A group of public health advocates is appealing to public school officials to remove certain soft drinks from school vending machines. It has nothing to do with concerns about obesity. Rather, the groups cite Food and Drug Administration findings that some soft drinks contain benzene, a carcinogen.

The groups have signed letters sent to all U.S. chief state school officers, asking them to stop the sale and marketing of these soft drinks in public schools, until they can be proven safe and free from benzene contamination.

"Benzene is classified as a known human carcinogen by the U.S. Environmental Protection Agency. Chronic exposure to benzene is associated with leukemia, aplastic anemia and other blood diseases. Children may be especially sensitive to benzene because their bone marrow cells are highly active," the letter said.

Why would soft drink manufacturers add a known carcinogen like benzene to their products?

They don't. Instead, the benzene is formed by a reaction of ascorbic acid (vitamin C) and sodium or potassium benzoate (which are used as preservatives) -- especially in the presence of light or heat.

Soft drinks that contain ascorbic acid and sodium or potassium benzoate include Diet Pepsi Wild Cherry, Fanta Orange, Hawaiian Punch, Mug Root Beer, Pepsi Vanilla, Sierra Mist, Sunkist and Tropicana Lemonade, among others.

The evidence of benzene contamination of soft drinks is coming from many quarters, and it is mounting, the groups argue.

On February 15th, Beverage Daily reported that recent tests had shown that some soft drinks contain benzene at levels "above the legal limit for water set by the US and Europe." According to Beverage Daily, independent tests at a laboratory in New York found benzene levels in a couple of soft drinks contain two-and-a-half and five times the World Health Organization limit for drinking water, which is more permissive than is the U.S. standard.

In early March the Times of London reported that just 100 of the 230 soft drinks tested for benzene met the standard for British water, "with some containing up to eight times the legal limit."

In 1990, the National Soft Drink Association told the FDA about the problem of benzene contamination in soft drinks. The FDA did some testing of benzene levels, but did not make its findings public.

The U.S. Environmental Protection Agency has set its limit on benzene in drinking water at 5 parts per billion (ppb). In its "consumer factsheet" on benzene, the EPA states that "EPA has found benzene to potentially cause the following health effects when people are exposed to it at levels above the MCL [Maximum Contaminant Level for benzene, 5 ppb] for relatively short periods of time: temporary nervous system disorders, immune system depression, anemia."