CAREER: Determining the mechanism and significance of microplastic pollution impacts on soil hydrology

微塑料的尺寸从0.001毫米到5毫米不等，来源多种多样，如洗涤剂、化妆品，以及薄膜、织物和汽车轮胎等大件物品的分解。大量证据表明，几十年来，微塑料污染一直在陆地环境中发生。然而，农业农场被确定为微塑料污染最严重的地区，主要是由于使用塑料覆盖和使用废水生物固体作为肥料。该项目旨在回答基本和至关重要的问题——微塑料污染能改变土壤-水-植物的相互作用吗？如果是这样，以何种机制，达到何种程度？微塑料通常不可降解，并在表土系统中积累，导致未来几十年污染呈指数增长。了解微塑料对土壤-水-植物相互作用的影响将使政策制定者、科学家和利益相关者能够减轻或防止负面结果。通过了解影响的机制，科学家可以制定有效的减缓战略。本项目的研究目标是进一步了解微塑料对土壤保水特性和非饱和导电性的影响程度和机制（目标1），利用微计算机断层扫描技术的土壤孔隙结构和形态（目标2），以及土壤干燥裂缝发育动力学（目标3）。该项目还将评估新的（未降解的）和老化的（降解的）微塑料对土壤-水-植物相互作用的影响之间的差异，索引微塑料的即时和长期影响（目标4）。本项目将通过对各种影响因素的综合研究，包括农业农场中发现的三种典型的壤土质地土壤、两种最常用的塑料类型（低密度聚乙烯和高密度聚乙烯）、五种微塑料形状（薄膜、纤维、泡沫、破碎和粉末）、四种尺寸范围（50-150、150-500、500-2000和2000- 5000µm）、两种有机质含量（1%和3%）、两种土壤疏水性条件、和五个环境相关的微塑料浓度（1%），利用先进的统计回归和方差模型，扩展蒸发土壤试验，和先进的微型计算机断层扫描技术。在两名研究生和六名本科生的支持下，这些目标将在五年内实现，重点是代表性不足的少数民族和残疾学生。该项目将通过以下方式将研究与教育和推广结合起来：1)为K-12教育工作者实施专业发展计划并创建基于网络的环境计划；2)向代表性不足的学生介绍环境科学、技术、工程和数学（STEM）的研究和职业；3)向当地和全国公众、科学家和政策制定者介绍土壤微塑料污染，4)将土壤污染主题引入孟菲斯大学的研究生和本科生课程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Microplastics, ranging from 0.001 to 5 mm in size, originate from various sources such as detergents, cosmetics, and the breakdown of larger items like films, fabrics, and vehicle tires. There is extensive evidence that microplastic pollution has been occurring in terrestrial environments for decades. However, agricultural farms are identified as the most microplastic-polluted areas, mainly due to the use of plastic mulching and the application of wastewater biosolids as fertilizer. This project aims to answer fundamental and critically important questions— Can microplastic pollution change the soil-water-plant interactions? If so, in what mechanism, and to what extent? Microplastics are generally not degradable and accumulate in topsoil systems, resulting in exponential pollution growth in the coming decades. Understanding microplastics’ impacts on soil-water-plant interactions will empower policymakers, scientists, and stakeholders to mitigate or prevent negative outcomes. By comprehending the mechanisms of impacts, scientists can develop effective mitigation strategies.The research objectives of this project have been formulated to advance understanding of the extent and mechanism of microplastics’ impact on soil-water retention characteristics and unsaturated hydraulic conductivity (Objective-1), soil pore structure and morphology using micro-computed tomography techniques (Objective-2), and soil desiccation crack development dynamics (Objective-3). This project will also assess the variance between impacts of new (non-degraded) and aged (degraded) microplastic on soil-water-plant interactions, indexing immediate and long-term impacts of microplastics (Objective-4). This project will generate generalizable outcomes through a comprehensive study of various influential factors, including three typical loamy-texture soils found in agricultural farms, two most commonly used plastic types (low and high-density polyethylene), five microplastic shapes (film, fiber, foam, fragment, and powder), four size ranges (50-150, 150-500, 500-2000, and 2000- 5000 µm), two organic matter contents (1% and 3%), two soil hydrophobicity conditions, and five environmentally relevant microplastic concentrations ( 1%), utilizing advanced statistical regressions and variance models, extended evaporation soil tests, and advanced micro-computed tomography techniques. The objectives will be pursued over five years with the support of two graduate and six undergraduate students, emphasizing on underrepresented minorities and students with disabilities. The project will integrate research with education and outreach by 1) implementing a professional development program for K-12 educators and creating a web-based environmental program, 2) introducing underrepresented students to environmental science, technology, engineering, and mathematics (STEM) research and careers; 3) introducing soil-microplastic pollution to local and national public, scientists, and policymakers, and 4) bringing soil pollution topics to the graduate and undergraduate curriculum at the University of Memphis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.