Chemicals derived from flowers may sound harmless, but new research raises concerns about compounds synthesized from chrysanthemums that are used in virtually every household pesticide.
For at least a decade, pyrethroids have been the insecticide of choice for consumers, replacing organophosphate pesticides, which are far more toxic to people and wildlife. But evidence is mounting that the switch to less-toxic pyrethroids has brought its own set of new ecological and human health risks.
About 70 percent of people in the United States have been exposed to pyrethroids, with children facing the highest exposure, according to a study published this month. Although the human health threats are unknown, animal studies have found evidence of damage to neurological, immune and reproductive systems.
In addition, pyrethroids are flowing off yards and gardens, contaminating some streams and rivers at concentrations that can kill small creatures vital to the survival of fish and other aquatic life. Both California and the U.S. Environmental Protection Agency are reevaluating the chemicals because of safety concerns.
“Pyrethroids are obviously a safer alternative to organophosphates, but just because they are safer doesn’t mean they are safe,” said Dana Boyd Barr, a research professor of environmental health at Emory University’s Rollins School of Public Health in Atlanta, Georgia. Barr authored a study that for the first time has measured pyrethroid exposure in the U.S. population.
Pyrethroids are found in more than 3,500 products used inside homes and on crops, yards, and gardens - including lice shampoos, indoor foggers, flea sprays for pets and pesticides to fight ants, wasps, mosquitoes, aphids and spiders. Consumers can identify pyrethroids in products by checking labels for compounds that end in “thrin,” such as bifenthrin, permethrin and cypermethrin.
The compounds are synthetic versions of naturally occurring insecticides called pyrethrins harvested from chrysanthemum flowers. Chemists alter the structure of the pyrethrin molecule to make it more stable in sunlight and to increase its toxicity. The chemicals kill insects by interfering with basic nerve cell functioning. Insects and other invertebrates are highly susceptible to them, while birds and mammals are better able to counteract their effects.
In the new study, 5,046 urine samples collected from U.S. adults and children between 1999 and 2002 were tested for five metabolites of pyrethroid insecticides. Metabolites are the result of the body breaking down a chemical.
Traces of at least one pyrethroid metabolite were found in 75 percent of the people tested in 2001-2002, up from 66 percent in 1999-2000. Children’s concentrations were more than 50 percent higher than the amounts found in adolescents and adults, according to the study by Barr and colleagues published online in Environmental Health Perspectives on Feb. 3.
Children are more highly exposed to pyrethroids because “they spend a lot more time on the floor and have much more hand to mouth activity,” Barr said. “Pyrethroids tend to accumulate in dust or on surface areas in homes because they don’t evaporate easily into the air.” A 2008 study found pyrethroids and their metabolites in vacuum cleaner dust collected from homes and daycare centers in North Carolina and Ohio.