Calcium cyanamide

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989-06-16 to 1990-04-27

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

BBA Part VI, 1-1

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Assey Calcium Cyanamide 43.2%

Analytical monitoring:

no

Details on sampling:

no analytical monitoring

Vehicle:

no

Details on preparation and application of test substrate:

Soil 1:
organic C: 0.75 %
microbial biomass: 5.0 mg/100 g
Total N: 0.060 %
pH: 5.4

Soil 2:
organic C: 1.01 %
microbial biomass: 27.1 mg/100 g
Total N: 0.137 %
pH: 6.2

Both soils were not treated with agrochemicals two years prior to the test.

Test organisms (inoculum):

soil

Total exposure duration:

90 d

Test temperature:

21-24 °C

Moisture:

44 % of the maximum capacity

Details on test conditions:

Analysis method of the dehydrogenase activity: TCC reduction method according to Thalmann (1968)
Analysis of the Nitrification: Extraction with 2 m KCl and measurement via steam distillation according to Keeney and Nelson (1982). Nitrit test with Merckoquant 10007.

Nominal and measured concentrations:

1) 1000 kg/ha = 1.3 g/kg soil = 276 mg N/kg soil
2) 5000 kg/ha = 6.7 g/kg soil = 1380 mg N/kg soil

Reference substance (positive control):

yes

Remarks:

Ammonium sulfate

Duration:

84 d

Dose descriptor:

NOEC

Remarks:

Result for loamy soil

Effect conc.:

561.6 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: dehydrogenease activity

Remarks on result:

other: Re-calculation of results to 100 % calcium cyanamide

Remarks:

43.2 % calcium cyanamide in sample tested

Duration:

84 d

Dose descriptor:

NOEC

Remarks:

Result for loamy soil

Effect conc.:

1 000 other: kg/ha

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

corresponding to 1.3 g/kg soil dw

Basis for effect:

other: dehydrogenase activity

Duration:

84 d

Dose descriptor:

other: LOEC

Remarks:

Result for loamy soil

Effect conc.:

5 000 other: kg/ha

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

corresponding to 6.7 g/kg soil dw

Basis for effect:

other: dehydrogenase activity

Duration:

84 d

Dose descriptor:

other: LOEC

Remarks:

Result for sandy soil

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: dehydrogenase activity

Key result

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

561.1 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: nitrate formation rate

Remarks on result:

other: Re-calculation of results to 100 % calcium cyanamide

Remarks:

43.2 % calcium cyanamide in sample tested

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

1 000 other: kg/ha

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

corresponding to 1.3 g/kg soil dw

Basis for effect:

nitrate formation rate

Duration:

90 d

Dose descriptor:

other: LOEC

Effect conc.:

5 000 other: kg/ha

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

corresponding to 6.7 g/kg soil dw

Basis for effect:

nitrate formation rate

Details on results:

Dehydrogenase activity:
Perlka decreases the dehydrogenase activity in both soils at a concentration of 5000 kg/ha compared to the untreated control. The decrease increases with the treatment time and leads to a reduction of 85 % at day 84.
A concentration of 1000 kg/ha leads to a small induction of the activity in soil 2 (loamy soil), but causes an inhibition of 85 % compared to the control in soil 1 (sandy soil).

Nitrification:
Perlka decreases the nitrification at 5000 kg/ha to a big extent in both soils. No decrease of the nitrification is seen in the lower concentration in both soils (1000 kg/ha).

Results with reference substance (positive control):

Dehydrogenase activity:
Ammonium sulfate inhibits the dehydrogenase activity in soil 1 to about 50 %. In soil 2 the decrease of the activity was comparable to Perlka.

Nitrification:
The Nitrification is inhibited for ammonium sulfate.

Reported statistics and error estimates:

mean and SD values

Validity criteria fulfilled:

not specified

Conclusions:

Nitrification and dehydrogenase activity in two different soils is inhibited by Perlka (formulation of calcium cyanamide) at a concentration of 5000 kg/ha and 1000 & 5000 kg/ha, respectively.
No inhibition of the nitrification was observed at a concentration of 1000 kg/ha equal to 1.3 g Perlka/kg dry soil corresponding to 561.1 mg calcium cyanamide/kg dry soil.

Executive summary:

The microbial activity of two different soils treated with Perlka (formulation of calcium cyanamide) was determined after 84 and 90 days by measuring the dehydrogenase activity or the nitrification rate, respectively.

