| The production and utilization of organic chemicals has expanded over the past half-century because of robust industrial and agricultural development.Some of these organic chemicals are highly toxic and bioaccumulative.Organic toxic substances(OTSs)enter the aquatic ecosystem from various points posing risks to human health and organisms.Polycyclic aromatic hydrocarbons(PAHs)and organophosphorus pesticides are common high-risk OTSs in the water,and their pollution impacts have raised serious concerns.Recent studies have confirmed that microplasticsin aquatic ecosystem can accumulate heavy metals and other pollutants through adsorption,and then release the pollutants after ingestion by aquatic organisms or human beings.On the other hand,extracellular DNA(eDNA),released from cell lysis or active secretion,coexists with OTSs and microplastics which can be adsorbed to the surface of particles,affecting enzymatic hydrolysis and horizontal gene transfer.Notably,some eDNA can harbor antibiotic resistance genes(ARGs)posing widespread population and ecological health risks.However,the adsorption of OTSs and microplastics by eDNA in aquoues environment and the influence of OTSs on enzymatic hydrolysis of eDNA is still unclear.Therefore,modern chemical and biological methods are needed to elucidate the interaction and influence of microplastics-OTSs-DNA in water.Therefore,batch adsorption experiments were employed to study the adsorption of PAHs by different microplastics,and construct a prediction model of OTSs adsorption based on a neural network algorithm.It also revealled the effect of ARGs on thermoplastic polyurethane adsorption behavior,the promotion effect and molecular mechanism of organophosphorus pesticides on DNA enzymatic hydrolysis in water.The main findings are as follows:1.Rubberized microplastics exhibit better adsorption performance than glassy microplastics.Batch adsorption experiments were conducted to investigate the adsorption of phenanthrene and pyrene on various forms of microplastics.The adsorption isotherms of phenylene and pyrene on 15 microplastics conformed to the Freundlich equation.The Log Kf value of phenanthrene adsorbed in glass microplastics and rubber;ranged from-0.3955 to 0.6041 and from 0.6382 to3.1818,respectively.Whereas,Log Kf value of pyrene adsorbed in glassy microplastics and rubber ranged from-0.1847 to 0.9091 and from 0.8918 to 1.3124,respectively.The Log Kf of phenanthrene and pyrene had a significant negative correlation with the glass transition temperature(Tg).The Pearson correlation coefficient R-value of Log Kf and Tg were-0.905**and-0.683**,respectively.Microplastic’s morphology on adsorption(TPX and PVAC)which can transform from glass to rubber state microplastics with the increase of temperature,was used analyze the influence of temperature.In the experimental temperature range(15～35℃),the Log Kf value of phenanthrene increased from 0.6763 and 0.5157 to 0.8078 and 0.8668,respectively,and the Log Kf value of pyrene increased from 0.7362 and 0.7103 to 0.9009 and 0.9653 for glassy and rubber microplastics,respectively.According to the WLF equation and theoretical calculation results,the free volume range of rubber microplastics range from 0.0287 to 0.0562,while the free volume of glass microplastics is a fixed value of 0.0250.Rubberized microplastics are mainly non-polar monomer structure.The molecular chains of glass-state microplastics all contain polar monomers.In the weak interaction analysis,the combination of phenylene and pyrene with 15 microplastics was achieved only by Van der Waals and π-π interaction forces.These results indicate that free volume fraction and polarity of the molecular chain are the key factors determining the adsorption capacity of non-polar PAHs when they are adsorbed on microplastics by non-covalent bonds.2.Predicting Aqueous Adsorption of OTSs onto microplastic with Deep Learning Neural Network.The NN-TLSER adsorption prediction model was constructed using adsorption data of 159 isothermal adsorption curves from the literature studies,and used to calculate the adsorption parameters Log Kd of OTSs on microplastics.The developed model had better goodness of fit,robustness and prediction ability with evaluation parameter goodness of fit(R2)and root mean square error(RMSE)of 0.9786 and 0.1861,respectively.Use random forest algorithm to determine the importance of a single input molecular structure descriptor to Log Kd.Weight analysis of the molecular structure descriptors of the prediction model showed that the mean square error(MSE)value of adsorption equilibrium