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 4 months. Arsenic volatilisation summed to 2.32 ng 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 10 mM NaN3 resulted in only 0.03 ng As volatilisation. In comparison, addition of 10 mM NaOAc stimulated microbial activity in fen soil and As volatilisation rose to 8.42 ng As, indicating that As volatilisation by fen soil is primarily biogenic. Spiking with 67 μM 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 10 mM FeCl3 and Na2SO4 decreased As volatilisation to 0.30 and 0.82 ng 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.