A University of Michigan study suggests that standard lab gloves that scientists use could be causing overestimation of microplastics levels. Researchers found that latex and nitrile gloves can transfer stearates onto lab tools, which are used to analyze water, air, and other environmental samples.
Stearates are salt-based, soap-like substances that are added to disposable gloves to help them easily separate from molds during manufacturing. Even though they are not plastics, stearates closely resemble them during testing, increasing the chances of false positives in regards to microplastic pollution. Despite the possibility of these false positives, researchers highlight that microplastics remain an important issue to discuss.
“We may be overestimating microplastics, but there should be none,” said Anne McNeil, senior author of the study and U-M professor of chemistry, macromolecular science and engineering. “There’s still a lot out there, and that’s the problem.”
This discovery began during a project involving the examination of airborne microplastics in Michigan. This project involved researchers from various U-M departments alongside McNiel. The team used air samples equipped with metal surfaces to capture particles. The samples were then analyzed using light-based spectroscopy to identify the types of particles present. When preparing the sampling surfaces, U-M researcher Madeline Clough wore nitrile gloves as part of standard protocol. However, the number of detected microplastics was thousands of times higher than expected.
“It led to a wild goose chase of trying to figure out where this contamination could possibly have come from, because we just knew this number was far too high to be correct,” Clough said. “Throughout the process of figuring it out—was it a plastic squirt bottle, was it particles in the atmosphere of the lab where I was preparing the substrates—we finally traced it down to gloves.”
To investigate this further, the researchers tested seven different types of gloves through experiments recreating typical lab conditions. On average, the gloves introduced around 2,000 false positive signals per square millimeter. However, cleanroom gloves released far fewer particles, likely because they are made without stearate coating.
The team also explored if they can visually determine the difference between microplastics and stearates. Using scanning electron microscopy and light-based microscopy, they discovered that stearates look similar to polyethylene, the world’s most widely used plastic. Despite this challenge, Clough and McNeil, working with graduate student Eduardo Ochoa Rivera and statistics professor Ambuj Tewari, developed methods to separate microplastics from stearates. These techniques could allow researchers to revisit earlier datasets and produce more accurate results.
“For microplastics researchers who have these impacted datasets, there’s still hope to recover them and find a true quantity of microplastics,” Clough said.
