Lab Gloves Leading to False Positives in Microplastic Studies, Michigan Research Finds
A University of Michigan study indicates that nitrile and latex gloves commonly used in scientific laboratories can lead to an overestimation of microplastic pollution measurements. Researchers, led by Madeline Clough and Anne McNeil, found that these gloves transfer non-plastic particles called stearates, which are chemically similar to microplastics and can result in false positives during detection and analysis.
Background: The Challenge of Microplastic Contamination
Microplastics, tiny plastic particles found in various environments and within human bodies, present significant challenges for accurate detection and quantification due to their small size and pervasive presence. The study addresses potential methodological issues in microplastic research, specifically related to contamination control.
A segment of the scientific community has expressed skepticism regarding widespread microplastic measurements due to concerns about potential methodological errors and inadequate contamination control.
The Unexpected Discovery: Tracing the Contamination Source
The issue was identified during a University of Michigan project focused on measuring airborne microplastics in Michigan. Researcher Madeline Clough observed microplastic counts that were unexpectedly high, at times thousands of times greater than previous reports.
"Researcher Madeline Clough observed microplastic counts that were unexpectedly high, at times thousands of times greater than previous reports."
This led to an investigation into various potential contamination sources, which eventually traced the problem to the nitrile gloves used for sample preparation.
Study Methodology and Key Findings
An experiment was designed to assess the extent of the contamination. Researchers tested seven types of gloves, including nitrile, latex, and cleanroom varieties, under conditions simulating typical contact between a gloved hand and laboratory equipment such as filters or microscope slides.
Key findings from the study include:
- Gloves transferred an average of approximately 2,000 false positive particles per square millimeter onto testing surfaces.
- Stearates, which are salt-based, soap-like substances used as mold-release agents in glove manufacturing, were found to be visually and structurally similar to common plastics like polyethylene.
- Standard identification techniques, including scanning electron microscopy, light-based microscopy, and vibrational spectroscopy, struggled to differentiate stearate particles from actual microplastics due to their chemical resemblance.
- The transferred stearate particles were largely less than 5 micrometers in size, a range considered to have potentially greater impacts on human and ecosystem health.
Mitigation and Differentiation Methods
To mitigate this contamination, the researchers offer several recommendations:
- Utilize cleanroom gloves, which are manufactured without stearate coatings and were found to release significantly fewer particles.
- Avoid using gloves in microplastic research when feasible.
- If glove use is necessary, consider stearate-free gloves designed for applications such as electronics manufacturing.
In collaboration with Eduardo Ochoa Rivera and Ambuj Tewari, the research team also developed methods to chemically differentiate glove-derived stearates from environmental microplastics. This development includes using spectral libraries of stearate standards and offers a pathway for researchers to potentially correct affected datasets from previous studies. The initial dataset from the University of Michigan project itself had to be discarded due to the identified contamination.
Broader Implications for Microplastic Research and Policy
The study emphasizes the importance of chemical expertise in microplastics research to accurately distinguish between true microplastics and other contaminants. While the findings suggest that previous microplastic measurements may be overestimated in some instances, the researchers clarify that this does not negate the overall problem of microplastic pollution.
A substantial amount of genuine microplastics remains in the environment, posing ongoing considerations for human and ecosystem health. The accuracy of measurements, particularly for smaller microplastic sizes, can influence studies that inform future policy decisions.