Submitted to: Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 8/12/1994
Publication Date: N/A
Interpretive Summary: Lead-enriched soils are common in areas used for deciduous tree fruit production because of application of lead arsenate insecticides applied between 1910 and 1968. The solubility of the lead in the soil, is a major concern in relation to drinking water. This study determined that adding monocalcium phosphate can reduce the solubility of lead in some soils.
Technical Abstract: Many soils in sites used for tree fruit production before 1968 contain elevated concentrations of lead (Pb) from past use of lead arsenate pesticides. The chemical form of Pb in these soils may influence its bioavailabilty and the need for and type of remediation actions. The competitive chelation method developed at Colorado State University was used to determine the single-ion activity of divalent Pb (Pb2+) in aqueous suspensions of 11 lead arsenate-contaminated soils and, for comparison, three roadside soils enriched with Pb from gasoline. The activity of Pb2+ ranged from 10-9.37 to 10-7.21,consistent with values published elsewhere, and was inversely related to pH. The soils appeared to fall into two solubility groups-one where Pb2+ activity was consistent with control by a Pb-phosphate mineral, possibly Pb5(PO4)3OH or Pb3(PO4)2, and a second group where Pb2+ activity was consistent with control by Pb(OH)2. Soils containing free calcium carbonate occurred in both groups. Adding monocalcium phosphate to two of the soils from the higher Pb solubility group apparently reduced Pb solubility in one soil but had no effect in the second soil. The behavior of the second soil, which had formed in volcanic parent materials, may have been influenced by allophanic mineralogy. The experimental results suggest that Pb solubility in lead arsenate-contaminated soils is not appreciably higher than in soils contaminated by Pb from gasoline. Furthermore,