Lead Bioaccessibility in Soil and Mine Wastes After Immobilization with Phosphate

Abstract

The immobilization of lead by the reaction with phosphate bearing materials is a promising remediation method for contaminated soils. Low soluble neo-formed lead-phosphate phases similar to chloropyromorphite [Pb 5 (PO 4 ) 3 Cl], can control availability and mobility of lead in the environment, and consequently reduce human exposure, if soils are the main contamination pathway. We used three phosphate source materials [NaH 2 (PO 4 ) 3 , commercial superphosphate and phosphate rock] to study lead immobilization in soil and mining waste samples. Products were examined after 1, 3 and 6 months of contact. The samples are from a contaminated area by former Pb mining and smelting activities, in southeastern Brazil, where epidemiological studies showed high lead blood levels in local population. The PBET (physiological based extraction test) bioaccessibility test was used to measure changes in the amount of soluble lead after sample treatment. Results show that the most efficient phosphate source was NaH 2 (PO 4 ) 3 , which reduced lead solubility to 92% in acidic gastric conditions after the first month of contact. Superphosphate and phosphate rock also diminished Pb solubility, but the effect was more time dependent. None specific Pb-phosphate phases could be identified by XRD in whole treated samples, but the PbCa-P elemental associations, observed on SEM images and EDS spectra of portions of the samples, combined with the reduced solubility, indicate that more insoluble lead phases were formed after the treatment. Based in these results, the in site phosphate application on soils to induce lead immobilization should be considered as a possible alternative to reduce human exposure at the area.

Agronomic and environmental aspects of phosphate fertilizers varying in source and solubility: an update review

“…The following additional references have been reported since 1998: Ma and Rao 1999;Cao et al 2002;Chen et al 2003;Bolan et al 2003;Lin et al 2005;Bosso et al 2008;Miretzky and Fernandez 2009. In general, WSP fertilizers (e.g., SSP and TSP) are more effective than PR in reducing soluble Pb content in the Pb-contaminated soils because of their higher water solubility and their ability to react with Pb to form more stable Pb-P compounds.…”

Assessment of In Situ Immobilization of Lead (Pb) and Arsenic (As) in Contaminated Soils with Phosphate and Iron: Solubility and Bioaccessibility

“…However, in the small intestinal phase, SSP appears to be the least effective amendment. Bosso et al (2008) used the NaH 2 (PO 4 ) 3 , super-phosphate and phosphate rock to immobilize Pb in soil and assessed the risk with the bioaccessibility tests. The results showed that the most efficient phosphate source was NaH 2 PO 4 , which reduced Pb solubility to 92% in gastric conditions after the first month of incubation.…”

“…Oral bioaccessibility test, which is a measure of solubility of heavy metal in the gastrointestinal compartment, is applicable to the soil ingestion pathway (Beak et al 2006;Ruby et al 1996). The bioaccessibility of metal has also been used to evaluate the effectiveness of heavy metal remediation in soils (Bosso et al 2008;Sarkar et al 2007). Bosso's (2008) study showed that the most efficient phosphate source was NaH 2 PO 4 , which reduced Pb solubility by 92% in acidic gastric conditions after the first month.…”

“…The bioaccessibility of metal has also been used to evaluate the effectiveness of heavy metal remediation in soils (Bosso et al 2008;Sarkar et al 2007). Bosso's (2008) study showed that the most efficient phosphate source was NaH 2 PO 4 , which reduced Pb solubility by 92% in acidic gastric conditions after the first month. In Pb and As-contaminated soil, Martin and Ruby (2003) found that in situ fixation of As can be achieved by addition of iron amendments, which can also reduce bioaccessibility of As.…”

Indicadores físicos e químicos de qualidade de solos de área de mineração e metalurgia de chumbo

“…Entre as atividades industriais, destaca-se a metalúrgica de metais pesados, que produz grandes quantidades de rejeitos ricos nesses poluentes (AMARAL SOBRINHO et al, 1998;BOSSO;ENZWEILER;ANGÉLICA, 2008 , 1997). Em 1995 a mineradora encerrou suas atividades deixando a céu aberto, sem nenhuma proteção, cerca de 177.000 t de resíduos de beneficiamento de Pb (EYSINK, 1988;CASSIANO, 2001 Os solos possuem características únicas quando comparados aos outros componentes da biosfera, pois se apresentam não apenas como um dreno para contaminantes, mas também como tampão natural que controla o transporte de elementos químicos e outras substâncias para a atmosfera, hidrosfera e biota (KABATA-PENDIAS;PENDIAS, 2001).…”