Degradation of the strobilurin fungicide mandestrobin in illuminated water–sediment systems

The degradation behavior of mandestrobin (1) was investigated in aerobic aquatic water–sediment systems exposed to continuous artificial sunlight (λ>290 nm). [¹⁴C]mandestrobin uniformly labeled at the phenoxy or benzyl ring was individually applied to the overlying water of the system at a rate equivalent to 262.5 g a.i./ha. The transformation of 1 was mainly proceeded via photoinduced bond cleavage at the benzyl phenyl ether and the subsequent rearrangement reaction. Interestingly, some of the photodegradates and microbial metabolites of 1 observed in the aquatic photodegradation and water–sediment (dark) studies, respectively, were never detected. Furthermore, the observed photoproducts were less formed and were steadily degraded or metabolized to carbon dioxide or strongly adsorbed to bottom sediment. The fate of 1 and its degradates in illuminated water–sediment systems was considered to reflect realistic conditions more precisely, as it accounts for various effects attributed to sunlight.

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