In Situ Investigation Of The Effect And Mechanism Of Carbon Nanomaterials On The Environmental Behavior Of PAHs On The Leaf Surfaces

PAHs are persistent organic pollutants that are ubiquitous in the environment.The exchange of environmental media is frequent.It is absorbed into crops related to human diet and will be transmitted and enriched through the food chain,thus posing a serious threat to human safety.Compared with the parent PAHs,alkyl PAHs have been proved to be more toxic due to their higher lipophilicity and abundance in the environment.In real life,PAHs exist as multiple components rather than one component in the environment.The environmental behavior of multi-component PAHs between media may be different from that of single-component PAHs.Moreover,PAHs will coexist with other environmental factors.As a new material,carbon nanomaterials are widely synthesized and used.When discharged into the environment,they will cause pollution.Coexistence with traditional pollutants may cause much serious pollution.The research on the composite pollution of carbon nanomaterials and PAHs on the surface of plants is not mature,so this topic is proposed.In this study,synchronous fluorimetry achieved the in situ simultaneous quantification of multiple PAHs,of which the spectra seriously overlapped,adsorbed onto spinach leaf surfaces.Moreover,synchronous fluorimetry is a good method to investigate the adsorption isotherms of PAHs onto leaf surfaces from water.Freundlich model was more suitable to describe the adsorption isotherms of Retene and Ant singly and as a mixture onto spinach and soybean leaf surfaces.The adsorption capacity of Retene singly on the leaf surface is more than that of Ant,which attributed to the lg KOW.For the same chemical,the concentration of PAHs adsorbed by the leaf surface varied with different leaf species with the decreasing order of soybean > spinach,indicating that PAHs have more stronger affinity with soybean than spinach,which attributed to soybean has more leaf-wax and more hair than spinach.The total amount of adsorption of Retene and Ant in a mixture is much more than that of PAH singly,which create harmful threat to food safety.The fiber-optic fluorimetry was applied to in situ examine the effects of graphene(GNS)and graphene oxide(GO)nanosheets on the quantification and depuration of three-ringed phenanthrene(Phe)and four-ringed fluoranthene(Fla)adsorbed individually onto the living spinach surfaces.When the GNS and GO dosages separately increased to the maximum values: a respective red-shift and blue-shift occurred for the optimal detection emission wavelengths(λem)of the two PAHs,indicating that individual GNS and GO resulted in different changes to the epicuticular wax(ECW)polarity;GNS inducing fluorescence quenching for the PAHs was about two times greater than GO,owing to the stronger π-π interactions between PAH molecules and GNS relative to GO;the volatilization coefficients(kC1)were reduced for Phe and Fla,mainly via providing an additional adsorbent and promoting the accessibility of the leaf cuticle;respective photolysis coefficients(kP2)of Phe and Fla decreased with GNS,primarily owing to the enhancement of the ECW light-adsorption capacity,but increased with GO due to its photocatalytic activities;overall,total depuration coefficients(kT1,kT2)of the two PAHs decreased.These findings demonstrate that GNS and GO significantly alter the depuration behavior of PAHs in vegetable systems,potentially posing a threat to the safety of edible vegetables.