Calcium cyanamide

Endpoint summary

Description of key information

Available terrestrial toxicity studies were conducted with calcium cyanamide fertilizer product (PERLKA). The mean concentration of calcium cyanamide in PERLKA is 44 %. Therefore, study results obtained with PERLKA were re-calculated to 100 % calcium cyanamide:

1) Macroorganisms:

- The 56-d NOEC for reproduction of Eisenia fetida is 82 mg product/ kg soil dry weight (equivalent to 36.1 mg calcium cyanamide/kg soil dw), reported by Scheffczyk, 2016a.

- The most sensitive acute LC50 for the earthworm (Eisenia foetida) was determined to be 261 mg product/kg dry soil (equivalent to 110 mg calcium cyanamide/kg dry soil), reported by Haque and Ebing, 1983. This is the same order of magnitude as the LC50 for Lumbricus terrestris reported by Heimbach (1984) to be 124 mg calcium cyanamide/kg dry soil.

- The application of 400 kg PERLKA/ha (533 mg PERLKA/kg soil, equivalent to 235 mg/kg pure calcium cyanamide) under natural conditions had no effect on earthworm populations one and 12 months after application (Bauchhenß, 1992).

2) Arthropods:

- PERLKA was not found to be toxic to the soil-dwelling carabid beetle (Bembidion lampros) up to a concentration of 450 kg/ha (Mead-Briggs, 1990), corresponding to a surface application of 198 kg calcium cyanamide/ha soil.

- In a field study (Stegger 2019, still ongoing) the effect of applied Perlka (200 kg Perlka/ha and 400 kg Perlka/ha, equaling ca. 88 and 176 kg calcium cyanamide) on the abundance of Collembola species was assessed. In the pitfall and soil core samples that are taxonomically evaluated up to date 15 different collembola species were determined. Results available up to date show that compared to the fertiliser control only short-term effects followed by recovery could be observed for both sampling techniques. For comparison to the untreated control effects were also only short-term. Recovery must be demonstrated for Sminthurinus aureus (effects on day 14 and 28 in pitfall samples) and Isotoma viridis (effect on day 185 in pitfall samples) by further data of the samplings in autumn 2019.

3) Microorganisms:

- Nitrification in two different soils is inhibited by PERLKA (formulation of calcium cyanamide) only at a very high concentration of 5000 kg/ha. No adverse effects were observed at a concentration of 1000 kg/ha equal to 1.3 g PERLKA/kg dry soil (43.2 % a.i.) resp. 561.6 mg calcium cyanamide/kg dry soil.

4) Birds:

- The oral LD50 of calcium cyanamide in Japanese quail was calculated to be 1665 mg/kg bw (equivalent to 703 mg/kg bw; Spanjers & Til, 1984).

Additional studies were conducted with the degradation product cyanamide and also in the form of cyanamide product (SKW Cyanamid L500). The mean concentration of cyanamide in SKW Cyanamide L500 is 51%. Therefore, study results obtained with SKW Cyanamid L500 were re-calculated to 100% cyanamide:

1) Macroorganisms:

Lührs (2001) tested the acute toxicity effects of cyanamide on earthworms in a 14-day laboratory study. The LC50 observed after 14 days of incubation was  > 111.3 mg/kg dry soil (active substance cyanamide), the highest rate tested.

Further investigations on the chronic toxicity of cyanamide to Esenia fetida are reported by Scheffczyk (2016b). The NOEC for reproduction is ≥ 1.05 mg cyanamide/kg soil dw, the highest concentration investigated during the study.

2) Arthropods:

A variety of studies investigating the effects of cyanamide on different arthropd species are available. The most sensitive effect is reported for the reproduction of the springtail Folsomia candida. The EC10 (reproduction) was determined to be 1.515 mg pure cyanamide/ka soil dw (Moser, 2009a). This value represents the chronic worst-case value for terrestrial arthropods and is carried forward as key value in the chemical safety assessment.

3) Plants:

The effects of cyanamide on non-target plants were investigated in a seedling emergence Tier 2 (LR50) test (Meister, 2001a) and vegetative vigour Tier 2 (LR50) test (Meister, 2001b). In both studies the most sensitive endpoint was shoot dry weight. The most sensitive species in the seedling emergence test was Allium cepa with a EC50 value of 1.722 kg Cyanamid L500/ha (corresponds to 0.87 kg ai/ha). In the vegetative vigour test the most sensitive species was tomato (Lycopersicon esculentum) with a EC50 of 33.2 kg cyanamide L 500/ha (corresponds to 16.8 kg a.i./ha).  

