Fractionation and bioavailability of arsenic in agricultural soils: Solvent extraction tests and their relevance in risk assessment

Abstract

Sequential extraction procedure (SEP) and a physiologically based extraction test (PBET) were performed with the aim to estimate the mobility, bioavailability (for plants and humans) and spatial variation of arsenic in agricultural soils in the Valleys of Arica and Parinacota Region (Northern Chile). For this purpose, 50 topsoil samples with different total arsenic contents in soil (36.2–729 mg kg⁻¹) were collected from 10 selected sites in the Valley of Lluta, Azapa and Camarones. The SEP test results showed that arsenic was mainly associated to the least mobile fractions: bound to amorphous and poorly crystalline hydrous oxides of Fe and Al (11.6–44.2%) and well-crystallized hydrous oxides of Fe and Al (24.8–48.9%). Calculated values for arsenic Chronic Daily Intake (CDI), based on the information obtained in the tests of bioaccessibility using PBET (range 1.6–9.6 mg kg⁻¹), were in the range of 0.021 to 0.128 μg As kg⁻¹ d⁻¹, not exceeding in any case the maximum Reference Dose for Chronic Oral Exposure, RfD = 0.3 μg kg⁻¹ d⁻¹, established by USEPA. In general, obtained results, allow us to establish that extraction processes using solvents can be utilized as a source of reliable and useful information for risk assessment of exposure to arsenic from soil, over the direct use of total arsenic contents, which can lead to an overestimation of the toxicity by direct ingestion.

Keywords:

• Arsenic in Chilean soils
• sequential extraction procedure
• bioavailability
• risk assessment

Acknowledgments

The authors thank the Centro de Investigaciones del Hombre en el Desierto (CIHDE/CODECITE).

Notes

*For CDI calculation it was considered daily soil ingest of 0.2 g and a body mass of 15 kg (child), Reference Dose for Chronic Oral Exposure^{[ 51 ]} (RfD) = 0.3 μg As kg⁻¹ d⁻¹.