Nitrification and dehydrogenase activity in two different soils is inhibited by Perlka at a concentration of 5000 kg/ha. While the dehydrogenase activity was not negatively influenced in loamy soil at 1000 kg/ha, an inhibition of 85 % compared to the control was observed for sandy soil.

No adverse effects were observed on nitrification inhibition at a concentration of 1000 kg/ha equal to 1.3 g Perlka/kg dry soil corresponding to 561.1 mg calcium cyanamide/kg dry soil. These data indicate a low toxicity of calcium cyanamide towards soil microorganisms.

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

Justification for read-across for ecotoxicological endpoints:
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 both in chemical structure and regarding 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 detailled description where read across is used/recommended and where it is preferrable to refain 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"

Reason / purpose for cross-reference:

read-across source

Duration:

76 d

Dose descriptor:

other: Deviation in respiration (compare to the control at the end of the study)

Effect conc.:

< 25 other: %.

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Remarks on result:

other: The result is obtained following an application rate of 19.8 kg cyanamide/ha (maximum recommended field rate) and following an application rate of 98 kg cyanamide/ha (5-times the max. recommended field rate) to sandy soil as well as to loamy soil.

Duration:

97 d

Dose descriptor:

other: Deviation in nitrate and nitrite levels (compare to the control at the end of the study)

Effect conc.:

< 25 other: %

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: The result is obtained following an application rate of 19.8 kg cyanamide/ha (maximum recommended field rate) and following an application rate of 98 kg cyanamide/ha (5-times the max. recommended field rate) to sandy soil as well as to loamy soil.

Details on results:

Deviations in the ammonium and nitrate/nitrite levels and respiration rate between control soil and soil treated with a 49 % (w/w) aqueous solution of cyanamide were < 25 % at the end of the study.

Results with reference substance (positive control):

No reference substrate

Reported statistics and error estimates:

Not applicable

Summary of effects of a 49 % (w/w) aqueous solution of cyanamide on ammonium and nitrate levels and respiration in sandy soil amended withm Lucerne meal:

Day	Deviation in ammonium levels (%)^a	Deviation in nitrate and nitrite levels (%)^a	Deviation in respiration (%)^a
Application rate: 19.8 kg cyanamide/ha (maximum recommended field rate)
7	4.9	-4.5	-
14	33.5	-18.2	3.2
21	28.3	-4.8	-
28	-11.3	1.8	-21.9
42	6.6	7.5	-
76	-1.1	-0.5	-
Application rate: 98 kg cyanamide/ha (5-times the max. recommended field rate)
7	2.4	-23.0	-
14	27.8	-6.2	34.5
21	45.0	-39.5	-
28	77.3	-37.3	-8.8
42	72.4	-23.8	-
76	2.6	1.7	-

a            % Deviation: [(measured parameter in control soil / measured parameter in treated soil) –1] x 100

-    not determined

Summary of effects of a 49 % (w/w) aqueous solution of cyanamide on ammonium and nitrate levels and respiration in a loamy soil amended withmeal:

Day	Deviation in ammonium levels (%)^a	Deviation in nitrate and nitrite levels (%)^a	Deviation in respiration (%)^a
Application rate: 19.8 kg cyanamide/ha (maximum recommended field rate)
7	-1.7	0.0	-
14	-8.7	6.0	-17.1
21	10.1	-5.9	-
28	-0.6	-4.9	-2.7
42	24.7	11.5	-
76	2.6	-4.2	-
Application rate: 98 kg cyanamide/ha (5-times the max. recommended field rate)
7	136.8	-47.1	-
14	222.7	-35.7	-22.4
21	31.0	-16.8	-
28	-2.9	1.9	7.1
42	3.8	8.6	-
76	-7.0	5.1	-

a   % Deviation: [(measured parameter in control soil / measured parameter in treated soil) –1] x 100

 

Validity criteria fulfilled:

yes

Conclusions:

Deviation in the rates of nitrogen transformation and respiration were < 25 % at the end of the study. Under anticipated conditions of field use, cyanamide is categorised as having low risk to soil microflora.

