(NaturalNews) Contamination of drinking water by a common herbicide poses a greater health threat than previously believed, according to a report issued by the nonprofit environmental organization Natural Resources Defense Council (NRDC).The Environmental Protection Agency (EPA) monitors average yearly levels of the popular herbicide atrazine in drinking water supplies, based on four tests per year. But the NRDC notes that levels of the toxin in drinking water regularly spike after heavy rains or during the spring when it is being widely applied, and that the four yearly testings may miss these events. The organization's researchers found several such spikes in its own testing of water supplies in towns in agricultural regions of the South and Midwest."Our biggest concern is early-life-stage development," said Jennifer Sass of the NRDC. "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."Because atrazine is compatible with no-till farming, it is popular among farmers seeking to acquire a "green" label by reducing their carbon footprint. It is known to disrupt the hormonal system, and may cause cancers and menstrual problems in adults. It is considered especially dangerous to the developing reproductive systems of fetuses and children. The chemical has been shown to kill aquatic microorganisms and suppress the immune systems of larger animals, and it can cause limb or reproductive deformities in amphibians at levels as low as 0.1 parts per billion.The EPA has set a threshold of 3 billion parts per billion for permissible atrazine levels, which the NRDC says would be too high even without periodic spikes. The NRDC analysis of 139 different municipal water systems found that 54 of them had a one-time spike higher than 3 parts per billion at some point in 2003 or 2004.Home or municipal carbon filters can remove atrazine from water, but many municipal treatment plants do not use such procedures.Sources for this story include: www.washingtonpost.com