Recent improvements in survey methods for microplastic (MP) pollution in natural waters have enabled quantification of MP particles < 300 μm in diameter. Historically, this putatively important size fraction of MP particles has not been sampled adequately, possibly leading to significant underestimations of plastic inventories in aquatic systems. Furthermore, reported MP particle numbers are poorly constrained proxies for MP mass loadings as sizes vary widely and densities differ within and among polymers, consequently compromising mass flux estimations. However, determination of MP number, identity, and mass can resolve these issues and enable more accurate estimations of MP loadings. Using Raman microspectroscopy coupled with three-dimensional (3D) spectral imaging, we have developed an automatable methodology to detect, identify, and quantify MPs retained on filters from discrete water samples. Raman spectral information enabled identification of plastic polymers in particles between 0.5 and 300 μm in diameter and generation of 3D chemical maps. To accelerate volume determinations of each identified MP particle, we developed an algorithm to derive volumes from image analysis of two-dimensional micrographs that are statistically indistinguishable from those directly measured by 3D Raman chemical maps. Masses of each Raman-identified MP particle are determined from their volumes and known plastic specific weights. This methodology provides accurate estimations of the smallest MP particles' contributions to total MP mass in discrete water samples, providing vital information for mass flux calculations of MPs in natural waters.

中文翻译：

---

评估水生系统中微塑料（~ 1–300 μm）的多样性、丰度和质量

天然水体中微塑料 (MP) 污染调查方法的最新改进已经能够量化小于 300 μ的 MP 颗粒 米直径。从历史上看，这种假定重要的 MP 颗粒尺寸分数尚未得到充分采样，这可能导致对水生系统中塑料库存的严重低估。此外，报告的 MP 粒子数对于 MP 质量负载的约束很差，因为尺寸变化很大，并且聚合物内部和之间的密度不同，因此会影响质量通量估计。然而，确定 MP 数量、身份和质量可以解决这些问题，并能够更准确地估计 MP 负载。使用拉曼显微光谱结合三维 (3D) 光谱成像，我们开发了一种可自动化的方法来检测、识别和量化保留在离散水样过滤器上的 MP。 μ m 的直径和 3D 化学图的生成。为了加速确定每个已识别 MP 粒子的体积，我们开发了一种算法，从二维显微照片的图像分析中得出体积，这些图像与 3D 拉曼化学图直接测量的那些在统计上无法区分。每个经拉曼鉴定的 MP 颗粒的质量由它们的体积和已知的塑料比重确定。该方法提供了对离散水样中最小 MP 粒子对总 MP 质量的贡献的准确估计，为天然水中 MP 的质量通量计算提供了重要信息。