Everyone knows that driving car is a risky business but what about just getting into one? Especially on a hot day! And we’re not talking about burning your rear by depositing it on the plastic seat. It is in a more insidious way that the plastic seat, along with numerous other plastic components in the car, are claimed to present a risk in a widely circulating email. We are urged to ventilate a car for a few minutes before turning on the AC to get rid of any “toxic” benzene that has outgassed from the car’s interior. Like with most such emails, there is a kernel of truth to the scare, but it is greatly exaggerated. Benzene is toxic alright, and can be detected in virtually any air sample, taken anywhere. It’s presence in cigarette smoke, wood smoke and gasoline vapours is well documented. So is the fact that it can outgas from plastics. Benzene is used to make styrene and phenol, both of which are common raw materials for plastic production and there is always a residual that remains in the plastic and can outgas, especially when the temperature rises. Nylon manufacture also relies on benzene which is used to produce cyclohexane, a compound eventually converted to adipic acid, a basic component of nylon. Benzene, which these days is produced from petroleum, is also extensively used in the detergent, glue, rubber, dye, lubricant and pharmaceutical industries. So it really comes as no surprise that the compound can be detected in the air, especially in the confines of a car’s interior.
Before panicking though, there are some questions that have to be raised and answered. What sort of toxicity is associated with benzene? What sort of exposure is required to produce the toxic effects? And most importantly, how does the level of dangerous exposure compare to that in a car? There is no do doubt that breathing high levels of benzene can cause dizziness, confusion, convulsions and even death. Benzene isn’t unusual in this capacity, many organic solvents can produce such effects. While such exposures can happen after an accidental spill or in some industrial setting, they are far from what is encountered in ambient air. The greater concern is low-level exposure over a protracted period. Studies investigating workers occupationally exposed to benzene have linked such exposure to leukemia. But how extensive is this exposure? The lowest levels that have been linked to leukemia are in the range of 30-80 milligrams per cubic meter. And that is when benzene at such concentrations is inhaled every working day for years. How does this compare with daily exposure for the general population? That exposure is in the range of 3 to 40 micrograms per cubic meter, in other words a thousand times less than the minimum occupational exposure that may cause a problem. How about inside a car? As one might expect, levels can be higher than outside, as much as 560 micrograms per cubic meter have been measured. This is still a hundred times less than the minimal occupational exposure linked to leukemia. And of course people are not exposed eight hours a day. Basically then, supposed benzene toxicity in a car is a non-issue. Of course it would not be a good idea to use benzene as an after-shave lotion as was done soon after its discovery by Michael Faraday two hundred years ago. We have learned a little about toxicity since that time. The extent of exposure is very important.