Relationship between photolysis mechanism and photo-enhanced toxicity to Vibrio Fischeri for neonicotinoids with cyano-amidine and nitroguanidine structures

Aquat Toxicol. 2023 Apr:257:106443. doi: 10.1016/j.aquatox.2023.106443. Epub 2023 Feb 20.

Abstract

Neonicotinoids are widely used pesticides that contaminate aquatic environments. Although these chemicals can be photolyzed under sunlight radiation, it is unclear for the relationship between photolysis mechanism and toxicity change in aquatic organisms. This study aims to determine the photo-enhanced toxicity of four neonicotinoids with different main structures (acetamiprid, and thiacloprid for cyano-amidine structure, imidacloprid and imidaclothiz for nitroguanidine). To Achieve the goal, photolysis kinetics, effect of dissolved organic matter (DOM) and reactive oxygen species (ROSs) scavengers on photolysis rates, photoproducts, and photo-enhanced toxicity to Vibrio fischeri were investigated for four neonicotinoids. The results showed direct photolysis plays a key role in the photo-degradation of imidacloprid and imidaclothiz (photolysis rate constants are 7.85 × 10-3 and 6.48 × 10-3 min-1, respectively), while the photosensitization process of acetamiprid and thiacloprid was dominated by ·OH reactions and transformation (photolysis rate constants are 1.16 × 10-4 and 1.21 × 10-4 min-1, respectively). All four neonicotinoid insecticides exerted photo-enhanced toxicity to Vibrio fischeri, indicating photolytic product(s) posed greater toxicity than their parent compounds. The addition of DOM and ROS scavengers influenced photo-chemical transformation rates of parent compounds and their intermediates, leading to diverse effects on photolysis rates and photo-enhanced toxicity for the four insecticides as a result of different photo-chemical transformation processes. Based upon the detection of chemical structures of intermediates and Gaussian calculations, we observed different photo-enhanced toxicity mechanisms for the four neonicotinoid insecticides. Molecular docking was used to analyze the toxicity mechanism of parent compounds and photolytic products. A theoretical model was subsequently employed to describe the variability of toxicity response to each of the four neonicotinoids.

Keywords: Molecular docking; Neonicotinoid pesticides; Photo-enhanced toxicity; Photolysis; Quantum chemistry; Quantum yield.

MeSH terms

  • Aliivibrio fischeri
  • Insecticides* / chemistry
  • Molecular Docking Simulation
  • Neonicotinoids / toxicity
  • Photolysis
  • Water Pollutants, Chemical* / toxicity

Substances

  • thiacloprid
  • imidacloprid
  • Insecticides
  • imidaclothiz
  • nitroguanidine
  • Water Pollutants, Chemical
  • Neonicotinoids