"Combining pesticides makes them more deadly for fish"

This is not surprising to me (and I imagine to a lot of people). And yet it says this was surprising to scientists??? (I'm surprised).

From the Seattletimes:

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...

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...

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

(....and people, perhaps???....)