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Experts develop a new method to estimate the age of microplastics in the ocean

In an exciting leap forward in understanding the life cycle of microplastics, a team of researchers from Kyushu University and Asahi Kasei Corporation has unveiled a novel method to discern the age of these minute pollutants prevalent in our oceans. 

The methodology makes use of an innovative mix of oxidation analysis of the plastics, along with a consideration of environmental factors such as exposure to UV rays and the surrounding temperature.

The team ventured out to field test their method, focusing their efforts on microplastics found in the North Pacific Ocean, both near the shore and offshore. 

The results, recently published in the Marine Pollution Bulletin, indicated that the microplastics in nearshore regions were as young as fresh to a maximum of five years old, while those in offshore regions were a little older, ranging from one to three years.

Defining microplastics

Microplastics, fragments of plastic waste that are smaller than 5mm, have taken over marine environments from lakes to oceans as the leading type of pollutant. As larger plastic waste endures the elements, it breaks down into these smaller particles.

“Microplastic pollution is recognized as a global problem. We found in a previous study that there are about 24 trillion grains of microplastics floating on the ocean’s surface layer,” said study lead author Professor Atsuhiko Isobe from Kyushu University’s Research Institute for Applied Mechanics.

“Despite this, our knowledge about the impact of microplastics on the environment or living organisms is still scarce. A pressing question we are grappling with is the duration microplastics spend drifting through the ocean.”

How the study was done

To answer this, Isobe’s team set out to first determine how to measure the age of microplastics. Rie Okubo, a researcher at Asahi Kasei Corporation and the study’s first author, explained that polyethylene is the most common material in plastic. 

“As it interacts with the environment, it oxidizes and degrades. We can measure this degradation level using the change in the material’s molecular weight and the carbonyl index. In simple terms, as polyethylene degrades, its carbonyl index rises, and molecular weight drops.”

But the team didn’t stop there. They recognized that microplastics are exposed to the elements, which means temperature and UV radiation also play a role in their degradation. 

To understand this, the team conducted a series of exposure experiments on polyethylene material, collecting data on how different combinations of UV and temperature affected the material’s molecular weight and carbonyl index. 

The results showed that ultraviolet erythemal radiation (UVER) – a measure of ground-level UV radiation – and seawater temperature were the prime contributors to plastic degradation. Armed with this data, the team then turned to their collected microplastic samples, all drawn from the upper ocean, up to one meter from the water surface. 

“We collected microplastics from a range of areas. Some samples were from nearshore to Japan, ranging from 10 to 80 km off the coast. Others were from offshore, in the middle of the North Pacific Ocean and the Philippine Sea,” said Okubo.

What the researchers learned

With their new method, the researchers could estimate the age of each sample. Nearshore microplastics varied from 0 to 5 years old, while offshore samples were between 1 and 3 years old. 

“Nearshore microplastics range from 0 to 5 years because they are frequently washed ashore and ‘survive’ for a longer time. Offshore microplastics take longer to reach that part of the ocean, explaining why we didn’t find microplastics over 3 years old. These offshore microplastics likely settle deeper into the waters, removing them from the upper oceans,” explained Okubo.

The researchers believe their new method will provide greater insights into the generation and dispersal of microplastics in the environment. The valuable data gathered could aid in creating more accurate simulations to track the journey of microplastics across the ocean.

“Our understanding of microplastics is still in its infancy, and this data provides us with a slightly clearer picture of the basic science surrounding these tiny pollutants. Our next move is to explore how mechanical stimuli such as ocean waves and currents can degrade plastics, allowing us to gather even more accurate data,” said Isobe.

Thus, this breakthrough could potentially be a game changer in comprehending the mysterious journey of microplastics, from creation to degradation. 

The pioneering work of the team at Kyushu University and Asahi Kasei Corporation promises to shed more light on the environmental hazards posed by these minute pollutants, and could be instrumental in devising more effective strategies to combat this global issue.

More about microplastics

Microplastics are tiny plastic particles less than 5mm in size, roughly the size of a sesame seed. These particles are either intentionally manufactured at a small size, often used in personal care products, or they result from the breakdown of larger plastic items due to exposure to the elements over time. As of my last training data in September 2021, microplastics are a significant source of environmental pollution, impacting both land and oceans.

Sources of Microplastics

Primary Microplastics

These are directly released into the environment as small particles. Examples include microbeads in cosmetics and personal care products, plastic pellets used in industrial processes, and fibers from synthetic clothing that are released during washing.

Secondary Microplastics

These originate from the degradation of larger plastic items, such as water bottles, bags, and fishing nets. These items can break down into microplastics due to physical processes (like abrasion) and environmental conditions (such as UV radiation and heat).

Impact on Oceans 

Microplastics have made their way into every corner of the world’s oceans, from the surface to the deepest trenches. They can be carried by winds, rivers, and ocean currents across vast distances. Here are some ways they affect marine ecosystems:

Ingestion by Marine Life

Microplastics can be mistaken for food by marine animals, from small plankton to larger mammals. Ingesting these particles can lead to physical harm, including blockage of the digestive tract or a false sense of satiety, which can result in starvation.

Toxic Chemicals

Microplastics can absorb and concentrate harmful chemicals from the surrounding environment. When ingested by marine creatures, these toxins can be released and cause harm.

Bioaccumulation and Biomagnification

As smaller organisms containing microplastics are consumed by larger ones, the concentration of microplastics and associated toxins can increase up the food chain, potentially reaching humans.

Impact on Land 

The impact of microplastics isn’t confined to oceans. They can also accumulate in terrestrial environments, including agricultural lands.

Soil Health

Microplastics can alter the physical properties of soil, affecting its structure, porosity, and permeability, which could potentially impact plant growth.

Organisms and Biodiversity

Microplastics can be ingested by terrestrial animals and soil-dwelling organisms, impacting their health and potentially leading to a decrease in biodiversity.

Food Safety

Microplastics can enter the human food chain directly through consumption of crops grown in contaminated soil or indirectly through the consumption of animals that have ingested microplastics.

Mitigation Efforts 

As of 2021, strategies to mitigate the impact of microplastics include:


Some countries have banned the use of microbeads in personal care products.

Recycling and Waste Management

Improving waste management systems and recycling rates can help reduce the amount of plastic that breaks down into microplastics.

Public Awareness

Education about the dangers of plastic pollution can encourage more responsible consumer behavior, such as reducing, reusing, and recycling plastic products.


More research is needed to fully understand the impact of microplastics on both human health and the environment, and to develop innovative solutions for plastic waste management.

Microplastic pollution is a complex and global issue that requires collaborative efforts from governments, industries, scientists, and individuals to address effectively.


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