A University of Michigan study suggests that nitrile and latex gloves commonly used by scientists may make microplastic levels appear higher than they really are.
Researchers have found that these gloves can unintentionally transfer particles to laboratory equipment used to analyze air, water, and other environmental samples. The source of the contamination is stearate, which is not plastic but can closely resemble plastic during testing. Because of this, scientists may be detecting particles that are not true microplastics. To alleviate this problem, UM researchers Madeline Clough and Anne McNeil recommend using cleanroom gloves, which emit far fewer particles.
Stearate is a salt-based soap-like substance that is added to disposable gloves to allow easier separation from the mold during manufacturing. However, because they are chemically similar to certain plastics, they are difficult to distinguish in laboratory analyzes and increase the risk of false positives when studying microplastic pollution.
The researchers stress that this does not mean microplastics are not a real problem.
“We may be overestimating microplastics, but there shouldn’t be any,” said McNeil, the study’s lead author and a UM professor in the Chemistry, Polymer Science, Engineering, and Environment Program. “There’s so much more out there, and that’s the problem.”
Professor Clough added: “As microplastics researchers looking for microplastics in the environment, we’re looking for a needle in a haystack, and there shouldn’t be a needle in the first place.”
The research, led by recent doctoral graduate Clough and published in the journal RSC Analytical Methods, was supported by the UM College of Letters, Science and the Arts’ Meet the Moment Research Initiative.
Unexpected causes behind inflated results
The discovery began during a collaborative project in Michigan investigating microplastics in the air. The effort involved researchers from multiple UM departments, including chemistry, statistics, climate and space science and engineering. Clough and McNeil worked with collaborators including chemistry professor Andy Ault and graduate students Rebecca Parham and Abigail Ayala to collect air samples.
To capture the particles, the team used an air sampler with a metal surface that collects material from the atmosphere. These samples were then analyzed using light-based spectroscopy to determine the types of particles present.
While preparing the sampling surface, Clough followed standard practice and wore nitrile gloves. But when she checked the results, the number of microplastics detected was thousands of times higher than expected.
“There was a huge rush to figure out where this contamination was coming from, because we knew the numbers were too high to be accurate,” Clough said. “Through the process of figuring it out, we were able to figure out whether it was a plastic squirt bottle, whether it was particles in the atmosphere in the lab where we were preparing the substrates, and finally to the gloves.”
Testing the impact of gloves on microplastic data
To investigate further, the researchers tested seven types of gloves, including nitrile, latex, and cleanroom gloves, as well as methods commonly used to identify microplastics.
Their experiments recreated typical laboratory situations, including gloved hands touching filters, microscope slides, and other equipment used during analysis. These routine interactions also transferred particles from the gloves to the test surface.
On average, the gloves introduced about 2,000 false-positive signals per square millimeter.
“The type of contact we tried to mimic is relevant to all kinds of microplastics research,” Clough said. “If you touch the sample with gloved hands, you may be feeding these stearates and may overestimate your results.”
Cleanroom gloves have significantly improved performance and emit far fewer particles. This may be because it is manufactured without a stearic acid coating and is intended for use in highly controlled environments.
Distinguish between real microplastics and false positives
The researchers also investigated whether they could visually distinguish real microplastics from stearic acid particles. Using scanning electron and light microscopy, they discovered that stearate is almost identical to polyethylene, a common plastic.
Despite this challenge, Clough and McNeil worked with graduate student Eduardo Ochoa Rivera and statistics professor Ambuj Tewari to develop a method to separate true microplastics from glove-related pollution. These techniques allow scientists to revisit previous data sets and potentially produce more accurate estimates.
“For microplastic researchers who have these affected datasets, there is still hope to recover them and discover the exact amount of microplastics,” Clough said.
The findings highlight the importance of chemical expertise in microplastics research, especially in identifying subtle differences between materials.
“Working in this field is very difficult because plastic is everywhere,” McNeil said. “But that’s why we need chemists and people who understand chemical structures to work in this field.”
