US EPA

357622 

Journal Article 

XAS evidence of As(V) association with iron oxyhydroxides in a contaminated soil at a former arsenical pesticide processing plant 

Cancès, B; Juillot, F; Morin, G; Laperche, V; Alvarez, L; Proux, O; Hazemann, JL; Brown, GE, Jr; Calas, G 

2005 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

39 

24 

9398-9405 

English 

16475314 

The molecular-level speciation of arsenic has been determined in a soil profile in the Massif Central near Auzon, France that was impacted by As-based pesticides by combining conventional techniques (XRD, selective chemical extractions) with X-ray absorption spectroscopy (XAS). The arsenic concentration is very high at the top (>7000 mg kg-1) and decreases rapidly downward to a few hundreds of milligrams per kilogram. A thin layer of schultenite (PbHAsO4), a lead arsenate commonly used as an insecticide until the middle of the 20th century, was found at 10 cm depth. Despite the occurrence of this As-bearing mineral, oxalate extraction indicated that more than 65% of the arsenic was released upon dissolution of amorphous iron oxides, suggesting a major association of arsenic with these phases within the soil profile. Since oxalate extraction cannot unambiguously distinguish among the various chemical forms of arsenic, these results were confirmed by a direct in situ determination of arsenic speciation using XAS analysis. XANES data indicate that arsenic occurs mainly as As(V) along the soil profile except for the topsoil sample where a minor amount (7%) of As(III) was detected. EXAFS spectra of soil samples were fit by linear combinations of model compounds spectra and by a shell-by-shell method. These procedures clearly confirmed that As(V) is mainly (at least 80 wt %) associated with amorphous Fe(III) oxides as coprecipitates within the soil profile. If any, the proportion of schultenite, which was evidenced by XRD in a separate thin white layer, does not account for more than 10 wt % of arsenic in soil samples. This study emphasizes the importance of iron oxides in restricting arsenic dispersal within soils following dissolution of primary As-bearing solids manufactured for use as pesticides and released into the soils. 

arsenic; iron oxides; iron oxyhydroxides; lead arsenate; oxalates; pesticide residues; pollutants; polluted soils; soil pollution; soil profiles; soil types; spectroscopy; topsoil; France; Western Europe; Europe; Mediterranean Region; Developed Countries; European Union Countries; OECD Countries; Pesticide and Drug Residues and Ecotoxicology (HH430) (New March 2000); Soil Chemistry and Mineralogy (JJ200); Pollution and Degradation (PP600); Techniques and Methodology (ZZ900)