Release characteristics and toxicity assessment of micro/nanoplastics from food-grade nonwoven bags

Micro/nanoplastic (M/NP) contamination in food has become a global concern. Food-grade polypropylene (PP) nonwoven bags, which are widely used to filter food residues, are considered environmentally friendly and nontoxic. However, the emergence of M/NPs has forced us to re-examine the use of nonwoven bags in cooking as plastic contact with hot water leads to M/NP release. To evaluate the release characteristics of M/NPs, three food-grade PP nonwoven bags of different sizes were boiled in 500 mL water for 1 h. Micro-Fourier transform infrared spectroscopy and Raman spectrometer confirmed that the leachates were released from the nonwoven bags. After boiling once, a food-grade nonwoven bag can release 0.12-0.33 million MPs (>1 μm) and 17.6-30.6 billion NPs (<1 μm), equivalent to a mass of 2.25 - 6.47 mg. Number of M/NPs released is independent of nonwoven bag size; however, it decreases with increasing cooking times. M/NPs are primarily produced from easily breakable PP fibers, and they are not released into the water at once. Adult zebrafish (Danio rerio) were cultured in filtered distilled water without released M/NPs and in water containing 14.4 ± 0.8 mg L released M/NPs for 2 and 14 days, respectively. To evaluate the toxicity of the released M/NPs on the gills and liver of zebrafish, several oxidative stress biomarkers (i.e., reactive oxygen species, glutathione, superoxide dismutase, catalase, and malonaldehyde) were measured. The ingestion of the released M/NPs by zebrafish induces oxidative stress in the gills and liver, depending on the exposure time. Food-grade plastics, such as nonwoven bags, should be used with caution in daily cooking because they release large amounts of M/NPs when heated, which can threaten human health.