Environmental Implications of Nanocellulose: Biodegradation and Toxicity Potential

过去十年的研究已经清楚地表明，各种商业相关的纳米材料对环境有有害的影响。不幸的是，人们对纤维素基纳米材料（纳米纤维素）的环境影响知之甚少。与此同时，纤维素基纳米材料的市场预计到2020年将超过10亿美元。考虑到这个市场的估计规模和纳米纤维素的预期化学和生物稳定性，有必要评估这些纳米材料对环境的影响。尽管纤维素通常被认为是一种环保材料，因为它在木材、纤维和被囊动物中无处不在，但纳米纤维素在物理和化学上都非常不同。这些差异意味着不能假设纳米纤维素像天然状态下的纤维素一样可生物降解和对环境无害。因此，拟议的研究将利用与废水处理厂（WWTPs）和受影响的水环境相关的细菌群落来评估生物降解（即纳米纤维素是否会自然分解）和毒性（即纳米纤维素是否对某些生物有害）。污水处理厂的微生物尤其重要，因为随着纳米纤维素产量的增加，进入污水处理厂的浓度也会相应增加。该研究将集中在两个假设上：假设一：细菌对纳米纤维素的生物降解将受到其表面特性（例如，表面官能团赋予的电荷、疏水性和位阻）的影响。假设二：带负电荷的纳米纤维素材料是无毒的，而带有正电荷表面修饰的纳米纤维素材料毒性更大，因为它们会粘附或破坏细胞膜（带负电荷）。为了验证这些假设，我们制定了一个由两个综合研究任务组成的研究计划：任务1。评价纳米纤维素的生物降解性，任务2。评价纳米纤维素引起的毒性和应激反应。由于对纳米纤维素生产和使用的环境影响知之甚少，任务1和任务2定义的实验室研究工作将与弗吉尼亚理工大学本科生LCA课程（ENGR 3134）的生命周期评估（LCA）清单模块的并行开发相辅相成。在这项努力中，选修ENGR 3134的本科生将编制考虑纳米纤维素生产和使用的清单。智力优势：提议的为期一年的研究是高风险/高回报的，将建立纳米纤维素生物降解和毒性潜力的关键基线信息。纳米纤维素作为一种潜在的“绿色”纳米材料有着巨大的前景。然而，验证这一假设是至关重要的，特别是在主要生产设施正在上线的情况下。不同纳米纤维素制备的物理化学状态（例如，表面部分、表面电荷、聚集状态）将与其生物降解性和微生物毒性联系起来，使用复杂的微生物群落（厌氧消化池和湿地沉积物），这些微生物群落与最有可能受到处置或其他释放影响的环境有关。由于纳米纤维素的核心材料被认为是“惰性的”，该方法最终可以提供一种方法，将表面化学的影响和纳米材料的行为作为一个整体来控制它们对环境的影响。这项研究还将推进厌氧纤维素降解的基础知识基础，厌氧纤维素降解是一个关键的生物地球化学过程，对气候变化和替代生物燃料的发展等关键问题具有重要意义。更广泛的影响：该项目将资助两名博士生，他们将获得纳米技术、可持续生物材料、环境微生物学、环境工程和分子工具应用等领域的跨学科培训。该项目将通过促进VT关键技术和应用科学研究所（ICTAS）可持续纳米技术（SuN）和水可持续性研究重点之间的跨学科合作产生机构影响，这将为研究生提供补充支持。跨学科研究生教育也将通过与之配套的中山大学跨学科研究生教育项目（IGEP）得到加强，该项目也将为学生提供支持机会。拟议的LCA清单将作为弗吉尼亚理工大学本科绿色工程项目的一个组成部分，为课堂上和独立的本科生研究人员提供一个动手的机会，同时也建立了一个范例，通过这个范例，纳米技术的“绿色”本质可以客观地评估。将向妇女和经济上代表性不足的群体作出外联努力，以支持社区教育，并协助招募博士和本科生研究人员协助这个项目。

CBET 1236005 Studies over the past ten years have made it apparent that various commercially-relevant nanomaterials have harmful impacts on the environment. Unfortunately, there is a void of knowledge about the environmental implications of cellulose-based nanomaterials (nanocellulose). At the same time, the market for cellulose-based nanomaterials is expected to exceed a billion dollars by 2020. Given the estimated size of this market and the expected chemical and biological stability of nanocellulose there is a need to evaluate the environmental implications of these nanomaterials. Even though cellulose is generally considered to be an environmentally-friendly material given its omnipresence in woods, fibers, and tunicate animals, nanocellulose is both physically and chemically very different. These differences mean that it cannot be assumed that nanocellulose is as biodegradable and environmentally benign as cellulose in its native state. Thus, the proposed research will evaluate biodegradation (i.e., will nanocellulose naturally break down) and toxicity (i.e., is nanocellulose harmful to some organisms) utilizing bacterial communities relevant to wastewater treatment plants (WWTPs) and impacted water environments. WWTP microbes are especially relevant because as production of nanocellulose escalates, concentrations entering WWTPs will correspondingly increase. The study will focus on two hypotheses: Hypothesis One: Bacterial biodegradation of nanocellulose will be influenced by its surface properties (e.g., charge, hydrophobicity, and steric hindrance imparted by surface functional groups). Hypothesis Two: Negatively charged nanocellulose materials are non-toxic, while those possessing positively-charged surface modifications will be more