Photodegradation of pesticides, photolysis rates and half-life of pirimicarb and its metabolites in reactions in water and in solid phase
1996
Pirisi, F.M. | Cabras, P. | Garau, V.L. | Melis, M. | Secchi, E.
The photodegradation of Pirimicarb under three different artificial lights and sunlight was studied in water solutions (buffers pH 5, 6, and 7) and in solid phase. Five photocompounds were formed in solution and two in solid phase. Pirimicarb undergoes fast degradation under all conditions. In buffer solutions it first gave three compounds with a kinetic parallel process. These compounds were assigned the structures of 2-[(methylformyl)amino]-5,6-dimethylpyrimidin-4-yl dimethylcarbamate (II), 2-(methylamino)-5,6-dimethylpyrimidin-4-yl dimethylcarbamate (III), and 2-(dimethyl-amino)-5,6-dimethyl-4-hydroxypyrimidine (V). V and II were stable to further photolysis (the latter with t1/2 = 849 h) whereas III undergoes further degradation to 2-amino-5,6-dimethylpyrimidin-4-yl dimethylcarbamate (IV), and to 2-(formylamino)-5,6-dimethylpyrimidin-4-yl dimethylcarbamate (IX). Both compounds were photodegraded to undetectable species, and IX shows a very high t1/2 (48 h). A different behavior was found in solid phase, and only II and III were formed. A kinetic parallel process was demonstrated. The environmental t1/2 and t1/100 calculated for Pirimicarb and its photoproducts suggest their reduced persistence in natural waters.
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