Relevance and environmental fate of methylthiolated arsenates in geothermal waters

地热水中甲硫基砷酸盐的相关性和环境归趋

• 批准号: 410123522
• 负责人: Professorin Dr. Britta Planer-Friedrich
• 金额: --
• 依托单位: Lehrstuhl für Umweltgeochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/410123522?language=en
• 关键词: Relevance; environmental; fate; methylthiolated; arsenates

Geothermal waters are one of the most important sources in the geochemical arsenic cycle. Investigations typically cover arsenite and arsenate, which can travel considerable distances from a hot spring discharge with negative impact on downstream sediments, rivers, or groundwaters used as drinking water. Lately, it has been shown that thioarsenates (AsVSnO4-n3-; n = 1 - 4) which form from arsenite and reduced sulfur can dominate geothermal arsenic speciation. Their long-distance transport, however, is likely limited by their reactivity towards oxygen.Here, we postulate that methylation is a much more common process at geothermal springs than currently assumed and that methylthiolated arsenates can contribute significantly to total arsenic, especially at slightly acidic pH, high sulfide and dissolved organic carbon concentrations. We further postulate that compared to inorganic thioarsenates, methylthiolated arsenates are less susceptible to abiotic and microbially mediated species transformation and that compared to arsenite and arsenate they show less and slower sorption to iron mineral phases and natural organic matter, enhancing their mobility in the environment and long-distance impact away from geothermal sources.To test our hypotheses, we will carry out field studies at two geothermal areas in China (Rehai, Yunnan and Daggyai, Tibet) investigating arsenic speciation at the geothermal vents and following their fate and transformation along natural drainage channels as well as in on-site incubation studies. We will identify other abiotic or biotic factors contributing to arsenic species transformation. In the laboratory, we will synthesize methylthiolated arsenates and study their formation and stability varying S/As ratios, temperatures, pH, and presence and amount of oxidizing agents. We will further study sorption extent and kinetics on commonly occurring iron mineral phases (ferrihydrite, goethite, mackinawite, pyrite) and a model natural organic matter compound in batch experiments. Adding complexity, we will identify the mineralogical and chemical compositions of sediments in the hot spring vents and their outflow channels and determine their sorption potential for methylthiolated arsenates.The study will be carried out in close cooperation between Prof. Dr. Britta Planer-Friedrich (Germany), an expert in thioarsenic chemistry and analytics, and Prof. Dr. Qinghai Guo (China), an expert in geothermal water geochemistry. Cooperation includes co-supervised PhD and MSc students, joint field trips in China, and joint lab experiments in Germany. A kickoff meeting in Germany and a closing workshop in China will frame the project. The overall output of the present proposal will be to derive a new model for geothermal arsenic species formation, transport, transformation, and fate, illustrate the importance, and predict occurrence of methylthiolated arsenates also in other environments.

地下沃茨是砷地球化学循环的重要来源之一。调查通常包括亚砷酸盐和砷酸盐，它们可以从温泉排放物中传播相当长的距离，对下游沉积物、河流或用作饮用水的地下水产生负面影响。最近，它已被证明，硫代砷酸盐（AsVSnO 4-n3-; n = 1 - 4），形成从亚砷酸盐和还原硫可以占主导地位的地热砷形态。他们的长途运输，然而，可能是有限的，他们对oxygen.here的反应性，我们假设，甲基化是一个更常见的过程，在地热温泉比目前假设的和甲基硫醇化砷酸盐可以显着贡献总砷，特别是在微酸性pH值，高硫化物和溶解有机碳浓度。我们进一步假设，与无机硫代砷酸盐相比，甲基硫代砷酸盐对非生物和微生物介导的物种转化不太敏感，并且与亚砷酸盐和砷酸盐相比，它们对铁矿物相和天然有机物的吸附更少和更慢，增强了它们在环境中的流动性和远离地热源的远距离影响。我们将在中国的两个地热区（云南热海和西藏达吉）进行实地研究，调查地热喷口处的砷形态，并跟踪它们的命运和沿着天然排水通道的转化，以及现场孵化研究。我们将确定有助于砷物种转化的其他非生物或生物因素。在实验室中，我们将合成甲基硫醇化砷酸盐，并研究它们的形成和稳定性，改变S/As比，温度，pH值，以及氧化剂的存在和量。我们将进一步研究吸附程度和动力学上常见的铁矿物相（水铁矿，针铁矿，mackinawite，黄铁矿）和模型天然有机物化合物在批实验。更复杂的是，我们将确定温泉喷口及其流出通道中沉积物的矿物学和化学成分，并确定其对甲基硫代砷酸盐的吸附潜力。这项研究将在硫代砷化学和分析专家Britta Planer-Friedrich教授（德国）和地热水地球化学专家Qinghai Guo教授（中国）的密切合作下进行。合作包括共同指导博士和硕士学生，在中国的联合实地考察，以及在德国的联合实验室实验。在德国举行的启动会议和在中国举行的闭幕研讨会将为该项目提供框架。本提案的总体产出将是得出一个新的地热砷物种的形成，运输，转化和命运的模型，说明的重要性，并预测发生在其他环境中的甲基硫醇化砷酸盐。