Environmental Fate Monitoring and Toxicity Prediction of Pesticidal Persistent Organic Pollutants (POPs) through Modeling Approaches

Abstract

Persistent organic pollutants (POPs) are organic substances that are persistent, bioaccumulative and toxic, (PBTs), likely to cause adverse effects on human health and environment. They are prone to long range environmental transport and accumulate in terrestrial and aquatic ecosystems. 16 out of 28 POPs listed in the Stockholm convention are agricultural pesticides, which despite their ban are being used in developing countries and owing to their persistent nature are still detected in the environment. In past various studies have been performed to analyze their toxicity in humans and different environmental segments. Their toxicity prediction through DFT methods at electronic level have not been explored yet. In the current study, environmental fate of these pesticidal POPs was monitored by calculating their atmospheric oxidation half-life, bioconcentration factor (log BCF), biodegradation probability, Henry’s law constant (HLC), soil sorption coefficient (Koc), octanol-water partition coefficient (log Kow), and water solubility. Moreover, DFT calculations were performed to explore & compare their chemical reactivity and toxicity. In this investigation GGA:BLYP approach and double zeta (DZ) basis set were utilized. Their toxic behavior was further analyzed by estimating their LD50 values and carcinogenic activity. Derivatization of all 16 pesticides under investigation has been done through functional group substitution followed by environmental fate monitoring of derivatives. Finally, molecular docking simulations were performed to compare the binding ability of pesticides and derivatives with voltage gated Na+ channel of human and Drosophila Melanogaster. Through environmental fate monitoring of derivatives, it was revealed that in contrast to their parent pesticides, derivatives have no potential for long range environmental transport due to their very low atmospheric oxidation half-lives of <1 hour. Lesser binding of derived pesticides with human VGSC was indicated by their scoring function values which reflected their low neurotoxicity when compared with original OCPs. In the case of human VGSC, the highest binding affinity was predicted for Pentachlorobenzene with scoring function of -6.3313 kcal/mol which was reduced for its derivative with scoring function value of -5.5113 kcal/mol. Whereas derived compound showed overall strong binding with Drosophila Melanogaster voltage gated Na+ channel with strongest binding for Lindane derivative having scoring function value of -9.318 kcal/mol. These results highlights the effectiveness of designed derivatives in pest control.