Quantitative Speciation of Arsenic in Water and Sediment Samples from the Mokolo River in Limpopo Province, South Africa

ABSTRACT

The Mokolo River is disposed to environmental contaminants such as arsenic (As) due to its proximity to several anthropogenic activities. Speciation of As in water and sediment samples from Mokolo River is crucial to evaluate the level and distribution of As in the river and underlying sediment since toxicity depends on its chemical forms. In this study, As species in water and sediment were determined by developing a new method for sediment extraction. Effective microwave-assisted extraction of As species in sediment samples was achieved using 0.3 M (NH₄)₂HPO₄ and 50 mM EDTA, which showed no species interconversion during extraction. The chromatographic separation and detection of As(III), dimethylarsinic acid (DMA), monomethylarsonic acid, and As(V) in water and sediment samples were achieved by coupling to high-performance liquid chromatography to inductively coupled plasma mass spectrometry. Baseline separation of four As species was achieved in 12 min using gradient elution with 10 and 60 mM NH₄NO₃ at pH 8.7 as the mobile phase. The analytical figures of merit and validation of analytical procedures were assessed and adequate performance and percentage recoveries ranging from 81.1 to 102% for water samples and 73.0–92.0% for sediments were achieved. The As species concentration in water and sediment samples was found to be in the range of 0.304–4.99 µg L⁻¹ and 74.0–92.0 ng g⁻¹, respectively. DMA was not detected in both water and sediment samples.

KEYWORDS:

• Arsenic
• high-performance liquid chromatography
• inductively coupled plasma mass spectrometry
• sediment
• speciation

Additional information

Funding

This work is based on research supported in part by the National Research Foundation (NRF) of South Africa under the Thuthuka Programme Grant Number 108672 and the Water Research Commission (WRC) of South Africa Project Number K5/2515//1. Mokgehle R. Letsoalo is grateful to Sasol Inzalo Foundation and National Research Foundation for the financial support.