Metabolism of Arsenic by Sheep Chronically Exposed to Arsenosugars as a Normal Part of Their Diet. 1. Quantitative Intake, Uptake, and Excretion

Abstract

Information on the effects of long-term organoarsenical consumption by mammals is limited despite the fact that foodstuffs, especially seafood, often contain organoarsenicals at very high concentrations. Here we evaluate the intake, uptake, and excretion (urine and feces) of arsenic by sheep that live on North Ronaldsay in the Orkney Islands and naturally consume large amounts of arsenosugars through their major food source-seaweed. The sheep eat a broad variety of seaweed species, and arsenic concentrations were determined in all the species observed eaten by the sheep (5.7-74.0 mg kg(-1) dry mass). Because of preference and availability, they feed mostly on the seaweed species found to contain the highest arsenic concentrations: Laminaria digitata and Laminaria hyperborea (74 +/- 4 mg kg(-1) dry mass). To quantify the arsenic intake by the sheep, a feeding experiment reflecting natural conditions as close as possible was set up. In the feeding trial, the average daily intake of arsenic by 12 ewes was 35 +/- 6 mg (97% of water-extractable arsenic was present as arsenosugars) gained from feeding on the two brown algae. To test the possible influence of microflora on the metabolism of arsenosugars, six of the sheep were adapted to feeding on grass for 5 months before the start of the trial (control sheep), and the remaining six sheep were kept on their normal seaweed diet (wild sheep). No significant difference in seaweed/arsenic intake and arsenic excretion was found between the two groups of sheep. The arsenic excreted in the feces represents 13 +/- 10% (n = 12) of the total consumed, and on the assumption of that, the average urinary excretion is estimated to 86%.The main arsenic metabolite excreted in urine was dimethylarsinic acid (DMA(V)) (60 +/- 22%) and minor amounts of dimethylarsinoylethanol (DMAE), methylarsonic acid (MA(V)),tetramethylarsonium ion (TMA+), and arsenate (As(V)) together with seven unknown arsenic compounds were also excreted. The urinary arsenic excretion pattern showed a lag period (>4 h) before significant quantities appeared in the urine, an excretion rate that peaked between 4 and 28 h after seaweed intake and a relatively slow half-life (17 h) after end of intake.

Commonalities in Metabolism of Arsenicals

“…[26][27][28] In seaweed-eating sheep from Orkney Island, Scotland, daily consumption of arsenic from arsenosugars ranges from 45 to 90 mg. Dimethylarsenic is the major arsenic-containing species in urine in these sheep. [29,30] Other metabolites identified in urine of these sheep are dimethylarsinoyl acetate and dimethylarsinothioyl acetate [31] (Fig. 4) of thioylated metabolites are considered below.)…”

Peer Reviewed: Arsenic Speciation

“…Instead, several new arsenic compounds were present in the urine samples collected 17 h and 42.5 h after the mus- (Figures 1d and e), which was the result of metabolism of the arsenosugars. Metabolism of arsenosugars has been confirmed by human ingestion of individual synthetic arsenosugar (19) and by sheep that consume seaweed as their primary diet (20). Although ICPMS offers specific detection of arsenic, it cannot provide molecular (structural) information, because all the arsenic species are broken apart in the high-temperature ICP.…”

Distribution of arsenic and risk assessment of activities on a golf course fertilised with arsenic-containing Ascophyllum nodosum seaweed

“…Up to 100 mg/kg dry weight (d.wt.) 36 of As has been observed in brown algae species (Castlehouse et al 2003; Hansen et al 2003). 37…”

“…Arsenosugars are organic and 49 not currently considered to be acutely toxic to humans (Castlehouse et al 2003;Hansen et al 2003). 50 However, it is now known that arsenosugars metabolise in the human body in a similar manner to that combination of increasing use of seaweed fertilisers in agriculture and horticulture, and the significant 66 lack of guidance and legislation could potentially expose many people to unknown toxic effects of 67 this marine product.…”

“…Arsenosugars are organic and 49 not currently considered to be acutely toxic to humans (Castlehouse et al 2003; Hansen et al 2003). 50 However, it is now known that arsenosugars metabolise in the human body in a similar manner to that 51 of inorganic As forms.…”