Photoformation of reactive oxygen species and their potential to degrade highly toxic carbaryl and methomyl in river water

Derbalah Aly

Sunday Michael

Kato Ryota

Takeda Kazuhiko

Sakugawa Hiroshi

Chemosphere

Reactive oxygen species (ROS) including singlet oxygen (1O2) and hydroxylradicals (radical dotOH) photogenerated in natural waters play important roles in indirect photolysis of man-made pollutants. This study was conducted to investigate how the generation of these two ROS influences the degradation of two highly toxic insecticides (methomyl and carbaryl) in river water. To accomplish this, the reaction rate constants of 1O2 and radical dotOH with carbaryl and methomyl were determined; the degradation rate constants of the tested insecticides in ultrapure water (direct photolysis) and in river water in the presence and absence of 1O2 and radical dotOH scavengers were also measured. The rate constants for the reaction of radical dotOH with carbaryl and methomyl were found to be (14.8 ± 0.64) × 109 and (4.68 ± 0.52) × 109 M−1 s−1, respectively. The reaction rate constant of 1O2 with carbaryl (2.98 ± 0.10) × 105 M−1 s−1, was much higher than that of methomyl (<104 M−1 s−1). Indirect photolysis by radical dotOH accounted for 63% and 62%, while 1O2 accounted for 26% and 30% and direct photolysis accounted for 1.4% and 7% of methomyl and carbaryl degradation, respectively. The high degradation rate in river water demonstrated by both insecticides suggests that indirect photolysis mediated by radical dotOH is an important means of their degradation in river water. In addition, kinetic calculations of radical dotOH-mediated degradation rate constants of the compounds agrees with their experimentally-determined values thereby confirming the importance of radical dotOH towards their degradation.

Hydroxyl radicals

Singlet oxygen

Methomyl

Carbaryl

Photolysis

Water

eng

Elsevier

© 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

This is not the published version. Please cite only the published version. この論文は出版社版ではありません。引用の際には出版社版をご確認、ご利用ください。

[ISSN] 0045-6535

[DOI] 10.1016/j.chemosphere.2019.125464

[DOI] https://doi.org/10.1016/j.chemosphere.2019.125464