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 Na2 SO4 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.