AMHERST, Mass. – While the threat that microplastics pose to human and ecological health has been richly documented and is well known, nanoplastics, which are smaller than one micrometer (1/50th the thickness of an average human hair), are far more reactive, far more mobile and vastly more capable of crossing biological membranes. Yet, because they are so tiny and so mobile, researchers don't yet have an accurate understanding of just how toxic these particles are. The first step to understanding the toxicology of nanoplastics is to build a reliable, efficient and flexible tool that can not only quantify their concentration in a given sample, but also analyze which specific plastics that sample contains.
An international team of scientists led by the University of Massachusetts Amherst recently announced in Nature Water the development of a new tool, known as the OM-SERS setup, which can do all of these things and can furthermore be used to detect particular nanoplastic concentrations and polymer types in solid samples, such as soils, body tissues and plants.
Plastic is an incredibly durable material, which can take up to 500 years to decompose. As plastic bottles, packaging and parts get older, teeny pieces of them break off. These microplastics have been found in every corner of the globe, from the top of Mount Everest to the depths of the Mariana Trench, and, according to recent reports, they are in many humans' blood, brain and heart tissue.
If that's not bad enough, each individual microplastic could theoretically be broken down into 1 quadrillion nanoplastic particles—which means that there are literally uncountable numbers of nanoplastics in our water, air and soils. These microplastics pose an as-of-yet unknown risk to the environment and to human health, and they're altering ecosystems throughout the world.
"Because nanoplastics are so tiny, they have a much higher overall surface area and functional groups than microplastics, which means more of them can concentrate in water, soil and body tissues," says Baoshan Xing , University Distinguished Professor of Environmental and Soil Chemistry at UMass Amherst's Stockbridge School of Agriculture and one of the paper's senior authors. "They travel more easily and can wind up in more places in the environment and in our bodies. And once in those places, they are more reactive and the chemicals and additives in them can more easily leach out into their surroundings."
However, in order for toxicologists to begin to understand just how dire is the threat that nanoplastics pose, they first need to be able to count how many nanoplastics are in a sample and what specific types of plastic—each of which has a different chemical composition—are represented.
Xing, along with his co-senior authors, Jian Zhao and Xiaofeng Shi, professors at the Ocean University of China, and their team developed a method called "optical manipulation and surface-enhanced Raman scattering," or OM-SERS, that involves lasers, gold and water. It is both the fastest, most efficient and reliable method that has yet been developed to count and analyze nanoplastics.
OM-SERS begins with a small water sample—just a few milliliters—into which Xing and Zhao place gold nanoparticles. Then they shoot the gold nanoparticles with a laser, and as the gold nanoparticles heat up, they attract the nanoplastics that are floating freely in the sample.
Once the various nanoplastic particles have all flocked to the gold stack, the team then rinses the sample with pure water, which flushes out the salts or any non-plastic debris—think tiny and prevalent soot particles or natural dissolved organic molecules that might be in the water. "What we have left behind are the plastic particles gathered around a gold center," says Zhao. "We can then conduct a very, very sensitive analysis right in place, without moving the sample, that will tell us what kinds of plastics we have and in what concentrations."
Not only can their method work with small samples, it can also be used to analyze nanoplastics in other matrixes. "We tested our OM-SERS system on samples gathered from a river, an ocean mariculture farm and a beach," says Xing, "but, once the samples have been properly processed, it could work to test the concentration and types of nanoplastics in soil, plant tissues or our own bodies."
