Speciation of arsenic in water, sediment, and plants of the Moira watershed, Canada, using HPLC coupled to high resolution ICP–MS

High-performance liquid chromatography (HPLC) coupled with high-resolution sector field ICP–MS was applied to the speciation of arsenic in environmental samples collected from the Moira watershed, Ontario, Canada. Arsenic contamination in Moira River and Moira Lake from historic gold mine operations is of increasing environmental concern to the local community. In this study, the current arsenic contamination status in water, sediment, and plants was investigated. Elevated levels of arsenic in the surface water of up to 75 ng mL−1 in Moira River and 50 ng mL−1 in Moira Lake were detected, 98% of which was present as arsenate. High concentrations of arsenic (>300 ng mL−1), mainly present as arsenite, were detected in sediment porewaters. A sediment profile of As from the West basin of Moira Lake showed lower As concentrations compared with data from the 1990s. An optimized extraction procedure using a phosphoric acid–ascorbic acid mixture demonstrated that an unknown "As-complex" which may consist of As, sulfide and organic matter is potentially responsible for the release of arsenite from the sediment to the overlying water column. Arsenic concentrations in plant samples ranged from 2.6 to 117 mg kg−1, dry weight. Accumulation of arsenic was observed in submerged plants collected from Moira River and Moira Lake. Only a small part of the arsenic (6.3–16.1%) in the plants was extractable with methanol-water (9:1), and most of this arsenic (70–93%) was inorganic arsenic. A variety of organic arsenic compounds, including simple methylated compounds (methylarsonic acid and dimethylarsinic acid), trimethylarsine oxide, and tetramethylarsonium cation were detected at trace levels. No arsenobetaine and arsenocholine was found in any plant sample. An unknown compound, most probably an arsenosugar was detected in the two submerged plants, coontail ( Ceratophyllum demersum) and long-stemmed waterwort ( Elatine triandra). These submerged plants are constantly exposed to high arsenic concentrations in the surrounding water. Apparently, they are able to grow in this environment without invoking the same biochemical defence known from marine algae to detoxify inorganic arsenic. The detoxification mechanism of these plants remains unknown.