Calcium cyanamide

Endpoint summary

Description of key information

Calcium cyanamide and cyanamide are concluded to be readily biodegradable based on the following information:

Abiotic degradation

Calcium cyanamide is rapidly transformed to cyanamide.

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"

At environmentally relevant pH and temperatures, cyanamide is hydrolytically stable. However, at low pH, the substance is hydrolysed to urea and eventually to carbon dioxide and ammonia in an acid-catalysed reaction. In alkaline solution, cyanamide dimerises to dicyandiamide.

Read-across data from cyanamide clearly show, a photolytically half-life of cyanamide in buffered aqueous solutions of 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).

Two studies examined the photo transformation 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 practically completely mineralised to CO₂in 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 in soil.

 

Biodegradation

According to the results of a ready biodegradation test (CO₂evolution), calcium cyanamide, cannot be classified as readily biodegradable.

However, results from simulation tests together with other environmental fate data from cyanamide show a rapid degradation within a few days to its major degradation products urea and/or CO₂.

In two water/sediment systems, DT₅₀values 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. Elimination of [14C]-cyanamide from the water/sediment systems proceeded mainly via mineralisation to CO₂. Only one major metabolite, identified as urea, was detected in the pond system. In the sediments, neither the parent substance nor degradation products were detected in significant amounts.

The following DT₅₀and DT₉₀values were calculated for the aerobic and anaerobic degradation of cyanamide in soil under laboratory conditions:

DT₅₀aerobic: 0.7–4.6 days

DT₉₀aerobic: 2.4–15.2 days

DT₅₀anaerobic: 34.7 days

DT₉₀anaerobic: 105 days

 

In soil samples that were incubated with the calcium cyanamide fertiliser product PERLKA at different soil moisture contents (ca. 25 % and 50 % of the maximum water holding capacity) and temperatures (12 °C or 20°C) DT₅₀values for PERLKA (= release of cyanamide from PERLKA) range between 0.60 -2.51 days. DT₅₀values for the subsequent degradation of cyanamide were determined to 0.55 -1.15 days.

The formation of secondary transformation products (i.e. dicyandiamide (DCD), urea (CH₄N₂O), nitrate (NO₃^-), nitrite (NO₂^-) and ammonia (NH₄⁺)) shows distinct differences depending on whether the soil is treated with Cyanamid F1000 or PERLKA. 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.

In a field study, cyanamide (a 50.5 % (w/w) aqueous solution of cyanamide) was applied to a set-up of soil plots in 2 locations in Phoenix, Arizona, USA. Cyanamide was degraded very fast in the soil, with a mean DT₅₀ field 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 anymore and thus, the DT90field is less than 2 weeks.

 

Conclusion on degradation data

Calcium cyanamide is rapidly transformed to cyanamide but cannot be considered as readily biodegradable. However, according to Regulation (EC) 1272/2008 on classification, labelling and packaging (CLP), Annex I, Section 4.1.2.9.2. besides the results obtained in a screening test on ready biodegradability also other evidence of rapid biodegradation in the environment may be considered. E.g. if the substance degrades biotically or abiotically in the aquatic environment by > 70 % in 28 days under environmentally realistic conditions. These criteria are met, as the DT₅₀resp. DT₉₀values resulting from studies performed with cyanamide (free acid from the Ca-salt) on aerobic degradation in soil, in the water/sediment compartment and in field studies are far below 28 days. Thus, taking all data together it can be concluded that calcium cyanamide is rapidly degraded in sediment and soil within a few days.

 

Bioaccumulation

From its physical-chemical parameters, calcium cyanamide is not expected to have a significant potential for bioaccumulation.

 

Adsorption/desorption

The log Koc of Calcium cyanamide, technical grade (Kalkstickstoff) was measured to be < 1.25 at pH 5.5 and 7.5.

Based on the very low log Kow of -0.72, calcium cyanamide is not expected to have a significant potential for adsorption to soil but is rather expected to be quite mobile in soil.

The derived Koc values for the read-across substance cyanamide range between 0 and 6.8 mL/g (pH range 5.3 - 7.1), indicating a low adsorption potential to soil, and supporting the result for calcium cyanamide.

However, taking into account information from lysimeter studies and column leaching experiments, complete degradation of calcium cyanamide takes place after application to soil. Repeated application does not lead to enrichment of calcium cyanamide. The degradation of calcium cyanamide in soil contributes to the finding that only traces of calcium cyanamide appeared in the lysimeter percolate (mean concentration < 0.03 µg/L). 

It can be concluded that calcium cyanamide is rapidly degraded in the upper soil layers and will not leach into deeper soil layers despite its high mobility.

Additional information

Information on the behaviour of cyanamide in the environment is used in a read-across approach for the assessment of calcium cyanamide:

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.

(Please note: EUSES modelling (implemented in Chesar v3.3) indicates negligible soil exposure via sludge and air. Release percentages of the modelled biological STP directed to air and sludge are 3.81E-04 % and 0.168%, respectively. Cyanamide is rapidly degraded in water/sediment and soil systems. Thus, rapid degradation of cyanamide is anticipated during storage of sewage sludge in digestion towers prior to soil application (if applicable), reducing the final concentration of hydrogen cyanamide in sludge to negligible values.)

For the agricultural application of calcium cyanamide the substance is formulated in a slow dissolving granule (PERLKA) that is applied to agricultural fields as a fertiliser. In contact with soil moisture, PERLKA granules will slowly release cyanamide. Thus, available data on the biodegradation of cyanamide in soil are relevant in the assessment of calcium cyanamide.

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"