The relevance of volatile arsenic emissions from volcanic areas

砷是普遍存在的，是岩石、土壤或水中研究得最好的元素之一。然而，人们对大气中的砷知之甚少。数量上最重要的通量来自点源，最主要的自然源是火山地区。大气中的命运以前被认为是由颗粒砷，而挥发性砷物种被忽略，尽管他们的高毒性，即使在低浓度。它们被认为是外来的，丰度低，寿命太短，与环境无关。然而，最近的调查表明，挥发性砷的稳定性被低估了。缺乏采样，稳定和分析技术，防止计算物种选择性的质量平衡的大气砷的释放和分布，以及区分非生物和生物的形成机制。本项目的假设是，挥发性砷物种对全球地球化学循环的贡献要大得多，而且迁移距离比目前假设的要大得多。它进一步假设，除了主要的非生物释放，火山源周围的微生物群落引起二次砷挥发，并决定其形态。第一个目标是开发一种新的，现场适用的挥发性砷采样方法，使用不锈钢针内的聚合物吸附剂萃取陷阱（针陷阱装置，NTDs）。NTD可通过主动泵送加载，从而允许流量定量和绝对浓度计算。NTD通常应用于有机化学。它们对挥发性砷的定量和物种保护捕集潜力尚不清楚。必须优化吸附剂材料、泵送速率和储存条件，并且必须消除其他挥发性金属或主要火山气体成分（H2O、SO2、H2S）的竞争效应。为了分析，应用了复杂的耦合技术（GC-MS分流ICP-MS）：色谱分离后，将样品流分流;质谱法能够对未知物种进行分子鉴定，电感耦合等离子体质谱法能够对元素进行定量。第二个目标是重新评估三个火山地区各种来源的挥发性砷释放和分布的相关性，根据不同的火山活动水平（埃特纳山>武尔卡诺山>黄石国家公园）选择。将对断面进行监测，以确定运输过程中挥发性砷的数量和形态。利用嗜极端细菌进行的现场培养试验将显示是否发生甲基化砷酸盐的微生物挥发和气相中砷化氢的甲基化。总的目标是提供一个现场方法，并显示挥发性砷的作用，在火山地区的示范，从而引发一个新的评估挥发性金属（类）的全球地球化学循环的重要性。

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.