Simplifying Microplastic via Continuous Probability Distributions for Size, Shape, and Density

Because of their diverse sizes, shapes, and densities, environmental microplastics are often perceived as complex. Many studies struggle with this complexity and either address only a part of this diversity or present data using discrete classifications for sizes, shapes, and densities. We argue that such classifications will never be fully satisfactory, as any definition using classes does not capture the essentially continuous nature of environmental microplastic. Therefore, we propose to simplify microplastics by fully defining them through a three-dimensional (3D) probability distribution, with size, shape, and density as dimensions. In addition to introducing the concept, we parametrize these probability distributions, using empirical data. This parametrization results in an approximate yet realistic representation of “true” environmental microplastic. This approach to simplifying microplastic could be applicable to exposure measurements, effect studies, and fate modeling. Furthermore, it allows for easy comparison between studies, irrespective of sampling or laboratory setup. We demonstrate how the 3D probability distribution of environmental versus ingested microplastic can be helpful in understanding the bioavailability of and exposure to microplastic. We argue that the concept of simplified microplastic will also be helpful in probabilistic risk modeling, which would greatly enhance our understanding of the risk that microplastics pose to the environment.由于环境微塑料（environmental microplastics）的尺寸、形状与密度均存在多样性，其往往被认为具有较高复杂性。诸多研究受限于这一复杂性，要么仅针对该多样性的部分维度展开研究，要么采用离散分类方式对微塑料的尺寸、形状及密度进行数据呈现。我们认为此类分类方式无法实现完全令人满意的效果，因为基于类别的任何定义都无法捕捉环境微塑料本质上的连续分布特性。据此，我们提出通过以尺寸、形状与密度为维度的三维（3D）概率分布对微塑料进行完整定义，以此实现微塑料的简化表征。除提出该概念外，我们还利用实测数据对这些概率分布进行参数化处理。该参数化过程可得到对‘真实’环境微塑料的近似且符合实际的表征结果。这种微塑料简化表征方法可应用于暴露量测量、效应研究以及归趋模拟领域。此外，无论采样方式或实验室配置存在何种差异，该方法均可实现不同研究间的便捷对比。我们通过实例展示了环境微塑料与摄入微塑料的三维概率分布，可如何助力理解微塑料的生物可利用性及其暴露情况。我们同时认为，简化微塑料的概念也可应用于概率风险建模，这将极大提升我们对微塑料所带来的环境风险的认知水平。