Academic Work

The growing amount of marine plastic pollution calls for the need to better understand the mechanisms of its dispersal. Transported by winds, waves and currents, plastic washes up on coastal shores, accumulates in wreck-bays above the highest astronomical tide (HAT) limit and sediments within the soil. While soil has been theorized to act as a sink, this study challenged the question of its permanence. 3 soil cores (1|2|3) from 3 different locations (A|B|C) above the HAT limit of wreck-bays on the remote island of Smøla on the western coast of Norway were selectively collected based on varying presence of macroplastic observed. With the aim to determine the extent of potential microplastic (MP) leakage from coastal soil back into the ocean, a laboratory experiment was set up that would simulate precipitation by pouring locally collected rainwater on top of the 9 soil core samples (A1-C3). Percolate water was collected during the experiment and examined for MP-particles (MPs) in the size range 100µm-1mm. The methodical approach involved vacuum filtration for separation by size and oxidation by Hydrogen Peroxide H2O2[30%] for removal of organic matter within the samples, followed by Nile-red fluorescence staining for visualization of MP-particles when exposed to ultraviolet light, and stereomicroscopy for optical identification and counting. The number of MPs per liter of percolated water was determined to be 19.98 ± 10.83 MPs/L(A.H.) / 10.04 ± 4.31 MPs/L(J.B.C.) based on two individuals respective separate triplicate count averages for all samples and adjusted for contamination levels measured in method blank samples. With no previous research on MP-leakage from coastal soils available at the time of writing, direct comparison of results was not possible. Surprisingly, however, they were found most comparable with those from studies examining leachate from Chinese landfills. The obtained MP-concentration results could be extrapolated to a measure of annual MP-leakage per square meter based on the average annual rainfall of the last 5 years (27473MPs/m2/year(A.H.) / 13810MPs/m2/year(J.B.C.)). Data concerning the macroplastic content in % of total sample dry weight for all soil core samples was obtained by courtesy of a parallel study and used to examine the relationship between MP-leakage and soil macroplastic content through XY-scatterplots and the non-parametric Wilcoxon signed rank test. A significant relationship between microplastic-leakage and soil macroplastic content was discovered (p=0.004(A.H.), p=0.012(J.B.C.)), and a positive trend observed, indicating a contribution of secondary microplastic degraded from macroplastic to the flux, which aligned with previous research findings. Challenges associated with microplastic-quantification methods requiring subjective evaluation were highlighted, suggesting the choice of digitally automated, physical, or chemical polymer quantification- and characterization-techniques in future studies. Being the first to examine the matter of microplastic leakage from coastal soil, this case study emphasizes the need for further research in this area, so that we may add yet another tile to the puzzle of the global plastic cycle.