Researchers have developed a new method that uses filtering marine species to collect nanoplastics from ocean water. This was done as part of the efforts of several organizations led by the National Institute of Standards and Technology (NIST) and the European Commission’s Joint Research Center (JRC).
Plastics often end up in the ocean, affecting not only marine life and the environment, but also endangering food safety and human health. Many of these plastics break down into microscopic sizes, making them difficult to quantify and measure for scientists. Researchers call these incredibly small fragments nanoplastics and microplastics because they are invisible to the naked eye.
Plastics are made up of synthetic materials known as polymers, which are usually made from petroleum and other fossil fuels. More than 300 million tons of plastic are produced annually, of which 8 million tons end up in the ocean. The most common plastics found in the marine environment are polyethylene and polypropylene. LDPE 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.
“Sunlight and other chemical and mechanical processes cause these plastic objects to get smaller and smaller. Over time, they change their shape and, possibly, even their chemical composition.”
NIST researcher Vince Huckley
While there is no official definition for these smaller nanoplastics, researchers usually describe them as artificial products that the environment breaks down into microscopic pieces. They are usually one millionth of a meter (one micrometer or micron) or less. These tiny plastic products pose many potential threats to the environment and the food chain.
“As plastic materials degrade and become smaller, they are consumed by fish or other marine organisms such as shellfish. Along this path, they enter the food system, and then into us. This is a big problem”
NIST researcher Vince Huckley
For help in measuring nanoplastics, the researchers turned to a group of marine species known as tunicates, which process large volumes of water through their bodies to obtain food and oxygen, as well as, but inadvertently, nanoplastics. What makes tunicates so useful for this project is that they can swallow nanoplastics without affecting their shape or size.
For their study, the researchers chose a species of tunicates known as C. robusta because they have good micro- and nanoparticle retention efficiency. The shells were exposed to various concentrations of polystyrene, a versatile plastic, in the form of nano-sized particles. The tunicates were then harvested and then chemically digested to separate the nanoplastics from the organisms. However, at this stage, some of the residual organic compounds digested by the shell were still mixed with the nanoplastics, possibly interfering with the purification and analysis of the plastics.
Therefore, the researchers used an additional isolation technique called asymmetric flow fractionation (AF4) to separate the nanoplastic from unwanted material. The separated or fractionated nanoplastics could then be collected for further analysis.
“This is one of the biggest challenges in this area: the ability to find these nanoplastics, isolate and separate them from the environment in which they exist.”
European Commission Researcher Andrea Valsesia
The nanoplastics samples were then placed on a specially designed chip designed to form clusters of nanoplastics, making them easier to detect and count in the sample. Finally, the researchers used Raman spectroscopy, a non-invasive laser technique, to characterize and identify the chemical structure of nanoplastics.
This approach could pave the way for the use of tunicates as biological indicators of ecosystem health. Scientists could analyze the shell at a specific location to study nanoplastic contamination in that area.