The Effects Of Neonicotinoids On The Transport Of Microplastics In Saturated Porous Media

Microplastic pollution poses a significant global challenge within the realm of environmental and ecological scientific research.More than 60%of the total content of microplastics on land is found in farmland soil,with farmland cover serving as the primary source of microplastics in agricultural soil.The transport of microplastics into the subsurface environment,along with other contaminants,leads to a wide array of ecological issues.Due to their non-polar nature,both microplastics and pesticide molecules,face difficulties in dispersing stably after mutual adsorption.The polar groups of neonicotinoid insecticides absorbed on microplastic surfaces have a high potential to enhance their hydrophilicity,thereby intensifying the migration of microplastics in the underground environment.Consequently,further investigation is necessary to explore the potential of neonicotinoid insecticides in promoting microplastic migration.This study aimed to examine the adsorption properties of neonicotinoids（acetamiprid,dinotefuran,and nitenpyram）on polyethylene（PE）and polypropylene（PP）microplastics through batch adsorption experiments.Additionally,the influence of solution chemical conditions（p H,ionic strength（IS）,and cation type）on the transport of PE and PP microplastics in the presence of neonicotinoids was explored using column experiments with quartz sand saturated porous media.To simulate adjuvants and active ingredients,surfactants（sodium dodecyl sulfate（SDS）and nonylphenol ethoxylate（NP-40））and neonicotinoids were employed,respectively.The solid-liquid static contact angle was measured,and the adhesion work of various treatments on the surface of microplastics was calculated using the Young and Gibbs equation.These analyses helped further elucidate the mechanisms underlying the transport of PE and PP in the presence of the two components.Subsequently,UV degradation experiments and column experiments were conducted to investigate the degradation characteristics of degradable microplastics,poly（lactic acid）（PLA）,poly（hydroxy fatty acid ester）（PHA）,and poly（adipic acid/butylene terephthalate）（PBAT）,and the influence of neonicotinoids on the transport behavior of degradable microplastics before and after aging.The research findings hold significant implications for understanding the migration and diffusion risks associated with microplastics under the influence of neonicotinoids,as well as for the prevention and mitigation of the environmental hazards posed by microplastics.The research conclusions are summarized as follows:（1）Acetamiprid,dinotefuran,and nitenpyram could adsorb onto PE and PP microplastics through hydrophobic interactions,electrostatic forces,and hydrogen bonding.The adsorption behavior of neonicotinoids on PE aligned more closely with the Langmuir model,indicating a stronger hydrophobic interaction between PE and neonicotinoids.The adsorption of neonicotinoids onto the two types of microplastics involved both physical and chemical interactions,which were categorized as endothermic spontaneous reactions.The adsorption of acetamiprid,dinotefuran,and nitenpyram on microplastics was favored under solution conditions with a p H of 3.5 and an IS of 0.005 mol L^-1.Among the cations tested,the adsorption of neonicotinoids by microplastics followed the order Na⁺>K⁺>NH₄⁺>Mg²⁺.Neonicotinoids were adsorbed onto microplastics through N-containing functional groups.Compared to PE,PP exhibited a larger specific surface area,pore volume,smaller average pore size,and more functional groups containing oxygen,resulting in a higher adsorption capacity for neonicotinoids.（2）The presence of acetamiprid,dinotefuran,and nitenpyram enhanced the transport of PE and PP in quartz sand saturated porous media,leading to an increase in the recovery of PE and PP by 8.90-18.83%and 9.26-17.26%,respectively.The presence of neonicotinoids reduced the sensitivity of microplastic transport to changes in p H.Increasing the IS of the solution to 0.005 mol L^-1 enhanced the recovery of both PE and PP microplastics to varying degrees.The influence of cations on microplastic migration followed the order Na⁺>K⁺>NH₄⁺>Mg²⁺,as it correlated with the changes in the neonicotinoid adsorption capacity under different environmental conditions.The migration of PE and PP initially increased and then decreased with an increase in neonicotinoid concentration.This behavior was attributed to the adsorption of neonicotinoids onto microplastics through hydrophobic interactions preferentially,which enhanced the stability of microplastics.However,at high concentrations,neonicotinoids further shielded the hydrophilic O-containing functional groups.（3）The mobility of microplastics was enhanced by surfactants,and neonicotinoids,individually.Acetamiprid and dinotefuran compromised the hydrophilic modification capacity of SDS towards PE microplastics,as well as the adhesion work of the mixed solution,due to competition for hydrophobic adsorption sites.For instance,the adhesion work decreased from 48.29 k T(0.2 mmol L^-1 SDS)to 22.46 k T(0.2 mmol L^-1 SDS and 2.5mmol L^-1 acetamiprid),consequently inhibiting the transport of PE microplastics.In contrast,nitenpyram,characterized by strong hydrophilicity,faced difficulties in competing with surfactant molecules for adsorption sites.However,spatial hindrance enhanced the mobility of PE microplastics.The inherent weak hydrophobicity of PP rendered the adhesion work of the mixed system less susceptible to the influence of neonicotinoids.Additionally,owing to the high surface tension of NP-40 and the weak electrostatic repulsion between NP-40 and neonicotinoids,neonicotinoids were more inclined to impede the transport of microplastics by reducing the adhesion work of the mixed system on the microplastic surface.In the coexistence system of NP-40 and neonicotinoids,the presence of 2.5 mmol L^-1 acetamiprid and nitenpyram led to a reduction of 19.43%and 35.77%,respectively,in the recovery of PE and PP.The nonyl and polyoxyethylene long chains of NP-40 contributed to the enhanced stability of microplastic particles within the mixed system.（4）PHA microplastics exhibited stronger resistance to UV degradation compared to PLA and PBAT,owing to their pronounced hydrophobicity.During the aging process,degradable microplastics experienced the breaking of ester groups（C-O）and the formation of carbonyl groups（C=O）.The adsorption of neonicotinoids on the surface of degradable microplastics supplemented their surface charge,but high concentrations of neonicotinoids effectively shielded this surface charge.The impact of light aging on transport revealed the following trend:PLA≈PBAT>PHA.As the degree of aging increased,the inhibitory effect of neonicotinoids on microplastic recovery became more pronounced.Neonicotinoid molecules had a higher inhibitory effect on the migration of aging PLA and PBAT microplastics,with dinotefuran exhibiting particularly strong inhibition.For instance,the presence of 2.5 mmol L^-1 dinotefuran inhibited the recovery of 24-PLA and 24-PBAT by38.63%and 34.18%,respectively.To summarize,neonicotinoids have the potential to significantly increase the mobility of PE and PP microplastics by virtue of their hydrophilicity and interaction with the microplastic surface.Furthermore,low concentrations of neonicotinoids can effectively supplement the surface charge of degradable microplastics and promote particle stability.The environmental risk of neonicotinoids exacerbating microplastic transport in the actual environment needs to be paid attention to.