A study was conducted to compare the effects of phosphate (P) materials in reducing cadmium extractability. Seven P materials (commercial P fertilizers - fused phosphate (FP), 'fused and superphosphate' [FSP], and rock phosphate [RP]; P chemicals-Ca[H2PO4]2.H2O, [NH4]2.HPO4, KH2PO4, and K2HPO4) were selected for the test. The selected P source was mixed with Cd-contaminated soil at the rate of 0, 200, 400, 800, and 1,600 mg P kg-1 under controlled moisture conditions at 70% of water holding capacity, then incubated for 8 weeks. FP, Ca(H2PO 4)2.H2O, KH2PO4, and K2HPO4 significantly decreased NH 4OAcextractable Cd (plant-available form) concentrations with increasing application rates. Compared to other phosphate materials used, K 2HPO4 was found to be the most effective in reducing the plant-available Cd concentration in soil, mainly due to the negative charge increase caused by soil pH and phosphate adsorption. Contrary to the general information, FSP and (NH4)2HPO4 increased Cd extractability at low levels of P application (<400 mg kg-1), and thereafter Cd extractability decreased significantly with increasing application rate. RP scarcely had an effect on reducing Cd extractability. Ion activity products of CdHPO4, Cd(OH)2, and CdCO3 analyzed by the MINTEQ program were significantly increased by K2HPO 4 addition, but the effect of Cd-P compound formation on reducing Cd extractability was negligible. Conclusively, the P-induced alleviation of Cd extractability can be attributed primarily to Cd immobilization due to the increase in soil pH and negative charge rather than Cd-P precipitation, and therefore, alkaline P materials such as K2HPO4 are effective for immobilizing soil Cd.
|Original language||English (US)|
|Number of pages||7|
|Journal||Archives of Environmental Contamination and Toxicology|
|State||Published - Feb 2010|
ASJC Scopus subject areas
- Health, Toxicology and Mutagenesis