Arsenic Bioavailability and Fate: X-Ray Absorption Spectroscopic Results From Feeding Studies of Contaminated Soil and Media.

Arsenic (As) is a human carcinogen that also causes gastrointestinal, cardiovascular, and reproductive diseases. Arsenic bioavailability and the pool of bioaccessible As are affected by the soil environment, the redox state of As, and its' coordinating environment. We performed feeding studies with mice with a number of contaminated soils including apple orchard and sugarcane soils sprayed with arsenical insecticides, mine soils and spoils, arsenic sorbed to ferrihydrite, and the NIST reference soil 2710a. We will present results from standard soil analyses including nitric acid digest, in vitro bioaccessiblity assay, and X-ray absorption spectroscopy.

Nitric acid digestion and Instrumental Neutron Activation Analysis confirmed total As concentrations ranging from 279.71 – 6899.17 mg/kg in soils. Absolute bioavailabilities of soil bound As ranged from 10-28%. Relative bioavailabilities of soil arsenic ranged from 11-53% (mean = 33%). In vitro soil arsenic bioaccessibility (IVBA) values were strongly correlated with soil arsenic relative bioavailability values (R² = 0.92).  In situ analyses by X-ray Absorption Near Edge Structure spectroscopy of soil excreted in feces found changes in As redox state and mineralogy. Depending upon soil ingested, pools of As(V) and As(III) sorbed to iron minerals changed, and monomethylarsonic acid and dimethylarsinic acid, the major metabolites of inorganic arsenic were detected in feces. Results from this study demonstrate that site-specific factors such as As mineralogy affect of the  bioavailability of As and suggest that routine use of a 100% bioavailability term for soil As may not be prudent. This information may be useful when determining the potential for adverse health effects after incidental ingestion of contaminated soils.