Optimized extraction of inorganic arsenic species from a foliose lichen biomonitor
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To assess the two most toxicologically relevant species of As, namely arsenite (As(III)) and arsenate (As(V)), chromatographic separations often require two separate chromatographic columns to address the co-elution of arsenobetaine (AsB) with As(III). This issue is typically observed using conventional isocratic methods on anion exchange columns, increasing cost and analysis time. Here, we optimize the extraction of inorganic As from a lichen air biomonitor and develop an isocratic method for the chromatographic separation of five common As species on a PRP X-100 anion exchange column, resulting in the complete baseline separation of all species under study. This method was then applied to lichen biomonitors from an urban and rural site to demonstrate its use. In order of abundance, the various arsenic species in lichens from the urban site in South Africa were As(V) > As(III) > AsB > dimethylarsinic acid (DMA) > monomethylarsonic acid (MMA), and As(V) > AsB > As(III) > DMA > MMA for the rural site, where MMA was present in extremely low, non-quantifiable concentrations in lichens from both sites. Total concentrations of As were higher in samples from the urban site (6.43 ± 0.25 μg/g) than in those from the rural site (1.87 ± 0.05 μg/g), with an overall extraction efficiency of 19% and 40%, respectively. The optimized method utilized relatively inexpensive solvents and is therefore low-cost and eco-friendly in comparison with conventional chromatographic techniques. This is the first study which addresses the optimized extraction and characterization of As species in a South African lichen biomonitor of air pollution.
KeywordsArsenic speciation HPLC-ICP-MS Extraction Biomonitor Air pollution Lichen
The authors would like to thank Johannesburg City Parks and Zoo and the Burri family for allowing sampling to take place on their premises. Special thanks are also given to the following people from PerkinElmer Inc. for their support of this study: Dr. Kenneth Neubauer for his guidance on HPLC-ICP-MS methods; Dr. Mark Upton for training; and Lisa Koorts, Chris de Jager, and Dr.Fadi Abou-Shakra for arranging a loan instrument. Further thanks are given to Rufaro Bhero for his assistance in the preparation of the organic arsenic stock solutions.
The financial assistance of the University of Pretoria, University of Johannesburg, and the Department of Higher Education and Training towards this research is hereby acknowledged.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The opinions expressed and conclusions arrived at are those of the authors and are not necessarily to be attributed to these Universities.
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