Drinking water containing a common herbicide could pose a greater public health risk than previously thought because regular municipal monitoring doesn't detect frequent spikes in the chemical's levels, according to a report released Monday by the Natural Resources Defense Council (NRDC).

The NRDC claimed in its report that there were documented spikes in atrazine in the water supplies of Midwestern and Southern towns in agricultural areas, where the herbicide is applied to the vast majority of corn, sorghum and sugar cane fields.

They said atrazine can interfere with the body's hormonal activity and the development of reproductive organs. The Environmental Protection Agency looks at annual average levels of the chemical in drinking-water systems, but the NRDC says this misses spikes likely to occur after rain and springtime application of the herbicide.

"Our biggest concern is early-life-stage development," said NRDC senior scientist Jennifer Sass. "If there's a disruption during that time, it becomes hard-wired into the system. These endocrine disrupters act in the body at extremely low levels. These spikes matter."

Syngenta fired back at the organization, saying that none of the 122 community water systems monitored last year in 10 states where atrazine is used most exceeded the federal standards set for atrazine in drinking water or raw water.

They added that the federal lifetime drinking water standard for atrazine is set at 3 parts per billion — a level containing a 1,000-fold safety factor. The EPA concluded recently that the triazine herbicides — including atrazine — pose "no harm that would result to the U.S. population."

"Atrazine can be occasionally detected in water at extraordinarily low concentrations, but these low levels pose no threat to human health," says Tim Pastoor, principal scientist for Syngenta. "A person could drink thousands of gallons of water containing 3 parts per billion atrazine every day for a lifetime, and still not be affected by atrazine."

Under the Safe Drinking Water Act, municipal water supplies are typically tested for chemicals, including atrazine, four times a year. The EPA considers an annual average atrazine level below 3 parts per billion as safe for human consumption.

According to the NRDC, biweekly data collected by the EPA from 139 municipal water systems found that atrazine was present 90% of the time and that 54 water systems had one-time spikes above 3 parts per billion in 2003 and 2004, according to an analysis by the NRDC. However, even as the NRDC reported spikes, they did not say how far those spikes exceeded EPA-accepted levels.

NRDC scientists and lawyers argue that the EPA's limits are too lenient. It's asking the EPA to step up its atrazine monitoring and make the results public. The group is also encouraging farmers to greatly reduce or end use of the herbicide.

Atrazine recently underwent an up-to-date safety evaluation by the EPA and was re-registered for use in agriculture. In 2006, the EPA looked at all of the triazine herbicides together — atrazine, simazine and propazine — and determined they pose "no harm that would result to the general U.S. population, infants, children or other major identifiable subgroups of consumers."

Syngenta says that tens of thousands of such tests continue to show that atrazine poses no dietary health risk to the general population or to children and infants. They say world-renowned institutions, including the World Health Organization, the National Cancer Institute and EPA, all have studied atrazine and found no health concerns when used as directed.

"Research has proven the positive effect atrazine has on farm production," says Chuck Foresman, senior technical brand manager for Syngenta. "Farmers simply can't meet the increasing demand for corn without controlling the grass and broadleaf weeds that compete with crops for moisture, sunlight and nutrients."

Foresman says atrazine also enhances the performance of other products. He cited a study that showed during the 20-year period from 1986 and 2005, the average corn yield was 5.1% higher with atrazine than without. He adds that in combined data from 236 university corn field trials during that period, atrazine treatments showed an average of 5.7 bushels more per acre than alternative herbicide treatments.

Similar research in sorghum trials in Kansas and Nebraska from 1986 to 1995 showed an 11.3-bushel-per-acre advantage in that crop. And, production experts estimate that the yield advantage in sugar cane ranges from 12% to 50%.

"Yield increases like that are necessary to produce more on limited farmland," Foresman adds. "At the same time, to be successful, growers need to manage their costs."

The U.S. Environment Protection Agency (EPA) estimates that farming without atrazine could cost corn growers $28 per acre due to yield loss and the use of more expensive herbicides.