Chapter 31 Arsenic speciation in soils: an analytical challenge for understanding arsenic biogeochemistry

Abstract

Abstract The mobility, fate, bioavailability, and overall biogeochemical cycling of arsenic in soil depend on the individual form in which arsenic exists as well as physical and chemical characteristics of the soil. Speciation analysis of arsenic poses a great challenge and is the key to understand the biogeochemistry of arsenic in soils and sediments. The speciation of arsenic in soil may be defined functionally (e.g., bioavailable fraction), operationally, or chemical species-specifically. The extraction of arsenic species from solid matrices generally constitutes a critical step for speciation analysis of arsenic in soils and sediments. Various sequential extraction procedures have been developed to extract operationally defined arsenic species such as water soluble, exchangeable, Fe/Mn oxides associated, organic matter bound, and residual arsenic fractions. Several extractants have been used to leach chemically specific arsenic species, mainly arsenite, arsenate, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) from a solid matrix. Efforts have been made to preserve the integrity of arsenic species during extraction. In this paper, extraction procedures with emphasis on the selection of extractants for chemical-species specifically and operationally defined arsenic species were reviewed. In addition, extraction method for evaluating bioavailable arsenic and spectroscopic technique for directly measuring arsenic species in soils were briefly discussed.