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A New Census of Plastic Debris Entering the Ocean

Plastic bottles and other pieces of trash float in blue water.

The vastness of the world’s oceans does not guarantee their cleanliness – plastic waste can be seen floating not just near shorelines, but also far out at sea. A recent study has estimated that approximately 500 million kilograms of plastic, including water bottles, fishing nets, and other debris, enter the ocean each year. This is a lower estimate than previously thought, but it does not change the fact that plastic pollution continues to rise, according to researchers.

A Perplexing Discrepancy

In 2014, scientists approximated that over 250 million kilograms of plastic waste was present in the ocean. This is equivalent to the weight of a fully-loaded cargo ship. However, other groups have calculated that significantly more plastic pollution, ranging from 5-50 billion kilograms, enters the ocean annually.

After taking into consideration the possibility of debris sinking or fragmenting into undetectable pieces over time, there remains a puzzling inconsistency, according to Mikael Kaandorp, a physical oceanographer at Germany’s Forschungszentrum Jülich research center. He likened it to a person earning a large annual income but having very little savings. “It doesn’t seem logical.”

Kaandorp and his team embarked on a quest to unravel this enigma. “We aimed to determine the reason behind this significant disparity,” Kaandorp explained.

The Plastics We Know

The scientists studied plastics that would initially remain afloat upon entering water. According to Kaandorp, this includes commonly seen materials such as polyethylene, polypropylene, and polystyrene, which are utilized in various products like water bottles and packaging materials. Kaandorp noted that these plastics are primarily used by consumers.

The group examined three main sources of plastic: coastlines, rivers, and fishing. In order to calculate the amount of debris entering the ocean from coastlines, Kaandorp and his team analyzed data from a study on mismanaged plastic waste in coastal regions. They also collected data from another study on plastic pollution carried by rivers. Additionally, they adjusted published estimates of fishing activity to determine the amount of plastic from fishing that was entering the ocean.

Overall, Kaandorp and his team used data sets that consisted of over 22,000 measurements of plastics found on beaches, the ocean’s surface, and in the deep ocean.

Then, the scientists approximated the range of sizes for the plastic. Understanding the dimensions of the debris was crucial as it impacts factors such as how the plastic moves in the water. The group used a size distribution that was partially influenced by plastic measurements taken at waste management facilities, considering items ranging from 0.1 millimeters to 1.6 meters.

Kaandorp and his team conducted a numerical simulation to predict the movement of plastic debris in the water. They studied potential processes that could potentially remove plastic from the ocean surface, including the possibility of marine algae attaching to the debris and causing it to sink, or the effects of ultraviolet light and waves breaking down the debris into smaller pieces. Eventually, these pieces could become too small to be detected.

There is a lower amount of debris, but it remains present for a longer period of time.

Our numbers vary significantly.

Using information collected from observations of plastic entering the ocean and predictions from a model on how quickly the debris breaks down, Kaandorp and colleagues determined that approximately 500 million kilograms of buoyant plastic enter the ocean every year. This estimate is much lower than some previous projections, according to the researchers. Kaandorp stated, “Our calculations differ significantly.”

While this may initially seem like positive information, Kaandorp and his team warned that it means there is a significant amount of plastic in the ocean. The updated calculations also indicate that plastic remains in the environment for a much longer time than previously believed.

A previous research projected that if plastic pollution were to cease suddenly, approximately 95% of the plastic currently floating would disappear from the surface within 1-2 years as it either sank or broke apart. However, Kaandorp and his team discovered a much less positive outcome: Only about 10% of the plastic mass would be eliminated during that time period.

According to the study, the quantity of lightweight plastics entering the ocean is rising at a rate of 4% annually. This growth has the potential to lead to substantial changes over time, similar to the concept of compound interest. If no action is taken to reduce this impact, the mass of plastics on the ocean’s surface could double by the 2040s. These findings were reported in Nature Geoscience.

“We currently do not possess sufficient data on the contents of the ocean.”

Kara Lavender Law, a oceanographer from the Sea Education Association in Woods Hole, Massachusetts, who was not involved in the research, described the work as an impressive effort. She noted that it was a more advanced form of modeling than what has been previously done. However, Law also acknowledged that there are still uncertainties due to our limited understanding of ocean debris. She explained, “We do not have sufficient data on the actual amount of debris present in the ocean.”

However, Kaandorp and his team proposed that there is a positive aspect to these recent discoveries. According to their estimation, over 90% of the plastic found on the ocean’s surface is larger than 25 millimeters in size. This presents a glimmer of hope for cleaning up efforts, as Kaandorp stated that larger items are much easier to remove compared to smaller microplastics.

“Katherine Kornei is a contributing writer for the publication.”

“Katherine Kornei is a writer who contributes to the publication.”

Reference: Kornei, K. (2023), A fresh count of plastic waste flowing into the ocean, Eos, 104, Published on October 10, 2023.

Text © 2023. The authors. CC BY-NC-ND 3.0

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