Upswing in Lesser Used, but More Potent Pesticides in California's Central Valley

[Use and Toxicity of Pyrethroid Pesticides in the Central Valley, California, USA, Environmental Toxicology and Chemistry] 2005; Vol. 24 (4);966-972

Newswise — In California alone, 360 metric tons of pyrethroid pesticides are used annually. University of California-Berkeley researchers have conducted a study to determine the harmful effects of this class of pesticides on aquatic organisms through sediment residues. What they have found is a trend toward using newer compounds that can be more toxic to aquatic life. The study appears in the April issue of Environmental Toxicology and Chemistry.

Increased monitoring of organophosphates resulted in a call for decreased use of these once popular pesticides. This may have only allowed for them to be replaced with pyrethroids. Peaking in 1993, pyrethroid use in the state's agricultural system declined in the 1990s but has shown a 25% increase in the past few years. Of the five pyrethroids used in 1993, permethrin accounted for 60%. In 2002, the number of pyrethroid compounds in use doubled to 10, but permethrin declined to 45% of the total. Newer compounds were found to be 20 times more toxic than permethrin.

The team of researchers studied six pyrethroids in three sediments taken from California's Central Valley, where two-thirds of the state's cropland is found. Study results showed acute toxicity and growth impairment in the amphipod Hyalella azteca, a sensitive test species. Animal biomass was roughly 38% below that of the control group when exposed to pyrethroid levels that were one-third to one-half of the lethal concentration. Except for permethrin, most pyrethroids would be acutely toxic to H. azteca at concentrations only slightly above detection limits. The six compounds tested in order of decreasing toxicity were bifenthrin, lambda-cyhalothrin, deltamethrin, esfenvalerate, cyfluthrin and permethrin.

Little research exists on the use and toxicity of pyrethroids and their prevalence in sediments despite the finding that sediments are likely the primary reservoir for environmental residues—not the dissolved phase as in previous studies. With increasing use of pyrethroids in agriculture, residences and commercial pest control, further study of sediment-associated residues is necessary to determine their ecological impact.

The study's authors are Erin L. Amweg, Donald P. Weston and Nicole M. Ureda of the Department of Integrative Biology at the University of California-Berkeley.

To read the entire study, click here: http://www.allenpress.com/pdf/entc_24_414_966_972.pdf

Environmental Toxicology and Chemistry is a monthly journal of the Society of Environmental Toxicology and Chemistry (SETAC). For more information, visit http://www.setac.org.