Quantitative Effect Of Pesticide Adsorption By Cyclodextrins And Theoretical Mechanism

Pesticides are a ubiquitous type of contaminant in environment. Owing to their higher hydrophobicity and lower water solubility, they often remain in soil for long term after application, moreover run off into the near water and leach to the groundwater, hence raising potential hazard to aquatic ecosystem and human health. Cyclodextrins, containing hydrophobic cavity and hydrophilic exterior, could be used to assess the bioavailability of organic compounds in contaminated sites. Cyclodextrin polymers, as a kind of environmental friendly material, could separate various organic compounds from water, and thus they could be used in the control of contaminated water.Batch equilibrium adsorption experiment confirmed the adsorption of cyclodextrins and pesticides, implying that their inclusion complexes could also be absorbed by on solid matrixes. Based on adsorption equilibrium, inclusion complexation and mass conservation, a theoretical model of pesticides edistribution was developed to distinguish the effect of cyclodextrin on the adsorption distribution of pesticides. Results indicated that the addition of cyclodextrin enhanced the amount of pesticides dissolved in solution, except that of metholachlor. Meanwhile, bioassay experiments showed that effects of cyclodextrins on the pesticides bioactivity were dependent on model organisms, and inclusion complex was bioactive as well as free pesticide. Therefore, all results in this part provided theoretical foundation for the use of cyclodextrin, in the evaluation of pollutants bioavailability and the remediation of contaminated sites.Seven cyclodextrin poklymers were prepared with onefold or composite cyclodextrin(s) as parent compound and epichlorohydrin as cross-linking reagent. They were used to adsorb a mixture of ten distinct pesticides in water. Adsorption kinetics and isothermal models analyzed multiple adsorption interactions in the process, and multivariate regression analysis distinguished the relative contributions of polymers properties to their adsorption potential, among which CD content, swelling capacity and pore size appear to be the most important factors. On the basis of the relationship, a facile mixture of three cyclodextrin polymers was screened to obtain above prerequisites properties. The multiplex polymer could superiorly separate mixed pesticides at environmentally level from water, and the total concentration of pesticides in water could be predicted by isothermal adsorption moel. Therefore, these observations provided theoretical guidance for the application of cyclodextrin polymers in the remediation of contaminated waters.