Solvent N-Hexane Attacks Nerves

N-Hexane-Causes Peripheral Neuropathy Among Automotive Technicians

A dangerous exposure situation, previously unrecognized, was reported by the Centers for Disease Control.

The investigative team included Dr. Kathie Hammond, a faculty member at UC Berkeley and a member of the UAW-GM-Delphi Occupational Health Advisory Board, and Dr. Robert Harrison, a member of the Oversight Committee for a study of UAW members at Boeing-NA Santa Suzana, CA.

Solvents, glues, spray paints, coatings, silicones, and other products contain normal (n-) hexane, a petroleum distillate and simple aliphatic hydrocarbon. N-Hexane is an isomer of hexane and was identified as a peripheral neurotoxin in 1964. Since then, many cases of n-hexane related neurotoxicity have occurred in printing plants, sandal shops, and furniture factories in Asia, Europe, and the United States.

In December 1998, the California Department of Health Services (CDHS) received a report from an occupational-medicine physician of a patient with peripheral neuropathy associated with occupational exposure to n-hexane at an automotive repair facility. The patient was a 24-year-old male automotive technician who had worked in the industry from June 1995 to April 1997. In January 1997, numbness and tingling developed in his hands and feet then spread proximally to his forearms and waist. In March, a neurologic evaluation revealed bilaterally diminished reflexes of the biceps, patellar, and Achilles' deep tendon. Nerve conduction velocity studies revealed a subacute progressive mixed motor-sensory neuropathy with distal nerve involvement. He had reported using from one to nine 15-oz. aerosol cans of brake cleaner per day during the 22 months of his employment. This brake cleaner contained 50%-60%
n-hexane (composed of 20%-80% n-hexane), 20%-30% toluene, and 1%-10% each of methyl ethyl ketone (MEK), acetone, isopropanol, methanol, and mixed xylenes. The technician sprayed the product on brakes, tools, small spills, and engine surfaces. His condition improved with cessation of n-hexane exposure; however, he continues to have numbness and tingling in the hands and feet.

The California Department of Health Services screened for n-hexane--related peripheral neuropathy at a local automotive dealership that used an aerosol product containing 1%--5% n-hexane and 2% MEK. This facility was chosen for convenience and the employees' willingness to participate. Air samples were not collected because management had removed the hexane-containing solvent from the facility at the onset of the investigation.

Six (40%) of 15 technicians from this facility participated in the screening. All participants had worked >20 years as technicians; one met the case definition for n-hexane--related peripheral neuropathy. Three of the six had detectable levels of n-hexane metabolites in urine. The exposure values identified are considered acceptable by this standard.

During August 2000, CDHS surveyed California neurologists to identify additional cases of n-hexane--related peripheral neuropathy. 20% of 291 neurologists responded to the survey. One automotive technician was identified with n-hexane--related peripheral neuropathy.

CDC concluded that the three cases of peripheral neuropathy described the report are related to occupational exposure to n-hexane. Inhalation is the primary exposure route. Dermal exposure also may occur, and latex gloves provide ineffective protection from organic solvents.

The neurotoxic effects of n-hexane may be intensified when used with other chemicals found in automotive degreasers (e.g., acetone, MEK, and isopropanol).

Removal from n-hexane exposure is the only known treatment for n-hexane--related neurotoxicity.

The current Occupational Safety and Health Administration permissible exposure limit (PEL) for n-hexane, adopted in 1971, is 500 ppm in air. NIOSH established a recommended PEL of 50 ppm in 1989; the ACGIH TLV and California PEL are 50 ppm.

http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5045a3.htm. Morbidity and Mortality Weekly Reporter, 50(45);1011-3, November 16, 2001

UAW Commentary

This report highlights the importance of following up sporadic cases of neurological disorders among workers exposed to organic solvents. This effect arose from release from aerosol cans of essentially a consumer product. However, the high number of cans used per day in a high volume auto repair facility greatly increases the risk. In addition, skin absorption of solvents can be very substantial, equivalent to 50 ppm inhalation exposure in some circumstances.

n-Hexane may appear in products in "disguise." Any product containing aliphatic hydrocarbons, petroleum distillates, naptha, heptane, gasoline, and similar materials should be suspected of containing n-hexane. If products listing these materials on the MSDS are found in your workplace, the supplier should be queried as to the n-hexane content.

The OSHA standard for n-hexane is more than 40 years old, and does not take into account the new scientific information. The UAW is not prepared to suggest a safe exposure level to n-hexane, or comment whether the TLV of 50 ppm confers any margin of safety. Nevertheless, work activities involving use of the above named materials in quantity, which result in substantial odors, symptoms of lightheadedness or irritation, or substantial skin contact, should be sampled for n-hexane exposure by a method sensitive enough to detect 5 ppm exposure.

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