Etiology
Toluene (C7H8) is a colorless aromatic hydrocarbon with a wide range of industrial utility. Toluene is used to manufacture plastics, nylon, and polyurethane and as a solvent in paints, inks, adhesives, fragrances, coatings, and cleaning agents. In veterinary medicine, toluene is used to remove ascarids and tapeworms. The United States military uses toluene to manufacture 2,4,6-Trinitrotoluene (TNT), a dangerously explosive nitroaromatic. Toluene is also an important petrochemical used to improve the octane rating of gasoline. [National Center for Biotechnology Information. PubChem Compound Summary for CID 1140, Toluene.]
Approximately 30 billion pounds or 13.6 million metric tons of toluene is produced yearly. Exposure limits have been established for manufacturing plants, construction sites, nail salons, printing establishments, maritime employment, and automobile repair facilities.
The Occupational Safety and Health Administration (OSHA) uses a reference concentration of 5 mg/m3. At this concentration, the acute minimal risk level is 2 ppm (exposure from 1 to 14 days), while the chronic minimal risk level is 1 ppm (greater than 365 days). The permissible exposure limit is 200 ppm for 8 hours, with an acceptable ceiling concentration of 300 ppm and an acceptable peak beyond the ceiling concentration of 500 ppm over 10 minutes. The National Institute for Occupational Safety and Health (NIOSH) recommends a more stringent standard of 100 ppm for 8 hours with an acceptable peak of 150 ppm over 15 minutes. (NIOSH. Toluene standards) Both organizations recommend the minimum use of personal protective equipment for chemical cartridge respirators with organic vapor cartridges, with additional recommendations based on time and concentration of exposure.
There is limited data on dermal exposure limits. However, multiple studies have reported defatting dermatitis, pruritus, and epidermal thickening with repeated exposures.[10][11] An estimated exposure concentration that resulted in dermatitis and pruritus was reported in female shoe workers as 65 ppm (15 ppm to 100 ppm) in winter to 100 ppm (10 ppm to 200 ppm) in summer over 40 months.[10][11]
Outside of occupational exposure, toluene can be found in the atmosphere, water sources, and soil. Domestic manufacturing and processing facilities release an estimated 22 million pounds (10,000 metric tons) of toluene into the atmosphere annually. Newly constructed buildings and areas of high gasoline emissions are noted in areas of heightened concentrations, eg, a new apartment has levels as high as 66.06 μg/m3. In comparison, the outdoor levels were 11.05 μg/m3. An estimated 54,000 pounds (245 metric tons) of toluene is released from industrial discharge and spill incidents into local water sources. Water sources neighboring hydraulic fracturing operations in Colorado had a mean sample concentration of 750 μg/L with a 95th percentile concentration of 1,900 μg/L. Approximately 1.3 million pounds (590 metric tons) of toluene are estimated to be released into the soil.
There are additional groups that have provided recommendations on occupational exposure limits. The Lower Olefins and Aromatics (LOA) REACH Consortium recognizes 100 ppm over 15 minutes or 20 ppm over 8 hours before side effects occur.[12] Excessive amounts greater than 500 ppm are associated with a range of clinical presentations, from acute euphoric effects to organ failure and sudden death.[13][14][15][16]