Aqueous Extraction of Water-soluble Inorganic Arsenic in Marine Algae for Speciation Analysis

An aqueous extraction of inorganic As species, such as arsenite (As(III)) and arsenate (As(V)), was developed for monitoring inorganic As in the edible brown alga Hizikia fusiforme (hijiki). The ultrasonic extraction with water, even without heating, was found to be an acceptable monitoring method for an evaluation of water-soluble inorganic As, since it could extract about 80% of total As. Such an extraction efficiency was almost the same as those of enzyme assisted extraction methods. The developed extraction procedure was applied to 15 hijiki samples that had been collected at different coasts in Japan. All samples contained a substantial proportion of As as arsenosugars; the relative amounts of the different As species extracted were dependent on the sample. The percentages of extractable As species in the hijiki samples were in the range from 70 to 90%, and the sums of the concentrations of As(III) and As(V), which was defined as i-As, were in the range from 36 to 79% of the total As concentration in each sample. The proposed method is appropriate for environmental monitoring for inorganic As speciation in algae.