Cyanamide

Endpoint summary

Description of key information

Biological degradation plays the most important role for cyanamide dissipation in aquatic systems. Hydrolysis and photolysis play a minor role in the degradation of cyanamide in water.

Only urea was detected as major metabolite in aquatic systems. Since urea is a substance, which is synthesised by organisms, effects on aquatic organisms are not expected. This is confirmed in several toxicological and ecotoxicological tests. Therefore, urea has not to be classified as relevant metabolite.

In summary, with regard to the very fast degradation of cyanamide both in soil and water, no negative effects concerning these environmental compartments are to be expected.

Additional information

Conclusion on stability in air, water and soil

Cyanamide was estimated to be stable in the atmosphere.

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

The degradation of cyanamide in soil 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.

 

Biodegradation

Biodegradation in water: screening tests

Results of a study of van der Hoeck (1988) showed that cyanamide can be regarded as not readily biodegradable by the terms of this test. A following study (Malta, 1990) showed that cyanamide was completely degraded within two weeks when it served as nitrogen source for degradation of a carbon-containing compound (sodium acetate), whereas the cyanamide degradation was rather slow when cyanamide served as both carbon and nitrogen source.

It can be concluded that the biodegradation of cyanamide in a standard ready biodegradability test is prevented by the presence of another easily available nitrogen source. But, as rapid degradation of cyanamide could clearly be demonstrated under environmentally realistic conditions in two aerobic water/sediment model systems (see IUCLID section 5.2.2), the substance can thus be considered as rapidly degradable according to the CLP Regulation (EC) No 1272/2008, Annex I sections 4.1.2.9.2 and 4.1.2.9.3 and therefore cyanamide was concluded to be "readily biodegradable".

 

Biodegradation in water and sediment

In two water/sediment systems DT50 values of 2.5 days (river) and 4.8 days (pond) for the whole systems and half-lives of 2.3 days (river) and 4.3 days (pond) for the water phase were calculated. Only one major metabolite, identified as urea, was detected in the Pond system at maximum amounts of 13.4 % of applied radioactivity at day 1. In the river system urea was also detected at concentrations up to 6.7 % of applied radioactivity at day 2. Thereafter, the urea concentration decreased continuously and after 21 days it was not longer detectable in both aquatic systems. For urea DT50 values of 2.9 days (river) and 7.6 days (pond) for the whole systems and half-lives of 2.7 days (river) and 7.5 days (pond) for the water phase were calculated. In the sediments, neither the parent substance nor degradation products were detected in significant amounts.

 

Biodegradation in soil

Reliable information on the biodegradation of cyanamide in soil is available. The following DT50 and DT90 values were calculated for the aerobic and anaerobic degradation of cyanamide in soil under laboratory conditions.

DT50 aerobic : 0.7 days – 4.6 days
DT90 aerobic: 2.4 – 15.2 days
DT50 anaerobic: 34.7 days
DT90 anaerobic: 105 days

The degradation of cyanamide under aerobic and anaerobic conditions was assessed in a GLP-compliant guideline study by Schmidt, 1990; Schmidt, 1991).

Under aerobic conditions, the primary aerobic pathway by which the parent compound disappeared from soil was the final degradation to [14CO2] (complete mineralization). This fraction accounted for approximately 94.6 % of applied radioactivity after 14 days. The half-life of cyanamide was calculated using a first order kinetic and was found to be 1.26 days. The calculated time to 90 % degradation was 1.94 days. One minor degradation product was identified as dicyandiamide accounting for 0.431 % of applied radioactivity at maximum.

Under anaerobic conditions, the degradation was slower (DT50anaerobic = 34.7 days), and mineralization did not occur to the same extent as under aerobic conditions. Four minor degradation products occurred and were identified as dicyandiamide, guanylurea, guanidine and urea. None of the degradation products exceeded the trigger value of 10 % of applied radioactivity. Guanylurea was found with 7.5 % of TAR at maximum value.

In a study of Heß (1978) the DT50 values of cyanamide ranged from 1 to 3 days in two loamy sand soils with different organic carbon content and from 6-12 days in a sand soil with a very low organic carbon content. The results show that the degradation of cyanamide in soil is influenced by the organic carbon content indicating that the biotic degradation prevails in soils. Furthermore, the degradation rate of cyanamide in the test soils depended on the application rate with a faster degradation observed in the test soils receiving the lowest application rate.

Additionally, information on the transformation and fate of Calcium cyanamide in soil matrices is available. It was demonstrated that upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Thus, for industrial manufacture and use, release of calcium cyanamide to water will result in potential environmental exposure of hydrogen cyanamide. Any subsequent potential soil exposure via sludge and air will be by cyanamide, not calcium cyanamide.

