Effect of ultrasonication conditions on polyethylene microplastics sourced from landfills: A precursor study to establish guidelines for their extraction from environmental matrices.

Establishing concentration of microplastics (MPs), designated as C, in aqueous, semi-solid and solid samples originating from unscientifically created landfills/dumpsites (UCLDs) and engineered landfills (ELFs) is of utmost importance to assess their impact on the geoenvironment. However, the accuracy of C will be guided by the extraction efficiency of MPs from these samples. The extraction of MPs from semi-solid and solid samples of UCLDs/ELFs would be cumbersome, mainly due to their trapping in solid aggregates (including organic matter). Such aggregates need to be dispersed to release the MPs, which can be achieved through the assistance of ultrasonication (US) in the presence of an appropriate dispersing agent. However, mere dispersion of solid aggregates during the US might not result in the complete release of MPs adhered (AMPs) to MPs native (NMPs) to these samples. This is because MPs would adhere to the surface of the adjacent ones due to various physical-mechanical-thermal-chemical processes that prevail in landfills. Hence, guidelines for US-assisted extraction of MPs should be developed by considering an approach that would ensure (i) cleaning of NMPs' surface and (ii) release of AMPs without damaging the former. This necessitates understanding the influence of US parameters such as energy applied (E), time (t) and direct/indirect exposure of NMPs from landfills that would control C. In this context, the influence of above mentioned US parameters on the (i) surface cleaning of polyethylene NMPs and (ii) release of AMPs and their concentrations (C) was investigated. It was observed that E equal to 500 kJ/L during the indirect method of US would result in surface cleaning of NMPs and complete release of AMPs without damaging the farmer's structure. The present work acts as a precursor study to establish the guidelines for the US-assisted extraction of MPs in environmental samples. Also, a generalized relationship between E and C, which can be employed to study the impact of landfill type on the release of MPs during the US was developed.