By Anne Fischer
Plastics have only been around since the 1950s and yet they’re everywhere: scattered in our lakes, rivers, floating on the top of oceans, and dropping to the bottom. Back in the 1950s and 60s, plastics were hailed as a useful invention, used primarily in packaging materials. Remember Tupperware parties and the one-word advice given to Dustin Hoffman’s character in The Graduate? Now the stuff is everywhere, and it just doesn’t go away.
In a 2017 study published in Science Advances, scientists estimated that 8300 million metric tons (Mt) of virgin plastic had been produced to date, and as of 2015, approximately 6300 mt of plastic waste had been generated. If current trends continue, approximately 12,000 mt of plastic waste will be in landfills or in the natural environment by 2050.
Floating through the food chain
Plastic breaks down into microplastics (< 5 mm in size), which are found in the earth and in the water, and subsequently now in living creatures. Plastics contain monomers that are joined to make a polymer structure, and then processed with additives such as plasticizers, flame retardants, pigments, antimicrobial agents, heat stabilizers, UV stabilizers and fillers. As plastics degrade, additive chemicals leach and accumulate in the environment. A 2018 study Microplastics in Seafood and the Implications for Human Health examined the accumulation of microplastics in our food chain and potential toxicity in humans through food consumption. While it is understood that toxicity associated with consumption of microplastics is dependent on size of plastics and the chemical additives, more research is needed including standardized data collection methods. Methods of study At the University of Rochester in Rochester, New York (US), a multidisciplinary team is using a variety of optical methods to look at microplastics in water. Greg Madejski, a postdoctoral fellow in the laboratory of James McGrath, professor of Biomedical Engineering, is coordinating the research with the lab of Wayne Knox, professor of Optics. The team wants to learn to what extent microplastics, present in drinking water, pass into organs in the human body. The researchers are collaborating with SiMPore, a Rochester-based company founded by McGrath that uses silicon-based nanomembrane technology developed at the University. Knox said that SiMPore makes these great silicon nitride nanomembrane filters, but had “never found the killer app,” until researchers started using the 9-micron filters to look at plastic microparticles in water from Lake Ontario. The silicon-based filters are plastic-free and provide a “silent” background for fluorescent labeling of microplastics and chemical fingerprinting by spectroscopy. Using various optical techniques, the researchers are analyzing the particles of debris that accumulate on the surface of the membranes. For example, they can be stained with Nile Red dye, which adheres to plastics. In the Knox lab, Raman microscopy shines a bright laser on the material to obtain chemical bond information “We use a combination of advanced optical microscopy techniques to identify different size, shapes and materials of microplastics,” Knox said. The researchers are also using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) techniques to further study the composition of microplastic particles. Madejski said that in terms of the optical systems, Raman microscopy is the cheapest, then when they move toward XPS and EDS, it gets more expensive because an electron source and vacuum systems are required. However, these techniques, Madejski said, are good for establishing the molecular details. “Raman is used more like you’d use your standard optical microscope, and it works down to 5 microns or so, “ he noted, adding that some say it can get down to a micron. But “the less material that you have to work on, the more time it takes, and scaling up to high speed testing will require more development,” he said. Once the microplastic particles are identified, they are separated by color and shape and will be “fed” to Caco2 human epithelial cell lines that are widely used as a model of the intestinal epithelial barrier. This will help determine the extent to which the plastic particles are absorbed into the body. According to Knox, the challenges are related to how exactly you distinguish between particles in an efficient manner. He drew the analogy to what he heard at a conference on ophthalmology, where retinal experts analyzed 500k000 images gathered by retinal mapping using techniques of artificial intelligence. The system was able to learn how to identify early forms of retinal disease from the study. Knox said he knew that that’s what they had to do to scale up. Water test kit The company parVerio was formed out of the University of Rochester work, and is focused on developing new plastic detection platforms to create an accurate and detailed microplastic watershed database. Using the optical techniques described above, the team studied water samples and began developing a map of microplastic distribution in the Western New York watershed. They aim to create a picture of microplastic contamination across the United States. To make the testing process available to environmental groups and others concerned about what’s in the water, the team is developing a test kit as a part of a an SBIR grant. At first Madejski wanted to use the kind of inexpensive, folding microscope that can attach to a smartphone, but now he’s recommending that the tests be done with a standard school-type microscope. The team has developed apparatus that allows capture of microplastics with just a little gravity. “There are no moving parts. You just set up the filter, the water drains through the filter, and it’s caught on SiMPore’s chips,” he explained. They’re also planning on developing a kit for home use, but that will likely include a collection vial that the homeowner collects water in, then sends to the Rochester lab where they’d conduct the analysis and provide a report. The team of researchers at the University of Rochester is one of many groups around the world that is helping us understand the types of microplastics in our water, how they travel through the food chain and the accumulation in the human body. This research is all relatively new, and the implication of microplastics on human health is not yet fully understood. While the trend toward eliminating plastics from daily use is a positive step, we’re a long way from curtailing use of plastics altogether. And even if we were to vastly reduce use, the plastic used over the past 50+ years are still with us. Being armed with the facts on how the plastics break down and where they end up, will go a long way toward understanding the effects of toxins in the human body. Written by Anne Fischer, Editorial Director, Novus Light Technologies Today