repair shop owners (n = 5) and government regulators (n = 4) showed that hexane was introduced into the California vehicle repair industry in 1990 in response to market pressures engendered by California EPA's 1991 listing of chlorine-contaminated used oil as a hazardous waste. An analysis of the period 1970 to 2003 indicated that environmental concerns were the primary driving force in the regulation of solvents, but that new occupational hazards were introduced in the wake of these otherwise successful initiatives. The study suggests that integrating worker health and safety into new environmental science and policy approaches would better address both environmental and occupational health goals.