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

Bouwer，EdwardCBET-0967236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。 多年的航行，海事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，水生生物造成毒性，并最终通过食物网中的生物积累对人类造成毒性。 铬就是这样一种金属，通常存在于受污染的沉积物中。 Cr的三价形式Cr（III）的毒性相对较小，并且比六价形式Cr（VI）的移动的较小，六价形式Cr（VI）是一种有效的人类致癌物。 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）（hydr）氧化物氧化为有毒的Cr（VI）。PI提出的研究将填补重要的知识空白，铬形态和行为的Cr（III）在污染的沉积物进行控制实验室研究，使用污染的沉积物从周围的巴尔的摩港，他们的研究工作的现场站点。他们的研究目标是获得一个系统的了解生态地球化学过程影响铬形态和命运的污染沉积物。 他们的初步结果表明，在巴尔的摩港沉积物中，铬主要是沉淀的Cr（III）Cr（OH）3（s）和CrxFe 1-x（OH）3（s），锰主要是可还原的Mn（III，IV）氢氧化物。 这些结果沿着从我们的初步穗实验支持他们的假设，通过生物扰动，洪水事件，疏浚，和人为活动的沉积物再悬浮可以通过铬（III）的氧化锰（III，IV）（氢）氧化物的条件有利于铬（VI）的形成。 拟议的实验工作将利用他们的HPLC-ICP-MS分析技术开发，以实现在散装沉积物中痕量环境浓度的铬的直接形态。 拟议的工作涉及收集沉积物岩心并确定其特性，以获得金属积累和氧化还原条件的年代和深度信息。 使用表层沉积物，第一组批实验将检查铬（III）氧化能力的锰（III，IV）（氢）氧化物存在于沉积物中，通过掺加沉积物悬浮液与含水铬（III）在有氧和厌氧条件下。这里包括的反应条件不同的水铬（III）浓度，沉积物负荷，和pH值。由于铬（III）固体限制其溶解度在近中性的pH值条件下的沉积物，第二组实验将研究的反应化学的Cr（OH）3（S）和CrxFe 1-x（OH）3（S）掺入沉积物在有氧和厌氧条件下。 第三组实验将检查的反应状态的Cr（III）存在于沉积物中的掺入好氧和厌氧沉积物悬浮液与实验室合成的Mn（III，IV）（氢）氧化物含有不同的Mn（III）含量水钠锰矿，锰矿，软锰矿在不同条件下的Mn（III，IV）（氢）氧化物表面积负荷，和沉积物负荷。 这组实验将提供额外的见解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，第四组实验将研究锰氧化微生物的影响，通过产生生物锰（III，IV）（氢）氧化物介导沉积物中的铬（III）氧化。 每个研究任务的实验结果将通过建模工作进行合成，这些模型将作为预测工具，以评估风险，并提供指导补救方案的金属污染的沉积sites.Results从这项拟议的工作将有助于马里兰州环境部（MDE）和其他政府机构在建立TMDLs的铬和类似的其他金属污染沉积物。 PI继续与巴尔的摩理工学院高中指导计划合作，该计划使贫困和/或少数民族高中学生在约翰霍普金斯大学（JHU）探索科学研究。此外，PI继续担任在科学和工程（WISE）计划，旨在通过提供研究经验，指导和指导女高中三年级学生促进妇女在科学和工程领域的代表性的妇女教师导师。 拟议的项目还将有助于继续在JHU的教师研究经验（RET）计划中发挥积极作用，在该计划中，来自巴尔的摩市公立高中的教师在PI的监督下在夏季开展研究项目。 这样的合作将使博士。及参与计划的本科生参与教育外展活动，汲取宝贵的辅导和教学经验，并培养更大的社会责任感。

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.