Degradation of chlorothalonil in irradiated water/sediment systems

Water/sediment systems were used to investigate partitioning behavior between waters and sediments, as well as the degradation of the fungicide chlorothalonil (CHT) in each matrix. Experiments were run in the light and dark simultaneously for 30 days in both creek and pond sediment systems. Of the total applied CHT, 87-88% dissipated from the water phase in both water/sediment systems within 1 day when irradiated by simulated sunlight. In contrast, 60-68% remained in the water at day 1 in the dark. Approximately 3-6 and 10-16% of the applied CHT was found in sediments under light conditions at day 1 and in the dark at day 3, respectively which are the highest amounts observed during the experimental period. CHT similarly behaved in irradiated water/sediments and sediment-free aqueous solutions, indicating that CHT primarily degraded by photodegradation rather than adsorption to sediment in the early stages of the experiment. 4-Hydroxychlorothalonil was detected only in water in the dark systems. Trichloro-1,3-dicyanobenzene and 3-cyano-2,4,5,6-tetrachlorobenzamide were also detected and identified with liquid chromatography-electrospray ionization-mass spectrometry. These results suggest that photodegradation is likely to be important to the dissipation of CHT in aqueous solutions and microbial degradation plays an important role for residues that would ultimately reside in sediment.