Justification for read-across for ecotoxicological endpoints:
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 both in chemical structure and regarding 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 detailled description where read across is used/recommended and where it is preferrable to refain 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"

Executive summary:

The effects of ALZODEF (a 49 % (w/w) aqueous solution of cyanamide) on soil microbial respiration (carbon mineralisation) and nitrogen transformation (ammonification and nitrification) were examined using a sandy soil and a loamy soil in a laboratory study. The test contained 3 replicates (nitrogen transformation) and 6 replicates (carbon mineralisation) of each treatment group: unamended soil, soil amended with Lucerne mean and soil amended with Lucerne meal and treated with a 49 % (w/w) aqueous solution of cyanamide at two rates: 40 L of a 49 % (w/w) aqueous solution of cyanamide/ha equivalent to 19.6 kg cyanamide/ha (maximum recommended annual application rate of 20 L of a 49 % (w/w) aqueous solution of cyanamide) and 200 L of a 49 % (w/w) aqueous solution of cyanamide/ha equivalent to 98 kg cyanamide/ha (5-times the maximum recommended annual application rate of 20 L 49 % (w/w) aqueous solution of cyanamide). Production of carbon dioxide by soil microbes and concentrations of ammonium, nitrate, and nitrite were determined periodically throughout the study.

Deviations in the ammonium and nitrate/nitrite levels and respiration rate between control soil and soil treated with a 49 % (w/w) aqueous solution of cyanamide were < 25 % at the end of the study. As the deviation is not higher than 25% for both examined parameters, it can be concluded that cyanamide has a low risk to soil microflora (under anticipated conditions of field use).

This information is used in a read-across approach in the assessment of the target substance.

For detailled description where read across is used/recommended and where it is preferrable to refain 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"

Reference 3

Endpoint:

toxicity to soil microorganisms

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

Justification for read-across for ecotoxicological endpoints:
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 both in chemical structure and regarding 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 detailled description where read across is used/recommended and where it is preferrable to refain 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"

Reason / purpose for cross-reference:

read-across source

Duration:

28 d

Dose descriptor:

other: carbon transformation - deviation from control not more than 25%

Effect conc.:

< 25 other: %.

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Remarks on result:

other: The deviation of the soil respiration rate from the control at 28 days after application of 52.19 mg Cyanamid L500/ kg soil was 6.74% (fullfiling the < 25% criteria).

Duration:

28 d

Dose descriptor:

other: carbon transformation - deviation from control not more than 25%

Effect conc.:

< 25 other: %

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Remarks on result:

other: The deviation of the soil respiration rate from the control at 28 days after application of 260.96 mg Cyanamid L500/ kg soil was 9.77% (fullfiling the < 25% criteria).

Duration:

97 d

Dose descriptor:

other: nitrogen transformation - deviation from control not more than 25%

Effect conc.:

< 25 other: %

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: The deviation of the soil nitrate content of the 52.19 mg Cyanamid L500/kg soil treated samples and the control soil samples after 97 days of exposure was 6.0 % (fullfiling the < 25% criteria).

Duration:

97 d

Dose descriptor:

other: nitrogen transformation - deviation from control not more than 25%

Effect conc.:

> 25 other: %

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: The deviation of the soil nitrate content of the 260.96 mg Cyanamid L500/kg soil samples from the control samples at the end of the test was 72.05% (not fullfiling the < 25% criteria). Nevertheless, it is not considered as an adverse effect (see below)

Details on results:

Soil Respiration Rates
The differences between the respiration rates of Cyanamide L500 treated and control soil samples were 6.74 %for 52.19 mg Cyanamide L500/ kg soil and 9.77% for the test concentration of 260.96 mg Cyanamide L500/kg soil at 28 days after application.
According to OECD 217, no long-term effects occur, if the deviation of the soil respiration rates from the control is less than 25% at 28 days after application. The variation between replicate control samples was 0.95% at day 28 after application, being lower than the validity criterion of the OECD test guideline 217 of 15%.

Soil Nitrogen Turnover
The differences between the soil nitrate content of Cyanamide L500 treated and control soil samples were 6.0% for 52.19 mg Cyanamide L500/kg soil and 72.0% for the test concentration of 260.96 mg Cyanamide L500/kg soil at 97 days after application. According to OECD 216, no long-term effects occur, if the deviation of the soil nitrate content from the control is less than 25% at 28 days after application. If the deviation at day 28 after application is more than 25%, the test is prolonged until the deviation is lower than 25% or to a maximum of 100 days. The variation between replicate control samples was 5.79% at day 97, being lower than the validity criterion of the OECD test guideline 216 of 15%.

