Size-dependent stability of pesticides adsorption on nanoplastics: Microsecond atomistic-scale molecular dynamics simulations.

Microsecond atomistic-scale molecular dynamics simulations were performed to compare the size-dependent adsorption stability of different pesticides on nanoplastic (NP) particles. Spherical particles of atactic polystyrene with diameters of 1.7-5.0 nm, representing NP particles in the final stage of polymer waste degradation, were considered. The results showed stable adsorption at 5 nm NP particle, while the desorption frequency of the least stable 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid (DCVA) pollutant increases exponentially with decreasing nanoparticle diameter as indicate 1 μs simulations. The binding energy of pesticides to the smallest considered NP particle increases as cypermethrin < PCB-169 < DDT < alpha-cyano-3-phenoxybenzyl alcohol (PBA) < DCVA, with only one desorption event observed for cypermethrin. For the 5.0 nm NP particle, however, this order changed, and no desorption occurred during 1 μs simulations, even for the least stable molecules (PBA and DCVA). This underscores the key role of NP size during microplastic degradation in the stability of pollutant adsorption.