- Washing dishes by hand with an antibacterial dishwashing
liquid can do more than just ensure that the plates, glasses, and silverware
are free from grease and germs, according to Peter Vikesland of the Virginia
Polytechnic Institute and State University. In research published this
week on ES&T's Research ASAP website (es048943+), he and his colleagues
show that the triclosan antimicrobial agent used in household dishwashing
soaps reacts with chlorinated water to produce significant quantities of
chloroform. The research also suggests that the reaction of triclosan with
chlorine could be producing highly chlorinated dioxins in the presence
- Because of its antibacterial, antifungal, and antiviral
properties, triclosan is found in toothpastes, acne creams, deodorants,
lotions, and hand soaps. It is also incorporated into a wide range of consumer
goods, including kitchen tiles, children's toys, cutting boards, toothbrush
handles, hot tubs, and athletic clothing. As triclosan flows down drains,
it is making its way into surface waters and sewage treatment plants, the
bile of fish, and breast milk, according to the Alliance for the Prudent
Use of Antibiotics, a consumer group. Since 2000, the American Medical
Association has been urging the U.S. Food and Drug Administration to closely
monitor and possibly regulate the home use of antimicrobials such as triclosan.
- The formation of chloroform from triclosan is of concern
because the U.S. EPA classifies the compound as a probable human carcinogen.
Moreover, the presence of trihalomethanes such as chloroform in drinking
water has been linked with human bladder cancers and miscarriages.
- The reaction of phenols such as triclosan with free chlorine
is well known, but Vikesland's research is important because "it ties
the use of a household product [to] increased exposure to a disinfection
byproduct," says David Sedlak, a professor in the civil and environmental
engineering department at the University of California, Berkeley. "This
research is important for demonstrating that the chlorination of triclosan
can occur under environmentally relevant conditions," says Kristopher
McNeill of the University of Minnesota's department of chemistry. "The
fact that you can chlorinate triclosan [under] pretty mild conditions is
troubling," he adds.
- Since writing the paper, Vikesland's team has conducted
follow-up research under conditions that more closely mimic those found
during home dishwashing. The new experiments used EPA's maximum allowable
residual disinfectant concentration of 4 milligrams per liter in tap water
and were conducted at 40 C, which fits well with the cleaning recommendations
of the Soap and Detergent Association. (The association's website says
that dishwater temperatures of less than 33 C, even with sufficient detergent,
are likely to leave a greasy film, while the hottest water most people's
hands can tolerate is about 43 C.)
- Under these conditions, triclosan reacts with free chlorine
to generate more than 50 parts per billion (ppb) of chloroform in the dishwater.
When combined with the other trihalomethanes in the water, the additional
chloroform could easily ratchet up the concentration of total trihalomethanes
to 80 ppb, which is EPA's maximum allowable amount, or higher, Vikesland
- "Since chloroform and other trihalomethanes and
disinfection byproducts are already likely to be present in the tap water,
and since chloroform, the other THMs, and many other [disinfection byproducts]
are highly volatile, there is a very real likelihood that washing dishes
with triclosan-containing liquid could cause additional and troubling significant
exposure to these volatiles through inhalation and potentially through
dermal absorbtion," says Erik D. Olson, senior attorney for the Natural
Resources Defense Council, a nonprofit environmental group. Olson calls
the research "significant."
- Water treatment plants are working hard to keep the levels
of trihalomethanes in tap water below 80 ppb, Vikesland says, noting that
the admissible level has recently decreased from 100 ppb. If there is any
bromide in the water, the level of trihalomethanes produced during dishwashing
is likely to shoot up even higher, he says.
- The research makes clear that it is always wise to wear
gloves when dishwashing, says Doris Day, M.D., an assistant professor of
dermatology at New York University Medical Center. In light of previous
studies showing that the levels of trihalomethanes in people's blood increase
when they shower, the research raises questions about exposures to chloroform
when antimicrobial soaps are used. At this point, however, no one knows
what risk they may pose.
- Vikesland's research also shows that triclosan's reaction
with free chlorine produces a number of chlorinated triclosan intermediates,
including 2,4 dichlorophenol. In the presence of sunlight, these chlorinated
intermediates could be producing dioxins, say McNeill and his colleague,
William Arnold of the University of Minnesota's department of civil engineering.
The two have recently demonstrated that sunlight readily converts triclosan
in river water to produce dioxins (Environ. Toxicol. Chem. 2005, 24, 517ñ525).
But the more highly chlorinated dioxins that could be generated photochemically
from chlorinated triclosan intermediates could be far more toxic, says
- It is unlikely that such dioxins would be generated during
dishwashing even near a window on a sunny day because the glass would screen
out most of the ultraviolet light necessary to produce the dioxin. But
the research suggests that dioxins could be forming near swimming pools
in some situations. "There's triclosan in hand soaps and moisturizers.
[If] someone who has triclosan-containing moisturizer [on jumps] into the
pool Ö they're a potential source for chloroform [and chlorinated
dioxin] formation," Vikesland says. The same is true for a child using
an antimicrobial soap before getting into the pool, McNeill and Arnold
agree. "You could produce a dioxin on the surface of your skin [that]
gets absorbed through the skin," Sedlak adds.
- McNeill and Arnold say that the research also calls for
more detailed studies of whether chlorinated triclosans are being released
from wastewater treatment plants. Because triclosan is widely found in
the environment, chlorinated triclosan could be a source of toxic dioxins
in the environment, says Arnold. Research has already shown that the presence
of triclosan can affect algae populations (Environ. Sci. Technol. 2003,
- Copyright © 2005 American Chemical Society