A Review of the Neurotoxicity Risk of Selected Hydrocarbon Fuels

Abstract

Over 1.3 million civilian and military personnel are occupationally exposed to hydrocarbon fuels, emphasizing gasoline, jet fuel, diesel fuel, or kerosene. These exposures may occur acutely or chronically to raw fuel, vapor, aerosol, or fuel combustion exhaust by dermal, respiratory inhalation, or oral ingestion routes, and commonly occur concurrently with exposure to other chemicals and stressors. Hydrocarbon fuels are complex mixtures of 150-260+ aliphatic and aromatic hydrocarbon compounds containing varying concentrations of potential neurotoxicants including benzene, n-hexane, toluene, xylenes, naphthalene, and certain n-C9-C12 fractions (n-propylbenzene, trimethylbenzene isomers). Due to their natural petroleum base, the chemical composition of different hydrocarbon fuels is not defined, and the fuels are classified according to broad performance criteria such as flash and boiling points, complicating toxicological comparisons. While hydrocarbon fuel exposures occur typically at concentrations below permissible exposure limits for their constituent chemicals, it is unknown whether additive or synergistic interactions may result in unpredicted neurotoxicity. The inclusion of up to six performance additives in existing fuel formulations presents additional neurotoxicity challenge. Additionally, exposures to hydrocarbon fuels, typically with minimal respiratory or dermal protection, range from weekly fueling of personal automobiles to waist-deep immersion of personnel in raw fuel during maintenance of aircraft fuel tanks. Occupational exposures may occur on a near daily basis for from several months to over 20 yr. A number of published studies have reported acute or persisting neurotoxic effects from acute, subchronic, or chronic exposure of humans or animals to hydrocarbon fuels, or to certain constituent chemicals of these fuels. This review summarizes human and animal studies of hydrocarbon fuel-induced neurotoxicity and neurobehavioral consequences. It is hoped that this review will support ongoing attempts to review and possibly revise exposure standards for hydrocarbon fuels.

Workplace Exposures and the Risk of Amyotrophic Lateral Sclerosis

“…n -Hexane, an organic solvent associated with a higher risk of ALS in our study, is a classic neurotoxicant (Ritchie et al 2001a) that caused polyneuropathy affecting both sensory and motor neurons (Chang 1990) and was associated with Parkinson’s disease (Canesi et al 2003). Hydrocarbons were shown to induce persisting changes in protein expression and neurotransmitter levels in the central nervous system and to impair neurobehavioral function in rats at the “real-world” concentrations experienced by human beings (Ritchie et al 2001b). Acute intoxication with glycol ethers increased free-radical production in the nervous system in rats (Kadiiska and Mason 2000), and an acute oral challenge with ethylene glycol in humans induced abnormal gait, loss of reflexes, central nervous system depression, and convulsions (Hess et al 2004).…”

In situ detection of anaerobic alkane metabolites in subsurface environments

“…Since many alkanes have appreciable water solubilites (in the tens of mg/L), some alkanes can also migrate in groundwater away from the spill source. Many alkanes have known toxicity (Ritchie et al, 2001), thus their presence in contaminated aquifers is also of concern and their levels are often regulated (Nascarella et al, 2002). …”

Different Occupations Associated with Amyotrophic Lateral Sclerosis: Is Diesel Exhaust the Link?

“…Diesel exhaust is composed of a complex mixture of gases and particulates [ 20 , 24 ]. A number of components of the exhaust, such as formaldehyde, benzene, hexane, and styrene may be involved in the pathogenesis of SALS [ 25 ].…”

“…For example, the cytotoxicity of the glutathione-depleting chemical styrene oxide varies with low or high superoxide dismutase 1 (SOD1) activity [ 30 ], and SOD1 mutations are one cause of familial ALS [ 31 ]. The potential neurotoxicity of a large number of components of hydrocarbon fuels has been reviewed by Ritchie et al (2001) [ 20 ]…”

“…Although two of the studies involved Persian Gulf war veterans [ 41 , 42 ], the third reported on servicemen before 1990 [ 5 ], which suggests that the SALS risk is not related to any particular war zone, but to the experience of war itself. One review of hydrocarbon fuel exposure, which paid particular attention to military uses, emphasised the widespread use of diesel and other hydrocarbon fuels in all service branches of the military during combat [ 20 ]. As well as the use of these fuels to power land, sea and air military vehicles, a number of unique applications lead to increased hydrocarbon fuel exposure.…”