Bachelor Thesis

Moss monitoring of emission and deposition of volatile metal(loid)s along a fumarole transect on Vulcano, Italy

Kathrin Struller (11/2012-08/2013)

Support: Britta Planer-Friedrich, Julia Arndt

Besides H₂O, CO₂ and SO₂ volcanic emissions also contain metallic trace elements, that are scarcely explored. Emission and deposition of volatile metal(oid)s were investigated along a transect across the fumarolic field of Vulcano island, Italy, using Sphagnum palustre moss bags for a 3-weeks active biomonitoring. Mosses were washed, frozen and oven-dried prior to exposure. At each of 8 sites, 3 moss bags at 5 heights (0,72 to 1,6 m) plus 1 bag at 1,6 m were exposed, and soil samples were collected. After exposition, triplicates of moss bags and soil samples were oven-dried, grinded and microwave-extracted with 32 % HNO3/32 % H₂O₂. Filtered extracts were analyzed for As, Se, Sb, Tl, Te and Bi by ICP-MS. The additional moss bag was microwave-extracted with 1 % HNO3 and analyzed for As speciation by HPLC-ICP-MS. A strong enrichment of all elements compared to background values in moss and soil samples proved metal(oid) emissions from the fumaroles. Decreasing concentrations of elements with increasing distance showed wind-driven dispersion of emissions. Differences in horizontal distribution patterns of individual elements were attributed to varying temperature and fumarolic chemistry as well as different binding affinity towards moss and carrier elements. For vertical distribution the chosen hights were too close to identify clear patterns exceeding vertical wind variations. Speciation analysis revealed inorganic arsenic as the domintant species; concentrations of As cations, mono- and dimethylarsenic were much lower. Comparing metal(oid) accumulation on moss bags to total concentrations in air measured on AgNO₃ traps by active pumping showed good correlations proving moss monitoring to be a useful method in observing volcanic emissions.