Arsenic in gases from shallow-water hydrothermal systems

与深海热液系统不同，海洋浅水热液系统发生在浅水近岸环境中，它们可以通过排放通常含有砷(As)的减少的高温热液对沿海海洋产生相当大的影响。流体的排放通常伴随着热液气体的大量排放。对这些气体中的砷浓度一无所知，尽管在热液系统中，砷被分配到气相中，并已知存在于类似的陆地火山气体中。为什么在MSWHS的气相中没有测量到砷，这是未知的，尽管收集足够的样本量和将其转移到合适的实验室很可能是一种威慑。从海底热液喷口收集10到25 L的气体并不是一件容易的事，运输这样的数量将是一个问题。考虑到这一点，拟议中的项目的目标是开发和测试一种在MSWHS气相中捕获和测量挥发性砷的程序。该方法将基于一种已建立的方法，即将水下气体收集到最初为汞(Hg)开发的气密特德拉®袋子中。在收集之后，砷将通过捕捉到硅树脂上或进入NaOCl溶液从气体中提取。首先，在实验室条件下对诱捕方法进行测试和优化。其次，它们将通过在希腊米洛斯南侧的Paleochori海湾的MSWHS采集热液气体样本进行现场应用和测试。在那里，热液中浓度的升高导致每年1.5×104公斤的砷从海湾流入地中海。尽管如此，对于挥发性砷组分的这一估计是不存在的，假设浓度类似于陆上热液系统，通过气相的砷通量将为4.5×104公斤，是通过水相的估计通量的三倍。因此，在古曹里湾进行的现场测试应该会在气相中提供足够的砷浓度，并为这个富砷的MSWHs提供第一批数据。一旦成功应用，新开发的方法将为全球MSWHS气体中砷的采样提供一个合适的现场程序。

Marine shallow-water hydrothermal systems (MSWHS), as opposed to deep-sea hydrothermal systems, occur in shallow-water nearshore settings where they can have a considerable impact on the coastal ocean through discharge of reduced, hot hydrothermal fluids that often contain arsenic (As). The emission of fluids is generally accompanied by the extensive discharge of hydrothermal gases. Nothing is known about the arsenic concentrations in those gases, although arsenic partitions into the gas phase in hydrothermal systems and is known to be present in comparable land-based volcanic gases.Why arsenic has not been measured in the gas phase in MSWHS is unknown, although it is likely that the collection of sufficient sample volume and the transport to a suitable laboratory were a deterrent. To collect anywhere from 10 to 25 L of gas from hydrothermal vents on the seafloor is not trivial, and shipping such volumes would be problematic.With this in mind, the objective of the proposed project will be to develop and test a procedure for trapping and measuring volatile arsenic in the gas phase in MSWHS. The method will be based on an established method of underwater gas collection into gastight Tedlar® bags initially developed for mercury (Hg). Following collection, arsenic will be extracted from the gas by either trapping onto a silicon resin or into a NaOCl solution. First, the trapping methods will be tested and optimized under laboratory conditions. Second, they will be applied and tested in the field by sampling hydrothermal gases from the MSWHS in Paleochori Bay on the south side of Milos, Greece. There, elevated concentrations in the hydrothermal fluids lead to an annual flux of 1.5 × 10^4 kg arsenic from the Bay into the Mediterranean Sea. Still, this estimation is missing for the volatile arsenic fraction and assuming concentrations similar to land-based hydrothermal systems, the arsenic flux via the gas phase would be 4.5 × 10^4 kg, three times the estimated flux via the water phase. Thus, a field test in Paleochori Bay should provide sufficient arsenic concentrations in the gas phase and provide first data for this arsenic-rich MSWHS. Once successfully applied, the newly developed method will provide a suitable field procedure for sampling arsenic in gases from MSWHS worldwide.