Theta-cypermethrin is composed of two of the four trans-cypermethrin
isomers of cypermethrin (1RtransaS and 1StransaR). The fate of these two
isomers (separately) has been reported for soils. Metabolite analysis was
conducted in enough detail to indicate that the fate of the components
was very similar to their fate when presented to biological systems as part
of cypermethrin. Thus reference can be made to the cypermethrin entry
for details. The structure and Scheme numbering used below refers to the
cypermethrin entry.
Theta-cypermethrin is stable as a solid but it is readily hydrolysed in
alkaline solution. Its half-lives at pH values 3,7 and 9 (25 °C) were 50,20
and 10 days (PM). By analogy with cypermethrin, the rate-determining
step in dilute solution is nucleophilic attack by OH-. Half-lives of transcypermethrin
in river water and sea water at 25 °C were 5 and 7 days,
respectively. Major products were 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic
acid (2, DCVA), 3-phenoxybenzaldehyde (9,
3PBAl) and a-carbamoyl-3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2-
dimethylcyclopropanecarboxylate (the amide 3); minor products were the
a-carboxy analogue of 3 (4) and 3-phenoxybenzoic acid (10,3PBA) (see
cypermethrin, Schemes la and 1b).
Photodecomposition would be expected to be similar to that of
cypermethrin.
