Effect Of Agricultural Organic Inputs And Plastics-related Pollutants On Nano-plastic Transport In Water-bearing Porous Medium

Plastic pollution has become one of the most raising environmental issues worldwide from last decade due to its proliferate manufacturing,improper management and disposal causing adverse effect on the ecology and human health.Investigation of terrestrial nanoplastics（NPs）has been largely overlooked compared to marine or aquatic pollution and is subject of active and urgent research.Interaction of NPs is highly dependent on both of their size and surface chemistry.Zeta potential is an important role player in the process of accelerated transportation or retardation of NPs in the colloids.Phthalates and dissolved organic matter of agricultural origin also control the movement of NPs differently based on their types that are listed below:（1）Transport behavior of different surface modified NPs was investigated using column experiments in the presence and absence of goethite（GT）.Quantum chemical computation was performed to reveal the transport mechanisms.The results showed that GT decreased the transport of NPs.Van der Waals forces and small electrostatic interactions coexisted between the polystyrene NPs（PSNPs）and GT and caused deposition.Ligand exchange caused greater deposition of PSNPs-COOH on GT-coated sand than that of PSNPs.Because of low absolute negative zeta potential values,PSNPs-NH₂ was sensitive to chemical heterogeneity,and thus fully deposited（over96.9%）in GT coated columns.Generally,the deposition of NPs due to chemical heterogeneity was more significant than that due to the formation of chemical bonds and van der Waals,electrostatic,and hydrogen interactions.Larger NPs（400nm）was found to show significantly higher blocking effects than the smaller one（50nm）that complies with the Derjaguin-Landau-Verwey-Overbeek（DLVO）theory.Our results highlight that the size,surface charge and functional groups significantly influence the transport behaviors of NPs and elucidate the fate of NPs in the terrestrial environment.（2）Influence of diethylhexyl phthalate（DEHP）on the transport behavior of different surface modified NPs was investigated using column experiments of varying proportion of GT coated sand media and used to simulate the leachate of PSNPs and changes in surface roughness of sand grains.Binding techniques and transport mechanisms among the colloidal particles were revealed by Quantum chemical computation.Existence of GT in the media significantly decreased the transport of NPs and the retention was further enhanced by DEHP up to 14.8%.Enhanced hindering effect of DEHP retained higher NPs in the column as it has strong affinity with plastic molecules.Active cation bridging coexisted between the PSNPs and GT and caused deposition.Higher GT and DEHP contents resulted in increased chemical and physical heterogeneity,yet the effect of physical heterogeneity on NPs deposition could be relatively small.Although hydrogen bonding existed between the DEHP and NPs with functional groups,an increase in the positive charge and chemical heterogeneity of the collector was the main reason for DEHP promoting the deposition of NPs.The PSNPs-NH₂ was highly sensitive to chemical heterogeneity as of low absolute negative zeta potential resulting fully deposited in GT and GT-DEHP coated media.The elongated morphology of GT might enhance its chemical heterogeneity and further improve the deposition of PSNPs–NH₂.The essence of our research concludes that,DEHP activates the surface charge and functional groups that significantly influence the transport behaviors of NPs and elucidate the fate of NPs in the terrestrial environment.（3）Co-transport of NPs with three types of dissolve organic matter（DOM）[biochar _DOM(BC_DOM),wheat straw _DOM(WS_DOM),and swine manure _DOM(SM_DOM)]was investigated in saturated goethite（GT）-coated sand columns.The results showed that co-deposition of 50-nm NPs（50NPs）with DOM occurred due to the formation of a GT-DOM-50NPs complex,while DOM loaded on GT-coated sand and 400-nm NPs（400NPs）aided 400NPs transport due to electrostatic repulsion.According to the quantum chemical calculation,humic acid and cellulose played a significant role in 50NPs retardation.Owing to its high concentration,moderate humification index（HIX）,and cellulose content,SM_DOM exhibited the highest retardation and promoting effects on the transport of 50NPs and 400NPs,respectively.Owing to a high HIX,the effect of BC_DOM on the mobility of400NPs was higher than that of WS_DOM.However,high cellulose content in WS_DOM caused it to exhibit a 50NPs retardation ability that was similar to that of BC_DOM.Our results highlight the significant influence of DOM type on the transport behaviors of NPs of different sizes and elucidate their micro-interface mechanism in a typical agricultural environment.