Development and application of an efficient microplastics extraction method based on glycerol flotation for environmental soil samples

Abstract

Risk assessment and removal of microplastics (size 1 µm to < 5 mm) from the environment necessitate continuous improvements in extraction methods, particularly for complex matrices such as soil. Glycerol exhibits flotation ability that can be used to improve microplastic extraction. In this study, we primarily evaluated glycerol flotation capability and measured its recovery rate, cost, and safety, compared to conventional microplastics extraction salts, including sodium chloride (NaCl) and sodium iodide (NaI). Our results showed that glycerol efficiently extracted five standard microplastic polymers (recovery rates 60 ± 10 % to 100 %), with recovery rates for polyethylene glycol terephthalate (PET) and polyvinyl chloride (PVC) in glycerol higher than that in NaCl. NaI is costly and toxic, and its color effects microplastic analysis, while glycerol is 40 times cheaper and safer than NaI. The glycerol flotation efficiency was highest at 0.5 h, and the recommended time for glycerol flotation was 0.5 h. This newly developed method was applied for extraction of microplastic from environmental soil samples, and we found PP and PS, with an abundance of 0.11 ± 0.04 items/g in tidal spreading soils, and PP, PVC, and PE, with abundance of 0.21 ± 0.13 items/g in agricultural soils. In conclusion, glycerol flotation, as an innovative flotation technique, demonstrates superior flotation efficiency compared to NaCl. The expense of glycerol is inferior to that of NaI, and it is relatively safer for microplastic extraction. Glycerol flotation provides an effective method for microplastic extraction from complex matrices, saves laboratory costs, and ensures environmental safety. This study provides practical and novel insights into the safe and efficient extraction of environmental microplastics from biological, solid, and liquid samples.