Fate of microplastics during composting and their leachability

The occurrence of chemical compounds specific to individual plastic polymers allowed the determination of components in compost feedstock (urban greenery and bio bins of households). The total concentration of plastic polymers is 431 mg/kg. The main identified polymers are polystyrene, polyethylene terephthalate, polyethylene, polycarbonate, and polypropylene. Additives used to modify the properties of plastics are present in the concentration of 195 mg/kg. Twelve compounds used as additives in the production of plastics in both the feedstock and the compost were identified. A statistically significant relationship was found between the decrease of concentration of organic matter and concentrations of compounds that identify plastic polymers (polyethylene terephthalate and polystyrene). The decrease of concentrations of compounds specific to polymers after three months was observed in the range between 33 and 84%, while the decrease for additives was 68%. After 18 months, the loss was higher than 82% except for polypropylene (only 70%). Compound leachability after three months of composting decreased to one-quarter for most polymers (except polypropylene and polyethylene), and to one-third for additives.