A growing number of scientists are questioning the validity of research that continually finds microplastics infiltrating nearly every corner of nature and even the human body. Concerns have mounted that flawed methodology and insufficient contamination control might be skewing these pervasive findings.

The Hidden Contaminant in Scientific Research

Researchers at the University of Michigan have identified a major potential source of error: the coating on standard nitrile and latex laboratory gloves. These disposable gloves are essential tools for scientists conducting sensitive environmental analysis.

Stearates: The Unintended Culprit

The issue stems from stearates, substances added to gloves to facilitate easy separation from their molds during manufacturing. While not technically microplastics themselves, these compounds share chemical similarities that make them nearly indistinguishable from actual plastic particles during lab analysis.

The findings were detailed in a recent publication in the journal Analytical Methods. Lead researcher, doctoral graduate Madeline Clough, emphasized that this discovery does not negate the entire field of study.

"As microplastic researchers looking for microplastics in the environment, we're searching for the needle in the haystack, but there really shouldn't be a needle to begin with," Clough stated.

Discovery Through Unexpected Results

The breakthrough occurred during a previous project focused on airborne microplastics. Clough was using light-based spectroscopy to analyze samples collected by air samplers equipped with metal surfaces.

While preparing these metal surfaces using standard nitrile gloves, Clough noticed the measured microplastic levels were orders of magnitude higher than anticipated. This prompted an intensive investigation into the contamination source.

"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," she explained. After ruling out atmospheric particles and plastic squirt bottles, the team ultimately traced the source back to the gloves.

Testing and Comparison

For their latest paper, the team tested seven different types of gloves. They observed that cleanroom varieties, which lack the stearate coating, performed significantly better, yielding fewer contaminating particles in the air samplers.

Clough noted that this contamination risk applies broadly. "If you are contacting a sample with a gloved hand, you're likely imparting these stearates that could overestimate your results," she said, noting the contact method mimics many research protocols.

Distinguishing Contaminants and Moving Forward

Under an electron microscope, researchers found it difficult to differentiate polyethylene, a common plastic, from the stearate particles. This highlights the methodological challenge in accurately quantifying environmental plastics.

However, Clough remains optimistic about correcting existing data. "For microplastics researchers who have these impacted datasets, there's still hope to recover them and find a true quantity of microplastics," she advised.

The researchers concluded that by integrating their spectral libraries of stearate standards, scientists can now address glove-based contamination in environmental datasets, leading to more accurate abundance estimates.

The Ongoing Challenge

Senior author and University of Michigan chemistry professor Anne McNeil acknowledged the inherent difficulty in the field. "This field is very challenging to work in because there's plastic everywhere," McNeil commented.

She stressed the necessity of chemists understanding chemical structures to navigate these issues. McNeil concluded, "We may be overestimating microplastics, but there should be none. There's still a lot out there, and that's the problem."