concentration Log Ce is 80.46%,microplastic BET specific surface area of the MSE=75.75%,and MSE=55.70%of π,which characterizes the dipole-dipole interaction,more important than the remaining 10 molecular structure descriptors.The results showed that adsorption of OTSs by microplastics mainly depended on the molecular polarity and concentration in solution,as well as the specific surface area of microplastics.To verify the prediction performance of the model,the adsorption data of naphthalene and its homolog on two microplastics polyamide-6(PA6)and thermoplastic polyurethane(TPU)were measured through experiments,and then the model was further used to forecast the experimental data.The absolute error between the adsorption coefficient Log Kf value of the thermodynamic curve fitting obtained from the experiment and the prediction was 0.0173 to 0.2168(PA6)and 0.0539 to 0.7142(TPU),respectively.Notably,the errors are within an order of magnitude.It shows that the NN-TLSER model constructed has good accuracy.3.DNA containing antibiotic resistance genes can be adsorbed on thermoplastic polyurethane.Thermoplastic polyurethane microplastics(TPU),linear and plasmid DNA(pUC19 and pBR322)containing ampicillin and kanamycin resistance genes were selected to study the adsorption of DNA on microplastics.The results showed that the adsorption capacity is affected by the length of the DNA fragment.The saturated adsorption capacity of linear DNA containing the same resistance gene is 29.87%(pUC19)and 88.23%(pBR322)higher than that of plasmid DNA,respectively.The adsorption of TPU to DNA was affected by temperature,pH,and electrolyte concentration.Within the test temperature range(15～35 ℃),at 25℃,the DNA adsorption capacity reached the maximum,which was the optimal temperature for TPU to adsorb DNA.The adsorption capacity of DNA on TPU decreased with the increase of pH(3.0～9.0),and the adsorption capacity decreased by 37.86%to 63.96%,increased concentration of electrolyte(NaCl)would inhibited TPU adsorption of DNA,and decreased by 14.21%to 30.35%.The total concentration of Zn2+on the surface of TPU was 128.36 ± 11.13 μg·-1,and the concentration of Zn2+ was 25.36± 4.35 μg·L-1 released into the solution.In the XPS spectrum,the binding energy of Zn3s changed by 0.3 eV,and the peak intensity decreased,while in the FTIR spectrum,the peak intensity of C=O in ester and carbonyl group on the TPU molecular chain increased or decreased to different degrees.The results indicate that the adsorption sites of DNA on TPU were C=O,and Zn2+plays a bridging role.Besides,The DNA structure adsorbed on TPU containing ARGs was preserved.4.Reveal the promoting effect and mechanism of organophosphorus pesticides on DNA enzymatic hydrolysis in the aqueous system.The effect of OPs on DNA enzymatic hydrolysis was studied using salmon sperm DNA,Chlorpyrifos(CPY),and Chlorpyrifos methyl(CPYM).CPY and CPYM promoted the enzymatic hydrolysis of 500～2000 bp DNA fragment into fragments less than 250 bp under the action of DNase I.The enzymatic hydrolysis led to absorbance of the conjugate structure exposed by DNA at 260 nm,which increased by 39.2%and 88.2%,respectively.In the fluorescence quenching titration experiment,the binding constants(KSV)of CPY and CPYM with DNA were 8.02×106 and 7.73×106 L·mol-1,respectively,while in the UV-visible spectrum,the maximum UV absorbance of double-stranded DNA treated by CPY(2.0 mg·L-1)and CPYM(4.0 mg·L-1)at 258 nm was reduced by 6.32%and 19.58%,respectively,which further proved that CPY and CPYM could bind to DNA molecules.The UV-visible spectra also showed that CPY and CPYM were intercalated into DNA base pairs.CD spectra proved that CPY and CPYM include groove binding as well as intercalative binding.FTIR spectra and theoretical calculation results showed that CPY and CPYM combine with D-2 deoxyribose,C,G,and T bases of DNA were dominated by Van der Waals attraction,forming weak hydrogen bonds,while CPYM can form strong π-π interaction with G bases.Molecular dynamics simulation results showed that CPY and CPYM intercalation increased the distance of the DNA groove.In the simulation time range,the average distance of the DNA minor groove at CPY and CPYM binding sites increased by 0.84-2.13 (?),while the distance of the major groove increased by 2.36～5.06 A.The water molecular density of DNA at 0.7 nm decreased from 0.743 to 0.716(CPY)and 0.724(CPYM).CPY and CPYM promoted DNA degradation through the expansion of the DNA groove and destruction of the hydration layer at binding sites. |
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