Plastic pollution extends far beyond known ocean hotspots, reveals German study

25 Mar 2024 --- A recent study conducted by researchers from the Helmholtz Centre for Environmental Research (UFZ), Germany, in collaboration with the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), has uncovered “large quantities of plastic waste and microplastics” in a remote marine protected area in the Pacific Ocean. 

The findings, published in Environmental Science & Technology, suggest that plastic pollution is more widespread than previously thought, posing a significant threat to marine ecosystems.

The study, led by UFZ environmental chemist professor Annika Jahnke and UFZ researcher Robby Rynek, sought to investigate the distribution of plastics in the oceans and identify areas particularly affected by pollution. 

During a five-week expedition on the German research vessel “Sonne” in 2019, the team collected surface water samples between Vancouver, Canada, and Singapore in the North Pacific Ocean. They selected sampling stations based on a prediction model from the University of Hawaii, US, targeting high and low plastic load areas.

“Plastics in the ocean are a serious problem. Every year, millions of tons of plastics end up in the ocean via rivers and wind as well as from shipping and fishing — and it remains there. It is still difficult to assess the consequences for the ocean ecosystem,” says Jahnke. 

Using a combination of litter surveys and neuston nets towed at the surface, the researchers found substantial quantities of plastic waste and microplastics in the sampled waters. The plastic particles, ranging in size and shape, showed varying degrees of weathering, indicating prolonged exposure to sun, wind, waves and seawater. 

The study revealed equally large quantities of microplastics in the remote marine protected area northwest of Hawaii, challenging previous assumptions about the distribution of plastic pollution.

“We selected stations with predicted high and low plastic loads for our investigations,” elaborates Jahnke.

 “Some stations were located in areas that had already been well researched, such as the so-called Great Pacific Garbage Patch. We also wanted to investigate zones in the open ocean that had hardly been explored. For example, we took samples in a marine reserve northwest of Hawaii, the Papahānaumokuākea Marine National Monument (PMNM).”Neuston net towed on the side of the German research vessel Sonne, collecting surface-floating plastic samples when crossing the North Pacific Ocean (Image credit: Philipp Klöckner/UFZ).

Unexpected findings
The research utilized a neuston catamaran to collect surface-floating plastic and Fourier-transform infrared spectroscopy for identification. It revealed baseline concentrations of surface-floating plastic ranging from 41,600 to 102,700 items per square kilometer, dominated by PE and PP.

“The mesh size was 0.3 millimeters. This allowed us to collect larger items and small plastic particles to determine the number of microplastics, which are less than five millimeters in diameter,” shares Rynek, lead author of the study. 

“The plastic particles from each sample were sorted by size and counted. We then used a special form of infrared spectroscopy to chemically analyze the particles and estimate their weathering state based on their appearance.”

While the North Pacific Subtropical Gyre (NPSG) area has been well-documented as a plastic accumulation zone with concentrations reaching 452,800 items per square kilometer, the second area, PMNM, analyzed by the researchers also exhibited elevated levels of plastic pollution, reaching 285,200 items per square kilometer. 

The discovery marks the first time such high concentrations have been reported in the PMNM and was not predicted by existing ocean current models, detail the researchers.

Visual observations of floating debris, including items larger than five centimeters, provided further insight into the distribution of plastic pollution. Similar patterns of baseline pollution and elevated concentrations of plastic debris were observed in both the NPSG and the PMNM, indicating that ocean currents alone may not be the sole factor contributing to plastic accumulation in these regions.

“As expected, we found the highest quantities of plastics in the samples we took in the area known as the Great Pacific Garbage Patch,” says Rynek. “The most surprising and, at the same time, most worrying result of our study is that we found equally large quantities of tiny microplastics in the remote marine protected area northwest of Hawaii. We hadn’t expected that. According to the calculations of the forecast model, there should be considerably less plastics in this area.” 

Co-author Dr. Melanie Bergmann from the AWI adds: “The items do not in any way form a carpet of plastic that densely covers an entire surface. This is important when considering plastic removal technologies, which would have to cover vast areas to collect significant amounts of plastic. Most plastics are small fragments that escape nets or can only be collected with considerable animal by-catch.”Selection of plastic particles collected with the neuston net, showing weathering and a large diversity in sizes, shapes and colors (Image credit: Annika Jahnke/UFZ).

Reduction and reuse measures
The study’s findings suggest that visual observations and scientific instrumentation can be crucial in increasing our understanding of large-scale plastic pollution in the world’s oceans. By identifying unexpected hotspots of plastic accumulation, researchers can better inform conservation efforts and policy interventions to mitigate plastic pollution’s impacts on marine ecosystems.

Jahnke expresses concern over the findings: “Microplastics are most likely distributed much further across the oceans than previously assumed. We found plastics at all of our sampling stations. There were no samples without plastics. So, we can’t assume that plastics are causing problems mainly in the known accumulation areas — the problem is much bigger and affects the entire ocean ecosystem.”

The researchers emphasized the urgent need to address plastic pollution globally. With UN member states set to adopt a legally binding Global Plastics Treaty this year, scientists are advocating for comprehensive measures to reduce plastic production, promote reuse systems, and improve the chemical composition of plastic products to facilitate safer reuse and higher recycling rates.

Bergmann from AWI underscores the importance of collective action, stating, “As independent scientists, we stand as part of the Scientists’ Coalition for an Effective Plastics Treaty to advise the delegates of the UN member states.”

In addition to reductions in plastic production and promoting reuse systems, researchers believe that the chemical composition of plastic products needs to be simplified and improved. “This is the only way to ensure safe reuse and higher recycling rates,” they write.

By Radhika Sikaria