Research over the past 30 years has shown that when chlorine interacts with natural organic matter in drinking water, the process can generate byproducts that are linked to an increased risk of certain cancers and birth and developmental defects.

Some of these byproducts are regulated by the Environmental Protection Agency (EPA), and the agency is now finalizing a new rule that will toughen the standards for chlorine byproducts with known health effects - a move expected to cause at least some water treatment facilities to switch to chlorine alternatives.

But the new findings highlight how little is known about the potential health effects of these chlorine alternatives, according to Michael J. Plewa, a genetic toxicologist at the University of Illinois at Urbana-Champaign and lead author of the new study

The findings are published in the current issue of the journal Environmental Science & Technology.

In an interview, Plewa stressed that no one should "panic" over the water situation in Corpus Christi. He and his colleagues, some with the EPA, found that iodoacids from the city's water were toxic to hamster ovary cells. But the researchers do not know whether there is a large concentration of iodoacids in the drinking water or whether it is enough to harm human health over time.

"If I were in Corpus Christi," Plewa said, "I'd still drink from a water fountain."

Water disinfection, the researcher pointed out, must be done to prevent outbreaks of infectious disease. What scientists must continue to do, he said, is to study the biological effects of known disinfection byproducts, and keep identifying and analyzing new byproducts.

According to Plewa, researchers have chemically defined only about half of the disinfection byproducts that can occur in chlorinated drinking water, and much less is known about the byproducts of chlorine alternatives. Overall, he estimated, experts have a handle on the biological effects of only about 30 percent of all identified byproducts.

To create sound policy, Plewa said, regulators should have the best scientific evidence on the range of disinfection byproducts - a "rank ordering" that defines those byproducts with the lowest potential for harming human health.

In their study, Plewa and his colleagues found that in hamster cells, the one iodoacid they tested was anywhere from twice as toxic to nearly 300 times more toxic than chlorine byproducts.

Corpus Christi was the only location in a nationwide study by the EPA to show iodoacids in drinking water. The water supply there has high levels of bromide and iodide due to the natural chemical makeup of the underlying seabed, and it's possible that the iodoacids found there reflect those conditions.

Plewa said the question of whether iodoacids should be added to the list of EPA-regulated disinfection byproducts needs further research.

A Corpus Christi newspaper, the Caller-Times, reported on Monday that over the next year the EPA will assess iodoacid levels in the city's water, but has no immediate plans to regulate the chemicals.

SOURCE: Environmental Science & Technology, September 15, 2004.