The relevance of volatile arsenic emissions from volcanic areas
Final Report Abstract
Volcanoes are assumed to be one of the most important natural point sources for the release of particulate and potentially also volatile arsenic (AsH3, (CH3)AsH2, (CH3)2AsH und (CH3)3As) to the atmosphere. So far, few studies have quantified and compared arsenic release from different volcanic areas which is mainly owed to a lack of reliable sampling techniques, especially for volatile arsenic species, adapted to the often remote locations of volcanic sites. The central aim of the present project was to develop and validate an easily field deployable, speciesselective, quantitative sampling method for volatile arsines, optimize storage conditions for transport from the field to the laboratory, and set up gas chromatography (GC) coupled to mass spectrometry (MS; for unknown peak identification) and inductively coupled plasma MS (ICP-MS; for quantification) for analysis in the laboratory. While the GC-MS//ICP-MS setup worked out very well, we had to abandon the original plan of using needle trap devices (NTDs) for easy field sampling after numerous, tedious laboratory and field tests. Despite promising preliminary results, NTDs were finally found to not trap AsH3, (CH3)AsH2, (CH3)2AsH, to not release sorbed (CH3)3As quantitatively, and to lead to artifact formation of dimethylchloroarsine. Instead, we optimized Tedlar bag gas sampling for use with volcanic gases, e.g. by installing an NaOH trap to remove SO2 which we found to lead to transformation of (CH3)2AsH and (CH3)3As to AsH3. The Tedlar bag sampling was not ideal, because it requires rapid transport of large gas volumes under controlled temperature and pressure conditions back to the laboratory, which limits its use in remote areas, and since there is no enrichment in the field, detection limits were not as low as we had hoped for with the NTDs. Yet, we were able to detect AsH3 and, to a lesser extent, (CH3)3As at volcanic exhalations from Vulcano and Solfatara, both Italy. Since the method development for species-selective, quantitative sampling of volatile arsines took so much longer than expected, we used in parallel active moss monitoring to pursue the second aim of the project, to learn more about potential differences in arsenic release from different volcanic areas. We had used active moss monitoring successfully before to monitor the spatial distribution of airborne metal(loid)s around one volcanic source (Vulcano, Italy) as a single-time snapshot. Now, we combined data from six different volcanic areas (the open conduit volcanoes Stromboli and Mt Etna (both Italy), Nyiragongo (Democratic Republic of the Congo), and the hydrothermal areas at Vulcano, Nisyros (Greece), and Yellowstone (USA)) where moss monitoring had been conducted at different times with different setups by different users. We carefully evaluated the extent to which moss species and shoot density, climate at each site (wind and specifically rainfall and the question whether to cover mosses or not during exposure), exposure height, exposure duration, etc. influence metal(loid) trapping on the mosses. Normalizing the data, we were able to show distinct release patterns based on the type and activity of volcanism. We were further able to show that mosses trap besides particulate arsenic also higher methylated volatile arsenic species, so (provided concentrations are high enough) moss monitoring can also be used for a first species-selective screening in volcanic areas.
Publications
- Evaluation of techniques for sampling volatile Arsenic on Volcanoes, Journal of Volcanology and Geothermal Research, 331, 16–25 (2017)
Arndt, J; Ilgen, G; Planer-Friedrich, B
(See online at https://doi.org/10.1016/j.jvolgeores.2016.10.016) - Using mosses as biomonitors to study trace element emissions and their distribution in six different volcanic areas, Journal of Volcanology and Geothermal Research, 343C, 220-232 (2017)
Arndt, J; Calabrese, S; D'Alessandro, W; Planer-Friedrich, B
(See online at https://doi.org/10.1016/j.jvolgeores.2017.07.004) - Moss bag monitoring as screening technique to estimate the relevance of methylated arsine emission, The Science of the Total Environment, 610–611, 1590-1594 (2018)
Arndt, J; Planer-Friedrich, B
(See online at https://doi.org/10.1016/j.scitotenv.2017.06.123)
