Scottish researchers find new arsenic compound.

Those of you who have been swept along by the latest sushi craze or who can't visit a Chinese restaurant without indulging in deep-fried seaweed may be getting a higher dose of arsenic than you think. A team of UK researchers has identified a new thio-organoarsenate compound in the urine of sheep fed a diet of seaweed, leading to concerns that previous estimates of the amount of arsenic that we consume in our diet may be too low.

A team of UK researchers has identified a new thio-organoarsenate compound in the urine of sheep fed a diet of seaweed, leading to concerns that previous estimates of the amount of arsenic that we consume in our diet may be too low.

A team of researchers from Aberdeen University and York University studied a primitive breed of wild sheep on North Ronaldsey, a remote Scottish island. The sheep feed almost exclusively on seaweed, which contains high concentrations of arsenic compounds. They were driven to their exotic diet by the humans on the island during a particularly harsh winter a couple of hundred years ago. As food supplies began to dwindle and there was not enough grass for the sheep to feed on, the islanders had the inspired idea of letting the sheep feed on North Ronaldsey's plentiful seaweed supply. Sure enough, the sheep thrived on the seaweed diet and have roamed the island's shores ever since.

The researchers analysed urine from the North Ronaldsey sheep using anion-exchange-high-performance liquid chromatography coupled to both an inductively-coupled plasma mass spectrometer and an electrospray mass spectrometer. Seaweed contains high concentrations of arsenosugars, which the chemists identified in the sheep's urine.

Most interesting was the researcher's claim to have found the first organoarsenic-sulphur compound ever identified in biological systems. The compound (2-dimethylarsinothioyl acetic acid) is a breakdown product of an arsenosugar and the researchers fully expect to find more sulphur-containing arsenic compounds in biological samples in the future.

In light of their finding, the chemists believe that 'the mammalian arsenic metabolism is much more complex than has been claimed'.

JÖrg Feldmann, who leads the research team, has concerns about the possible toxicity of the organoarsenic-sulphur compound and he is working hard to unravel the mystery of how arsenosugars are metabolised. The general perception is that arsenosugars are non-toxic but, according to Feldmann, conclusive toxicological tests have not been conducted, either on the arsenosugars or their metabolites, despite the huge increase in seaweed consumption in Western cuisine.

'Very little information is available about these compounds, but because they are breakdown products of the arsenosugars, they are highly interesting because we are eating more and more of these arsenosugars. Just think of sushi or the traditional Welsh breakfast: laverbread. All of the algae or seaweed contain large amounts of arsenosugars,' notes Feldmann. 

Emma Davies