(Beyond Pesticides, February 16, 2010)
Pyrethroids, among the most widely-used home pesticides, are winding up in California rivers at levels toxic to some stream-dwellers, possibly endangering the food supply of fish and other aquatic animals, according to a study by researchers at the University of California, Berkeley, and Southern Illinois University (SIU). The study, “Urban and Agricultural Sources of Pyrethroid Insecticides to the Sacramento-San Joaquin Delta of California,” in the journal Environmental Science & Technology, is the first published work to document toxic levels in the water column as well as in the sediments at the bottom of streams.
Pyrethroid insecticides, commonly used to kill ants and other insects around the home, have been found in street runoff and in the outflow from sewage treatment plants in the Sacramento, California area. The insecticide ended up in two urban creeks, the San Joaquin River and a 20-mile stretch of the American River, traditionally considered to be one of the cleanest rivers in the region. Although the pyrethroid levels were low, around 10-20 parts per trillion, they were high enough to kill a test organism similar to a small shrimp that is used to assess water safety.
“These indicator organisms are, lab rat’ species that are very sensitive, but if you find something that is toxic to them, it should be a red flag that there could be potential toxicity to resident organisms in the stream,” said study leader Donald P. Weston, Ph.D, UC Berkeley adjunct professor of integrative biology. Fish would not be affected by such low levels, Dr. Weston said, but aquatic larvae that the fish eat, such as the larvae of mayflies, stoneflies and caddisflies, could be, and should be studied.
Dr. Weston first began looking at pyrethroid levels in streams bordering farm fields in 2004, and reported levels in some creek sediments high enough to kill the shrimp-like amphipod, an organism used by the U.S. Environmental Protection Agency as an indicator of the health of freshwater sediment. He subsequently found even higher pyrethroid levels in the sediments of urban streams, contributing to the California Department of Pesticide Regulation’s decision in August 2006 to re-evaluate some 600 pyrethroid products on the market, a process that is still underway.
“This work opens a whole new can of worms and will probably substantially expand that re-evaluation,” Dr. Weston said.
Pyrethroids are synthetic versions of pyrethrin, a natural insecticide found in certain species of chrysanthemum. It initially was introduced on the market as a safer’ alternative to the heavily regulated and highly toxic organophosphates such as chlorpyrifos and diazinon which were banned for homeowner use in 2001 and 2004, respectively. Despite the fact that there are plenty of effective pest control methods that are not nearly as toxic, it is now one of the most popular class of household pesticides, available in the form of powders and sprays to control ants, mosquitoes, fleas, flies, and cockroaches. These high-volume uses of pyrethroid pesticides are cause for concern to consumers because of their link to serious chronic health problems. Synthetic pyrethroids are suspected endocrine disruptors, and have been found lingering in the dust at daycare centers. Pyrethroids are particularly dangerous to aquatic life even at the same concentrations used to fend off mosquitoes. Studies in urban streams have found levels toxic to sensitive “indicator” species in California’s Central Valley as well as in Texas and Illinois. The crustacean Hyalella azteca, for example, is paralyzed and killed at levels of 2 parts per trillion.
The main sources appear to be readily available insecticides applied around the home by the homeowner or by professional pest control firms to control pesky ants, Dr. Weston said. Of the varieties of pyrethroids marketed, however, one — bifenthrin — was found most often in the rivers and creeks in the Sacramento area, and pest control companies in California use four times as much as homeowners do, he said. He noted that in some areas, pest control companies heavily market monthly or bimonthly sprayings outside the home to control ants.
“I question whether most people need routine insecticide treatment of their property, which results in residues on the lawn, in the garden and around the house that, when it rains, go down the storm drains and out into the creeks and rivers,” Dr. Weston said. “Average homeowners, when they hire pest control companies to regularly spray their property to cut down on ants, don’t realize that those same compounds end up in the American River at toxic levels.”
The study found, surprisingly, that pyrethroids were present in effluent from sewage treatment plants at concentrations just high enough to be toxic to the test organisms, but well below levels found in urban runoff. Farm runoff, however, only occasionally contained pyrethroids at toxic levels, although some agricultural runoff did contain toxic levels of organophosphate insecticides.
The new study, conducted with Michael J. Lydy, Ph.D. of SIU in Carbondale and funded by the Surface Water Ambient Monitoring Program of the California Environmental Protection Agency, took place in the Sacramento-San Joaquin Delta area last winter, one of the driest in the past 10 years. As a result, water flow in the American River, which is controlled by dam releases, was at very low levels, and provided little dilution of pyrethroids entering the river in storm runoff. Preliminary tests this season, with water flow twice what it was in 2009, show that “the pyrethroid toxicity we found last year is somewhat diminished, but nevertheless still continuing,” Dr. Weston said.
A study from 2009 also found home pesticide use to be a significant contributor to water pollution leading to fish kills and loss of aquatic specifies diversity. The study found that runoff from rainfall and watering lawns and gardens ends up in municipal storm drains and washes fertilizers, pesticides and other contaminants into rivers, lakes and other bodies of water. Organophosphates and pyrethroid pesticides were found in all water samples taken over a two year period on a weekly, bi-weekly and monthly basis for the study. In addition, a study published in 2008 found pyrethroid contamination in 100 percent of urban streams sampled.
Take Action: To lessen your impact on water pollution and protect your health, avoid using hazardous pesticides by choosing non- and least toxic pest management strategies. For more information on issues related to pesticides and water pollution, see Beyond Pesticides Threatened Waters program page and the Daily News Blog. Visit Beyond Pesticides’ Lawns and Landscapes program page for information on lawn pesticides and their alternatives.