The relevance of volatile arsenic emissions from volcanic areas

砷无处不在，是岩石、土壤和水中研究最多的元素之一。然而，人们对大气中的砷知之甚少。定量上最重要的通量来自点源，最主要的自然通量是火山地区。在大气中的命运以前被认为是由颗粒砷决定的，而挥发性砷被忽视了，尽管它们即使在低浓度下也具有高毒性。它们被认为是外来物种，丰度低，寿命太短，与环境无关。然而，最近的调查表明，迄今为止，挥发性砷的稳定性被低估了。采样、稳定和分析技术的缺乏阻碍了大气砷释放和分布的物种选择性质量平衡的计算，也阻碍了非生物和生物形成机制的区分。本项目的假设是，挥发性砷物种对全球生物地球化学循环的贡献更大，运输距离比目前假设的要大得多。进一步推测，除了原生非生物释放外，火山源周围的微生物群落还引起砷的次生挥发并决定其形态。第一个目标是开发一种新的，适合现场的挥发性砷采样方法，使用不锈钢针内带有聚合物吸附剂的提取陷阱（针头陷阱装置，NTDs）。NTDs可以通过主动泵送加载，允许流量量化和计算绝对浓度。NTDs通常应用于有机化学。它们在捕获挥发性砷的数量和物种保存方面的潜力尚不清楚。必须优化吸附剂材料、泵速和储存条件，并消除其他挥发性金属（样物质）或主要火山气体成分（H2O、SO2、H2S）的竞争效应。为了进行分析，采用了一种复杂的耦合技术（GC-MS分裂ICP-MS）：色谱分离后，样品流被分裂；质谱法使未知物种的分子鉴定，电感耦合等离子体质谱法使元素定量。第二个目标是重新评估三个火山区域中不同来源的挥发性砷释放和分布的相关性，这些区域因其不同的火山活动水平而被选中（埃特纳火山区，黄石国家公园，火山区，黄石国家公园）。将对样本进行监测，以确定运输过程中挥发性砷的数量和形态。使用嗜极细菌的现场培养试验将显示甲基化砷酸盐的微生物挥发和砷在气相的甲基化是否发生。总体目标是提供一种实地方法并显示挥发性砷的作用，例如在火山地区，从而引发对挥发性金属（样物质）对全球生物地球化学循环重要性的新评估。

Arsenic is ubiquitous and one of the best investigated elements in rock, soil, or water. Little, however, is known about arsenic in the atmosphere. The quantitatively most important fluxes originate from point sources with the most dominant natural ones being volcanic areas. The fate in the atmosphere has previously been assumed to be determined by particulate arsenic while volatile arsenic species were neglected despite their high toxicity even at low concentrations. They were regarded as exotic, of low abundance, and with a life time too short to be of environmental relevance. Recent investigations, however, indicate that volatile arsenic stability was underestimated so far. A lack of sampling, stabilization, and analytical techniques has prevented calculating a species-selective mass balance of atmospheric arsenic release and distribution as well as differentiating abiotic and biotic formation mechanisms. The hypothesis for the present project is that volatile arsenic species contribute significantly more to the global biogeochemical cycle and transportation distances are much larger than currently assumed. It is further postulated that besides primary abiotic release, microbial communities around volcanic sources cause secondary arsenic volatilization and determine its speciation. The first goal is to develop a new, field-suitable method for volatile arsenic sampling using extraction traps with polymeric sorbents inside a stainless steel needle (Needle Trap Devices, NTDs). NTDs can be loaded by active pumping allowing flow quantification and calculation of absolute concentrations. NTDs are routinely applied in organic chemistry. Their potential for quantitative and species-conserving trapping of volatile arsenic is not known, yet. Sorbent material, pump rates, and storage conditions must be optimized and competitive effects by other volatile metal(loid)s or major volcanic gas components (H2O, SO2, H2S) must be eliminated. For analysis, a sophisticated coupling technique is applied (GC-MS split ICP-MS): After chromatographic separation the sample flow is split; mass spectrometry enables molecular identification of unknown species, inductively coupled plasma-MS enables element quantification.The second goal is to reassess the relevance of volatile arsenic release and distribution from various sources in three volcanic areas, selected for their different levels of volcanic activity (Mt.Etna > Vulcano > Yellowstone National Park). Transects will be monitored to determine the fate of volatile arsenic in amount and speciation during transport. On-site incubation tests using extremophilic bacteria will show whether microbial volatilization of methylated arsenates and methylation of arsine in the gas phase occurs. The overall goal is to provide a field method and show the role of volatile arsenic, exemplary in volcanic areas, thereby triggering a new assessment of the importance of volatile metal(loid)s for global biogeochemical cycles.