4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-5-oxo-4,5-dihydro-1H-tetrazole-1-carboxamide

Phototransformation in air

Additional information

Data on the phototransformation in air is not a standard requirement under Regulation (EC) No. 1907/2006 Annexes VII - X. However, calculations on the chemical lifetime of the test substance in the troposhere were conducted and are provided in the dossier in order to present available data and to further add information on the potential photodegradation of the substance in air.

A report calculating the chemical lifetime of the test substance in the troposphere is available (1998). Since according to the guideline "Federal Biological Institute for Agriculture and Forestry (BBA), Germany: Guidelines for the Testing of Plant Protection Products in Registration Procedure, Part IV, 6-1 (July 1990) entitled: Determination of the volatilisation and the fate of plant protectants in the air" the test substance was not degraded by 50% within 4 days after application either by hydrolysis or by direct photolysis in aqueous solution, the lifetime of the test substance in air was assessed based on the calculation according to Atkinson by AOPWIN (version 1.87).

The calculated overall OH reaction rate of 28.72 x 10^-12 [cm3/molecules sec] is mainly obtained by several hydrogen abstractions at various sites (k_H-abstotal= 23.10 x 10^-12 [cm3/molecules sec]). Furthermore, contributions were assumed by reactions at two nitrogen sites (k_{N total}= 2.00 x 10^-12 [cm3/molecules sec]) and by additions to the aromatic ring (k_ar= 3.62 x 10^-12 [cm /molecules sec]).

Based on the before-mentioned calculated overall OH-rate constant a half-life of the test substance in air of 4.4 hours corresponding to a chemical lifetime in air of 6.4 hours is assessed using a 12-hrs-day with 1.5 x 10^6 OH-radicals/cm3.

The before-mentioned estimations do not consider any contribution of an attack by other radicals (i.e. by nitrate radicals). If exposition occurs during the early afternoon, as opposite to the early morning or to the late afternoon, it is to be expected that the chemical lifetime will be shorter at that moment, as during the day the OH-radical concentration may increase unto 5 x 10^6 radicals/cm3 in the troposphere. On the other hand the OH-radical concentration in the night decreases to zero. A more conservative assessment of the overall OH-radical rate constant (e.g. not considering the assumed contributions in the modelling) would result in a maximum chemical lifetime of the test substance of about 8 hours in the air.

The chemical stability of the test substance in air is not determined by an attack of OH-radicals at one single site, but at different parts of the molecule. This should result in the formation of various primary radicals leading to secondary oxidation products, which can be eliminated from the air by wet and/or dry deposition. On account of the relatively short chemical lifetime of the test substance in the air it is to be expected that it can neither be transported in gaseous phase over large distances nor accumulate in the atmospheric compartment.