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), monomethylarsonic acid (MMAA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA), arsenobetaine (AsB), arsenocholine (AsC), dimethylarsinoyl ethanol (DMAE) and four common dimethylarsinoylribosides (arsenosugars). The arsenic species were determined in seaweed extracts and in the urine and blood serum of seaweed-eating sheep from Northern Scotland. The sheep eat 2-4 kg of seaweed daily which is washed ashore on the most northern Island of Orkney. The urine, blood and wool of 20 North Ronaldsay sheep and kidney, liver and muscle from 11 sheep were sampled and analysed for their arsenic species. In 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 arsenite and arsenate being the most toxic, and organoarsenic compounds such as arsenobetaine the least toxic compounds, the determination of the arsenic species in the diet and their body fluids are important. The major arsenic species in their diet are arsenoribosides. The major metabolite excreted into urine and blood is DMAA (95 +/- 4.1%) with minor amounts of MMAA, riboside X, TMA and an unidentified species. The occurrence of MMAA is assumed to be a precursor of the exposure to inorganic arsenic, since demethylation of dimethylated or trimethylated organoarsenic compounds is not known (max. MMAA concentration 259 microg/L). The concentrations in the urine (3179 +/- 2667 microg/L) and blood (44 +/- 19 microg/kg) are at least two orders of magnitude 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 microg/kg, kidney: 565 +/- 193 microg/kg, muscle: 680 +/- 224 microg/kg) and wool samples (10470 +/- 5690 microg/kg) show elevated levels which are also 100 times higher than the levels for the unexposed sheep.
In the marine environment, arsenic accumulates in seaweed and occurs mostly in the form of arsenoribofuranosides (often called arsenosugars). This study investigated the degradation pathways of arsenosugars from decaying seaweed in a mesocosm experiment. Brown seaweed (Laminaria digitata) was placed on top of a marine sediment soaked with seawater. Seawater and porewater samples from different depths were collected and analysed for arsenic species in order to identify the degradation products using high-performance liquid chomatography-inductively coupled plasma mass spectrometry. During the first 10 days most of the arsenic found in the seawater and the shallow sediment is in the form of the arsenosugars released from the seaweed. Dimethylarsenoylethanol (DMAE), dimethylarsinic acid (DMA(V)) and, later, monomethylarsonic acid (MMA(V)) and arsenite and arsenate were also formed. In the deeper anaerobic sediment, the arsenosugars disappear more quickly and DMAE is the main metabolite with 60-80% of the total arsenic for the first 60 days besides a constant DMA(V) contribution of 10-20% of total soluble arsenic. With the degradation of the soluble DMAE the solubility of arsenic decreases in the sediment. The final soluble degradation products (after 106 days) were arsenite, arsenate, MMA(V) and DMA(V). No arsenobetaine or arsenocholine were identified in the porewater.
In this study sequential extraction was used to fractionate cadmium (Cd) and zinc (Zn) from soils into six operationally defined groups; water soluble, buffer-exchangeable, carbonate, FeMn oxide, organic, and residual. Soil samples from agricultural areas surrounding Pha Te village, Mae Sot District, Tak Province, Thailand, were classified into four categories; forest soil, upland soil, upper-paddy soil and lower-paddy soil. Total soil Cd and Zn concentrations ranged from 0.63 to 30.4 mg kg-1and 14.4 to 594 mg kg-1, respectively. Cd and Zn concentrations were higher in the upper-and lower-paddy soil (5.93 to 30.4 mg kg-1for Cd and 286 to 594 mg kg-1for Zn). These soils are considered as polluted. Cd in the polluted soil was dominantly associated with the buffer-exchangeable and carbonate-bound (40 to 70 % of total Cd), while in non-polluted soils; the residual fraction was dominant (50 to 80 % of the total Cd). The major proportion of Zn (37 to 46 % of total Zn) in the non-polluted soil and the upper-paddy soil occurred in the residual fraction. On the other hand, the major proportion of total Zn in the lower-paddy soil was associated with FeMn oxides (36% of total Zn). The results show that mobility and potential bioavailability of Cd and Zn (61 and 25 %) in polluted soil were higher than in non-polluted soils (15 and 19 %in Cd and Zn, respectively). Metal distribution in different chemical fractions in these soils depended on the respective total metal concentrations.
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