Assessing the Impact of Shipping on Microplastic Concentration of Filtered Samples

Background: As microplastics research expands across laboratories worldwide, filtering samples onto inexpensive metal filters and shipping them in metal tins could become the standard practice, replacing the impractical transportation of large water or environmental samples. Despite extensive research on microplastic distribution, there remains a notable absence of standardized methods, including sample transportation, highlighting the need to understand how shipping and packaging methods affect microplastic concentration variability. This study aims to evaluate the influence of different shipping and packaging methods on the recovery rate of microplastic particles that are collected on metal filters. Findings: Water samples spiked with polyethylene spheres were filtered onto 20 µm metal filters. The metal meshes were then placed in metal tins and subjected to six different packaging and shipping methods, ranging from paper boxes and envelopes to insulated hard and foam coolers. Laser Direct Infrared Spectroscopy was employed for the detection and quantification of polyethylene particles. The results revealed significant variation in recovery rates based on the shipping method. The highest recovery rates were observed in samples shipped in insulated hard or foam coolers, with at approximately 91-92% of the microplastics retained, while the lowest recovery was found in samples shipped in a flat rate mailing envelope (10%). Paper boxes with materials that eliminate space for movement inside the box offered moderate protection, with recovery rates of approximately 70%. Conclusions: This study demonstrates that shipping methods can substantially influence the retention of microplastics during transport from field sites to laboratories for analysis. Shipping methods where the packing remains upward such as with a cooler with a handle provided the highest recovery rates. We infer that this is due to the better care in handling from mail/shipping carriers; however, this method cost more. Lowest recover rates occurred when metal tins could freely move within the packaging and the package was allowed to be in any orientation. The findings highlight the importance of packaging choice in minimizing microplastic loss during shipping. Further research is necessary to standardize sample handling protocols and ensure consistent results across various transportation conditions, ultimately improving the reliability of microplastic contamination assessments.