http://pubs.acs.org/subscribe/journals/esthag-w/2005/oct/science/pt_pyrethroids.html
October 26, 2005
Science News
Household pesticides are poisoning city
creeks
Although safer for humans, pyrethroid
insecticides pose unforeseen dangers to the environment.
By PAUL D. THACKER
Researchers
suspect that pyrethroids bind to small bits of dirt that
wash off lawns and into nearby streams.
|
When Don Weston, an adjunct professor of ecotoxicology at the
University of California, Berkeley, checked streams in a suburban
neighborhood outside Sacramento, Calif., he found sections devoid
of Hyalella azteca, a small bottom-dwelling crustacean that the
U.S. EPA happens to use to test for toxicity in sediments. In
a study recently posted to ES&T’s Research ASAP website
(es0506354), Weston and his co-workers report that the sediment
from these streams contains toxic levels of pyrethroids, a class
of insecticides found in household sprays and lawn care products.
These findings have caught the attention of EPA, which is now
in the process of reregistering these insecticides.
Although they have been on the market for decades, pyrethroids
have only dominated the popular garden insecticide market in recent
years (see chart). This began after 2000, when EPA reached agreements
with pesticide manufacturers to start phasing out many residential
uses of organophosphates, a class of insecticides that has troubling
health risks for humans. Although substantially safer for humans
than organophosphates, pyrethoids were never properly tested to
see whether they pose an environmental risk, say experts.
Chart courtesy Of Don Weston
Data Source: California Department Of Pesticide Regulation
Pyrethroid use has increased in recent years as more dangerous
insecticides have been banned for residential application.
This chart only shows numbers for professional treatments
and does not list applications by homeowners. Permethrin is
the least toxic member of the pyrethroids. |
Data Source: California Department Of
Pesticide Regulation
Pyrethroid use has increased in recent years as more dangerous
insecticides have been banned for residential application. This
chart only shows numbers for professional treatments and does
not list applications by homeowners. Permethrin is the least toxic
member of the pyrethroids.
“These are the products you find on the shelves that end
in ‘thrin’,” says Weston. Although these products
are commonly found on the shelves of hardware stores and garden
centers, he says, the data on their environmental toxicity are
sparse. “These compounds have been around for 20 years,
and nowhere in the literature was there any information on what
was dangerous to [some] standard testing species,” he points
out.
Weston says that other than the U.S. Geological Survey, which
checks for permethrin as part of its extensive monitoring program
for pesticides, his group is the only one that has monitored these
compounds in the environment. Westin adds that his group’s
other studies have found that permethrin is the least toxic compound
of the pyrethroid group.
In earlier research, Weston’s group discovered high concentrations
of pyrethroids in creeks that pass through agricultural land (Environ.
Sci. Technol. 2004, 38, 2752–2759). In the new study, they
descended on Roseville, a classic suburban California community
that is completely surrounded by houses and receives no water
runoff from industry or agriculture.
“We found [pyrethroids] in every one of our samples, not
always at toxic levels, and in about half of our samples they
caused total or near-total mortality [to H. azteca],” Weston
says.
To calculate toxicity, Weston exposed the crustaceans to sediments
collected from 21 sites around Roseville. After 10 days, samples
from 9 sites had killed more than 90% of the test animals. Analysis
of these sediments for 28 pesticides, including 7 pyrethroids,
found a correlation between H. azteca mortality and high levels
of pyrethroids. In fact, one of the pyrethroids,
bifenthrin, was found at levels about 15 times higher than those
reported in areas of California with intensive agriculture.
Reported toxicity data are lacking because companies were never
required to submit all possible environmental impacts of pyrethroids
to EPA, says Kelly Moran, president of TDC Environmental, a consulting
company for many California water-quality agencies. Industry did
test these insecticides for toxicity to fish, but the results
are probably not very useful because pyrethroids do not readily
dissolve in water, she adds. Instead, they quickly bind to dirt
and other surfaces.
EPA is conducting a reregistration
for pyrethroid insecticides, as required by the 1996 Food Quality
Protection Act, says Bill Jordan with EPA’s Office of Pesticide
Programs. A manufacturer seeking to register a new pesticide or
reregister an existing one is required to demonstrate safety to
EPA or meet the statutory safety requirement, Jordan adds.
When Jordan was asked to comment on Weston’s paper, press
officer Eryn Witcher broke into the interview and steered the
discussion away from Weston’s findings. However, another
EPA official later agreed to speak with ES&T. The official
refused to be identified because EPA had sent out an email in
early October that instructed agency staff not to discuss pyrethroids
with the press. The official explained that although pyrethroid
insecticides have been sold for decades, EPA did not have sediment
toxicity data on this class of compounds until industry submitted
the data just last month.
“You’ve got a compound that is now taking over the
market,” says the official. “Mammals and birds can
quickly break it down, but for fish and invertebrates, it’s
quite toxic.”
Regulatory concern
Given these new data, limits will probably be placed on pyrethroid
applications, says the EPA source. The official added that because
the compounds bind so tightly to particles, one way to protect
waterways would be to prevent erosion in areas that have been
sprayed with insecticides. This comment was echoed by Moran, who
says that EPA may move to require new labeling on products to
reduce the rate or frequency of application.
Another strategy to limit the poisoning of streams would be to
require buffer zones around areas where pesticides are sprayed.
Weston says that creeks probably become polluted when small particles
wash off a lawn that was fertilized with a product containing
an insecticide or when heavy rains wash contaminated dirt down
a street and into a storm drain that runs directly into a creek.
“Legally, the city of Roseville is responsible to ensure
that the water in its creek is not polluted,” says Moran.
“But they don’t have control over what is sold in
stores, and they can’t prevent the use of pesticides.”
