Drinking Water: Chloramine complications

[Guest guest]

http://pubs.acs.org//journals/esthag-w/2004/aug/science/rr_chloramine.h\

tml

 

Science News - August 18, 2004

 

Chloramine complications

 

Alternatives to drinking-water chlorination, such as

chloramines, may produce increased concentrations of

disinfection byproducts (DBPs) with toxicities far

more potent than those currently regulated, according

to research just posted to ES & T’s website (es049971v).

 

The research was inspired by a 2002 drinking-water

survey conducted by the U.S. EPA, which revealed that

iodide-containing compounds were forming in some

drinking water at concentrations on the order of 10

micrograms per liter (µg/L). The water came from a

utility where source waters with high levels of

bromide and organic matter were disinfected with

chloramines. Finding the iodinated DBPs was “totally

unexpected,” says Susan Richardson, a chemist with

EPA’s Ecosystems Research Division lab in Athens, Ga.,

and head of the 2002 survey. Now, University of

Illinois toxicologist and corresponding author Michael

Plewa, together with Richardson and colleagues, has

identified some of the specific iodinated DBPs and

reports that one, iodoacetic acid (IA), is the most

genotoxic to mammalian cells of any DBP ever

identified.

Web Links

 

Michael Plewa’s homepage

cropsci.uiuc.edu/faculty/plewa/index.cfm

 

EPA 2002 study: The Occurrence of Disinfection

By-Products (DBPs) of Health Concern in Drinking

Water: Results of a Nationwide DBP Occurrence Study

www.epa.gov/athens/publications/DBP.html

 

Fact sheet about results of the national occurrence

survey

www.epa.gov/athens/publications/factsheets.html

(select, “What’s in Our Drinking Water?”)

 

The findings suggests that the switch in

drinking-water disinfectants may cause increased

adverse health effects in the U.S. population, says

Plewa, who notes that current EPA regulations are

based on limited toxicological and chemical knowledge.

Water companies have been adopting chloramines and

other chlorine-alternative disinfection strategies to

comply with the first part, or stage, of EPA’s 1998

DBP rule, because chloramines, a mixture of chlorine

and ammonia, dramatically reduce levels of regulated

DBPs. Part 2 of the DBP rule further encourages

drinking water utilities to use chloramines and other

alternatives to chlorine disinfection. But the new EPA

study and other data indicate that alternative

disinfectants may encourage the formation of new

toxicologically significant DBPs, he says.

 

At least one organization, the National Rural Water

Association (NRWA), is urging EPA to delay

implementing the stage 2 DBP rule because these

studies point to unforeseen consequences. “There is

significant uncertainty around the health impacts of

these iodinated DBPs—the changes initiated by stage 2

could actually make the health problem worse,” says

Mike Keegan, an NRWA analyst in Washington, D.C. The

stage 2 rule is set to be finalized next year, and EPA

does not intend to delay the rule, according to

environmental engineer Stig Regli at EPA’s Office of

Water in Washington, D.C.

 

In mammalian cells, IA is by far the most potent DBP

tested, says Plewa. The DBP most toxic to bacteria,

dichloromethylhydroxyfuranone, a chlorinated furanone

commonly known as MX, is 80 times more potent than IA

as a mutagen in bacteria, as measured by the Ames

test. But in mammalian cells, IA is 93 times more

cytotoxic than MX and 28 times more mutagenic. Because

mammalian cells are more indicative of effects in

humans, Plewa concludes that IA is likely to be more

hazardous to humans. IA is particularly toxic to

mammalian cells because it inhibits cellular

detoxification mechanisms, he says.

 

Drinking-water sources with high bromide

concentrations often also contain iodide, since both

usually come from a saltwater source. The source of

this saline water can be either saltwater intrusion

into coastal fresh water or “connate water” locked

away underground from a time in the geological past

when ocean waters covered a region. For example, the

high concentrations of iodinated DBPs in the national

survey came from a source affected by connate waters.

 

Chloramination favors the formation of iodinated DBPs

in such waters because chloramines, with less

oxidizing power than chlorine, allow hypoiodous acid

to accumulate and react with organic matter to form

them, according to Swiss Federal Institute for

Environmental Science and Technology (EAWAG) chemist

Urs von Gunten, who has studied the kinetics of these

reactions (Environ. Sci. Technol. 1999, 33,

4040–4045).

 

Some of the iodinated DBPs may be significantly more

toxic than those that we are currently aware of,

agrees Regli. But it’s unlikely they pose a

significant health risk, because it takes a rare set

of conditions to produce them in significant

quantities, he says. “The 2002 national study targeted

extreme water—with extremely high levels of bromine

and natural organic matter. As such, the finding is

unlikely to affect a great number of people,” he says.

 

Epidemiological studies have linked chlorinated

drinking water from surface sources with a higher risk

of bladder and colorectal cancers, and DBPs are the

most likely culprit. But to date, the particular DBP

or mixture of DBPs responsible for the risk has yet to

be identified, according to research chemist Stuart

Krasner with the Metropolitan Water District of

Southern California in LaVerne, Ca. It’s unlikely that

iodinated DBPs could be the culprit, because

epidemiological studies show that people who drink

chloraminated waters have a lower risk for those

cancers than those who drink chlorinated water, says

Regli.

 

Krasner, a coauthor of the 2002 study, agrees with

Regli. The iodinated DBPs typically occurred at

submicrogram-per-liter levels, except for the one

utility in the nationwide survey that had about 10

µg/L of iodinated trihalomethanes (THMs), he says. The

utilities included in the survey were chosen to be

representative and highlight the worst-case

situations.

 

The stage 2 DBP rule is likely to prompt many surface

water plants to switch to chloramines. But in many

cases, utilities will be using chloramines for

secondary disinfection during distribution, not for

primary disinfection at the plant, says Krasner.

 

“Ultimately, it will be important to know the levels

at which these iodo-acids occur, in order to assess

the potential for adverse environmental and human

health risks,” says Plewa. Richardson is currently

working on a project to acquire those data. —REBECCA

RENNER

 

 

Return to Top | Science News Home | ES & T Home