Biogenic arsenic volatilisation from an acidic fen.

To quantify arsenic (As) volatilisation by peatlands and to elucidate the environmental factors governing As volatilisation, a series of anoxic incubations with acidic fen soil collected in northeast Bavaria in Germany were performed at 15°C for 4months. Arsenic volatilisation summed to 2.32ng As in the control, which was 1.6% and ~0.01% of the porewater As and the total As storage in the fen soil, respectively. Treatment with 10mM NaN3 resulted in only 0.03ng As volatilisation. In comparison, addition of 10mM NaOAc stimulated microbial activity in fen soil and As volatilisation rose to 8.42ng As, indicating that As volatilisation by fen soil is primarily biogenic. Spiking with 67µM As(III) increased As volatilisation eightfold, supposedly caused by the largely enhanced As availability in porewater for microbes (~10 times higher than the control). Adding 10mM FeCl3 and Na2SO4 decreased As volatilisation to 0.30 and 0.82ng As, respectively, apparently due to the change of microbial activity. Speciation of gaseous As in the headspace using GC-ICP-MS/EI-MS showed the predominance of arsine and trimethylarsine in treatments with low and high porewater As concentrations, respectively, suggesting different formation pathways of arsine and methylarsines. This study demonstrated the strong linkage between microorganisms and As volatilisation by peatlands and furthermore indicated the minor role of As volatilisation in the natural As biogeochemical cycle in the semi-terrestrial environment.

Sample pre-treatment to eliminate cationic methylated arsenic for determining arsenite on an anion-exchange column by high performance liquid chromatography-inductively coupled plasma mass spectrometry.

Co-elution of cationic methylated arsenic, e.g. arsenobetaine may interfere with the determination of arsenite on the Hamilton PRP-X100 anion-exchange column using a phosphate buffer isocratically. Therefore, a sample pre-treatment method with self-packed AG MP-50 cation-exchange cartridges was proposed, which enables the arsenite determination in samples containing arsenobetaine on a PRP-X100 column using a phosphate buffer (pH 5.6) isocratically. Methylated arsenic, including dimethylarsinic acid, trimethylarsine oxide, tetramethylarsonium ion, arsenobetaine and arsenocholine, with concentrations below 1000microgAsL(-1), may be completely retained in the AG MP-50 cartridge without any changes of arsenite, arsenate and monomethylarsonic acid speciation. Such retention was independent of the pH and matrix. It is proposed to be based on hydrophobic interaction. With the help of AG MP-50 cartridges, 11 arsenic species were detected in fish (DORM-2), mussels (BCR-477) and red algae (Porphyra tenera) in 10min on the PRP-X100 column using a phosphate buffer isocratically. Arsenite was the only minor species (up to 0.9%) among all water extractable arsenic species in fish, mussel and red algae.

GC-ICP-MS determination of dimethylselenide in human breath after ingestion of (77)Se-enriched selenite: monitoring of in-vivo methylation of selenium.

The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 microg (77)Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping-cryofocussing-GC-ICP-MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP-MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath-dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked (77)Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10-300 pg, R (2)=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L(-1), when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of (77)Se-enriched selenite. Additional DM(77)Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of (77)Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R (2)=0.80). Furthermore, the sub-toxic dose of 300 microg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L(-1) whereas the dietary background level was less than 0.4 ng Se L(-1). Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.