Quantification, speciation, and impact of arsenic leaching from in-service and disposed CCA-treated wood on the environment.

摘要

Leaching of arsenic from CCA-treated wood structures can result in soil and groundwater contamination and become a major health concern. Arsenic is present as inorganic As(V) in the chemical CCA, which along with inorganic As(III), are generally more toxic than the organoarsenic species. Laboratory leaching experiments where new and weathered CCA-treated wood and CCA-treated wood ash were leached with different solvents were set up to determine the speciation and quantification of arsenic leaching from CCA-treated wood. Two field-scaled experiments, a deck and a lysimeter study, were employed to examine the impact of arsenic leaching from in-service and disposed CCA-treated wood products. Information obtained from these studies were used to develop mathematical models that forecasted disposal quantities and estimated the extent of arsenic leaching over time. Groundwater samples near Florida C&D landfills, presumably containing CCA-treated wood, were also analyzed to determine if arsenic concentrations exceeded natural background levels. Speciation analysis was conducted using HPLC coupled with either HG-AFS or ICP-MS. Laboratory leaching tests showed that both pH and the type of leaching solvent were factors that influenced arsenic leaching. Inorganic As(V) was the predominant species leaching with inorganic As(III) concentrations higher in weathered than new wood. CCA-treated wood ash leached generously more arsenic than unburned wood and organoarsenic species were undetected. All samples surpassed Florida's 0.05-mg/L Groundwater Cleanup Target Level and many exceeded the 5-mg/L TCLP arsenic regulatory limits for distinguishing hazardous wastes. After one year, the average arsenic concentration leaching from the CCA-treated deck was 0.73 mg/L and rainwater infiltrating through the sand below the CCA-treated deck rose from 2 to 18 mug/L. In the lysimeter study, DMAA was the predominant species detected in the control lysimeters, whereas, for the wood monofill, C&D, and MSW lysimeters, it was the inorganic species. The leaching models estimated that by the year 2000, 7,000 tons of arsenic from CCA-treated wood had already been released to Florida soils and that this amount would double by 2040. Arsenic concentrations in groundwater near Florida C&D landfills ranged between 8 and 10 mug/L and all four major arsenic species were detected.