[Pharmwaste] combining pesticides makes them more deadly for fish - article

Tenace, Laurie Laurie.Tenace at dep.state.fl.us
Tue Mar 3 10:45:11 EST 2009


" The findings suggest that the current practice of testing pesticides - one
at a time to see how much is needed to kill a fish - fails to show the true
risks..."



Study: Combining pesticides makes them more deadly for fish 
Common agricultural pesticides that attack the nervous systems of salmon can
turn more deadly when they combine with other pesticides, researchers have
found.
http://seattletimes.nwsource.com/html/localnews/2008804563_aporsalmonpesticid
es.html 
By JEFF BARNARD

AP Environmental Writer

GRANTS PASS, Ore. - 
Common agricultural pesticides that attack the nervous systems of salmon can
turn more deadly when they combine with other pesticides, researchers have
found.

Scientists from the NOAA Fisheries Service and Washington State University
were expecting that the harmful effects would add up as they accumulated in
the water. They were surprised to find a deadly synergy occurred with some
combinations, which made the mix more harmful and at lower levels of exposure
than the sum of the parts.

The study looked at five common pesticides: diazinon, malathion,
chlorpyrifos, carbaryl and carbofuran, all of which suppress an enzyme
necessary for nerves to function properly.

The findings suggest that the current practice of testing pesticides - one at
a time to see how much is needed to kill a fish - fails to show the true
risks, especially for fish protected by the Endangered Species Act, the
authors concluded in the study published Monday in the journal Environmental
Health Perspectives.

"We need to design new research that takes into effect the real-world
situation where pesticides almost always coincide with other pesticides,"
co-author Nathaniel Scholz, a research zoologist at the NOAA Fisheries
Service Northwest Fisheries Science Center, said from Seattle.

Inge Werner, director of the aquatic toxicology laboratory at the University
of California at Davis, was not involved in the study. She said while the
idea was not new, the findings were definitive, even at levels that don't
kill fish outright.

"We may not see the big fish kills out there anymore like we used to," she
said from Davis, Calif. "But the subtle, sublethal effects that basically
render them unfit for survival in the wild are much more important. In
certain areas, pesticides really are a very important factor" in salmon
survival.

Jeffrey Jenkins, professor of environmental and molecular toxicology at
Oregon State University, was not part of the study. He said the study was
well done, but it would take more research to push the U.S. Environmental
Protection Agency to change its pesticide testing standards as they relate to
fish, which are defined by law.

Last year, NOAA Fisheries issued findings under the Endangered Species Act
that diazinon, malathion and chlorpyrifos jeopardize the survival of all 28
species of Pacific salmon listed as threatened or endangered in the West.

The three chemicals, found by the U.S. Geological survey to contaminate
rivers throughout the West, interfere with salmon's sense of smell, making it
harder to avoid predators, locate food and even find their native spawning
streams and reproduce. At higher concentrations, they kill fish outright.

NOAA Fisheries and EPA must evaluate 34 more pesticides by 2012 under terms
of a settlement reached in a lawsuit brought by Northwest Coalition for
Alternatives to Pesticides and others.

In the study, scientists combined the pesticides two at a time at various
concentrations, then exposed juvenile coho salmon in tanks for four days.
Many of the fish died outright.


Fish that survived were killed, and their brains analyzed for the levels of
the enzyme acetylcholinesterase, which allows impulses to move between
neurons in the brain. In every fish, the levels of the enzyme were below the
level considered healthy.

Earlier research found that lower levels of the enzyme affected the ability
of fish to feed and swim, which would affect their ability to survive, Scholz
said.

The researchers suggested that the reason harmful affects of combinations of
chemicals were greater was that they also suppressed another enzyme, which
helps the body rid itself of toxins.

The amounts of the individual pesticides were calculated to have a standard
effect on the fish nervous systems, and in some cases were higher than would
be expected to be seen in the environment, Scholz said. Some combinations
produced effects that added up to the sum of the parts. But as the doses of
the individual pesticides increased, the effects became more synergistic - in
effect multiplying rather than just adding.

The results indicated that similar effects would occur at much lower levels,
and future research will consider just how little exposure is needed to harm
fish, he added.

Another new avenue for research will be how pesticides combine with other
water quality problems, such as warm water, to harm salmon, Scholz said.


Laurie Tenace
Environmental Specialist
Waste Reduction Section
Florida Department of Environmental Protection
2600 Blair Stone Rd., MS 4555
Tallahassee FL 32399-2400
P: 850.245.8759
F: 850.245.8811

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