In a long-term toxicity test according to ISO 22030 (2005) the no observed adverse effect concentration (NOAEC) in Avena sativa and Brassica rapa for the endpoints biomass and number of inflorescences per seed pod is ≥ 100 mg a.s./kg soil dry mass (Förster, 2009).

4) Microorganisms:

- From the results of two soil microflora tests (soil respiration test and nitrogen transformation) conducted with cyanamide, it can be concluded that the use of cyanamide (around 20 kg ai/ha and the 5-fold thereof (100 kg ai/ha)) is safe for soil non-target microorganisms as the deviation of investigated endpoints from control levels of both tests in both studies were practically below 25 %.

5) Birds:

- Cyanamide was of low toxicity to birds and caused no mortalities at the maximum dose level of 5000 ppm (feed) in bobwhite quail (Colinus virginianus) and mallard duck (Anas platyrhynchos), reported by Lynn et al, 1991.

- In a reproduction test with 14-day old chicks a NOEC of 152 mg/kg feed, (equivalent to 13.3 mg cyanamide/kg bw/d) was reported (Johnson, 2001).

Discussion and conclusion on key value for chemical safety assessment:

The lowest NOEC value is reported by Scheffczyk (2016b). Please note, however, that this NOEC is an unbounded value.

The study by Scheffczyk (2016b) investigates the 56-d reproduction toxicity of cyanamide in earthworm (Eisenia fetida) in accordance with OECD guideline 222 and ISO 11268-2.

In the first step a 28-d range-finding study (non-GLP) was conducted at 0 (control), 0.1, 1, 10, 100 and 100 mg cyanamide/kg soil (dw) in two replicates. Based on the dose-response relationship observed in the range-finding study, the concentration range for the definitive test (GLP) was chosen as follows: 0 (control), 0.017, 0.031, 0.056, 0.10 mg, 0.18, 0.32, 0.58, and 1.05 mg cyanamide/kg soil (dw).

 

In the definitive test, no adverse effects could be observed at the highest concentration evaluated in the test. Thus, the NOEC from this study is ≥ 1.05 mg cyanamide/kg soil dw, a definitive LOEC value could not be derived.

Although the validity criteria of OECD guideline 222 are met (mortality in control ≤ 10 %; number of juveniles per control replicate ≥ 30; coefficient of variation for the number of juveniles in control ≤ 30 %), the variability between replicates in the control and in samples of all test concentrations is relatively high, thus reducing the robustness of the data.

 

In accordance with the ECHA Guidance on information requirements and chemical safety assessment, Chapter R.10: Characterisation of dose [concentration]-response for environment (May 2008, p. 11), the NOEC is defined as “the highest concentration tested at which the substance is observed to have no statistically significant effect (p<0.05) when compared with the control, within a stated exposure period” (OECD 211, 1998b) or the test concentration immediately below the LOEC, which when compared with the control has no statistically significant effect (p<0.05) within a stated period (OECD 211, 1998b).” Furthermore, “[t]here has to be a concentration-effect relationship.”

However, in the present main test by Scheffczyk (2016b), no concentration-effect relationship was observed.

 

Any bounded NOEC of cyanamide for the reproduction of E. fetida under the conditions of OECD guideline 222 would presumably be higher than the highest test concentration chosen is the test by Scheffczyk (2016b). However, such a bounded NOEC value is currently not available and could only be determined by repeat testing.

 

Besides, preliminary information from the agricultural field study (Ebke, 2018; see IUCLID section 6.6) indicate no adverse effects on populations of earthworms at a single annual application rate of 400 kg PERLKA/ha that corresponds to a concentration of 11.8 mg cyanamide/kg soil (dw) (see ESCAPE V2 calculations in IUCLID section 13.2; Kiefer, 2018). This concentration is considerably higher compared to the highest test concentration applied in the study by Scheffczyk (2016b).

