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Title: EFFECT OF LIME, PHOSPHORUS AND IRON ON LEAD AND ARSENIC SOLUBILITY IN LEAD-ARSENATE CONTAMINATED ORCHARD SOILS

Author
item Codling, Eton
item Dao, Thanh

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2006
Publication Date: 4/15/2007
Citation: Codling, E.E., Dao, T.H. 2007. Effect of lime, phosphorus and iron on lead and arsenic solubility in lead-arsenate contaminated orchard soils. Communications in Soil Science and Plant Analysis. 38:903-919.

Interpretive Summary: Lead arsenate was used as pesticide in orchards for several years. There are concerns that arsenic and lead will become solubilized when orchard soils are used for other purposes. Chemical stabilization such as phosphorus to reduce Pb solubility in Pb contaminated soils has been investigated as a possible method for Pb remediation. The objectives of this study were to determine the effectiveness of calcium carbonate (lime), phosphate and iron on reducing the solubility of arsenic and lead in lead arsenate soils. Two orchard soils, Thurmont and Burch, were amended with calcium carbonate (CaCO3), iron (Fe) and phosphorus (P) and incubated for 16 weeks at 26oC. Soil pH in the un-limed soil increased with P and Fe application. There was a slight reduction or no change in pH when P was added to the limed soils. Phosphorus application significantly increased electrical conductivity in both soils. Water extractable arsenic concentration increased with addition of P and Fe +P treatments. However, As concentration for the -lime + Fe +P treatment was more than 50 % lower than the 'lime +P treatment. The P and Fe +P treatments increased water extractable Pb levels compared to the +lime 'Fe -P treatment. The results from this experiment suggested that the solubility of As and Pb were controlled not only by pH, Fe and P, but possible also by organic matter, which require further study.

Technical Abstract: Lead arsenate was an effective insecticide used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated levels of lead and arsenic in these orchard soils. There are concerns that arsenic and lead will become solubilized when these soils are used for other purposes. Soil types and properties control the solubility and mobility of lead and arsenic in soils. In situ chemical stabilization such as the use of phosphorus to Pb solubility in Pb contaminated soils has been investigated as a possible method of remediating these soils. The objectives of this study were to determine the effectiveness of calcium carbonate (lime), phosphate and iron on reducing the solubility of arsenic and lead in lead arsenate soils. Two orchard soils, Thurmont and Burch, were amended with calcium carbonate (CaCO3), iron (Fe) and phosphorus (P) and incubated for 16 weeks at 26oC. Soil pH in the un-limed soil increased with P and Fe application. There was a slight reduction or no change in pH when P was added to the limed soils. Phosphorus application significantly increased electrical conductivity in both soils. Water extractable arsenic concentration increased with addition of P and Fe +P treatments. However, As concentration for the -lime +Fe +P treatment was more than 50 % lower than the 'lime +P treatment. The P and (Fe +P) treatments increased water extractable Pb levels to 7 and 34 mg kg-1, respectively, compared to the +lime 'Fe -P treatment. The results from this experiment suggested that the solubility of As and Pb were controlled not only by pH, Fe and P, but possible organic matter, which require further study.