Exploring sorption of pesticides and PAHs in microplastics derived from plastic mulch films used in modern agriculture.

The sorption and vector effect of microplastics on the transfer of pesticides and polycyclic aromatic hydrocarbons (PAHs), as well as its impact on agriculture remain largely unexplored. This comparative study is first to investigate the sorption behavior of different pesticides and PAHs at environmentally realistic concentrations by model microplastics and microplastics derived from polyethylene mulch films. Sorption was found to be up to 90% higher in the case of microplastics derived from mulch films as opposed to pure polyethylene microspheres. For microplastics from mulch films, the sorption percentages for pesticides in media containing CaCl2 were reported to be: pyridate (75.68% and 52.44%), fenazaquin (48.54% and 32.02%), pyridaben (45.04% and 56.70%), bifenthrin (74.27% and 25.88%), etofenprox (82.16% and 54.16%) and pyridalyl (97.00% and 29.74%) at 5 µg/L and 200 µg/L pesticide concentration levels respectively. For PAHs, the sorption amounts were: naphthalene (22.03% and 48.00%), fluorene (38.99% and 39.00%), anthracene (64.62% and 68.02%) and pyrene (75.65% and 86.38%) at 5 µg/L and 200 µg/L PAH concentration levels respectively. Sorption was influenced by the octanol-water partition coefficient (log Kow) and ionic strength. Kinetics of the process in the case of sorption of pesticides were best explained by pseudo-first order kinetic model (R2 between 0.90 and 0.98) while the best fitting isotherm model was Dubinin-Radushkevich (R2 between 0.92 and 0.99). Results suggest the presence of surface level physi-sorption through a micropore volume filling mechanism and the role of hydrophobic and electrostatic forces. Pesticide desorption data in polyethylene mulch films indicate that pesticides with high log Kow were almost completely retained in mulch films, while those with lower log Kow were desorbed rapidly into the surrounding media. Our study highlights the role of microplastics from plastic mulch films as vectors for pesticide and PAH transport at environmentally realistic concentrations and the factors that influence it.

Supercritical fluid chromatography separation of chiral pesticides: Unique capabilities to study cyhalothrin and metalaxyl as examples.

Evaluation of chiral pesticides remains a frequently neglected matter in routine food control laboratories. This fact is due to the existence of many residue definitions but also due to the lack of robust instrumental methods for the evaluation of these isomeric compounds. However, supercritical fluid chromatography coupled to mass spectrometry (SFC-ESI-MS/MS) has been demonstrated to perform fast and highly efficient separations without the need to change the mobile phase employed in multiresidue pesticide analyses. Regarding chiral stationary phase columns, the polysaccharide-based ones clearly demonstrate the best separation technology. Two polysaccharide-based columns were tested in this study, and the robustness of their combination with SFC was verified. The enantiomers of lambda-cyhalothrin and metalaxyl were studied precisely due to their markedly distinct toxicity and enantioselectivity. Furthermore, the acute reference dose for gamma-cyhalothrin is half in comparison with its enantiomer (0.0025 and 0.005 mg/kg respectively), which is present in the lambda-cyhalothin residue definition. These enantiomers were analyzed in terms of linearity, reproducibility, and matrix effects in four representative matrices (tomato, orange, leek, and cayenne). Additionally, field tests under greenhouse conditions for these compounds were performed. The results obtained after different sample collections revealed a similar degradation in lambda-cyhalothrin enantiomers (R, S, S, and S, R, R) but not in the case of metalaxyl-M (mefenoxam) where the degradation in tomato was 2 to 6 times less in comparison with its S-enantiomer.