Stability of pesticides' residues under ultraviolet germicidal irradiation.

Legislation for food safety is limited mostly to pesticides monitoring and no attention is paid to the presence and toxicity of by-products formed after pesticide application. Stability studies of three selected transformation products: IMP - 2-isopropyl-6-methyl-4-pyrimidinol (diazinon hydrolysis product), TCP - 3,5,6-trichloro-2-pyridinol (chlorpyrifos transformation product), and 6CNA - 6-chloronicotinic acid (imidacloprid and acetamiprid transformation product) were performed under exposure to sunlight at room temperature (22 °C) and in the dark at 4 °C over 90 days. The results showed slight change in concentration with samples under refrigeration in darkness.Alternatively, an aqueous solution of TCP exposed to sunlight resulted in a high decrease of initial concentration within time. The toxicity assessment was performed using luminescent bacteria Vibrio fischeri and the results expressed low toxicity in the case of IMP and 6CNA. However, for TCP the calculated EC50 value after 30 minutes of exposure equated to roughly 15.1 mg L-1. Stability of the selected transformation products upon 245 nm irradiation indicated little decrease in concentration for IMP and 6CNA in deoxygenated and oxygenated aqueous solutions. In the case of TCP, the photochemical behaviour appeared to depend on oxygen concentration in the medium. For more detailed comparison, the degradation quantum yields were calculated.