Phototransformation pathways of the fungicide dimethomorph((E,Z) 4-[3-(4-chlorophenyl)-(3,4-dimethoxyphenyl)-1-oxo-2-propenyl]morpholine), relevant to sunlit surface waters

Dimethomorph (DMM) is a widely used fungicide that shows low toxicity for birds and mammals but can be quite toxic to aquatic organisms. The persistence of DMM in surface waters is thus of high importance, and this work modelled its water half-life time due to photochemical processes. Depending on environmental conditions (e.g.water chemistry, depth, season), DMMlifetime could vary froma fewdays to a fewmonths. For lifetimes of a few weeks or shorter, photochemistry would be an important pathway for DMM attenuation in surface waters. Such conditions could be reached in summer, in shallow water bodies with low dissolved organic carbon (DOC) and high nitrate and/or nitrite. Themain pathways accounting forDMMphotodegradation in environmentalwaters would be the reactions with •OH and with the triplet states of chromophoric dissolved organic matter, 3CDOM* (under the hypothesis that 3CDOM* reactivity is well described by the triplet state of anthraquinone- 2-sulphonate), while direct photolysis would be less important. The •OH pathway would be favoured in low- DOC waters, while the opposite conditions would favour 3CDOM*. It was possible to detect and identify some intermediates formed upon reaction between DMM and 3CDOM*, namely N-formylmorpholine, 4- chloroacetophenone and 4-chlorobenzoic acid. The transformation of DMM into the detected compounds would not increase the acute toxicity of the fungicide towardsmammals, and the acute effects for freshwater organisms could be decreased significantly.