Study on the distribution of arsenic in sediment at the Northwest Hanoi by single-step extraction procedure

Abstract

In this study, the authors used the single-step extraction procedure with different extractants to extract arsenic (As) associated with iron phases in the sediment at the Northwest Hanoi. Five extraction steps, including 1) 50mM NH4H2PO4; 2) 0.5M Formic acid, pH 3; 3) 0.5M Formic acid + 10mM Ascorbic acid, pH 3; 4) 0.2M NH4oxalate + 0.1M Ascorbic acid, pH 3; and 5) HNO3/ H2O2  microwave digestion, corresponded to five phases: (1) Adsorbed ions; (2) Acid extractable; (3) Reactive iron; (4) Crystalline oxyhydroxide iron;  and (5) Residual phase, respectively. The results showed that the range of As concentration in the sediment was 1-6 mg/kg (2 mg/kg at average). Among them, most of the As in the sediment was bound to Fe oxides fractions, and the content of As in adsorbed ions phase also accounted for a significant fraction of the total extracted arsenic (10-25%). The presence of As in acid extractable phase only constituted a small part of the extracted As (less than 10%), and the fraction of As derived from reactive iron phase was negligible. These results indicated that As has a strong association with iron minerals, particularly, iron oxyhydroxides.