Cyanamide

Phototransformation in air

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in air

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Study period:

2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline required

Principles of method if other than guideline:

For details on method see below (model calculation)

GLP compliance:

no

Remarks:

study is a model calculation.

Estimation method (if used):

The photo-chemically and oxidative decomposition of cyanamide in air was evaluated based on a theoretical calculation according to Atkinson.
The calculation was performed with the help of the programme AOPWIN, Atmospheric Oxidation Programme v1.90 for Microsoft Windows 3.1, Windows 95/98, Windows NT (© 2000 US Environmental Agency).

Light source:

other: not applicable

Details on light source:

Not applicable

Details on test conditions:

Not applicable

Reference substance:

no

Preliminary study:

Not applicable

Test performance:

Not applicable

Results with reference substance:

Not applicable

Model results: The total OH radical reaction rate constant (kOH) is given by: kOH = k (H-atom abstraction from C-H and O-H bonds) + k (OH radical addition to CC double and triple bonds) + k (OH radical addition to aromatic rings) + k (OH radical interaction with N-, S- and OH-containing groups) For cyanamide it is: kOH = k (OH radical interaction with N bonds) The reaction rates with the amino group of cyanamide (OH radical interaction with N containing groups) have a value of k = 0.0000 × 10-12 cm3 molecule-1 sec-1. That means, that for cyanamide the OH radicals do not react with the N containing groups and therefore, the overall rate constant was estimated to be 0.0 cm3 molecule-1 sec-1.

Validity criteria fulfilled:

not applicable

Conclusions:

Cyanamide was estimated to be stable in the atmosphere. Cyanamide is not supposed to react with hydroxyl radicals and ozone.

Executive summary:

An estimation of the photochemical degradation of cyanamide was performed using the Atkinson calculation method. The reaction rates with the amino group of cyanamide (OH radical interaction with N containing groups) have a value of k = 0.0000 × 10-12 cm3 molecule-1 sec-1. That means, that for cyanamide the OH radicals do not react with the N containing groups and therefore, the overall rate constant was estimated to be 0.0 cm3 molecule-1 sec-1.

 

It can therefore be concluded that cyanamide is stable in the atmosphere. It is, however, questionable whether the Atkinson calculation allows for an adequate estimation of the photochemical degradation of cyanamide. It has to be considered that cyanamide is a substance that is chemically far away from typical organic molecules like phenols or halogen-hydrocarbons, for which the model seems to be better suited.

Description of key information

Release of cyanamide to the air from water and moist soil surfaces is rather limited as experimental results imply that cyanamide fast degradation in soil and surface water is likely to limit volatilisation after application as well as its high solubility in water. Nevertheless a calculation according to Atkinson as an estimation method for photolysis of cyanamide in air was conducted and concluded that cyanamide is stable in the atmosphere.

Additional information

For evaluation of the photolysis in air, an estimation method was used which is a calculation according to Atkinson (Peter, 2003, Doc. No., 743-003). According to Atkinson calculation the overall rate constant was estimated to be 0.0 cm³ molecule-1sec-1 . It was therefore concluded that cyanamide is stable in the atmosphere. It is, however, questionable whether the Atkinson calculation allows for an adequate estimation of the photochemical degradation of cyanamide. It has to be considered that cyanamide is a substance which is chemically far away from typical organic molecules like phenols or halogen-hydrocarbons, for which the model seems to be better suited.

Few experimental results add more information on cyanamid´s fate and behaviour in air: Although cyanamide has a vapour pressure of 0.51 Pa at 20 °C which is an indicator of the volatilisation potential of cyanamide, the Henry’s law constant calculated as 2.68 × 10-5 Pa m3 mol-1 indicates that the high water solubility of cyanamide is likely to counteract the tendency of cyanamide to volatise from water and moist soil surfaces.

Furthermore, cyanamide is rapidly degraded in the environment with a realistic “worst case” DT50field value in soil of 1.6 days and in surface water with 4.3 days. The photolytical half-life of cyanamide on soil surfaces is even shorter with 1.45 days. Therefore, it can be assumed that the fast degradation of cyanamide in soil and surface water is likely to limit volatilisation after application.