Thermally induced changes in metal solubility of contaminated soils is linked to mineral recrystallization and organic matter transformations.
Soils are biogeochemical systems under continual modification by biological and chemical processes. Trace element solid-solution partitioning is thus influenced by long-term changes to these solid phases. We study Pb, Cd, Zn, and Cu solution speciation and solid-phase dynamics in two soils of volcanic origin (Te Akatea and Egmont, high in noncrystalline aluminosilicates), an oxisol from Brazil (Oxisol, high in oxides of Al and Fe), and several sludge-treated soils (labeled NYS soils, high in organic materials). Total soluble (by ICP) and labile (by ASV) concentrations of Pb, Cd, Zn, and Cu were determined after incubation of the soils for about 1.5 yr at room (23 degrees C) and elevated (70 degrees C) temperatures. Changes occurring to the solid phases were monitored by FTIR and extraction with oxalate and pyrophosphate. It is shown that induced hydrolysis or decomposition of organic materials in soils results in increases in both labile and total soluble concentrations of Pb, Cd, Cu, and Zn in solution. Labile and total soluble concentrations of Cu and Zn increase concomitantly with dissolved organic carbon (DOC); the nonlabile soluble fraction also increases with increasing DOC. Similarly, the concentration of Cd and Pb in solution increases with increasing DOC; however, most soluble Cd and Pb is asv-labile. Only in the Egmont soil (mineralogy dominated by proto-imogolite allophane) was reduced Pb solubility observed after prolonged equilibration and heating. Lead solubility increased after partial crystallization of amorphous minerals in the Te Akatea and the Oxisol. Thus, for most of the metal-soil systems studied, prolonged thermal treatment at 70 degrees C increased total soluble and asv-labile metals, suggesting that aging effects on metals in contaminated soils could release metals to labile forms in some cases.
Martínez
C E
CE
Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, USA. cem20@cornell.edu
Jacobson
A
A
McBride
M B
MB
D019216:Metals, Heavy / Q000737:chemistry*; D009930:Organic Chemicals; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D013696:Temperature
D019216:Metals, Heavy; D009930:Organic Chemicals; D012989:Soil Pollutants