Mutagenicity of the C-nitroso analog of fenitrothion

Area of Science:

• Environmental toxicology
• Chemical mutagenesis
• Bacterial genetics

Background:

• Fenitrothion is an organophosphate insecticide widely used globally.
• Assessing the genotoxicity of pesticides is crucial for environmental and human health risk assessment.
• The Ames test using Salmonella typhimurium is a standard method for mutagenicity screening.

Purpose of the Study:

• To evaluate the mutagenicity of fenitrothion and its metabolites, including nitroso fenitrothion, amino fenitrothion, and 3-methyl-4-nitrophenol.
• To investigate the metabolic activation pathways of these chemicals in Salmonella typhimurium strains TA98 and TA100.
• To determine the efficacy of the Ames test in predicting the genotoxicity of fenitrothion.

Main Methods:

• Bacterial mutagenicity assays were performed using Salmonella typhimurium strains TA98 and TA100.
• Tests were conducted both in the presence and absence of rat liver S-9 mix to assess metabolic activation.
• The chemicals tested included fenitrothion, nitroso fenitrothion, amino fenitrothion, and 3-methyl-4-nitrophenol.

Main Results:

• Nitroso fenitrothion exhibited strong mutagenicity to both Salmonella strains, irrespective of S-9 mix presence.
• Fenitrothion itself did not display mutagenicity in either strain, with or without metabolic activation.
• The results suggest that Salmonella strains TA98 and TA100 lack the necessary nitroreductases to metabolize fenitrothion into a mutagenic form.

Conclusions:

• The standard Ames test may underestimate the genotoxic potential of fenitrothion due to the inability of tester strains to perform essential metabolic activation.
• Nitroso fenitrothion serves as a potent mutagen, highlighting the importance of considering its formation.
• Further research is needed to develop or utilize screening systems capable of accurately assessing the genotoxicity of pesticides like fenitrothion.