By Sean Henahan, Access Excellence

CHICAGO- Chemical disinfectants used to kill microorganisms in drinking water may themselves be contributing toxic byproducts to the water supply, reported Purdue researchers at the annual meeting of the American Chemical Society.

Chlorine is a case in point. Chlorine is a very effective disinfectant against bacteria, viruses and other microorganisms. However, chlorine can react with natural organic matter to produce trihalomethanes (THMs) , some of which are thought to be carcinogenic.

Though the Environmental Protection Agency currently regulates chlorine water treatment processes to keep THMs within certain limits, some water treatment facilities have begun using agents other than chlorine to disinfect water. Indeed, several states are now using ozone as a primary or initial disinfecting agent.

''One problem with this method is that ozone doesn't stay in the water very long, so there's no residual ozone left to act as a disinfectant until the water gets to your tap,'' says Erik J. Pedersen, a doctoral student in environmental engineering at Purdue. ''For this reason, chloramines, chlorine substitutes that do not produce THMs, are added in the final stage of ozone treatment.''

Though this water treatment process eliminates the production of THMs, routine quality control tests done for the utilities using the system have detected the presence of another hazardous byproduct, called cyanogen chloride. In its gaseous form, cyanogen chloride is highly toxic. Though the toxicity of dissolved cyanogen chloride at levels present in drinking water is not known, it is thought by scientists to be potentially harmful.

''Though cyanogen chloride is currently not regulated by the EPA, it is listed on the agency's priority list and is being looked at very closely to determine what levels, if any, are safe for consumption,'' Pedersen says. Up to this point, scientists didn't know how the agent formed. Pedersen and colleagues determined that cyanogen chloride forms through the interaction of monochloramine, the form of chloramine most frequently used in such treatments, and formaldehyde.

''Though low levels of formaldehyde are sometimes present in water, the process of treating water with ozone appears to enhance this interaction, or perhaps increase the amount of formaldehyde present,'' Pedersen says.

Using a stopped-flow spectrophotometer, an instrument designed to measure very rapid reactions, he monitored the reaction between monochloramine and formaldehyde over a wide range of concentrations and time intervals.

''The results show that the combination of formaldehyde with monochloramine result in a rapidly forming intermediate, which slowly decomposes over a period of hours to form cyanogen chloride,'' Pedersen says. ''The initial reaction is very fast on the order of seconds.''

The cyanogen chloride probably forms in drinking water through other pathways as well, he notes. ''It's highly probable that the chloramines used in treatment will react with other organic molecules to produce cyanogen chloride,'' he says.

Another team of Purdue researchers are looking at the role copper plays in forming trihalomethanes. Civil engineering Professor Ernest Blatchley and doctoral student Ravi Duggirala designed experiments to see how copper contributes to the formation of THMs - especially chloroform - during water treatment processes using chlorine. Chloroform causes cancer in animals.

Copper, which occurs naturally in water, also is used sometimes in water treatment in the form of copper sulfate to control algae. In addition, drinking water may interact with copper as the water travels through copper pipes or fixtures. The results of the study show that the presence of copper increases the formation of chloroform in water when chlorine is present, says Duggirala.

''This suggests that copper may play a role in the formation of some THMs,'' Duggirala says. ''It also might imply that, by minimizing water's exposure to copper, we could reduce the production of disinfection byproducts in water.''