Arsenic metabolism in seaweed-eating sheep from Northern Scotland

Cation exchange and anion exchange liquid chromatography were coupled to an ICP-MS and optimised for the separation of 13 different arsenic species in body fluids (arsenite, arsenate, dimethylarsinic acid (DMAA), monomethylar sonic acid (MMAA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (T MA), arsenobetaine (AsB), arsenocholine (AsC), dimethylarsinoyl ethanol (DM AE) and four common dimethylarsinoylribosides (arsenosugars). The arsenic s pecies were de;ermined in seaweed extracts and in the urine and blood serum of seaweed-eating sheep from Northern Scotland. The sheep eat 2-4 kg of se aweed daily which is washed ashore on the most northern Island of Orkney. T he urine, blood and wool of 20 North Ronaldsay sheep and kidney, liver and muscle from Il sheep were sampled and analysed for their arsenic species, i n addition five Dorset Finn sheep, which lived entirely on grass, were used as a control group. The sheep have a body burden of approximately 45-90 mg arsenic daily. Since the metabolism of arsenic species varies with the ars enite and arsenate being the most toxic, and or,organoarsenic compounds suc h as arsenobetaine the least toxic compounds, the determination of the arse nic species in the diet and their body fluids are important. The major arse nic species in their diet are arsenoribosides. The major metabolite excrete d into urine and blood is DMAA (95 +/- 4.1%) with minor amounts of MMAA, ri boside X, TMA and an unidentified species. The occurrence of MMAA is assume d to be a precursor of the exposure to inorganic arsenic, since demethylati on of dimethylated or trimethylated organoarsenic compounds is not known (m ax. MMAA concentration 259 mu g/L). The concentrations in the urine (3179 /- 2667 mu g/L) and blood (44 +/- 19 mu g/kg) are at least two orders of ma gnitude higher than the level of arsenic in the urine of the control sheep or literature levels of blood for the unexposed sheep. The tissue samples ( liver: 292 +/- 99 mu g/kg kidney: 565 +/- 193 mu g/kg, muscle: 680 +/- 224 mu g/kg) and wool samples (10470 +/- 5690 mu g/kg) show elevated levels whi ch are also 100 times higher than the levels for the unexposed sheep.