Determination of arsenic in acid mine drainage and river water in Ranau, Sabah

The colorimetric analysis of arsenic (As) in aqueous solution according to the molybdenum blue method was investigated. Maximum absorbance reading can be obtained at λ =880 nm at least 20 minutes after addition of molybdate reagent to the arsenate, As(V) solution. The absorbance-concentration relationship obeyed the Beer- Lambert law at low arsenate concentrations (≤5 µgmL⁻¹) but showed a negative deviation at high (>5 µgmL⁻¹) concentrations. At fixed arsenate concentration, the presence of phosphate ion gave a higher absorbance reading, which increased with the increase in phosphate concentration. Analysis of river water and acid mine drainage( AMD) samples gave total As concentration in the range of 0.013-0.019 µgmL⁻¹ (Mean=0.016f0.003 µgmL⁻¹) and 0.012-0.024 µgmL⁻¹ (Mean=0.017±0.005 µgmL⁻¹), respectively. These values are higher than the WHO guideline value (0.01 µgmL⁻¹) for arsenic concentration in water. Arsenite, As(III), and arsenate, As(V), is dominant in river water and AMD, respectively