toxic because they adhere to or disrupt cellular membranes (which are negatively charged). To test these hypotheses we have developed a research plan consisting of two integrated research tasks: Task 1. Evaluate the biodegradability of nanocellulose, and Task 2. Evaluate the toxicity and stress responses elicited by nanocellulose. Because very little is known about the environmental implications of nanocellulose production and use, the laboratory research efforts defined by Tasks 1 & 2 will be complemented by the parallel development of a life cycle assessment (LCA) inventory module for an undergraduate LCA course (ENGR 3134) at Virginia Tech. In this effort, undergraduate students taking ENGR 3134 will produce inventories that consider nanocellulose production and use. INTELLECTUAL MERIT: The proposed one year investigation is high risk/high reward and will establish critical baseline information on nanocellulose biodegradation and toxicity potential. Nanocellulose holds great promise as a potentially "green" nanomaterial. However, it is critical that this assumption be validated, especially as major production facilities are now going online. The physicochemical state (e.g., surface moieties, surface charge, aggregation state) of varying preparations of nanocellulose will be linked both to its biodegradability and microbial toxicity using complex microbial communities (anaerobic digester and wetland sediment) relevant to environments most likely to be impacted by disposal or other release. As the core material of nanocellulose is thought to be "inert", the approach could eventually provide a means to isolate the effects of surface chemistry and the behavior of nanomaterials as a whole in governing their environmental implications. This investigation will also advance the fundamental knowledge base of anaerobic cellulose degradation, a key biogeochemical process important for critical issues such as climate change and the development of alternative biofuels. BROADER IMPACTS: Two Ph.D. student researchers will be funded by this project and will gain interdisciplinary training across fields of nanotechnology, sustainable biomaterials, environmental microbiology, environmental engineering and application of molecular tools. The project will have institutional impact by catalyzing interdisciplinary collaboration between the VT Institute for Critical Technology and Applied Science (ICTAS) Sustainable Nanotechnology (SuN) and Water Sustainability research thrusts, which will provide complementary graduate student support. Interdisciplinary graduate education will also be enhanced via the companion VT SuN Interdisciplinary Graduate Education Program (IGEP), which will also provide opportunities for student support. The proposed LCA inventory will serve as an integral component of the undergraduate Virginia Tech Green Engineering program, providing a hands-on opportunity for in-class and independent undergraduate researchers, while also establishing a paradigm by which the "green" nature of nanotechnologies can objectively be assessed. Outreach efforts to women and economically underrepresented groups will be made to support community education as well as to aid in recruiting Ph.D. and undergraduate researchers to assist in this project.