Unveiling the geometric relationship between the mass and projected surface area of meso- and microplastic particles

Our research group clarified the geometric relationship between the mass and projected surface area of mesoscale (5-25 mm) and microscale (<5 mm) plastic particles collected from 35 sites in 17 Japanese rivers and demonstrated that this relationship can be used to accurately estimate the mass of these particles. Our results are expected to contribute significantly to understanding the plastic budget in aquatic environments and to clarifying its impact on ecosystems.

Plastic particles, which are known as “transport vectors” of toxic chemicals, have leaked from land to the ocean. In particular, mesoscale (5-25 mm) and microscale (<5 mm) plastic (MMP) particles have been ingested by various organisms at lower and higher trophic levels and are thus recognized as a threat to marine ecosystems. Therefore, the plastic budget in aquatic environments (plastic emissions from land and plastic accumulation in the environment) and risk assessments of ecosystems have been explored.

A number of studies have estimated the mass of individual MMP particles by multiplying their polymer densities by the geometric volume estimated under the assumption of their shape, resulting in uncertainty in the determination of particulate mass from the three-dimensional shape of MMP particles.

To evaluate the uncertainty in these previous methodologies, we directly measured the mass of 4,390 MMP particles collected from 35 sites at 17 Japanese rivers by an ultramicrobalance and then evaluated the mass concentration through direct measurement. The mass of each particle was linearly regressed on its projected surface area on a log scale, indicating that the projected surface area is an important parameter for determining the MMP particulate mass. The linear relationship was geometrically validated by assuming the shape and polymer density of the MMP particles. Furthermore, the applicability of the geometric relationship to the estimation of mass concentration (the mass of MMP particles per unit water volume) was discussed. Consequently, this geometric relationship could be used to estimate the mass concentrations at the 35 sites, which resulted in more accurate estimations than those of previous methods based on geometric volume assuming four three-dimensional shapes (i.e., spheres, ellipses, cylinders, and flakes).

Our study demonstrated that the geometric relationship between the projected surface area and the mass of MMP particles is significant for accurately estimating the mass concentration in aquatic environments. Our results can be used to provide insights into the geometric relationship between the mass and size of MMP particles and to contribute significantly to understanding the plastic budget in aquatic environments and to clarifying the impacts on ecosystems.

Bibliographic Information

Geometric relationship between the projected surface area and mass of a plastic particle,
Tomoya Kataoka, Yota Iga, Rifqi Ahmad Baihaqi, Hadiyanto Hadiyanto and Yasuo Nihei,
Water Research, 261, 122061,
doi: 10.1016/j.watres.2024.122061, 2024 (September 1).

Fundings

• The Environment Research and Technology Development Fund of the Environmental Restoration and Conservation Agency of Japan (ERCA) Grant Number JPMEERF21S11900 and JPMEERF20231004
• Japan Society for the Promotion of Sciences (JSPS) KAKENHI Grant Number 21H01441 and 24K00992
• The New Energy and Industrial Technology Development Organization (NEDO) Grant Number JPNP18016

Media

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  Geometric relationship between the mass and projected surface area of plastic particles

  The linear relationship between the mass and projected surface area of meso- and microplastic (MMP) particles was clarified by directly measuring those of 4,390 MMP particles, which was geometrically validated by assuming the shape and polymer density of the MMP particles. This relationship can be used to accurately estimate the mass concentration of MMP particles in aquatic environments.

  credit : Tomoya Kataoka
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