FATE AND BEHAVIOR OF METAL (LOID) CONTAMINANTS IN AN ORGANIC MATTER-RICH SHOOTING RANGE SOIL: IMPLICATION OF REMEDIATION

摘要

This study investigates the fate and behavior of Pb, Cu, Sb, and As in a shooting range soil. The soil samples were collected from the surface (0-15cm) and the subsurface (15-40cm and 40- 55cm) from the impact area behind a firing position. Optical microscopy images indicate significant amounts of corroded bullet fragment and organic wood chips in the surface soil. Analysis by XRPD and SEM-EDS shows that metallic Pb has been transformed into lead oxides (litharge PbO and massicot PbO) and lead carbonates (hydrocerussite Pb{sub}3(CO{sub}3){sub}2(OH){sub}2, cerussite PbCO{sub}3, and plumbonacrite Pb{sub}5(CO{sub}3){sub}3O(OH){sub}2). By employing Rietveld refinement it was found that the surface soil contains 14.1% metallic Pb, 17.9% hydrocerussite, 5.2% plumbonacrite, 5.9% litharge, and 3.9% massicot on a dry weight basis. As a result, the shooting range is extremely contaminated with as high as 39.7% Pb. Metallic Cu appears inactive since no secondary minerals were found at the surface soil. Although Cu concentration in the contaminated soil is higher than the uncontaminated soil, it is still well below Cu Total Threshold Limit Concentrations (TTLC) of 2,500mg/kg. As and Sb were found to be 1,057mg/kg and 845mg/kg respectively, thus exceeding the TTLC of 500mg/kg for As and Sb. The high soil pH coupled with high organic carbon content probably caused metal downward migration, especially for Pb, since 4,153mg Pb/kg was observed at a depth of 55cm. More than 60% of Pb is concentrated in the soil coarse (>0.425mm) fraction, which makes soil clean-up possible by means of soil physical washing. The concentrations of Pb, As, and Sb in the TCLP extracts which are 8,869mg/L, 6.72mg/L, and 6.42mg/L respectively, are well above the USEPA non-hazardous regulatory limits of 5mg/L. Overall, the soil is greatly contaminated with Pb. Moreover, Sb and As should be also of environmental concern when the loading of bullets in the soil is high enough. Copper contamination can be considered negligible in shooting range soils. Application of organic matter as a cover to prevent the range soil erosion is questionable from the view of the environmental risk, since it appears to enhance Pb leaching and downward mobility.