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Solvents, Ethanol, Car Crashes & Tolerance

How risky is inhalation of organic solvents?

Philip J. Bushnell

Mitigating Factors

Are acute exposures to low concentrations of solvents really so dangerous? If so, why does it take such an elaborate analysis to identify the problem? One possibility is that the small increase in deaths (half an additional fatality per year) from exposures at these levels is simply not noticed among all the other factors that influence the statistics. Improvements in the safety of automobiles have reduced the incidence of fatalities, whereas new forms of distraction (for example, use of cell phones while driving) have increased it. Thus this small annual effect may simply be lost in the noise.

On the other hand, the well-known ability of people and animals to compensate for the effects of an intoxicating chemical will reduce the impact of exposure. A decrease in sensitivity to a drug or chemical acquired from experience with the agent is generally known as “tolerance.” Tolerance arises through a number of physiological and psychological processes, and has been shown to develop to ethanol and solvents in very similar ways. Tolerance to these chemicals involves changes both in metabolism (metabolic tolerance) and in the response of the brain to the presence of the chemical (dynamic tolerance). Metabolic tolerance speeds clearance from the body and lowers concentrations of the chemical in the blood and brain. Dynamic tolerance reduces the impact of the chemical that enters the brain, and occurs both acutely (that is, during a single exposure) and more gradually after repeated exposure to the chemical.

Could tolerance mitigate or even eliminate the increased risk of fatal car crashes? One promising statistic in the NHTSA data indicates that adult female “heavy drinkers” actually show a reduced risk of fatal crashes at very low BECs. Perhaps this group has developed sufficient tolerance to the effects of ethanol to eliminate the risk. What is the experimental evidence for this possibility?

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