Arsenic Speciation and Phytoavailability in Contaminated Soils Using a Sequential Extraction Procedure and XANES Spectroscopy

• Published in: Environmental science & technology 2011-09, Vol.45 (17), p.7135-7142
• Main Authors: Niazi, Nabeel K, Singh, Balwant, Shah, Pushan
• Format: Article
• Language: English
• Subjects: Applied sciences; Arsenic; Arsenic - analysis; Biological and physicochemical properties of pollutants. Interaction in the soil; Characterization of Natural and Affected Environments; Correlation analysis; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Monitoring - methods; Exact sciences and technology; Humans; Mustard Plant - chemistry; Mustard Plant - metabolism; Oxidation-Reduction; Pollution; Pollution, environment geology; Risk assessment; Soil and sediments pollution; Soil contamination; Soil Pollutants - analysis; Solid Phase Extraction - methods; Spectrum analysis; X-Ray Absorption Spectroscopy - methods
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es201677z

In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (AsV) form in the soils; in a few samples As was also present in arsenite (AsIII) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001–0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils.