Abstract
A laboratory investigation was conducted to evaluate the efficiency of four phosphate fertilizers, including diammonium phosphate (DAP), potassium phosphate monobasic (MPP), calcium superphosphateon (SSP), and calcium phosphate tribasic (TCP), in terms of the toxicity and bioavailability of Cd in contaminated soils. The efficiency of immobilization was evaluated on the basis of two criteria: (a) the reduction of extractable Cd concentration below the TCLP regulatory level and (b) the Cd changes associated with specific operational soil fractions on the basis of sequential extraction data. Results showed that after 50 d immobilization, the extractable concentrations of Cd in DAP, MPP, SSP, and TCP treated soils decreased from 42.64 mg/kg (in the control) to 23.86, 21.86, 33.89, and 35.59 mg/kg, respectively, with immobilization efficiency in the order of MPP > DAP > SSP > TCP. Results from the assessment of Cd speciation via the sequential extraction procedure revealed that the soluble exchangeable fraction of Cd in soils treated with phosphate fertilizers, especially TCP, was considerably reduced. In addition, the reduction was correspondingly related to the increase in the more stable forms of Cd, that is, the metal bound to manganese oxides and the metal bound to crystalline iron oxides. Treatment efficiency increased as the phosphate dose (according to the molar ratio of PO4/Cd) increased. Immobilization was the most effective under the molar ratio of PO4/Cd at 4:1.
Highlights
Heavy metal contamination in soils is undoubtedly one of the major issues in modern soil science
TCLP extractable Cd concentration can be significantly decreased after application of TCP, SSP, diammonium phosphate (DAP), and MPP treatment to the contaminated soils with reductions of 16.52%, 20.51%, 44.05%, and 48.73%, respectively, as compared with the control sample
The results suggest that TCLP extractable Cd concentration was significantly negatively correlated with soil available phosphate concentration
Summary
Heavy metal contamination in soils is undoubtedly one of the major issues in modern soil science. Such heavy metal contamination may adversely affect water resources, soil ecology, and agricultural product quality while causing serious health problems for humans and animals. Increasing awareness of the public health hazard presented by Cd has necessitated the restoration of Cd-contaminated soils. The demand for Cd immobilization has increased with its increasing content in soil environment over the last decades [2]. Among the varieties of promising remediation technologies [3,4,5,6,7,8], in situ chemical immobilization is an effective remediation technology that may reduce the extractable potential of heavy metals. Phosphate fertilizers are considered as PLOS ONE | DOI:10.1371/journal.pone.0124022 April 27, 2015
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