Study Pinpoints 2 Air Toxics Posing Greatest Danger

The greatest risk posed by air toxics to nearly the entire population of Los Angeles and Orange counties comes from benzene, a product of gasoline, and chromium from metal plating operations, the South Coast Air Quality Management District reported Tuesday.

The rankings of the two air contaminants among 20 examined during a two-year study, funded by a $220,000 Environmental Protection Agency grant, marked the first time that the relative risks from breathing air toxics have been estimated for the South Coast Air Basin, which includes Los Angeles, Orange, San Bernardino and Riverside counties.

Benzene and chromium each increase an individual’s risk of cancer over a 70-year lifetime to as high as 100 in a million in the most populated areas of the two counties, compared to the one-in-a-million risk considered to be acceptable by various government agencies.

In some areas, including metropolitan Los Angeles, the individual risk of a lifetime exposure to benzene may even be as high as one in 1,000.

The scientists who participated in the study cautioned that the risk estimates, which in some cases could be high and in other cases low, should not be viewed as hard and fast predictions of cancer.

“The probability is of an individual having a risk of greater than 100 in a million, not that there are going to be 100 cases per million,” study co-author Emily Nelson said.

Smoking or Diet

Put in perspective, the individual lifetime risk of cancer from all causes is one in four, or about 250,000 cases per million people. It has been estimated that about 65% of annual cancer deaths are related to smoking or diet. The number of cancer cases that have been attributed to all environmental pollution, including toxics in the air and water, is about 2% of the total. Air toxics, in turn, account for a small portion of that 2%.

The study comes at a time when the state Air Resources Board is poised to consider new benzene control measures and when the South Coast district is preparing to adopt new rules for controlling a wide range of toxic air contaminants that either cause cancer or are believed to be a probable cause of cancer in humans.

Mark Abramowitz of the Coalition for Clean Air called the results “fairly startling.”

“I think that it shows that there’s an extremely major problem with air toxics in the basin, and it’s one that needs to be acted on fairly quickly,” Abramowitz said.

But, Michael Cardin, manager of environmental regulations and legislation for Unocal and a spokesman for the Western Oil and Gas Assn., said the benzene risk estimates are “excessively high.” Cardin said that if they are true, oil refinery workers, who are presumedly exposed to higher concentrations of benzene, would be dying of leukemia in numbers greater than found in the overall population. He said they are not.

Benzene is a natural component of crude oil and is also formed during the production of gasoline and the burning of gasoline in motor vehicles. Emissions are about equally divided between motor vehicles and stationary sources such as gasoline stations and oil refineries.

The risks posed by benzene and chromium take into account air pollution controls already in effect, such as vapor recovery systems on cars and at the gasoline pump.

Benzene Decrease Forecast

Last year, the state Air Resources Board estimated that overall benzene emissions in California will decrease to 18,000 tons a year by the year 2000 from 21,400 tons in 1984.

Also included in the AQMD air toxics study were arsenic, beryllium, cadmium, carbon tetrachloride, chloroform, ethylene dibromide, ethylene dichloride, lead, mercury, methyl bromide, methylene chloride, nickel, perchloroethylene, toluene, 1,1,1-Trichloroethane, trichloroethylene, vinyl chloride and xylene.

Nelson said the rankings will help regulators decide where to focus future air toxic control efforts.

“It helps the risk managers. Do they start getting concerned about perchloroethylene from dry cleaners or look at the whole relative risk of all 20 and focus their resources on pollutants that pose the great risk? We’re trying not to scare people with these numbers,” she said. “We’re trying to make a call for a rational use of these resources.”