Cars and Trucks and Toxics

One of the character in Douglas Adam’s novel Hitchhiker’s Guide to the Galaxy, an interstellar traveler observing Earth from afar, concluded that motor vehicles are the dominant form of life on the planet. Sometimes it’s easy to become blind to the obvious, such as the pervasive influence of automobiles on public health. It’s such a concern there’s even an institute devoted to its study.

One of the enduring memories of the past two weeks of travel in California and Arizona was the endless streams of motor vehicles flowing over the roads, either as a raging torrent or a trickle. The most substantial reminder about the environmental health impact came after my arrival at the Phoenix airport. Upon departing the baggage claim area to the area where arrivals are picked up, I encountered the spectacle of six lanes packed with idling vehicles between the tall baggage claim building and a tall parking structure, constituting an area source of emissions producing a nice air toxics hot spot. While searching for a taxi, I became aware of my eyes smarting a bit after a few minutes in this atmosphere.

Automobiles produce a number of combustion products that are eye irritants. The best recognized one is acrolein. The lowest observed adverse effect level (LOAEL) associated with mild eye irritation was 60 ppb, following a 5-minute exposure period. Unless I was unusually sensitive to eye irritation, which I doubt, I had been exposed to something above 60 ppb for some five to ten minutes. Short-term concentrations in air can fluctuate a few orders of magnitude above a long-term average, which the California Air Resources Board reported to be 0.6 ppb in 2005 based on a 24-hour sample (EPA’s Urban Air Toxics Monitoring Program doesn’t measure acrolein in air). If this two order of magnitude relationship holds up for the other combustion products, I wonder how much benzene, 1,3-butadiene or formaldehyde I inhaled during my brief stint in the arrival area. Understanding these things intellectually is one thing. It’s another to get a visceral reminder, such as a good dose of emissions right in the face.

Good thing there weren’t a lot of diesel-powered vehicles operating there (there were some buses running to long-term parking and rental car areas and I don’t think there were natural-gas fueled). Diesel exhaust particulates are reasonably anticipated to be, or likely to be human carcinogens, according to the National Toxicology Program’s 11th Annual Report of Carcinogens and EPA. EPA isn’t sufficiently confident in the data to calculate a unit risk factor for quantifying the cancer risk from inhalation, but the State of California routinely quantifies the cancer risk from diesel inhalation. Statistics published by the California Air Resources Board show that the estimated lifetime cancer risk from diesel particulates routinely exceeds the risks from the other combustion products related to automobile emissions. These days, the average estimated lifetime cancer risk from toxic air pollutants in California is around 200 in one million (possibly double or triple that when the risks from diesel particulate matter are included), again with most of the emissions related to mobile sources.

I didn’t even touch the contribution of motor vehicles on criteria pollutants that principally affect respiratory health, such as ozone, particulate matter and oxides of nitrogen, or the resource impact of all our vehicles (currently accounting for 45% of our total petroleum consumption), or the greenhouse gas impact (in 2004, accounting for 33% of the total carbon dioxide emissions). A side benefit from James Howard Kunstler’s efforts to bestir us and release ourselves from thralldom to our cars could eventually be better health.

Someone else gets to blog about the traffic accident injuries and fatalities piece.