Selective, stepwise photodegradation of chlorothalonil, dichlobenil and dichloro- and trichloro-isophthalonitriles enhanced by cyanidin in water.

Chlorothalonil, a widely used chloroisophthalonitrile fungicide, is highly toxic to aquatic organisms and amphibians. It is essential to understand the persistence and fate of chlorothalonil in aquatic environments. Cyanidin is one of the most common phytopolyphenolics in nature and is a strong antioxidant. This study was designed to understand fate of chlorothalonil and its analogs in surface water in the presence of cyanidin under sunlight and artificial lights. The photodegradation rates of chlorothalonil were increased by 9.6, 19, 26 and 9.1 fold, respectively, under solar, high-pressure mercury lamp (HPML), UV and Xenon lamp light irradiation, in comparison to the cyanidin-free control. Cyanidin also enhanced 2,5-dichloroisophthalonitrile and 2,4,5-trichloro isophthalonitrile (degradation products of chlorothalonil) for 20 and 4.7 fold under HPML irradiation compared to the absence of cyanidin. Chlorothalonil was transformed to 5-chloroisophthalonitrile quantitatively after stepwise dechlorination. The concentration profiles of chlorothalonil and its degradation products were well simulated in the cyanidin-triggered photoreductive dechlorination process, in which donation of hydrogen atom from cyanidin was also agreed by the density functional theory calculations. Cyanidin accelerated photolysis of dichlobenil for 4.3 fold as high as the cyanidin-free control under HPML irradiation. The results warrant an interest in further understanding photolysis of chloroarenes in natural waters and exploring the potential of using phytochemicals to abate chloroarenes-caused pollution.