Mass concentration of plastic particles from two-dimensional images

Imaging techniques play a crucial role in characterizing environmental plastics. However, most reported findings rely on two-dimensional projections of particles resting on flat surfaces. This limitation makes it challenging to accurately determine mass concentration, which is essential for deriving toxicologically relevant exposure data. The primary issue arises from the loss of information regarding particle height or thickness. This study aims to evaluate the assumptions necessary to compensate this loss of information. To achieve this, we used a set of environmental plastic particles, mesoplastics and microplastics, from marine campaigns, and precisely measured their three spatial dimensions and mass. Our study demonstrated the feasibility of estimating the mass of plastic particles through two-dimensional images. However, for enhanced accuracy, additional information derived from the dataset of particles under examination is necessary. Specifically, estimating the mass of platelike particles requires information about their height. Similarly, calculating the volume for elongated shapes as cylinders, should be limited to particles with the same width and height and for which their length can be precisely determined, even if the image depicts twisted forms. In conclusion, while obtaining mass concentration from single two-dimensional images enables reasonable estimations, achieving the precision needed for exposure data requires acquiring additional information from the sample and carefully considering the shape of each individual particle.