Scientists at the US Department of Energy's Pacific Northwest National Laboratory have developed a material that can remove mercury and other toxic substances from coal burning power-plant wastewater.

According to PNNL, mercury pollution is widely recognised as a growing risk to both the environment and public health. It is estimated that coal-burning power plants contribute about 48 tons of mercury to the United States environment each year. The Centres for Disease Control and Prevention estimate that one in eight women have mercury concentrations in their body's that exceed safety limits.

The US Environmental Protection Agency is currently reconsidering proposed rules on the release of mercury from coal-burning power plant effluents and may impose greater restrictions. Mercury found in liquid effluents comes from water-based processes the facilities use to scrub, capture and collect the toxic material.

PNNL's synthetic material is said to feature a nanoporous ceramic substrate with a specifically tailored pore size and a very high surface area. The surface area of one teaspoon of this substance is equivalent to that of a football field. "This substance has proven to be an effective and voracious tool for absorbing mercury," said Shas Mattigod, lead chemist and PNNL project manager. Pore sizes can be tailored for specific tasks.

The material relies on technology previously developed at PNNL, namely self-assembled monolayers on mesoporous support, or SAMMS. SAMMS integrates a nanoporous silica-based substrate with a method for attaching monolayers, or single layers of densely packed molecules, that can be designed to attract mercury or other toxic substances.

In recent tests at PNNL, a customised version of SAMMS with an affinity for mercury, referred to as thiol-SAMMS, was developed. According to Mattigod, test results revealed mercury-absorbing capabilities that surpassed the developers' expectations.

After three successive treatments, 99.9 percent of the mercury in the simulated wastewater was captured, reducing levels from 145.8 parts per million to 0.04 parts per million. This is below the EPA's discharge limit of 0.2 parts per million.

The mercury-laden SAMMS is also said to have passed Washington State's Dangerous Waste regulatory limit of 0.2 parts per million allowing for safe disposal of the test solution directly to the sewer. Tests have shown that the mercury-laden SAMMS also passed EPA requirements for land disposal.

"We expect this technology will result in huge savings to users who are faced with costly disposal of mercury in the waste stream."

Mattigod added that SAMMS technology can be adapted to target other toxins such as lead, chromium and radionuclides.