Jay Gan and his group at UC Riverside are seeing pyrethroids in almost every stream where people have lived in California.

In the 1990s, problems were discovered from the use of organophosphate pesticides. These were banned and pyrethroids, synthetic pesticides that chemically mimic natural pyrethrins found in chrysanthemums, have taken their place. They are selectively toxic in the environment and were purported to be a safer replacement for organophospates. Now, there are problems with pyrethroids commonly in use, such as diazinon.

Jay Gan, Professor of Environmental Chemistry at UC Riverside, and his research group are trying to understand the fate and effects of pyrethroids in the environment, particularly with water quality.

The use of pyrethroids has picked up since the end of the 1990s. Urban areas are the dominant source. "If you buy something at Home Depot to kill ants," said Gan, "9 out of 10 products are pyrethroids." Gan said these chemicals are poorly regulated.

Pyrethroids have hydrophobic properties - once they get into streams, they attach to particles and accumulate in biota. "They are designed to kill insects, but unfortunately we have insects in the water," explained Gan. Aquatic invertebrates are often killed as a result of pyrethroid contamination in streams. The hydrophobic nature and high levels of aquatic toxicity of pyrethroids make these chemicals very important to study, especially their impact on aquatic ecosystems.

Pyrethroids are designed to kill insects in the home, but they often end up in urban streams wiping out the aquatic invertebrates.

Gan and his research group are seeing these chemicals show up in almost every stream where people have lived in California. For baseline levels from uncontaminated streams, Gan has had to ask his students to use their connections to get sediments from streams in other states like Oregon.

In 2007 Gan's group became involved in a statewide project supported by CalFed to monitor pyrethroids from residential runoff. "Storms can really flush the chemicals out from the residences into the waterways," said Gan. He reported that they are seeing pyrethroids in all of their samples.

Hydrophobic chemicals like pyrethroids are compartmentalized into soil, sediment and water. Before 10 years ago, there were no good techniques for measuring these chemicals. Gan's research will help us understand how these chemicals cause toxic effects in the environment. "Ideally from the regulatory perspective," said Gan, "we can hopefully set limits and revise chemical monitoring methods."

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