A team of researchers from Kyushu University and Asahi Kasei Corporation have developed a new technique to estimate the age of microplastics in the upper oceans. The method involves analysing plastic oxidation levels and environmental factors such as UV exposure and ambient temperature. The team applied their technique to microplastics found in nearshore and offshore sites in the North Pacific Ocean. Their findings, which were published in the journal ‘Marine Pollution Bulletin’, reveal that microplastics in nearshore regions range from 0 to 5 years old, whereas microplastics in offshore regions range from 1 to 3 years old.
According to Professor Atsuhiko Isobe of Kyushu University’s Research Institute for Applied Mechanics, who led the study, plastic waste is the most abundant type of pollutant in marine environments. As plastic waste breaks down and fragments, it eventually becomes microplastics, which are less than 5 mm in length. Microplastic pollution is considered a global problem, with about 24 trillion grains of microplastics floating on the surface layer of the ocean. However, there is still little known about the effects of microplastics on the environment or on living creatures, and how long they drift through the ocean.
The team first investigated what metrics could be used to measure the age of microplastics, starting with the most common plastic material, polyethylene. They found that as polyethylene interacts with the environment, it oxidizes and degrades, which can be measured using the change in the material’s molecular weight and carbonyl index. However, as microplastics are exposed to the elements, the team also needed to standardize how temperature and UV radiation affect plastic degradation. The team conducted a series of exposure experiments and found that UVER and seawater temperature were the two biggest contributors to plastic degradation.
By analysing the collected microplastics, the team could estimate the age of each sample. They found that nearshore microplastics ranged from 0 to 5 years old, whereas offshore samples ranged from 1 to 3 years old. The researchers hypothesise that nearshore microplastics survive for a longer time as they are frequently washed ashore, whereas offshore microplastics take longer to reach that part of the ocean and are removed from the upper oceans by settling deeper into the waters.
The new method could provide better insights into how microplastics are generated and spread in the environment and help in developing more accurate simulations to track microplastics across the ocean. The researchers plan to investigate how ocean waves and currents can degrade plastics to collect even more accurate data.
