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Prediction of fate of selected priority pollutants considering their transformation products using in-silico methods

Barlas, Nezahat Gülücük
As the number of chemicals used in commerce is continuously increasing, the task of evaluating the fate of chemicals along with their impacts on the environment becomes challenging. In this study, fourteen priority pollutants, namely, aclonifen, alachlor, atrazine, BDE-153, bifenox, chlorfenvinphos, chlorpyrifos, DEHP, dicofol, diuron, hexachlorobutadiene, pentachlorobenzene, trichloromethane, and trifluralin as well as p,p’-DDT as an impurity of dicofol, were selected among the 45 priority pollutants regulated by the European Union (EU). Selection of chemicals was made based on abundance of literature studies, availability of kinetic data, as well as compatibility with modeling tools. Then, experimentally verified degradation products of each selected chemical were found from the literature. A total of 45 transformation products (TPs) were compiled, with the aim of investigating their contribution to the persistence of the parent compound and their individual tendency to distribute into the environment. Selected chemicals were evaluated according to how they distribute into the environment depending on mode-of-entry. Additionally, the primary persistence (PP) of each parent compound was determined to understand the effect of PP on joint persistence (JP). In-silico or computational methods offer simple, affordable, and safe quantitative chemical evaluation with respect to chemical distribution, fate, and persistence by introducing, physicochemical properties, degradation half-lives, and emission amount. EPI SuiteTM v4.11, June 2017 was employed for chemical-specific physicochemical property estimation in this study, whenever experimental data was unavailable. An evaluative multimedia (MM) model, namely, the Equilibrium Criterion (EQC) model Level III was used to evaluate the persistency and environmental distribution of selected priority pollutants and their TPs. PP is the ratio of the amount of parent compound at a steady-state to its initial emitted amount. Persistence evaluation could not be satisfactory if only persistence of a parent compound, namely, PP is considered. This is because parent compounds convert into their TPs. These TPs pose secondary persistence (SP), so PP and SP are added to obtain JP for a substance family. Ratio between JP and PP indicates the influence of TPs on persistence of a parent compound. As the number of TPs increases, JP will increase. In addition to the number of TPs, persistence of TPs, namely SP of TPs have a considerable effect on JP. For hexachlorobutadiene and aclonifen, presence of their TPs does not have a significant contribution to JP. That’s why JP/PP for hexachlorobutadiene and aclonifen is 1.3 and 1.4, respectively. On the other hand, this ratio is 105 and 12 for trichloromethane and dicofol, respectively. These high ratios demonstrate a high contribution of TPs on the joint persistence for trichloromethane and dicofol families. Lastly, the input media to which chemical is introduced in other words mode-of-entry of chemicals as well as half-life in a dominant medium are shown to have the highest impact on all types of persistence (i.e. PP, SP, JP).