Grantee Research Project Results

Final Report: Phytoextraction and Recycling of Arsenic From CCA-Contaminated Soils

EPA Contract Number: 68D03017
Title: Phytoextraction and Recycling of Arsenic From CCA-Contaminated Soils
Investigators: Blaylock, Michael J.
Small Business: Edenspace Systems Corporation
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)

Description:

The overall goal of this Phase I research project was to demonstrate the feasibility of using a recently discovered arsenic (As) hyperaccumulating fern as a cost-effective remediation alternative for chromated copper arsenate (CCA) contaminated soils. More than 70 percent of U.S. arsenic consumption, representing approximately 37 million pounds of As per year, is used to produce CCA, a wood preservative. Weathered lumber in decks, docks, playground equipment, and garden construction can leach significant amounts of As 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 As introduced into populated areas. The existing stock of an estimated 70 billion board feet of CCA-treated wood products, however, will continue to leach As for years to come. At present, there is no cost-effective method to clean As-contaminated soils.

Specific Phase I objectives for Edenspace Systems Corporation were to: (1) determine As bioconcentration by the edenfern in the growth chamber using different soils collected from CCA-contaminated sites, (2) investigate the effect of soil pH and light intensity on As bioconcentration and biomass production of the fern, (3) characterize fern uptake of chromium and conversion in fern roots of Cr (VI) to Cr (III), (4) determine the phytoremediation performance of the edenfern under field conditions at a CCA-contaminated site, and (5) investigate two methods of concentrating and refining recovered As for storage and future recycling.

Summary/Accomplishments (Outputs/Outcomes):

Phase I results established the technical feasibility of the concept, with growth chamber fern As uptake in eight different CCA-contaminated site soils achieving an average frond concentration of up to 28 times the soil concentration without the addition of chelating agents or other soil amendments (see Figure 1). Ferns grown concurrently in CCA-contaminated residential soil in Austin, TX, attained bioconcentration ratios of up to 11. Data on the effect of soil pH and light intensity on As bioconcentration and biomass production of the fern were obtained. Preliminary tests were conducted with two methods of concentrating and refining recovered As for storage and future recycling as an alternative to landfill disposal, with demonstrated recovery rates greater than 70 percent. No Cr(VI) was detected in study soils.

 

Figure 1. Comparison of shoot As concentration to that of the soil As concentration for each project soil. The line depicts the 1:1 line with values above this line indicating successful hyperaccumulation of arsenic.

In absolute terms, average shoot As concentrations as high as 1,700 mg/kg were recorded, with maximum removal of As (product of uptake and biomass yield) at 13 mg of As per fern plant. As two fern plants per pot were used for all soils, As uptake by the ferns can account for a 12 mg/kg decrease in the soil arsenic concentration over a 20-week growth period. This maximal rate translates to approximately 30 mg/kg/year, provided the ferns could be grown perennially. Such a removal rate would enable many As-contaminated sites to meet their target concentration within 1 to 2 years. Biomass measurements ranged between 5.7 and 12.1 g per plant, equating to a biomass yield of 600 to 1,300 kg/ha (0.3 to 0.6 tons/acre), when assuming a plant density of one plant per square foot.

Conclusions:

Phase I results provide a solid foundation for followup field demonstrations and related activities in Phase II. The anticipated result of this research is a demonstrated As phytoextraction technique, accessible to homeowners as well as to environmental professionals, that uses commercially available plants to provide cost-effective remediation of contaminated soils associated with the use of CCA-treated wood products.

Supplemental Keywords:

CCA, chromated copper arsenate, phytoremediation, treated wood, fern, arsenic, As, contaminated soils, pH, phytoextraction, small business, SBIR., RFA, Scientific Discipline, Waste, Toxics, Hazardous, National Recommended Water Quality, Remediation, Chemistry, Environmental Chemistry, Contaminated Sediments, Hazardous Waste, Arsenic, Physics, arsenic mobility, contaminant transport, arsenic transformation, Chromium, redox metabolism, contaminated sediment, phytoextraction, adverse human health affects, chromated copper arsenate, chemical contaminants, soil sediment, processes influencing mobility, sediment transport, human health effects, arsenic exposure