Evaluation of different extractants to estimate bioavailable arsenic in soil

Abstract

Abstract Owing to the similar chemistry of phosphorus (P) and arsenic (As), sodium bicarbonate (0.5 N NaHCO3) is commonly used to extract plant accessible As in soil. However, 0.5 N NaHCO3 is not compatible with the ICP-MS measurement due to the large amount of dissolved solids. This investigation set out to devise a suitable extractant for determining extractable As in soil and measured by the ICP-MS. Paired soil and plant samples were collected from paddy fields in West Bengal, India. Soil was extracted with 0.5 M NaHCO3, 0.03 M (0.1 N) and 0.17 M (0.5 N) phosphoric acid (H3PO4), 0.05 M (0.1 N) and 0.25 M (0.5 N) sulfuric acid (H2SO4), and 0.01 M calcium chloride (CaCl2). This made it possible to measure As by hydride generation-atomic absorption spectrophotometer (HG-AAS), while ICP-MS was used for the determination of As extracted from soil with different concentrations (0.1-1.5M) of HNO3. The NaHCO3 extractable As was 1.45 and 1.23 mg kg− 1 for soil to extractant ratio of 1:20 and 1:5, respectively. Of these extractants, 1.5 N HNO3 extractable As had the best correlation with As content in rice grain (r = 0.45**) and straw (r = 0.71**), comparable with standard extractant i.e. 0.5 N NaHCO3 (r = 0.47** and r = 0.64** in case of grain and straw, respectively). A significant positive relationship of 1.5 N HNO3 was obtained with 0.5 N NaHCO3. Thus, 1.5 N HNO3 may serve as an extractant for soil As, which is compatible with ICP-MS analysis.