Detection of microplastics in soil by non-invasive imaging - Analyzing microplastic effects on soil properties and root-soil interaction

世界各地的土壤受到越来越多的人为污染物的污染，如微塑料。微塑料的持续投入改变了土壤生境的条件，影响了土壤生物群。然而，我们对微塑料如何改变土壤的结构和功能的了解仍然非常有限。目前尚不清楚微塑料如何影响根际过程，以及这对植物构成什么风险。各种分析方法已经可以用来研究土壤中微塑料的不同方面。然而，所有这些方法都涉及破坏样品完整性的采样或处理步骤。因此，有关微塑料在样品中的分布与土壤微结构和水力学之间关系的基本信息不可避免地会丢失。然而，最近，我们开发了一种非侵入性的方法，可以检测沙质土壤中的微塑料。互补中子和X射线层析成像可以检测干燥土壤中的微塑性颗粒，并同时绘制土壤基质和孔隙空间的三维结构图。在这个项目中，将对该方法进行测试、优化，然后应用于更好地从机理上理解不同大小和形状的微塑料如何影响土壤的微结构和特性。我们将研究微塑性纤维在土壤团聚体中的作用，并探索其可能的影响。我们还将研究微塑料的存在是否改变了根际中与根系生长和水分吸收相关的条件，并在不同大小、形状的微塑料存在的情况下跟踪土壤中的水分运动。首先，组合断层扫描的分辨率将被优化，以检测微塑料纤维和薄膜碎片等精细结构。形状描述子的考虑和机器学习的集成将通过将微塑性颗粒与土壤有机质区分开来来支持对它们的分割。利用高分辨率双模层析成像技术，对天然沙土进行了团聚体实验，分析了微塑性纤维对土壤团聚体形成和稳定性的影响。下一步是研究生长在含有不同形状微塑料的沙土中的玉米和羽扇豆幼苗的根际，以确定当地根系结构、土壤基质结构和水分运动的变化。最后，我们将使用高速中子层析成像技术在有根和无根两种情况下捕捉土柱中的动态水分入渗模式。对入渗锋的形状和传播速度的评估将为土壤润湿性是否以及如何受到嵌入的微塑料颗粒的影响提供新的见解。非侵入性分析方法的实施将为微塑料改良的土壤微结构和水力学提供独特的见解，并从机理上更好地理解它们对沙质土壤的形状中介效应。

Soils around the world are increasingly polluted with anthropogenic contaminants such as microplastics. The continuous input of microplastics changes the conditions in the soil habitat and affects soil biota. However, our understanding of how microplastics alters the structure and functioning of soil is still very limited. It is unclear how microplastics affect processes in the rhizosphere and what risks this poses for plants. Various analytic methods have become available to study different aspects of microplastics in soil. However, all of these methods involve sampling or processing steps that destroy the integrity of the sample. Thus, essential information about the relationship of the distribution of microplastics in the sample and soil microstructure and hydraulics is inevitably lost. Recently, however, we have developed a non-invasive approach that can detect microplastics in sandy soil. Complementary neutron and X-ray tomography allows for detection of microplastic particles in the dry soil and simultaneous mapping of the 3D structure of soil matrix and pore space. In this project, the method will be tested, optimized, and then applied to develop a better mechanistic understanding of how microplastics of different sizes and shapes affect soil microstructure and properties. We will investigate the incorporation of microplastic fibers in soil aggregates and explore their possible effects. We will also study whether the presence of microplastics modify the conditions in the rhizosphere relevant for root growth and water uptake and track water movements in soil in the presence of different sizes, shapes of microplastics. To begin with, the resolution of the combined tomography will be optimized for detection of fine structures such as microplastic fibers and film fragments. The consideration of shape descriptors and the integration of machine learning will support the segmentation of microplastic particles by distinguishing them from soil organic matter. For a natural sandy soil, the influence of microplastic fibers on the formation and stability of soil aggregates is analyzed in an aggregation experiment using high-resolution dual-mode tomography. The next step is to study the rhizosphere of young maize and lupine plants growing in sandy soil containing microplastics of various shapes to determine local changes in root structure, soil matrix structure and water movement. Finally, we will use high-speed neutron tomography to capture the dynamic water infiltration patterns in soil columns in 3D, with and without root systems. Evaluation of the shape and propagation speed of infiltration fronts will provide new insights into whether and how soil wettability is affected by embedded microplastic particles. Implementation of the non-invasive analytical approach will provide unique insights into soil microstructure and hydraulics modified by microplastics and provide a better mechanistic understanding of their shape-mediated effects on sandy soil.