Microplastics, defined as plastic fragments smaller than 5 millimeters, now appear in nearly every environment on Earth. Scientists detect them in remote ocean trenches, urban air, tap water, and even human blood. These particles vary enormously in size. Larger fragments are visible to the naked eye, while the smallest measure just a few micrometers across. The size differences matter significantly. Smaller particles are far more numerous and behave differently in water. They may also pose greater risks to aquatic organisms and human health due to their ability to enter biological systems more easily.
Despite growing concerns about microplastic pollution, researchers have not established common standard methods for measurement and comparison. Studies investigating river contamination often examine different particle size ranges using incompatible methods. Moreover, most scientists focus on counting particle numbers rather than measuring mass, even though mass concentration provides a clearer picture of pollution severity. A research team from Tokyo University of Science addressed these gaps by studying the Tsurumi River in Japan. This river flows through densely populated areas where treated wastewater makes up roughly three-quarters of its flow. The team conducted seven field surveys at four sites, collecting particles ranging from 0.03 to 5 millimeters using multiple sampling techniques.