Country-wide assessment of plastic removal rates on riverbanks and water surfaces.

Plastic pollution in river basins poses a significant environmental challenge, particularly in Japan, located in the northwestern North Pacific, often referred to as a hotspot for plastics. This study quantified the annual recovery of anthropogenic plastic litter from riverbanks and water surfaces, utilizing a nationwide cleanup dataset provided by the Japanese Ministry of Land, Infrastructure, Transport and Tourism. The dataset includes the amount of litter recovered through volunteer and administrative cleanup campaigns from 2016 to 2020 in 109 Japanese river basins.

Geometric relationship between the projected surface area and mass of a plastic particle.

The quantification of the mass of meso/microplastic (MMP) particles is crucial for assessing the global inventory of ocean plastics and assessing environmental and human health risks. Herein, linear regression models between mass and projected surface area on a log scale were established by directly measuring the masses of 4390 MMP particles collected at 35 sites in 17 Japanese rivers with an ultramicrobalance. The linear regression models estimated mass concentrations more accurately than any previous method based on geometric volume assuming several three-dimensional shapes.

Comparison of concentration, shape, and polymer composition between microplastics and mesoplastics in Japanese river waters.

While plastics are classified by size as microplastics (<5 mm), mesoplastics (5-25 mm), and macroplastics (>25 mm), research in rivers has centered on microplastics, followed by macroplastics, with limited research on mesoplastics (research gap). This study aims to clarify the concentration, shape, and polymer composition of microplastics and mesoplastics in Japanese river water. We conducted field surveys for microplastics and mesoplastics in 147 rivers and at 185 measurement stations.

An analytical approach to confidence interval estimation of river microplastic sampling.

Microplastics (MPs), plastic particles <5 mm in diameter, are emerging ubiquitous pollutants in natural environments, including freshwater ecosystems. As rivers facilitate efficient transport among landscapes, monitoring is crucial for elucidating the origin, dynamics, and fate of MPs. However, standardized methodologies for in situ sampling in freshwater environments remain undefined to date.

Experimental uncertainty assessment of meso- and microplastic concentrations in rivers based on net sampling.

Meso- and microplastics have been collected via net sampling in marine and freshwater environments, but the effect of net clogging on evaluations of their concentrations (mPC) remains uncertain. We experimentally investigated the mPC uncertainties resulting from net clogging in the Ohori and Tone-unga Rivers, typical urban rivers in Japan, throughout 16 samplings with five filtration durations in one day. The weighted mean concentration in the Ohori River was significantly lower than that in the Tone-unga River, allowing us to examine the effect of clogging in rivers with different contamination levels.

Variance and precision of microplastic sampling in urban rivers.

Microplastics (MPs), plastic particles <5 mm in diameter, have become an emerging ubiquitous concern for the environment. Rivers are the primary pathways that transport MPs from the land to the ocean; however, standardized methodologies for in-situ sampling in freshwater environments remain undefined. Notably, uncertainties in MP sampling methods lead to errors in estimating MP discharge through rivers.

Rapid analytical method for characterization and quantification of microplastics in tap water using a Fourier-transform infrared microscope.

Studies have recently focused on microplastics (MPs) in tap and drinking water. Directly comparing the results of different studies is difficult owing to the use of various methodologies. In particular, a study of particles on a part of the filter to reduce the analysis time can lead to uncertainty regarding the number of MPs in tap water.

Quantification of floating riverine macro-debris transport using an image processing approach.

A new algorithm has been developed to quantify floating macro-debris transport on river surfaces that consists of three fundamental techniques: (1) generating a difference image of the colour difference between the debris and surrounding water in the CIELuv colour space, (2) detecting the debris pixels from the difference image, and (3) calculating the debris area flux via the template matching method. Debris pixels were accurately detected from the images taken of the laboratory channel and river water surfaces and were consistent with those detected by visual observation. The area fluxes were statistically significantly correlated with the mass fluxes measured through debris collection.

Assessment of the sources and inflow processes of microplastics in the river environments of Japan.

The numerical and mass concentrations of microplastics collected at 36 sites on the surfaces of 29 Japanese rivers were mapped and compared with four basin characteristics (basin area, population density, and urban and agricultural ratios) and six water quality parameters (pH, biochemical oxygen demand (BOD), suspended solids (SS), dissolved oxygen (DO), total nitrogen (T-N), and total phosphorus (T-P)) in each river basin. Microplastics were found in 31 of the 36 sites, indicating that some plastics fragment into small pieces before reaching the ocean. The microplastic concentrations are significantly correlated with urbanisation and population density, indicating that the microplastic concentrations in the river depend on human activities in the river basin.