Theoretical Calculation on the Reaction Mechanisms, Kinetics and Toxicity of Acetaminophen Degradation Initiated by Hydroxyl and Sulfate Radicals in the Aqueous Phase.

Mengmeng Xu,Jingyu Sun,Suding Yan,Junfang Yao,Simei Sun

doi:10.3390/toxics9100234

Abstract

The •OH and SO4•− play a vital role on degrading pharmaceutical contaminants in water. In this paper, theoretical calculations have been used to discuss the degradation mechanisms, kinetics and ecotoxicity of acetaminophen (AAP) initiated by •OH and SO4•−. Two significant reaction mechanisms of radical adduct formation (RAF) and formal hydrogen atom transfer (FHAT) were investigated deeply. The results showed that the RAF takes precedence over FHAT in both •OH and SO4•− with AAP reactions. The whole and branched rate constants were calculated in a suitable temperature range of 198–338 K and 1 atm by using the KiSThelP program. At 298 K and 1 atm, the total rate constants of •OH and SO4•− with AAP were 3.23 × 109 M−1 s−1 and 4.60 × 1010 M−1 s−1, respectively, considering the diffusion-limited effect. The chronic toxicity showed that the main degradation intermediates were harmless to three aquatic organism, namely, fish, daphnia, and green algae. From point of view of the acute toxicity, some degradation intermediates were still at harmful or toxic level. These results provide theoretical guidance on the practical degradation of AAP in the water.

Highlights

The problem of water pollution caused by the drug residues have been paid much more attention
Reaction mechanisms are investigated by Density functional theory (DFT)
The thermodynamic and kinetic data for ibuprofen reactions with hydroxyl and sulfate radicals reported by Yang et al were calculated with M06-2X

Summary

Introduction

The problem of water pollution caused by the drug residues have been paid much more attention. Even though the content of these drugs in the water environment is very low, they brings potential dangers to human health and ecological environment due to its strong persistence, bioaccumulation and slow biodegradation [1,2]. Acetaminophen (AAP), as one kind of antipyretic analgesics, enters to water environment by the excretion of humans and animals. The concentration of AAP rose to 6 μg/L in European STP effluents [3]. Its concentration up to 10 μg/L was detected in natural waters in the United. States [4], and over 65 μg/L concentration was measured in the Tyne river in the United. The removal of micropollution is challenging for water treatment technology

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Results

Conclusion