The relevance of volatile arsenic emissions from volcanic areas

砷在岩石、土壤或水中普遍存在，也是被研究得最多的元素之一。然而，人们对大气中的砷知之甚少。从数量上讲，最重要的通量来自点源，最主要的自然来源是火山区。大气中的去向以前被认为是由颗粒砷决定的，而挥发性砷即使在低浓度下也具有很高的毒性，但却被忽视了。它们被认为是外来的，丰度低，生命周期太短，与环境无关。然而，最近的研究表明，挥发性砷的稳定性到目前为止被低估了。由于缺乏采样、稳定和分析技术，无法计算大气砷释放和分布的物种选择性质量平衡，也无法区分非生物和生物形成机制。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明显更大，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会引起二次砷挥发，并决定其形态。第一个目标是开发一种新的、适用于现场的挥发性砷采样方法，使用不锈钢针(Needle Trap Devices，NTDS)内带有聚合物吸着剂的萃取捕捉器。NTDS可以通过主动泵送加载，从而实现流量量化和绝对浓度计算。NTDS是有机化学中的常规应用。它们对挥发性砷的定量和物种保护捕获的潜力尚不清楚。必须优化脱硫剂材料、泵速和储存条件，并消除其他挥发性金属(LOID)S或主要火山气体成分(H2O、SO2、H2S)的竞争效应。为了进行分析，采用了复杂的耦合技术(GC-MS分离-电感耦合等离子体质谱)：色层分离后，样品流动分离；质谱仪能够对未知物种进行分子鉴定，电感耦合等离子体-MS能够对元素进行定量。第二个目标是重新评估三个火山区(Mt.Etna&Gt；Vulcano&Gt；Yellowstone National Park)不同来源挥发性砷释放和分布的相关性。将对横断面进行监测，以确定运输过程中挥发性砷的数量和形态的去向。使用极端细菌的现场培养试验将显示气相中是否发生微生物挥发的甲基化砷酸盐和砷的甲基化。总的目标是提供一种现场方法，展示挥发性砷的作用，在火山区发挥示范作用，从而引发对挥发性金属(LOID)S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.