Leaching of Lead and Arsenic in Soils Contaminated with Lead Arsenate Pesticide Residues

摘要

Use of high rates of phosphate fertilizers in orchards contaminated with lead arsenate pesticide residues may influence Pb and As solubility and accelerate or retard translocation of these elements deeper into the soil where they may enter groundwater. To determine the extent of translocation, six Washington orchard soils heavily contaminated with lead arsenate (PbHAsO4) pesticides were sampled. A bulk soil sample was collected from a contaminated apple orchard to determine the influence of soil application of monoammonium phosphate (MAP, NH4H2PO4) and triple superphosphate (TSP, Ca(H2PO4)2) on lead and arsenate leaching. Most of the soil Pb and As was restricted to the upper 40 cm of soil. In all cases there was depletion of Pb and As at the immediate soil surface (0 to 5 cm). Arsenic was depleted relative to Pb in the A horizon and was enriched relative to Pb in the subsoil. Arsenic was apparently more mobile than Pb in all soils surveyed. Laboratory soil columns were amended with MAP or TSP at three P rates and leached using two leaching regimes. Addition of either MAP or TSP increased the amount of As leached from the soil but did not influence leaching of Pb. The amount of water that percolated through the soil influenced the total amount of leached As, the pH, and the salinity. The results indicate that surface-applied Pb and As are mobile in soils contaminated with lead arsenate pesticide residues. Potential for As contamination of shallow groundwater acquifers that lie below contaminated soils therefore exists.