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From July 28, 2006                                                                                                        

Research Shows Pesticide Bans Alone May Lead to New Problems
(Beyond Pesticides, July 28, 2006) Environmentalists, while pleased when toxic pesticides are taken off the market, have long warned that pesticide bans without promotion of non- and least toxic pest management strategies may lead to substitution with other toxic pesticides. On July 26, 2006, Environmental Science and Technology (ES&T) Online reported that since the reduction in residential organophosphate insecticide uses in the early 2000’s, has led to an increase in pesticides formulated with the synergist piperonyl butoxide (PBO), a chemical added to increase the potency and stability of certain pesticides. The concern is that PBO, which is commonly formulated with natural pyrethrum and synthetic pyrethroid insecticides, will react with pesticide residues, drift and runoff already present in the environment, increasing the toxicity and breakdown of these chemicals. The combination of pyrethroids and PBO is also commonly used by communities for mosquito control.

In May 2004, Don Weston, Ph.D., an adjunct professor of ecotoxicology at the University of California, Berkeley, found toxic levels of pyrethroids in creeks flowing through Sacramento, CA. Dr. Weston’s latest paper, published today on ES&T’s Research ASAP website, examines how piperonyl butoxide (PBO) increases the toxicity of these insecticides that are bound up in stream sediments. Although pyrethroids are less acutely toxic to humans than the organophosphates that they have replaced in consumer insecticides, many are linked to chronic effects such as endocrine disruption, and they have not adequately been studied for their impacts on the environment, especially to aquatic invertebrates.

According to ES&T, Dr. Weston’s interest in the environmental effects of PBO was piqued in the summer of 2005 when Sacramento County officials began an aerial spraying program for mosquitoes, to combat West Nile virus. The pesticide was a mix of 60% PBO and 6% pyrethrins. Pyrethrins are natural insecticides produced by certain species of the chrysanthemum plant, and pyrethroids are their synthetic counterparts. Weston wanted to know what would happen when the PBO washed off city streets and into the local creeks where he had already found high levels of pyrethroids. “I felt it was an opportunity that could not be passed up,” he told ES&T, noting that, because of health concerns, California officials rarely conduct aerial spraying anymore. Plus, nobody had ever examined how a pesticide synergist might interact with legacy pesticides.

Dr. Weston found widespread occurrence of PBO at concentrations of up to 4 ppb. Further research showed that this concentration of PBO found that adding the PBO doubled the mortality rate of hyalella, a small bottom-dwelling crustacean. The interaction between synergists like PBO and pesticides already in the creek is something that EPA has not addressed in its regulations.

ES&T reported that Dr. Weston’s coauthor, Michael Lydy, an associate professor of zoology at Southern Illinois University, Carbondale, believes the problem of pesticide synergists may be widespread. “We know that DDT is still at high concentrations in sediments,” he says. “It may also synergize as well.” Dr. Lydy says that he is now applying for grants to study other U.S. streams.

The new study “underscores the complexity of pesticide regulation,” says the director of California’s Department of Pesticide Regulation, Mary-Ann Warmerdam. She says that California must work with local water boards and pesticide manufacturers to protect the environment. To do so, California is beginning a reevaluation of 600 pyrethroid products. The state is one of the largest U.S. markets for pyrethroids, and their use there has climbed in recent years.

TAKE ACTION: Write to EPA Admintstrator Stephen Johnson and encourage EPA to take a serious look at the potential imapacts of PBO and other pesticide synergists. Let the agency know about your concerns posed by the potential interaction of PBO and pesticide residues in the environment. Include a link to Dr. Weston's latest study.