Evaluation of nitrate effects in the photodegradability of cyprodinil. Kinetics study and transformation products elucidation.

The effects of nitrate in the kinetics and the transformation routes of the fungicide cyprodinil (CYP) were investigated using aqueous solutions, ultrapure water and river water samples, spiked with the precursor compound and containing different levels of nitrate. Samples were exposed either to 254 nm radiation or to solar light, depending on the experiment. Time course of CYP and formation of transformation products (TPs) were simultaneously assessed by direct injection of different irradiation time aliquots in a liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) system. Empirical formulae and structures of TPs were inferred from their accurate MS and MS/MS scan spectra, respectively. Under all investigated situations, nitrate anions enhanced the degradability of CYP with a noticeable reduction of its half-life (t 1/2). TPs arising from aqueous photodegradation of CYP were formed through three different routes: (1) hydroxylation of the benzenic ring; (2) hydroxylation of the pyrimidine cycle, followed by ring opening and further dealkylation; and (3) nitration of the benzenic ring. The latter group of TPs display higher estimated acute toxicities than CYP and remained stable for long irradiation times. Graphical Abstract Photonitration of cyprodinil.