A comparative study on the adsorption behavior of pesticides by pristine and aged microplastics from agricultural polyethylene soil films.

Compared with pristine agricultural polyethylene (PE) soil films microplastics (MPs), aged agricultural polyethylene (APE) soil films MPs have a rougher surface, more cracks and have some oxygen-containing functional groups that makes them adsorb organic pollutants, such as pesticides more easily. This may be more harmful to human beings than marine MPs as the agricultural soil films are closer to our living environment. But few works focused on the adsorption of pesticides on pristine or aged agricultural polyethylene soil films MPs. In order to promote the risk assessment of co-exposure of pesticides and agricultural polyethylene soil films MPs, a comparative study on the adsorption behavior and mechanism of four pesticides (carbendazim, diflubenzuron, malathion, difenoconazole) by pristine PE MPs and APE MPs were carried out in this paper. The results showed microcracks and surface oxidation observed on APE MPs. The adsorption kinetics and isotherm models indicated that the adsorption capacity of APE MPs was higher than that of PE MPs, which attribute to the larger surface area of APE MPs. The adsorption capacities of pesticides on APE MPs were positively correlated with LogKow (Water octanol partition coefficient) values of these four pesticides, showed the hydrophobic partitioning played the most important part in the adsorption, but also some H-bonding between secondary amines in the molecular of diflubenzuron and polar O-containing functional groups on APE MPs may be formed. And electrostatic forces or interactions are not the determining factor for these pesticides adsorption behavior of PE MPs, and the effect of pH is mainly driven by changes in sorbate properties rather than changes in surface properties of MPs. The results presented herein show the APE MPs can be a better vector of most hydrophobic pesticides than pristine MPs in the agricultural field, and more attention should be paid to the problem of films and pesticides residue in farmland soil.

A comparative study on the adsorption behavior and mechanism of pesticides on agricultural film microplastics and straw degradation products.

Straw will degrade into segment, powder and crystalline cellulose, while the agricultural film will degrade into microplastics (MPs) in farmland soils. The specific surface area of these micro-particles increases and many new functional groups are formed in the degradation process, which can be a good vector of pesticides. To more accurately and truly analyze the risk of main imported substances and their degradation products against pollutants in soil, the adsorption behavior and mechanism of four commonly used pesticides on aged polyethylene microplastics (APE), wheat straw segment (WSS), wheat straw powder (WSP), and straw crystalline cellulose (SCC) were analyzed and compared through batch adsorption experiments and infrared spectrum. The adsorption kinetics of four pesticides on MPs and straw degradation products tended to be pseudo-second-order kinetics; the adsorption isotherms of pesticides on APE and SCC tended to fit the Freundlich model, while on WSP and WSS tended to fit the Langmuir model. The adsorption was a spontaneous endothermic increase process, suggesting that the main adsorption force of pesticides on MPs and straw degradation products was hydrophobic diffusion. The adsorption of pesticides against WSP and WSS still had a certain π-π conjugation and electrostatic interaction. And the adsorption amount on the straw degradation products followed the order of WSP > WSS > APE > SCC, presumably related to the specific surface area and pore volume of the adsorbent. As WSP, WSS could adsorb more pesticides, the straw returning to the field can be used for slow-release of pesticides to reduce the dosage of pesticides.

Adsorption behavior and mechanism of five pesticides on microplastics from agricultural polyethylene films.

Polyethylene (PE) agricultural soil films are easily embrittled and decomposed to microplastics (MPs) in environment. As widely used pesticides in vegetable farmland, carbendazim, dipterex, diflubenzuron, malathion, difenoconazole have potential environmental and human safety risks. They are often coexisting with MPs in the environment, and may cause consequential pollution to the ecosystem. Studying the adsorption behavior between pesticides and PE agricultural soil films MPs would be helpful for the risk assessment of co-exposure of pesticides and MPs. Herein, a systematic study on batch adsorption experiments was performed to determine the adsorption process of pesticides on MPs, the environmental factors on adsorption capacity were evaluated, and the adsorption mechanisms were discussed. Results suggested that all these five pesticides can adsorb on MPs, especially for diflubenzuron and difenoconazole. The adsorption kinetics and isotherm fitted to the Pseudo-second-order and Freundlich model, respectively, indicating that besides the adsorption onto surface sites, mass transfer and intraparticle diffusion were involved in the adsorption process, and the adsorption process was mostly controlled by physical and chemical interactions. The adsorption amounts of 5 pesticides on PE MPs follow the order of DIF > DIFE > MAL > CAR > DIP with KF correlated positively with octanol-water partition coefficients (LogKow). The thermodynamic study indicates the adsorption of all pesticides as spontaneous and exothermic processes. The results of this study illustrated that PE MPs can be a good carrier of pesticides in agricultural field.