Low-cost screening method for estimating inorganic arsenic in soil

Abstract

People facing pollution do not always have the resources needed to investigate their environment for harmful contaminants. In this paper, we report on a low-cost, accessible method to screen soil for inorganic arsenic, a substance associated with a growing list of acute and chronic diseases. The method adapts a commercial water test kit, which measures inorganic arsenic between 0 and 500 µg L⁻¹ on a quantitative, discrete color scale. We evaluated two extraction solutions in determining bioaccessible and total inorganic arsenic. We characterized soil samples and standards containing total arsenic between 0.8 and 3240 mg kg⁻¹ (n = 151) with the screening methodology and established laboratory methods. While the total screening method requires additional investigation, we propose the bioaccessible screening method for two purposes. First, it estimates in vitro bioaccessible assay (IVBA) arsenic (\(y=0.0972x\), \({R}^{2}=0.576\)) to provide physiological insight. Second, it estimates a predicted minimum amount of total arsenic to compare to regulatory soil levels. Screening measurements above 82.5 and 132.0 µg L⁻¹ are predicted to exceed the Arizona Department of Environmental Quality (AZDEQ) and New York Department of Environmental Conservation (NYDEC) regulatory soil levels: 10 and 16 mg kg⁻¹, respectively. False positives are almost entirely avoided, while the occurrence of false negatives increases approaching the predicted thresholds. Screening measurements in the ranges [0, 10), [10, 25), and [25, threshold] µg L⁻¹ were false negatives (false omission rate) 0, 18.8, and 81.4% (AZDEQ) and 0, 8.7, and 68.5% (NYDEC) of the time, respectively. Our analysis supports screening total arsenic to at least as low as 8.5 mg kg⁻¹.