Microplastic pollution in the oceans, a growing concern invisible to the naked eye, is being tackled by scientists using advanced detection techniques. Each year, an estimated 52 million tonnes of plastic waste enter the ocean, contributing to approximately 24 trillion microplastic particles that disrupt marine ecosystems.
These tiny plastic fragments, less than 5 millimetres in diameter, are found throughout the water column, from the surface to the depths. Their presence raises critical questions about how they enter the sea, how they can be identified, and their impact on marine life.
At the Flanders Marine Institute (VLIZ) on the Belgian coast, a research group led by senior researcher Ana Catarino is actively investigating marine microplastics, collecting data directly from the North Sea. Plastics enter the ocean through various pathways, including detached fishing gear and inadequate waste management systems.
Microplastics are broadly categorized into primary and secondary types. Primary microplastics include manufactured items like nurdles, while secondary microplastics result from the degradation of larger plastic debris due to environmental factors such as waves, wind, and sunlight. This degradation process is influenced by climate change; for instance, more sunny days and higher UV radiation can accelerate plastic breakdown.
The impact of microplastics on marine species is a complex issue, often exacerbated by climate change. While ingesting microplastics might not always pose a significant immediate threat, it can become critical when marine organisms are already stressed by rising sea temperatures. "These combined effects, they can be cumulative in the organism," explained Catarino, highlighting the synergistic harm caused by multiple stressors.
Identifying and quantifying microplastics presents considerable challenges due to their small size, irregular shapes, and varied colours. However, VLIZ postdoctoral researcher Nelle Meyers has developed a semi-automated method to address this. The technique involves collecting sea samples with a net, removing organic matter, and then staining the sample with Nile Red. Under a fluorescence microscope, a colouration analysis is performed, feeding results into automated programs that identify and classify the microplastic particles.
"We wanted to automate to speed up the whole process," Meyers stated. "We wrote a code so when you upload the picture, the image analysis is done automatically." This semi-automated approach, combined with the use of a fluorescence microscope, which is a common laboratory instrument, makes the technique both cost- and time-effective. However, the method has limitations, as it does not provide information on the chemical composition of the particles and can only identify certain types of polymers.
Just as larger plastic debris is ingested by marine animals, microplastics can be consumed by smaller organisms, including plankton. Catarino noted that microplastics can clog the digestive systems of these organisms, preventing them from consuming nutrients. "And this is worrying because then it brings other issues because these organisms are not able to reproduce and their population will not strive, so it will be affected," she said.
The specific consequences of microplastic ingestion vary depending on the marine species, the type of microplastic, and other environmental stressors like ocean acidification and temperature changes. "Sometimes it’s not just one issue or another, it’s the accumulation of all these effects that may be harmful to the organisms," Catarino concluded.
According to the United Nations, each year 52 million tonnes of plastic waste enter the ocean, resulting in an estimated 24 trillion microplastic particles.
Specifically, microplastics polluting the ocean can be divided into two categories: primary microplastics and secondary microplastics.