 

The most sensitive bounded NOEC value that is currently available is reported for collembola (Folsomia candida). The study by Moser (2009a) investigates the long-term toxic effects on the reproduction of F. candida after 28-d exposure in artificial soil spiked with cyanamide at 0.4, 1.26, 4.00, 12.46, 40.00, 60.00, 80.00, 100.00 mg a.s./kg soil (dw). This GLP guideline study (ISO 11267) reports a clear dose-response relationship with a significant reduction of the number of juveniles in comparison to the control at 1.26 mg cyanamide/kg sol (dw), resulting in a NOEC and EC10 of 0.4 and 1.515 mg cyanamide/kg soil (dw), respectively. 
In accordance with the ECHA Guidance on information requirements and chemical safety assessment, Chapter R.10:  Characterisation of dose [concentration]-response for environment (May 2008, p. 11), EC10 values for long-term test which are obtained using an appropriate statistical method will be used preferentially. Therefore, the EC10 of 1.515 mg cynamide/kg soil (dw) is considered the key value for chemical safety assessment.
Please note: The EC10 of 1.515 mg cynamide/kg soil (dw) has been recalculated by the German Competent Authority (UBA) and was used for the calculation of the PNECsoil in the Assessment Report for the evaluation of cyanamide as active biocidal substance (July 2016;http://dissemination.echa.europa.eu/Biocides/ActiveSubstances/1280-03/1280-03_Assessment_Report.pdf).

 

In conclusion, the unbounded NOEC of ≥ 1.05 mg cyanamide/kg soil (dw) in E. fetida reported byScheffcyzk (2016b) is not considered relevant for hazard assessment purposes. Instead, the EC10 of 1.515 mg cynamide/kg soil (dw) for the reproduction of F. candida (Moser 2009a) is considered the key value.

Additional information

Environmental fate and exposure are critical factors when assessing environmental risk. Calcium cyanamide is formulated in a slowly dissolving granule (PERLKA) that is applied to agricultural fields as a fertiliser. When dissolved calcium cyanamide is rapidly converted to (hydrogen) cyanamide. These two substances are similar in both chemical structure and fate in the environment. Cyanamide is the environmentally relevant transformation product upon application of calcium cyanamide (PERLKA) to soil as a fertiliser. Therefore, terrestrial data on cyanamide are considered in the hazard assessment of calcium cyanamide. (For further information on read-across for environmental endpoints please refer to the document in IUCLID section 13.)

However, the slow dissolution kinetics of commercially formulated granules (PERLKA) will have a significant effect on cyanamide exposure in the terrestrial environmental compartment, in addition to application frequency and loading.

Please note, however, that for the environmental endpoint ‘Toxicity to birds’, cyanamide is not considered a suitable read-across partner for calcium cyanamide. This conclusion is drawn based on the composition and on the comparison of toxicological studies from endpoints, where experimental results are available for both compounds, calcium cyanamide and cyanamide.

Calcium cyanamide consists of approx. 50% (w/w) calcium. In aqueous solution, Ca²⁺ions are released, and CN₂transforms into hydrogen cyanamide (H₂CN₂) with hydrogen being covalently bound to the CN₂ moiety. Dissolution kinetics, including dependency on the aqueous milieu, is difficult to predict for calcium cyanamide. Therefore, even though cyanamide will be released from calcium cyanamide, the appropriateness of using cyanamide data for extrapolation adverse effects needs to be based on a case by case decision. It is not a default assumption.

The differences between cyanamide and calcium cyanamide are pronounced for any test where classification is based on a limit dose, or for in vitro tests, where test systems are generally sensitive to pH shifts and osmolarity, or for any test with oral application (i.e. toxicity studies with birds). In the latter case, dissolution kinetics will determine if the compound is already resorbed in the oral cavity (i.e. in feeding studies), in the stomach, or not until it reaches the intestines. Dissolution kinetics also determines if and at what speed cyanamide is released from calcium cyanamide. A delayed release will lead to lower systemic concentrations that may not exceed the metabolic capacities of protective pathways or repair mechanisms, compared to a bolus effect that might occur after application of cyanamide.

This line of argumentation is supported by differences in experimental results from calcium cyanamide versus cyanamide studies. For example, in acute oral toxicity studies in rat, the LD50 for “calcium cyanamide 20.5%N” is calculated to be 765 mg/kg bw (de Groot, 1976), which is equal to 639 mg/kg calcium cyanamide, technical grade (Kalkstickstoff) or approx. 270 mg/kg cyanamide. In contrast, the acute oral LD50 of pure active substance cyanamide in rats was estimated to be 142 mg/kg bw for the sexes combined (Engel, 1973). Another example is the result of the pre-natal developmental toxicity studies according to OECD 414, in rat. Here, the study on cyanamide leads to a classification as Repro 2 (s. RAC opinion, CLH-O-0000001412-86-67/F, from 5.6.2015, based on diaphragmatic hernias reported in Morseth (1989)), while a comparable study with calcium cyanamide was clearly negative [WIL Research Europe-Lyon, 2014].”