The new method reveals small microplastics across the Japanese subtropical ocean

Six areas around Okinawa were visited to collect samples for analysis of marine microplastics – two were in the south of the island, two around the center and two in the north. Credit: Okinawa Institute of Science and Technology

A study conducted in the Department of Light Interactions with Quantum Technologies at the Okinawa District Institute of Science and Technology (OIST) revealed the presence of small microplastics in the ocean surrounding Okinawa. The study was published in The science of the overall environment.

“Significant research has been done on larger pieces of plastic in the ocean,” said Christina Ripken, Ph.D. student in the Unit and lead author of the paper. “But smaller pieces, those smaller than 5 mm, were not in the spotlight, so it was important to determine if they were present and what impact they could have on living organisms.”

Okinawa was an interesting place to conduct this study. A small, subtropical island in southern Japan, it is surrounded by bordered coral reefs, meaning the ocean around the beaches relies on surface water and wind. It is also considered a “blue zone” – a region whose inhabitants are extremely long-lived. Therefore, researchers considered it crucial to monitor ocean pollution, because it can negatively affect these inhabitants.

Christina, in collaboration with the Okinawa Prefecture Government, conducted sampling in September 2018. Six locations were visited near the coast of the island. To look through different areas, two sites were south of the island, two were around the center, and two north. In Naha, the capital of Okinawa prefecture, samples were taken next to the industrial port and airport. Naha is estimated to have more than 300,000 inhabitants, representing a quarter of the island’s total population. In contrast, Cape Hedo, in the far north of the island, has a very small population and is much less urbanized.

At each location, surface water was drawn for one kilometer, which allowed approximately 800 liters of water to be filtered and small particles removed. These particles were then analyzed in a laboratory at OIST.

The new method reveals small microplastics across the Japanese subtropical ocean

In each of the six areas visited, surface water was drawn one kilometer, which filtered approximately 800 liters of water. Credit: Okinawa Institute of Science and Technology

Christina collaborated with dr. Domn Kocifaki, a researcher in the Department of Light Matter Interactions for Quantum Technologies, who combined two techniques – optical tweezers and micro-Raman – to provide a new way to analyze particles.

The optical tweezers technique uses lasers to keep particles in the liquid, while the micro-Raman technique has identified a unique molecular footprint of each particle. This allowed the researchers to see exactly what was present, whether it was organic material, trace metal or various plastics such as polyethylene or polystyrene.

“This method is what sets this study apart from other marine microplastic research,” said Dr. Kotsifaki. “That meant we didn’t have to filter the plastic first, so we could see if there was plastic embedded in the organic material or if trace metals and plastic concentrations were present in the sampled seawater.”

As might be expected, the researchers found that there was more plastic in the water in the south of the island than in the north. But somewhat surprisingly, they found that plastic correlates more with places where people live rather than with particularly industrial areas.

As for, they found plastic in all the samples.

The new method reveals small microplastics across the Japanese subtropical ocean

Microplastics – tiny pieces of plastic – were found in all six sample areas around Okinawa. These samples were analyzed in a laboratory at OIST, which revealed the size and molecular composition of the plastic and the concentration in each sample. Credit: Okinawa Institute of Science and Technology

Over 75% of the plastic found in the samples is made of polyethylene, which researchers theorized could come from broken fishing gear, water bottle caps, household utensils, plastic bags, plastic containers and packaging.

“In fishing communities, in ports and on beaches where fish are landed, workers use woven plastic bags to store and transport items, including fish,” Christina said. “This is an example of how small pieces of plastic can be washed into the ocean.”

Another way is to pass the plastic in the dust from the road. Recent research has revealed a high concentration of microplastics in dust samples taken from the roads of highly urbanized areas of Okinawa, which have a significant amount of vehicle traffic. Some of this travel dust can now be found in the ocean around Okinawa.

“We found more plastic around a highly urbanized area in the south of the island than around the industrial center or rural north, but we found plastic everywhere,” Christina said. “Our method means we have a clearer view of the prevalence of microplastics around Okinawa, and that can lead to risk analysis and policy impact. We hope it will help strengthen the field of environmental research.”

Plastic blows in the wind

More information:
Christina Ripken et al., Analysis of small microplastics in surface water samples of the subtropical island of Okinawa, Japan, The science of the overall environment (2020). DOI: 10.1016 / j.scitotenv.2020.143927

Provided by the Okinawa Institute of Science and Technology

Citation: New method detects small microplastics across the Japanese subtropical ocean (2020, December 24) downloaded December 24, 2020 from

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