To what extent are we really free from airborne microplastics?

Highlights: • The efficiencies of washing and ashing in removing airborne MPs were determined. • No significant difference was noted between washing and ashing. • Trace amounts of airborne MPs were still detected although rigorous measures were taken. • Airborne contamination is almost inevitable. • Background contamination should be paid attention to in microplastic studies. Quality assurance and quality control (QA&QC) procedures are vital for ensuring data reliability, but little is known about the use of such procedures in reducing airborne microplastic (MP) contamination. To address this issue, we tried to determine the efficiency of two common methods (washing and ashing experimental glassware) for removing airborne MPs and identified airborne contamination during MP analytical procedure. The results showed the removal efficiencies of washing and ashing were an average of 88%–98% and 100%, respectively, indicating that both methods could eliminate most of the spiked airborne MPs with no significant difference noted between the two methods. Although rigorous measures were taken to prevent contamination from ambient air, trace amounts of airborne MPs were still detected, which is an issue that has not been adequately investigated in previous studies. All of the procedural contaminants detected in this study were fibrous. Approximately 88% of these fibers were cotton-like (cotton, cellulose, and cellophane) fibers, and 13% of them were plastic. Surprisingly, cotton-like fibers and MPs had a similar size distribution, suggesting that they may have undergone a similar weathering process. In the end, to cope with inevitable airborne contamination, several measures were proposed for further research. Such measures will provide the necessary methodological assistance for accurate quantification of MP pollution in the field.