Results with reference substance (positive control):

No reference substrate

Reported statistics and error estimates:

Not applicable

Effects of Cyanamid L500 on soil respiration in a loamy sand soil:

Soil Carbon Turnover Test (Soil Respiration)
	Control		Cyanamid L500 52.19 g/kg soil dry weight		Cyanamid L500 260.96 mg/kg soil dry weight
	mg CO^2/ 100 g hr	V variation %	mg CO^2/ 100 g hr	D deviation %	mg CO^2/ 100 g hr	D deviation %
Day 0	1.815	3.89	2.212	+ 21.9	1.494	- 17.7
Day 7	1.720	6.10	1.770	+ 2.91	2.040	+ 18.6
Day 14	1.542	27.9	1.480	- 4.02	1.318	- 14.5
Day 28	1.811	0.95	1.933	+ 6.74	1.634	- 9.77

D= % deviation from control

V = % variation within control replicates (calculated as the difference of max/min values to max value)

+ = stimulating effect

- = inhibitory effect

Effects of Cyanamid L500 on soil nitrogen turnover in a loamy sand soil:

Soil Nitrogen Turnover Test (Nitrate)
	Control		Cyanamid L500 52.19 g/kg soil dry weight			Cyanamid L500 260.96 mg/kg soil dry weight
	mg NO3- N/100 g	V variation %	mg NO3- N/100 g	deviation^D mg NO3-N/100 g*	D deviation %	mg NO3- N/100 g	deviation^D mg NO3-N/100 g**	D deviation %
Day 0	1.11	1.79	0.83	0.28	- 25.2	0.83	0.28	- 25.2
Day 7	0.35	10.8	0.98	0.63	+ 180	1.27	0.92	+ 263
Day 14	0.82	10.2	1.55	0.73	+ 89.0	4.23	3.38	+ 416
Day 28	2.49	4.72	2.79	0.30	+ 12.0	7.37	4.81	+ 196
Day 56	5.91	1.35	6.05	0.14	+ 2.37	11.0	5.09	+ 86.5
Day 84	6.99	5.59	7.46	0.47	+ 6.72	12.5	5.51	+ 79.1
Day 97	7.71	5.79	8.16	0.45	+ 5.84	13.3	5.59	+ 72.0
D= % deviation from control D = deviation from control mg NO3-N/100 g soil dry weight V = % variation within control replicates (calculated as the difference of max/min values to max value) + = stimulating effect - = inhibitory effect *by application of 51.19 mg/kg soil, 17.8 mg N are added per kg soil corresponding to 1.78 mg/100 g soil **by application of 260.96 mg/kg soil, 88.9 mg N are added per kg soil corresponding to 8.89 mg/100 g soil

The results of the soil carbon turnover test indicate there is no long-term effect of Cyanamide L500 on the soil microflora up to 260.96 mg/kg soil dry weight.

After 97 days of incubation, the soil nitrate content (as an indicator for soil nitrogen turnover) of the soil treated with Cyanamide L500 at the one-fold application rate (52.19 mg/kg soil dry weight) differed from the control by <25%. The 5-fold application rate (260.96 mg/kg soil dry weight) resulted in an increased nitrate level in soil. This, however, cannot be interpreted as a toxic effect of Cyanamide L500 on the soil microflora. It has to be taken into account that Cyanamid L500 contains 51.1 % (w/w) of the pure active substance cyanamide. The cyanamide molecule itself contains 66.7 % N. As a consequence, by mixing 260.96 mg Cyanamide L500 into one kg of soil, 88.9 mg N per kg soil are added. It is known that the cyanamide molecule hydrolytically breaks down in soil to form urea. Urea itself is transformed to NH4 and further to NO3. The increased nitrate levels in the treatment with the 5-fold concentration as compared to the control soil – can be fully explained by the fertilising effect of Cyanamide L500. In the 5-fold treatment, nitrate levels were found exceeding the concentrations in the untreated control soil up to 55.9 mg/kg soil (corresponding to 5.59 mg/100 g soil dry weight on day 97). The addition of 260.96 mg Cyanamide L500/kg soil in the 5-fold treatment corresponds to the addition of 88.9 mg nitrogen per kg soil. Thus, the increased nitrate levels are within the expected range. However, neither the nitrate nor the Nmin contents measured in the 5-fold treatment fully reflect the extra nitrogen quantity applied through administration of Cyanamide L500. Incorporation of a part of the added nitrogen in the soil micro-organisms seems to be the most likely explanation for this observation.

