Insights to Selenium Cycling and Remediation Revealed by Stable Oxygen Isotopes

由于侵蚀、采矿、燃烧、石油加工和灌溉活动涉及富硒土壤、页岩和矿石，地表沃茨和沉积物的硒（Se）污染在美国西部普遍存在。 它在湖泊和沉积物中的积累对野生动物造成了不利的生物影响，并对人类健康构成威胁，因此需要进行大规模的监测和生物补救工作。 硒在水中的迁移性和生物有效性很大程度上取决于硒的化学形态。 本项目将利用一种新的同位素技术，研究溶解的硒氧阴离子（硒酸盐和亚硒酸盐）的动员机制及其在不同地球化学环境下的自然和修复系统中的固定化。 在过去的十年中，其他研究人员的稳定同位素研究提供了有价值的见解硒地球化学和环境硒源识别。 然而，稳定的氧同位素研究硒含氧阴离子，迄今缺乏，将提供一种新的方法来表征硒氧化还原循环和扩大适用性的同位素分馏反应以前不敏感的硒同位素分馏，如氧原子通过氧化加成。 该项目的目标是开发一种稳定的氧同位素方法，并将其应用于解决水硒地球化学中的关键知识缺口。 实验室实验将检查反应途径，包括：（1）描述溶解的硒酸盐和亚硒酸盐如何从母体矿物的氧化形成并进入水道，（2）探测在氧阴离子吸附到环境金属氧化物期间发生的界面氧交换机制，和（3）组装氧同位素分馏指示剂，所述氧同位素分馏指示剂特异于氧阴离子固定化途径，例如与矿物的还原和吸收反应，细菌藻类和真菌 在反应过程中，将使用同位素比质谱法监测含氧阴离子、水、氧化物和氧化剂的稳定氧同位素值。 氧同位素示踪实验将确定可能的来源，氧阴离子的形成和氧化物的相互作用过程中的氧掺入和交换，导致一个更清晰的概念模型硒污染物动力学。 与Se同位素一样，预计测得的氧同位素分馏值对于不同的还原途径是独特的，因此可用于区分负责溶解Se处理的化学反应和微生物反应。 该项目将通过同位素标记追踪反应途径，扩大硒含氧阴离子如何在水生系统中形成和转化的科学知识。 更好地理解将开发的化学和微生物控制硒动员和固定。 预计这些结果将成为通过使用直接揭示现场反应的同位素信息来改进现场监测和补救工作的基础。 稳定氧同位素的方法来评估机制将有广泛的适用性，以评估其他无机含氧阴离子污染物，如砷和铬。 该项目将为一名研究生和几名本科生，高中生和K-12教师提供研究机会，在多学科环境中研究化学，生物和矿物学试剂与金属水污染物的相互作用。 除了通过动手实验室参与体验式学习外，这些K-12参与者还将以实地考察演示和课程模块的形式开发教育材料，以指导广大受众了解水污染和处理的原则。

1236182Philip Larese-CasanovaSelenium (Se) pollution of surface waters and sediments is pervasive in the western U.S. due to erosion, mining, combustion, petroleum processing, and irrigation activities that involve Se-rich soils, shales, and ore. Its accumulation in lakes and sediments has lead to adverse biological effects in wildlife and to health threats to humans, prompting a need for large-scale monitoring and bioremediation efforts. The mobility and bioavailability of Se in water strongly depends on the chemical form of Se. This project will investigate mechanisms of mobilization of dissolved Se oxyanions (selenate and selenite) and their immobilization in natural and remediation systems under diverse biogeochemical settings using a novel isotopic technique. Over the past decade, stable Se isotope studies from other researchers have provided valuable insights to Se biogeochemistry and environmental Se source identification. However, stable oxygen isotopic studies of Se oxyanions, so far lacking, will provide a new approach to characterizing Se redox cycling and expand applicability of isotope fractionations to reactions previously not sensitive to Se isotope fractionation, such as oxygen atom addition via oxidation. The objective of this project is to develop a stable oxygen isotopic approach and apply it to answer key knowledge gaps within aqueous selenium biogeochemistry. Laboratory experiments will examine reaction pathways including: (1) describing how dissolved selenate and selenite form from the oxidation of parent minerals and enter waterways, (2) probing interfacial oxygen exchange mechanisms that occur during oxyanion sorption to environmental metal oxides, and (3) assembling oxygen isotope fractionation indicators specific to oxyanion immobilization pathways such as reduction and uptake reactions with minerals, bacteria, algae, and fungi. Stable oxygen isotope values of oxyanions, water, oxides, and oxidants will be monitored during reactions using isotope ratio mass spectrometry. The oxygen isotope tracing experiments will identify likely sources of oxygen incorporation and exchange during oxyanion formation and interaction with oxides, leading to a clearer conceptual model of Se pollutant dynamics. Like Se isotopes, the measured oxygen isotope fractionation values are expected to be unique to different reduction pathways and therefore can be used to distinguish between chemical and microbial reactions responsible for dissolved Se processing. This project will expand the scientific knowledge of how selenium oxyanions form and transform in aquatic systems through reaction pathway tracing with isotope labeling. A better understanding will be developed for the chemical and microbial controls on selenium mobilization and immobilization. The results are expected to form the basis of improved field site monitoring and remediation efforts by using isotopic information that directly reveal field site reactions. The stable oxygen isotope approach to evaluating mechanisms will have broad applicability to evaluating other inorganic oxyanion contaminants such as arsenic and chromium. This project will provide research opportunities for one graduate student and several undergraduate students, high school students, and K-12 teachers within a multidisciplinary setting that investigates chemical, biological, and mineralogical agents interacting with metallic water contaminants. In addition to engaging experiential learning through hands-on laboratory engagement, these K-12 participants will also develop educational materials, in the form of field trip demonstrations and curriculum modules, for the instruction of broad audiences about the principles of water contamination and treatment.