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Collecting and analyzing the amount of toxic micro- and nanoplastics (MNPs) in water is comparatively easy: fill a bucket from your source, evaporate the water and count and characterize the plastics that are left behind. But what if you want to know how many MNPs are in that apple you’re about to eat, the tree in your backyard, or even in your brain? 

Before we can determine how toxic MNPs may be for human health, we need to be able to measure and analyze their composition and concentration in samples taken from living organisms including human bodies—a task made difficult by the small size of the samples that can be harvested, as well as the complication of collecting from a living subject. 

A survey led by the University of Massachusetts Amherst of the extant scientific literature on the subject, recently published in Nature Reviews Bioengineering, points to a series of best practices that could get us one step closer to determining MNPs real threat to human health.

“Every biological sample represents a different matrix,” says Baoshan Xing, University Distinguished Professor of Environmental and Soil Chemistry at UMass Amherst’s Stockbridge School of Agriculture and leader of the international team that conducted the survey. “That apple, for instance, is composed of fibrous material, while MNPs in your body can be embedded in fats and proteins. MNPs in clams will have shell material as part of their matrix, and trees and plants will have lignin. Which means each of these different kinds of biological samples will need to undergo a different preparatory treatment—called “digestion”—in order to be accurately accounted for.

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“We also need to take into account the shape of the MNPs,” continues Xing, who notes that most studies to date assume a perfectly spheroid particle. Shape is important because it influences how MNPs can move through a biological system, as well as what potential pathogens or toxic substances can hide in their nooks and crannies.

Unfortunately, there are no commonly accepted guidelines for preparing, processing and analyzing MNP-containing biological samples. “This is a headache,” says Xing, “but it also means there’s tremendous opportunity for a real breakthrough that can help us move toward understanding the role plastics play in our bodies.”

To help move toward that ultimate goal, Xing and his colleagues from China’s Ocean University, East China Normal University and Jiangnan University have proposed a number of best practices.

The first involves settling on specific strategies for processing and detecting MNPs tailored to the kind of matrix in which they are found. In other words, we need to know what works when one wants to separate MNPs from fatty tissue, and another for separating MNPs from fibrous plant material.

We also need specific protocols for examining the polymer types, shapes and MNP surface characteristics—and since the shape, size and surface characteristics can be nearly infinite, the study authors point to various machine learning algorithms as a promising way to efficiently accomplish this task.

“There are no accepted protocols yet,” says Xing, “but we’re pointing the way, and the day is not far off when we’ll be able to accurately detect, characterize and quantify MNPs in biological samples.”