A new method to better study microscopic plastics in the ocean

If you’ve been to your local beach, you may have noticed the wind tossing around litter such as an empty potato chip bag or a plastic straw. These plastics often make their way into the ocean, affecting not only marine life and the environment but also threatening food safety and human health.

Eventually, many of these plastics break down into microscopic sizes, making it hard for scientists to quantify and measure them. Researchers call these incredibly small fragments nano plastics and microplastics because they are not visible to the naked eye. Now, in a multi-organizational effort led by the National Institute of Standards and Technology (NIST) and the European Commission’s Joint Research Centre (JRC), researchers are turning to a lower part of the food chain to solve this problem.

The researchers have developed a novel method that uses filter-feeding marine species to collect these tiny plastics from ocean water. The team published its findings as a proof-of-principle study in the scientific journal Microplastics and Nano plastics.

Plastics consist of synthetic materials  known as polymers that are usually made from petroleum and other fossil fuels. Each year more than 300 million tons of plastics are produced, and 8 million tons end up in the ocean. The most common kinds of plastics found in marine environments are polyethylene and polypropylene. Low-density polyethylene is commonly used in plastic grocery bags or six-pack rings for soda cans. Polypropylene is commonly used in reusable food containers or bottle caps.

These tiny plastics pose many potential hazards to the environment and food chain. As plastic materials degrade and become smaller, they are consumed by fish or other marine organisms like mollusks. Through that path they end up in the food system, and then in us. That’s the big concern.

For help in measuring nanoplastics, researchers turned to a group of marine species known as tunicates, which process large volumes of water through their bodies to get food and oxygen—and, unintentionally, nanoplastics. What makes tunicates so useful to this project is that they can ingest nanoplastics without affecting the plastics’ shapes or size.

NIST, collaborators develop new method to better study microscopic plastics in the ocean

In their study, researchers chose a tunicate species known as C. robusta because “they have a good retention efficiency for micro- and nanoparticles,” said European Commission researcher Andrea Valsesia. The researchers obtained live specimens of the species as part of a collaboration with the Institute of Biochemistry and Cell Biology and the Stazione Zoologica Anton Dohrn research institute, both in Naples, Italy.

The tunicates were exposed to different concentrations of polystyrene, a versatile plastic, in the form of nanosize particles. The tunicates were then harvested and then went through a chemical digestion process, which separated the nanoplastics from the organisms. However, during this stage some residual organic compounds digested by the tunicate were still mixed in with the nanoplastics, possibly interfering with the purification and analysis of the plastics.

Among other possibilities, this approach might pave the way for using tunicates to serve as biological indicators of an ecosystem’s health. “Scientists might be able to analyze tunicates in a particular spot to look at nano plastic pollution in that area,” said Jérémie Parot, who worked on this study while at NIST and is now at SINTEF Industry, a research institute in Norway.

The NIST and JRC researchers continue to work together through a collaboration agreement and hope it will provide additional foundations for this field, such as a reference material for nanoplastics. For now, the group’s multistep methodology provides a model for other scientists and laboratories to build on. The most important part of this collaboration was the opportunity to exchange ideas for how we can do things going forward together.

Andrea Valsesia et al, Detection, counting and characterization of nanoplastics in marine bioindicators: a proof of principle study, Microplastics and Nanoplastics (2021). DOI: 10.1186/s43591-021-00005-z

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