Arsenic, chromium, and copper leaching from CCA-treated wood

Abstract

This study was conducted to determine the potential risks of arsenic, chromium, and copper from the disposal of chromated copper arsenate (CCA)-treated wood when its service life ends. The study consisted of batch leaching tests and lysimeter tests. The TCLP and WET were conducted in batch tests of CCA-treated wood and ash burned from CCA-treated wood. A total of six 2-meter high and 20.32-cm in diameter lysimeters were prepared for the lysimeter test: two lysimeters simulated wood monofills, two simulated construction and demolition (C&D debris landfills, and two simulated MSW landfills. Each set of two lysimeters was identical except for the wood components, which were CCA-treated wood and untreated wood. All lysimeters were fed with simulated rainfall during the rainy season. The quantity of leachate generated from each lysimeter was measured daily and the leachate characteristics were analyzed weekly. The experiment was conducted over a period of six months. The results from the batch leaching tests showed that two of the five wood samples from the TCLP test and three of five wood samples from the WET test leached out arsenic in levels that exceeded the TC and STLC concentration of 5 mg/L. In addition, the leaching of all metals found in ash from burned CCA-treated wood exceeded the TC and STLC limits (i.e., the TC and STLC limits are 5 mg/L for As and Cr, and the STLC limit for Cu is 25 mg/L). The lysimeter study results showed that leachates generated from the CCA-treated wood monofill lysimeters contained significantly high concentrations of Cr, Cu, and As, compared with those of the other lysimeters. The highest average concentrations of Cr, Cu, and As were investigated in the monofill of the CCA-treated wood lysimeter, followed by C&D debris with CCA-treated wood lysimeter and MSW with CCA-treated wood lysimeter, respectively (except for As, for which the concentration in the C&D debris lysimeter was lower than that of the MSW lysimeter). In this study, amounts equal to 10 times the regulated limits listed in the Groundwater Standards for Drinking Purposes in Thailand from the Notification of the Ministry of Industry were used as the criteria to evaluate the potential risks to humans and the environment. It was found that the As concentrations in the generated leachate from all three experimental lysimeters were higher than the criterion of 0.5 mg/L. On the other hand, the average concentrations of Cr and Cu in the leachates from all lysimeter were less than the criteria of 20 and 15 mg/L, respectively. These results clearly illustrate that the appropriate disposal of CCA-treated woods necessitates the appropriate handling of arsenic. It can be concluded that the disposal of CCA-treated wood in a wood monofill, an unlined C&D landfill, or a MSW landfill could result in groundwater contamination.