Insights to Selenium Cycling and Remediation Revealed by Stable Oxygen Isotopes

稳定氧同位素揭示的硒循环和修复见解

• 批准号: 1236182
• 负责人: Philip Larese-Casanova
• 金额: $ 30.47万
• 依托单位: Northeastern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1236182&HistoricalAwards=false
• 关键词: Insights; Selenium; Cycling; Remediation; Revealed

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.

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，地表水和沉积物中的硒(Se)污染在美国西部普遍存在。它在湖泊和沉积物中的积累已对野生动物造成不利的生物影响，并对人类健康构成威胁，因此需要进行大规模监测和生物修复工作。水中Se的移动性和生物有效性强烈依赖于Se的化学形态。本项目将利用一种新的同位素技术，研究在不同的生物地球化学环境下，溶解的硒氧阴离子(亚硒酸盐和亚硒酸盐)在自然和修复系统中的动员机制及其固定化。在过去的十年里，其他研究人员的稳定Se同位素研究为Se生物地球化学和环境Se来源识别提供了有价值的见解。然而，迄今缺乏的Se氧阴离子的稳定氧同位素研究将为表征Se氧化还原循环提供一种新的方法，并扩大同位素分馏对以前对Se同位素分馏不敏感的反应的适用性，例如通过氧化加成氧原子。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中硒生物地球化学方面的关键知识空白。实验室实验将研究反应途径，包括：(1)描述溶解的亚硒酸盐和亚硒酸盐如何从母矿物的氧化中形成并进入水道，(2)探索环境金属氧化物吸附氧阴离子过程中发生的界面氧交换机制，以及(3)组装氧阴离子固定途径的氧同位素分馏指示器，例如与矿物、细菌、藻类和真菌的还原和吸收反应。在反应过程中，将使用同位素比质谱仪监测氧阴离子、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氧阴离子形成和与氧化物相互作用过程中可能的氧掺入和交换来源，从而获得更清晰的Se污染物动力学概念模型。与Se同位素一样，测得的氧同位素分馏数值预计对不同的还原途径是唯一的，因此可以用来区分负责溶解Se加工的化学反应和微生物反应。这个项目将通过同位素标记的反应途径追踪，扩大关于硒氧阴离子如何在水生体系中形成和转化的科学知识。将更好地了解化学和微生物控制对硒的动员和固定。预计这一结果将成为改进现场监测和补救工作的基础，方法是利用直接揭示现场反应的同位素信息。稳定氧同位素评价机理的方法将广泛适用于评价其他无机含氧阴离子污染物，如砷和铬。这个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，在多学科背景下调查化学、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进行体验式学习外，这些从K-12岁到12岁的学员还将以实地考察演示和课程单元的形式开发教材，向广大受众传授水污染和处理的原理。