Comparison of three digestion methods for microplastic extraction from aquaculture feeds

Microplastics (MPs) are ubiquitous pollutants found in aquaculture animals that may threaten human health through the food chain. However, there is a lack of effective methods for extracting MPs from aquaculture feeds containing complex components such as organic matter and fish bones. Therefore, in the present study, the extraction efficiency of three digestion methods using 30 % H2O2, Fenton reagent, and 30 % H2O2 + HNO3 for different particle sizes and types of MPs in aquaculture feeds was investigated and compared. The total digestion efficiency of the aquaculture feeds by 30 % H2O2 was 97.3 ± 0.1 %, while the recovery efficiency of MPs was 91.3 ± 1.1 % -103.1 ± 0.9 %. However, there was a large deviation in the extraction efficiency of MPs from aquaculture feeds by the Fenton reagent and 30 % H2O2 + HNO3. Notably, the surface morphology, particle size distribution, and oxidation degree of MPs hardly changed after 30 % H2O2 digestion. More importantly, the changes in the spectral features and carbonyl index of MPs after 30 % H2O2 digestion were smaller than those of the Fenton reagent and 30 % H2O2 + HNO3, which did not affect the identification of MPs. Overall, 30 % H2O2 was more efficient in extracting MPs from aquaculture feeds, and no significant effect on the characteristics of MPs was observed. This work provides novel insights into the effect of chemical pretreatment on the extraction of MPs in aquaculture feeds and provides an optimal protocol for the detection of MPs in aquaculture feeds.