Influence of Biogeochemical Conditions on the Stability and Fate of Cr(III) Species in Contaminated Harbor Sediments

拟议的研究重点是确定三价铬Cr（III）在受污染的港口沉积物中的命运。多年的航海、航海和工业活动在美国沿海海湾和港口留下了沉积物污染的遗产。沉积物中发现的污染物的复杂混合物，其中金属是主要成分，对底栖生物、水生生物产生毒性，并最终通过食物网中的生物积累对人类产生毒性。铬就是这样一种金属，通常存在于受污染的沉积物中。三价形式的铬，即铬（III），相对于六价形式的铬（VI）毒性较小，流动性较差，而六价形式的铬（VI）是一种强有力的人类致癌物。在还原环境条件下，Cr（VI）被还原为Cr(III)，而在氧化条件下，Cr（III）被天然存在的水合锰氧化物Mn(III，IV)（水合）氧化物氧化为有毒的Cr（VI）。pi提出的研究将通过对巴尔的摩港周围不同地点的污染沉积物进行控制的实验室研究，填补有关污染沉积物中Cr形态和Cr（III）行为的重要知识空白，这是他们研究工作的实地地点。他们的研究目标是系统地了解影响污染沉积物中Cr形态和命运的生物地球化学过程。他们的初步结果表明，巴尔的摩港沉积物中的Cr主要是沉淀的Cr(III) Cr(OH)3(s)和CrxFe1-x(OH)3(s)， Mn主要是可还原的Mn（III，IV）氢氧化物。这些结果以及我们从初步峰值实验中得到的结果支持了他们的假设，即通过生物扰动、洪水事件、疏浚和人为活动对沉积物进行再悬浮，可以通过Mn(III，IV)（水）氧化物氧化Cr（III）创造有利于Cr（VI）形成的条件。提出的实验工作将利用他们开发的HPLC-ICP-MS分析技术来直接形成大块沉积物中痕量环境浓度下的Cr。建议的工作包括沉积物岩心的收集和表征，以获得金属积累和氧化还原条件的时间和深度信息。使用表层沉积物，第一组批量实验将通过在好氧和厌氧条件下将含水Cr（III）注入沉积物悬浮液来检测沉积物中Mn(III，IV)（氢）氧化物的Cr（III）氧化能力。这里包括不同的水中Cr（III）浓度、沉积物负荷和pH的反应条件。由于Cr（III）固体在接近中性的沉积物pH条件下限制了其溶解度，第二组实验将研究Cr(OH)3(s)和CrxFe1-x(OH)3(s)在好氧和厌氧条件下加入沉积物的反应化学。第三组实验将通过实验室合成的Mn(III，IV)（水合）氧化物在不同Mn(III，IV)（水合）氧化物表面积负载和沉积物负载条件下，在含不同Mn(III)，IV)（水合）矿、锰矿和软锰矿的好氧和厌氧沉积物悬浮液中添加不同Mn（III，IV）含量的锰氧化物，来检测沉积物中Cr（III）的反应状态。这组实验将进一步深入了解Mn（III）或Mn（IV）物种在Cr（III）氧化中的重要性。微生物影响金属的生物利用度，因此，第四组实验将检查Mn氧化微生物通过产生生物源性Mn(III，IV)（氢）氧化物介导沉积物中Cr（III）氧化的影响。每个研究任务的实验结果将通过建模工作进行综合，这些模型将作为评估风险的预测工具，并为金属污染沉积物场地的补救方案提供指导。这项工作的结果将有助于马里兰州环境部（MDE）和其他政府机构在受污染沉积物中建立Cr和类似其他金属的TMDLs。PI继续与巴尔的摩理工学院高中指导计划合作，该计划将贫困和/或少数民族高中生带到约翰霍普金斯大学（JHU）探索科学研究。此外，PI继续担任科学与工程女性（WISE）项目的教师导师，该项目旨在通过向女高中生提供研究经验、指导和指导，促进女性在科学和工程领域的代表性。拟议的项目还将帮助私人教师在JHU的教师研究经验（RET）项目中继续发挥积极作用，在该项目中，来自巴尔的摩市公立高中的教师在私人教师的监督下进行暑期研究项目。这种合作将使参与该项目的博士和本科生参与教育推广活动，获得宝贵的指导和教学经验，并灌输更大的社会责任感。

Bouwer, EdwardCBET-0967236The proposed research focuses on determining the fate of trivalent chromium, Cr(III), in contaminated harbor sediments. Years of navigational, maritime, and industrial activities have left a legacy of sediment contamination in the coastal bays and harbors across the U.S. The complex mixture of contaminants found in sediments, of which metals are a major component, causes toxicity to benthic organisms, aquatic life, and eventually to humans by bioaccumulation in the food web. Cr is one such metal which commonly occurs in contaminated sediments. The trivalent form of Cr, Cr(III), is relatively less toxic, and less mobile than the hexavalent form Cr(VI), which is a potent human carcinogen. Under reducing environmental conditions Cr(VI) is reduced to Cr(III), whereas under oxidizing conditions Cr(III) is oxidized to toxic Cr(VI) by naturally occurring hydrous manganese oxides, Mn(III,IV) (hydr)oxides. The PIs proposed research will fill important knowledge gaps regarding Cr speciation and behavior of Cr(III) in contaminated sediments by conducting controlled laboratory studies using contaminated sediments from various locations around the Baltimore Harbor, the field site for their research efforts.The goal of their research is to obtain a systematic understanding of the biogeochemical processes influencing Cr speciation and fate in contaminated sediments. Their preliminary results reveal that Cr in Baltimore Harbor sediments is predominantly precipitated Cr(III) Cr(OH)3(s) and CrxFe1-x(OH)3(s), and Mn is predominantly as reducible Mn(III,IV) hydroxides. These results along with the ones from our preliminary spike experiments support their hypothesis that