Wednesday November 11, 2008 (foodconsumer.org) -- A new study suggests that pesticides can pose a serious threat to the environment and possibly human health when used in combination in agricultural products at even levels the EPA allows although they may not cause any harm when used individually.

The study led by researchers from the University of Pittsburgh found that concentrations of 10 most commonly used pesticides that fell within EPA safe-exposure levels when combined killed 99 percent leopard frog tadpoles.

Amphibian populations have been on the decline while the number of deformed frogs has been seen to increase in states like Illinois and Pennsylvania.

For the study published Nov. 11 in the online edition of "Oecologia", Rick Relyea and colleagues tested five insecticides-carbaryl, chlorpyrifos, diazinon, endosulfan, and malathion-and five herbicides-acetochlor, atrazine, glyphosate, metolachlor, and 2,4-D in four preparations.

The researchers found a mixture of all 10 chemicals killed 99 percent of leopard frog tadpoles as did the insecticide only mixture. The herbicide mix had no effect on the tadpoles.

They also found that Endosulfan - a neurotoxin banned in several nations but still used extensively in the U.S. agriculture - was more deadly to leopard frog tadpoles than previous thought. This pesticide when used alone killed 84 percent of the leopard frogs.

The findings are alarming because current regulations from the U.S. Environmental Protection Agency (EPA) did not require amphibian testing, Relyea said.  This chemical is most lethal among the tested pesticides.

"Endosulfan appears to be about 1,000-times more lethal to amphibians than other pesticides that we have examined," Relyea said. "Unfortunately, pesticide regulations do not require amphibian testing, so very little is known about endosulfan's impact on amphibians, despite being sprayed in the environment for more than five decades."

For most of the pesticides, the concentration used in the study was far below the human-lifetime-exposure levels set by the EPA and also fell short of the maximum concentrations found in natural bodies of water.

The study suggests that the potential harm by pesticides should be considered when they are used in combination, but not individually.

Many people may not know this, but multiple pesticides have already been detected in many types of fruits and vegetables.  

According to the Environmental Working Group, the data from the US government show that apple can contain more than 30 types of pesticides.   Although, the pesticides individually may not pose too much of a risk, the risk from these pesticides in combination remain unknown.

Those who want to avoid as much as of pesticides may want to consider avoiding certain produce. The conventionally grown fruits and vegetables that contain highest levels of pesticides include peaches, apples, sweet bell peppers, celery, nectarines, strawberries, cherries, lettuce, imported grapes, pears, spinach, potatoes, carrots, green beans, hot peppers, cucumbers, raspberries, plums, oranges, and domestic grapes according to the EWG.

But the fruits and vegetables with lowest concentrations of pesticides include broccoli, eggplant, cabbage, banana, kiwi, asparagus, sweet peas (frozen), mango, pineapple, sweet corn (frozen), avocado and onion , according to foodnews.org, a website of the EWG .