Validity criteria fulfilled:

yes

Conclusions:

In the carbon transformation test (soil respiration test) deviations from control were <25% in the end of the exposure period at both application rates, indicating that the test substance induce no long – term effect (to soil microorganisms).
In the nitrogen transformation test deviations from control were <25% in the lower concentration rate but >25% in the higher test concentration at the end of the test. The deviation can be fully explained with the fertilising effect of cyanamide. It is not an adverse effect.
Thus, it can be concluded from the results of the two tests that the use of the test substance, Cyanamid L500 is safe for soil non-target microorganisms.

Justification for read-across for ecotoxicological endpoints:
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 both in chemical structure and regarding 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 detailled description where read across is used/recommended and where it is preferrable to refain 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"

Executive summary:

The effects of cyanamide L500 on the activity of soil microflora was tested in the labaoratory according to the OECD test guidelines 216 and 217. The test was conducted in accordance with GLP.

The effects of Cyanamide L500 applied at 52.19 and 260.96 mg per kg soil dry weight on carbon mineralisation and the soil nitrogen turnover of the soil microflora were tested in the laboratory. The test concentrations correspond to a field application rate of 20 kg as/ha and the 5-fold thereof (100 kg as/ha).

The carbon mineralisation and the soil nitrogen turnover were determined in two separate experiments. Three treatment groups (control and the test item at two concentrations) with three replicates each were incubated at 20 +/- 2 °C in the dark. At different sample times, the soil respiration and the nitrogen content were determined.

Soil Respiration Rates: The differences between the respiration rates of Cyanamide L500 treated and control soil samples were 6.74% for 52.19 mg Cyanamid L500/ kg soil and 9.77% for the test concentration of 260.96 mg Cyanamid L500/kg soil at 28 days after application. According to OECD 217, no long-term effects occur, if the deviation of the soil respiration rates from the control is <25% at 28 days after application. The variation between replicate control samples was 0.95% at day 28 after application, being lower than the validity criterion of the OECD test guideline 217 of 15%.

Soil Nitrogen Turnover The differences between the soil nitrate content of Cyanamide L500 treated and control soil samples were 6.0% for 52.19 mg Cyanamid L500/kg soil and 72.0% for the test concentration of 260.96 mg Cyanamide L500/kg soil at 97 days after application. According to OECD 216, no long-term effects occur, if the deviation of the soil nitrate content from the control is <25% at 28 days after application. If the deviation at day 28 after application is >25%, the test is prolonged until the deviation is <25% or to a maximum of 100 days. The variation between replicate control samples was 5.79% at day 97, being lower than the validity criterion of the OECD test guideline 216 of 15%. This, however, cannot be interpreted as a toxic effect of Cyanamide L500 on the soil microflora. It has to be taken into account that Cyanamide L500 contains 51.1% (w/w) of the pure active substance cyanamide. The cyanamide molecule itself contains 66.7 % N. As a consequence, by mixing 260.96 mg Cyanamid L500 into one kg of soil, 88.9 mg N per kg soil are added. It is known that the cyanamide molecule hydrolytically breaks down in soil to form urea. Urea itself is transformed to NH4 and further to NO3. The increased nitrate levels in the treatment with the 5-fold concentration as compared to the control soil – can be fully explained by the fertilising effect of Cyanamid L500. In the 5-fold treatment, nitrate levels were found exceeding the concentrations in the untreated control soil up to 55.9 mg/kg soil (corresponding to 5.59 mg/100 g soil dry weight on day 97). The addition of 260.96 mg Cyanamid L500/kg soil in the 5-fold treatment corresponds to the addition of 88.9 mg nitrogen per kg soil. Thus, the increased nitrate levels are within the expected range. However, neither the nitrate nor the Nmin contents measured in the 5-fold treatment fully reflect the extra nitrogen quantity applied through administration of Cyanamid L500. Incorporation of a part of the added nitrogen in the soil micro-organisms seems to be the most likely explanation for this observation. It can be concluded from the results of the two tests that the use of the test substance, Cyanamid L500 is safe for soil non-target microorganisms.

This information is used in a read-across approach in the assessment of the target substance.

