Efficient Extraction of Polyethylene Microplastics from Soil by Sieve Flotation Method

Objective  Efficient separation and extraction of polyethylene microplastics from soil is a key link to study the behavior of polyethylene microplastics in terms of environmental pollution and toxicology, with a view to constructing a separation method for in situ separation and efficient extraction of polyethylene microplastics from soil.

Method  Polyethylene microplastics in soil were extracted by using sieve flotation method, density separation method and Soxhlet extraction method, and the extraction rate of polyethylene microplastics in soil was calculated by the three separation methods. Scanning electron microscopy (SEM) was used to analyze the changes of surface micromorphological features of polyethylene microplastics; thermogravimetric (TG) was used to analyze the changes of pyrolytic characteristic parameters of polyethylene microplastics; Fourier transform infrared spectroscopy (FT-IR) was used to analyze the changes of characteristic functional groups of polyethylene microplastics.

Result  All three separation methods can extract polyethylene microplastics from soil, with the highest extraction rate of 95.58% by sieve flotation method, 89.60% by density separation method and 86.10% by soxhlet extraction method. SEM analysis showed that the surface of polyethylene microplastic particles separated by Soxhlet extraction method had fine fish scale pattern or flake structure; the surface of polyethylene microplastic extracted by density separation method had a large amount of soil impurity particles attached; the surface of polyethylene microplastic particles separated by sieve flotation method almost had no soil impurity and the surface microscopic morphological features were not destroyed. Thermogravimetric (TG) and Fourier infrared spectroscopy (FT-IR) analysis showed that the main components of polyethylene microplastics extracted by the three separation methods were all polyethylene microplastics and did not destroy the original functional group structure of polyethylene microplastics.

Conclusion  The extraction rates of polyethylene microplastics in soil by the three separation methods ranked as: sieve flotation method > density separation method > Soxhlet extraction method, and the integrity of microscopic surface characteristics showed as: sieve flotation method > density separation method > Soxhlet extraction method, the sieve flotation method is better than the other two separation methods in terms of extraction rate and retention of microscopic surface characteristics information of the extracts.