USGS Finds Atrazine Herbicide Adversely Affects Fish Reproduction

(Beyond Pesticides, June 1, 2010)

Atrazine, one of the most commonly used herbicides in the world, has been shown to affect reproduction of fish at concentrations below U.S. Environmental Protection Agency’s (EPA) water-quality guideline, according to a new U.S. Geological Survey (USGS) study. “Concentrations of atrazine commonly found in agricultural streams and rivers caused reduced reproduction and spawning, as well as tissue abnormalities in laboratory studies with fish,” said USGS scientist Donald Tillitt, Ph.D., the lead author of the study, “Atrazine Reduces Reproduction in Fathead Minnow (Pimephales promelas)” published in Aquatic Toxicology.

Fathead minnows were exposed to atrazine at the USGS Columbia Environmental Research Center in Columbia, Missouri, and observed for effects on egg production, tissue abnormalities and hormone levels. Fish were exposed to concentrations ranging from zero to 50 micrograms per liter of atrazine for up to 30 days. All tested levels of exposure are less than the EPA Office of Pesticides Aquatic Life Benchmark of 65 micrograms per liter for chronic exposure of fish.

Study results show that normal reproductive cycling was disrupted by atrazine and fish did not spawn as much or as well when exposed to atrazine. Researchers found that total egg production was lower in all atrazine-exposed fish, as compared to the non-exposed fish, within 17 to 20 days of exposure. In addition, atrazine-exposed fish spawned less and there were abnormalities in reproductive tissues of both males and females.

Atrazine is one of the most commonly used herbicides in the world and is used on most corn, sugarcane and sorghum acreage in the United States; and can also be used on golf courses and residential lawns. In the U.S. alone, 60-80 million pounds are used per year to stop pre- and post-emergence broadleaf and annual grassy weeds, and is generally applied in the spring. Thus, noted Dr. Tillitt, atrazine concentrations are greatest in streams during the spring, when most fish in North America are attempting to reproduce.

The herbicide is a common contaminant of municipal drinking water because it does not cling to soil particles and washes easily with the rain into surface and ground water. In previous studies, the USGS found atrazine in approximately 75 percent of stream waters and 40 percent of all groundwater samples from agricultural areas tested.

Atrazine has been linked to a myriad of health problems in humans including disruption of hormone activity, low sperm quality, low birth weight, impaired immune system function and cancer. A 2009 study by Paul Winchester, PhD, linked birth defects to time of conception, with the great impact on children conceived when concentrations of atrazine and other pesticides were the highest in the local drinking water.

Previous studies show that atrazine harms the immune, hormone, and reproductive systems of aquatic animals. For example, a study of fish and amphibians exposed to atrazine exhibited hermaphrodism, creatures with both male and female sexual characteristics. Male frogs exposed to atrazine concentrations within federal standards can become so completely female that they can mate and lay viable eggs. Other research by Tyrone Hayes, Ph.D. and others demonstrates that exposure to doses of atrazine as small as 0.1 parts per billion, turns tadpoles into hermaphrodites. In yet another study, a mixture of small amounts of ten of the most commonly used pesticides, including atrazine, was found to kill 99 percent of leopard frog tadpoles.

The results of this new study add an important ecological perspective to findings on atrazine concentrations in streams reported by the USGS National Water-Quality Assessment (NAWQA) Program, as well as others, and highlights the potential risks to aquatic species of this high-use chemical, Dr. Tillitt said.

“Results of studies over the past 20 years show that atrazine is the most frequently detected pesticide in agricultural streams and rivers nationwide, and particularly in the Corn Belt states,” according to Robert Gilliom, Chief of the NAWQA Pesticide National Synthesis Project. “Atrazine concentration data for Corn Belt streams and rivers show that 21-day average concentrations, similar to the exposure conditions studied by Dr. Tillitt, exceeded levels found to affect fish reproduction for most sites and years sampled.”

In 1991, Germany and Italy banned the use of atrazine. The European Union banned atrazine in 2004, after repeated testing found the herbicide in drinking water supplies, and health officials were unable to find sufficient evidence that the chemical is safe. In much of Europe the burden of proof falls on the pesticide manufacturer to prove it is safe, unlike in the U.S. where EPA has assumed the burden of proving a pesticide does not meet acceptable risk standards before taking regulatory action.

On April 22, 2010, U.S.
Representative Keith Ellison (D-MN) introduced H.R.5124, legislation to prohibit the use, production, sale, importation, or exportation of any pesticide containing atrazine.