Effects of Lime, Phosphorus and iron amended Orchard Soils on In Vitro, Water and 1 N HNO3 Extractable Lead.
Eton E. Codling, USA-ARS, 10300 Baltimore Ave, Beltsville, MD 20705
There are public health concerns about the conversion of old orchard land, with a history of lead arsenate application for urban use. Amendments such as phosphorus and iron have been shown to be effective in reducing water-extractable lead from soils contaminated from lead paint and leaded gasoline. A laboratory study was established to test the effects of lime, phosphorus and iron amendments on the bioaccessibility of Pb in two orchard soils, Thurmont and Burch, with histories of lead arsenate application. calcium carbonate at the rates of 1.0 and 1.5 g kg-1 were used to treat Thurmont and Burch soils, respectively. One percent Fe [as Fe (OH)3] and 43.9 g kg-1 P (as KH2PO4) were added to the soils. Each treatment was replicated three times and incubated moist for 60 weeks. Samples were taken at 2, 16 and 60 weeks for pH and water-extractable Pb; in-vitro Pb and 1 N HNO3-extractable Pb were determined only in the samples taken at 60 weeks. The – lime + Fe +P treatment increased soil pH from 4.16 to 6.05 and from 5.08 to 7.4 in the Thurmont and Burch soils, respectively. Iron + P application increased water-extractable Pb in both soils. This increase may have resulted from strong affinity of iron for phosphate which releases Pb in solution. The P + Fe treatments reduced in-vitro Pb concentration by 24 and 50 % for the –lime + P + Fe treatments and 28 and 42 % for the + lime + P + Fe treatment in the Thurmont and Burch soils, respectively. The 1N HNO3 extraction removed the most Pb form both soils. Results from this experiment demonstrated that it is essential to take into account the source of Pb contamination and extraction method when selecting and combining amendments to reduce Pb solubility.