The transformation from cyanamide to secondary transformation products depended on the tested material. Whereas for Cyanamid F1000 only urea and ammonia in larger amounts could be detected, for PERLKA also nitrate and DCD were determined. The observed nitrate is not a transformation product but represents the original amount of nitrate in PERLKA.

The normalised DT50 value of 0.78 days at 20°C (Klein et al., 2019) is used for the risk assessment according to Regulation (EC) No 1907/2006 (REACH). It is concluded that Cyanamide is rapidly degraded in soil and that there is hence no indication for persistency regarding this environmental compartment.

 

 

Abiotic degradation (Hydrolysis/Photoysis)

Photolysis

In addition to the biotic degradation cyanamide is also photolytically degraded on the soil surface with a photolytic half-life of 1.45 days. Two major degradation products occurred in the photolysis study and were identified as urea and dicyandiamide. The occurrence of these metabolites is restricted to the artificial laboratory testing conditions during the soil photolysis study. Thus, these metabolites are considered as not relevant under realistic outdoor conditions. This assessment was further confirmed by results from a higher Tier soil photolysis study conducted under more realistic conditions, where no major metabolites of cyanamide were encountered and cyanamide was almost completely mineralised to CO2 in both irradiated and dark control samples.

 

Hydrolysis

The hydrolytic degradation of cyanamide in water is both temperature and pH dependent. At 25°C cyanamide was hydrolytically stable, regardless of the pH values. With increasing temperature and pH value of the buffer solutions cyanamide was degraded with DT50 values of 1100 h (pH 5), 563 h (pH 7), 302 h (pH 9) at 50°C and 60.7 h (pH 5), 147 h (pH 7) and 7.2 h (pH 9) at 80°C, respectively.

 

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 at maximum concentrations of 12.2 % of IMD at pH 7 and 42.4 % of IMD at pH 5. Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD.

 

According to the Atkinson calculation, 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.

 

Bioaccumulation

In accordance with column 2 of REACH Annex IX, 9.3.2, examination of the bioaccumulation of the test substance cyanamide in aquatic/sediment (required in section 7.8) does not need to be conducted as the test substance has a log Pow value smaller than 3 (log Pow = -0.72), implying a low potential for bioaccumulation and/or a low potential to cross biological membranes.

 

Transport and distribution (Adsorption, Henys Law constnat)

Adsorption

The derived Kd (0 – 0.09 ml/g) and KOC-values (0 – 6.8 ml/g ) indicate a low adsorption to soil. But although these adsorption coefficients point towards a high potential mobility of cyanamide in soil, in the column leaching study only 0.13 to 2.8 % of the applied cyanamide could be found in the leachate after a 2-day irrigation period starting immediately after application of the test substance. Thus, in the column leaching study cyanamide was only slightly mobile with the mobility decreasing with increasing fineness of soil texture and soil organic carbon content. In general, the leaching potential of a substance is determined both by its adsorption behaviour and its persistence. Substances with low adsorption coefficients but short half-lives are not expected to leach within the soil profile unless a rain event takes place immediately after application. The same applies to cyanamide and is confirmed in the lysimeter study where the fast degradation of cyanamide contributed to the finding that only traces of cyanamide were detected in the leachate.

 

Therefore, it can be concluded that under realistic outdoor conditions cyanamide will not be transported at significant amounts into deeper soil layers although laboratory trials indicate a potential mobility of cyanamide. This fact is mainly due to the fast degradation of cyanamide in soil.

 

Henry's Law constant

Its high vapour pressure of 0.51 Pa at 20 °C is an indicator of the high volatilisation potential of cyanamide. However, 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” DT50 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, and on plant surfaces cyanamide is completely degraded in less than 1 day. Therefore, it can be assumed that the fast degradation of cyanamide in soil and surface water is likely to limit volatilisation after application.

 

Environmental Data, field study

Under field conditions cyanamide was degraded with a mean DT50field value of 1 day and a worst-case DT50 field value of 1.6 days. Two weeks after application no cyanamide residues could be detected any more and thus, the DT90field is less than 2 weeks. Degradation rates of cyanamide under different controlled storage conditions it has been proved that the compound is significantly degraded even if the samples are kept below –20°C. The study as performed (field trials, storage trials) gives enough evidence for the conclusion that cyanamide is rapidly degraded in the upper soil layers and will not leach into deeper soil layers.

 

Overall summary

In summary, biological degradation plays the most important role for cyanamide dissipation in aquatic systems. Hydrolysis and photolysis play a minor role in the degradation of cyanamide in water.

Only urea was detected as major metabolite in aquatic systems. Since urea is a substance, which is synthesised by organisms, effects on aquatic organisms are not expected. This is confirmed in several toxicological and ecotoxicological tests. Therefore, urea has not to be classified as relevant metabolite.

In summary, with regard to the very fast degradation of cyanamide both in soil and water, no negative effects concerning these environmental compartments are to be expected.