Phytoextractionand Recycling of Arsenic From CCA-Contaminated Soils

More than 70 percent of U.S. arsenic consumption¿representing approximately 37 million pounds of arsenic per year¿is used to produce chromated copper arsenate (CCA), a wood preservative. Weathered lumber in decks, docks, playground equipment, and garden construction can leach significant amounts of arsenic into soil and water, where it poses health risks to humans and animals. Effective December 31, 2003, the U.S. Environmental Protection Agency will limit the use of CCA to the treatment of wood in forest products, substantially reducing levels of new arsenic introduced into populated areas. The existing stock of CCA-treated wood products, however, will continue to leach arsenic for the next 6 years. At present, there is no cost-effective method to clean arsenic-contaminated soils. This Phase I research project will demonstrate the feasibility of using a recently discovered arsenic-hyperaccumulating fern to provide a cost-effective remediation alternative for CCA-contaminated soils. Preliminary data demonstrate that when grown on an arsenic-contaminated soil, this fern achieves a biomass arsenic concentration more than 200-fold higher than that of any other plant species tested. The fern concentrates arsenic in its fronds at levels more than 50 times the soil concentration without the addition of chelating agents or other soil amendments. In a growth chamber study for this project, Edenspace Systems Corporation will evaluate arsenic removal by the fern from 12 different CCA-contaminated site soils, assessing the effects of soil pH and light intensity on the efficiency of arsenic phytoextraction. A small field demonstration will be conducted concurrently at a CCA-contaminated field site to demonstrate arsenic uptake and biomass production. The project also will explore two methods of concentrating and refining recovered arsenic for storage and future recycling, as well as the ability of the fern to reduce chromium (VI) in the CCA soils to the insoluble and less hazardous chromium (III) form. Successful Phase I results will lay the foundation for Phase II demonstration of the technique in yards, gardens, and playgrounds, together with a recycling demonstration of recovered arsenic by one or more of four major U.S. chemical manufacturers of CCA products. The anticipated result of this research will be a demonstrated arsenic phytoextraction technique, accessible to homeowners as well as environmental professionals, that uses commercially available plants to provide cost-effective remediation of contaminated soils associated with the use of CCA-treated wood products.