Abstract
Seaweeds contain arsenic primarily in the form of arsenosugars, which can be metabolized to a wide range of arsenic compounds. To characterize human exposure to arsenic from seaweed consumption, we determined concentrations of arsenic species in locally available seaweeds, and assessed urinary arsenic compounds in an experimental feeding study. A total of 11 volunteers consumed 10 g per day of three types of seaweeds (nori, kombu, and wakame) for three days each, while abstaining from rice and seafood following a three-day washout period. Urinary arsenosugars and their metabolites (including dimethyl arsenate (DMA), thio-dimethylarsinoylethanol (thio-DMAE), thio-dimethylarsinoylacetate (thio-DMAA), and thio-DMA) were measured in spot urine samples prior to seaweed consumption, and in 24-hour urine samples while consuming seaweed. Commercial products made from whole seaweed had substantial concentrations of arsenic (12–84 µg/g), dominated by arsenosugars. Intact arsenosugars along with DMA, thio-DMAA, thio-DMAE all increased in urine after ingesting each type of seaweed, and varied between seaweed types and between individuals. Only trace levels of the known toxic metabolite, thio-DMA, were observed, across individuals. Thio-DMAE and thio-DMAA are unique products of arsenosugar breakdown, thus assessment of these compounds may help to identify dietary intake of arsenic from seaweed from other exposure pathways.
Highlights
Seaweeds contain arsenic primarily in the form of arsenosugars, which can be metabolized to a wide range of arsenic compounds
While inorganic arsenic is an established human carcinogen[2], less is known about organic arsenic species, such as arsenosugars found in seaweeds
We used a repeated consumption design with three different seaweed types, where 24 h urine samples were collected throughout the feeding period, and extensively characterized the arsenic compounds excreted in urine, including the arsenosugar metabolites thio-DMAE and thio-DMAA
Summary
Seaweeds contain arsenic primarily in the form of arsenosugars, which can be metabolized to a wide range of arsenic compounds. A total of 11 volunteers consumed 10 g per day of three types of seaweeds (nori, kombu, and wakame) for three days each, while abstaining from rice and seafood following a three-day washout period Urinary arsenosugars and their metabolites (including dimethyl arsenate (DMA), thio-dimethylarsinoylethanol (thio-DMAE), thio-dimethylarsinoylacetate (thio-DMAA), and thio-DMA) were measured in spot urine samples prior to seaweed consumption, and in 24-hour urine samples while consuming seaweed. Following intake of synthetic arsenosugar, more than 10 other metabolite species have been characterized in urine[3,4], including the compounds thio-dimethylarsinoylethanol (thio-DMAE) and thio-dimethylarsinoylacetate (thio-DMAA), which were the most abundant metabolites after DMA (Table 1S Supplemental). We used a repeated consumption design with three different seaweed types, where 24 h urine samples were collected throughout the feeding period, and extensively characterized the arsenic compounds excreted in urine, including the arsenosugar metabolites thio-DMAE and thio-DMAA
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