The U.S. Environmental Protection Agency Tuesday issued guidance about how public water systems can monitor and sample for the contaminant hexavalent chromium.

The agency said the recommendations are in response to emerging scientific evidence that hexavalent chromium, also known as chromium-6, could pose health concerns if consumed over long periods of time, the EPA said in a release.

EPA data indicate no public water systems are violating the standard, officials said. The agency regularly re-evaluates drinking-water standards and, based on new science on chromium-6, has begun a comprehensive review of the contaminant's health effects.

"Protecting public health is EPA's top priority. As we continue to learn more about the potential risks of exposure to chromium-6, we will work closely with states and local officials to ensure the safety of America's drinking water supply," EPA Administrator Lisa Jackson said. "This action is another step forward in understanding the problem and working towards a solution that is based on the best available science and the law."

The enhanced monitoring guidance offers recommendations on where the systems should collect samples and collection frequency, as well as analytical methods for laboratory testing, the EPA said. Systems conducting enhanced monitoring can better inform their customers about any presence of chromium-6 in their drinking water and assess the effectiveness of existing treatment on chromium-6 levels in drinking water.

When the human health assessment is finalized in 2011, the agency will review the conclusions and consider relevant information to determine whether a new standard must be set, the EPA said.