Abundance and characteristics of microplastics in treated organic wastes of Kaunas and Alytus regional waste management centres, Lithuania

The widespread use of plastic without the sustainable management of the plastic waste has led to its accumulation in the environment. The presence of microplastics even in drinking water and food products is of immense concern. This situation is getting even more complicated due to the limited knowledge about the sources of microplastics and their impact on the environment and human health. This article focuses on a poorly understood but potentially significant source of microplastic-treated organic waste. Quantitative and qualitative analyses of microplastics down to 50 µm in the stabilised organic waste (SOW) output after mixed municipal solid waste (MSW) processing and green and food composts are presented in the article. Nile Red staining and FTIR analysis were adopted for the identification of microplastics. The highest average microplastic abundance was found in the SOW: 17407 ± 1739 particles kg in autumn and 15400 ± 1217 particles kg in winter. Nevertheless, even separately collected treated organic waste contained a significant amount of microplastics. Green compost contained 5733 ± 850 particles kg in autumn and 6433 ± 751 particles kg in winter, while food compost 3783 ± 351 particles kg in autumn and 4066 ± 658 particles kg in winter. Microplastics < 1 mm accounted for 83.8-94.9% of all microplastics, which reflects the need to control not only large but also small microplastics in organic waste fertilisers to prevent soil pollution. The dominant shape of microplastics in compost samples was films, while in the SOW, it was fragments. Based on morphological and FTIR analyses, the majority of microplastics in green and food composts were considered as the residuals of plastic bags and packaging materials.