resuspension of sediments through bioturbation, flood events, dredging, and anthropogenic activities could make conditions conducive to Cr(VI) formation via Cr(III) oxidation by Mn(III,IV) (hydr)oxides. The proposed experimental work will take advantage of their HPLC-ICP-MS analytical technique developed to achieve direct speciation of Cr at trace environmental concentrations in bulk sediments. The proposed work involves the collection and characterization of sediment cores to obtain chronological and depth information of metal accumulation and redox conditions. Using surficial sediments, the first set of batch experiments will examine the Cr(III) oxidizing capacity of the Mn(III,IV) (hydr)oxides present in sediments by spiking sediment suspensions with aqueous Cr(III) under aerobic and anaerobic conditions. Included here are the reaction conditions of varying aqueous Cr(III) concentrations, sediment loading, and pH. Since Cr(III) solids limit its solubility under the near-neutral pH conditions of the sediments, the second set of experiments will study the reaction chemistry of Cr(OH)3(s) and CrxFe1-x(OH)3(s) spiked into the sediments under aerobic and anaerobic conditions. A third set of experiments will examine the reactive state of Cr(III) present in the sediments by spiking the aerobic and anaerobic sediment suspensions with laboratory synthesized Mn(III,IV) (hydr)oxides containing varying Mn(III) content birnessite, manganite, and pyrolusite under varying conditions of Mn(III,IV) (hydr)oxide surface area loading, and sediment loading. This set of experiments will give additional insights into the importance of Mn(III) or Mn(IV) species in Cr(III) oxidation. Microbes influence the bioavailability of metals and hence, a fourth set of experiments will examine the influence of Mn-oxidizing microbes in mediating Cr(III) oxidation in sediments by producing biogenic Mn(III,IV) (hydr)oxides. The experimental results from each research task will be synthesized through modeling efforts, and these models will serve as predictive tools to assess risks and provide guidance for remedial options on metal-contaminated sediment sites.Results from this proposed work will aid the Maryland Department of the Environment(MDE) and other government agencies in establishing TMDLs for Cr and similarly other metals in contaminated sediments. The PI has continued his collaboration with the Baltimore Polytechnic Institute High School Mentoring Program, which brings underprivileged and/or minority high school students to explore scientific research at Johns Hopkins University (JHU). Additionally, the PI continually serves as a faculty mentor in the Women in Science and Engineering (WISE) program, which is designed to foster representation of women in science and engineering fields by providing research experience, guidance, and mentoring to female high school juniors. The proposed project will also help continue the PIs active role in the Research Experience for Teachers (RET) program at JHU, in which teachers from Baltimore City public high schools pursue research projects over the summer under the PIs supervision. Such collaborations will enable the Ph.D. and undergraduate students involved in this project to engage in educational outreach activities, gain valuable experiences in mentoring and teaching, and instill a greater sense of social responsibility.