For detailled description where read across is used/recommended and where it is preferrable to refain 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"

Description of key information

The toxicity of calcium cyanamide as well as its degradation product cyanamide to soil microorganisms was investigated in different studies. In conclusion, these data indicate a low toxicity of calcium cyanamide and/or its degradation product cyanamide towards soil microorganisms:

Nitrification and dehydrogenase activity in two different soils is inhibited by the calcium cynamide fertiliser product PERLKA at a concentration of 5000 kg/ha and at 1000 & 5000 kg/ha, respectively (Schönborn, 1990a). No adverse effects were observed on nitrification at a concentration of 1000 kg/ha equal to 1.3 g Perlka/ kg dry soil corresponding to 561.6 mg calcium cyanamide/kg dry soil. Inhibition of nitrification is considered the relevant endpoint. The NOEC of 561.6 mg calcium cyanamide/kg dry soil corresponds to 295.1 mg cyanamide/kg dry soil. This value is carried forward in the risk assessment.

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 %.  

For detailled description where read across is used/recommended and where it is preferrable to refain 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"

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

295.1 mg/kg soil dw

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

Therefore, the toxicity of calcium cyanamide and its degradation product cyanamide to terrestrial organisms is reported here:

 

- Toxicity of calcium cyanamide to terrestrial micro-organisms reported by Schönborn, 1990a:

The microbial activity of two different soils treated with PERLKA (formulation of calcium cyanamide) was determined after 84 and 90 days by measuring the dehydrogenase activity or the nitrification rate, respectively.

Nitrification and dehydrogenase activity in two different soils is inhibited by PERLKA at a concentration of 5000 kg/ha and at 1000 & 5000 kg/ha, respectively. No adverse effects were observed on nitrification at a concentration of 1000 kg/ha equal to 1.3 g PERLKA/ kg dry soil corresponding to 561.6 mg calcium cyanamide/kg dry soil (= NOEC). These data indicate a low toxicity of calcium cyanamide towards soil microorganisms.

 

- Toxicity of cyanamide to terrestrial micro-organisms reported by Schönborn, 1990b and Reis, 2002:

The effects of cyanamide (49% or 51.1% (w/w) aqueous solution of cyanamide) on soil microorganisms were examined by Schönborn (1990b) and Reis (2002). In the study from Schönborn (1990b) the effects of ALZODEF (a 49 % (w/w) aqueous solution of cyanamide) on soil microbial respiration (carbon mineralisation) and nitrogen transformation (ammonification and nitrification) were examined using a sandy soil and a loamy soil in a laboratory study. The test contained 3 replicates (nitrogen transformation) and 6 replicates (carbon mineralisation) of each treatment group: unamended soil, soil amended with Lucerne mean and soil amended with Lucerne meal and treated with a 49 % (w/w) aqueous solution of cyanamide at two rates:

-       40 L of a 49 % (w/w) aqueous solution of cyanamide/ha equivalent to 19.6 kg cyanamide/ha (maximum recommended annual application rate of 20 L of a 49 % (w/w) aqueous solution of cyanamide), and

-       200 L of a 49 % (w/w) aqueous solution of cyanamide/ha equivalent to 98 kg cyanamide/ha (5-times the maximum recommended annual application rate of 20 L 49 % (w/w) aqueous solution of cyanamide).

Production of carbon dioxide by soil microbes and concentrations of ammonium, nitrate, and nitrite were determined periodically throughout the study.

Deviations in the ammonium and nitrate/nitrite levels and respiration rate between control soil and soil treated with a 49 % (w/w) aqueous solution of cyanamide were < 25 % at the end of the study. As the deviation is not higher than 25% for both examined parameters, it can be concluded that cyanamide has a low risk to soil microflora (under anticipated conditions of field use).

Similar results were obtained in the second study by Reis (2002). In the carbon transformation test (soil respiration test) deviations from control were less than 25% in the end of the exposure period at both application rates (20 kg ai/ha and the 5-fold thereof (100 kg ai/ha)), indicating that the test substance does not induce long-term effect (to soil microorganisms).

In the nitrogen transformation test deviations from control were less than 25% in the lower concentration rate but more than 25% in the higher test concentration at the end of the test. The deviation can be fully explained with the fertilising effect of cyanamide (> incorporation of a part of the added nitrogen in the soil micro-organisms seems to be the most likely explanation for this observation). It is not considered as an adverse effect.

Thus, as in the key study, it can be concluded that the use of the test substance, Cyanamid L500, at the above indicated application rates is safe for soil non-target microorganisms.