Calcium cyanamide

Endpoint summary

Description of key information

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. The transformation product cyanamide is hydrolytically stable at pH 5, 7, and 9 at 25 °C. However, it is hydrolytically unstable at low pH values, and dimerises to dicyandiamide in alkaline solution.

In addition, the environmental fate and behaviour of calcium cyanamide was further assessed based on read-across to cyanamide. Cyanamide is photolytically stable in air and water. The photolytical degradation of cyanamide in soil is negligible in comparison to the rate of degradation caused by biodegradation.

For detailed description where read across is used/recommended and where it is preferable to refrain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Additional information

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Thus, upon release of calcium cyanamide via water, the environmental distribution and exposure is driven by the physico-chemical/fate properties of cyanamide.

For the agricultural application of calcium cyanamide the substance is formulated in a slow degrading granule (PERLKA). In contact with soil moisture, PERLKA granules will slowly release cyanamide. Thus, again the environmental distribution and fate of cyanamide is relevant in the assessment of calcium cyanamide. 

 

Phototransformation in air:

Cyanamide is not expected to react with hydroxyl radicals and ozone and is thus considered to be stable in the atmosphere.

Hydrolysis of hydrogen cyanamide:

Cyanamide was hydrolytically stable at a temperature of 25 °C and pH 5,7, and 9. However, a low pH cyanamide is hydrolysed to urea and eventually to carbon dioxide and ammonia in an acid-catalysed reaction with half-lives ranging between 77 min (pH ~1.5, 85 °C) and 310 -320 min (pH 0, 25 °C). In alkaline solution (ca. pH 12), cyanamide dimerises to dicyandiamide with an half-life of ca. 11.5 d at 18 -24 °C.

 

Stability of Cyanamide in water:

Photolysis of Cyanamide is a more significant degradation pathway at pH 5 and pH 7 (25°C) than hydrolysis. The photolytical half-life of cyanamide in buffered aqueous solutions was calculated to be 28.9 days and 38.5 days at pH 5 and pH 7. Urea was detected as major degradation product in the light exposed samples (Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD).

 

Stability of Cyanamide in soil:

Two studies examined the phototransformation of Cyanamide in soil. In the newer higher tier soil photolysis that was conducted under more realistic conditions, no major metabolites of Cyanamide were encountered and cyanamide was almost completely mineralised to CO2 in both irradiated and dark control samples. The degradation of cyanamide was fast both in irradiated and in the dark samples with DT50 values of 2.4 and 2.0 h, respectively, indicating that the rate of degradation due to photolysis is negligible compared to the rate of degradation caused by biodegradation.