Calcium cyanamide

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2000-02-07 until 2000-02-15

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.4400 (Aquatic Plant Toxicity Test using Lemna spp. Tiers I & II))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Mean measured concentrations of the 51.1 % (w/w) aqueous solution of cyanamide were 0.31, 0.86, 2.95, 10.18 and 34.5 mg /L, corresponding to 0.16, 0.44, 1.51, 5.20 and 17.63 mg ai/L and ranged from 76 to 109 % of nominal concentrations.

Vehicle:

no

Details on test solutions:

No vehicle

Test organisms (species):

Lemna gibba

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

7 d

Post exposure observation period:

No post exposure observation period

Hardness:

Not indicated

Test temperature:

All chemical and physical parameters (pH, temperature) in the definitive test were within expected ranges.

pH:

All chemical and physical parameters (pH, temperature) in the definitive test were within expected ranges.

Dissolved oxygen:

Not indicated

Salinity:

Freshwater

Nominal and measured concentrations:

Test concentrations of 0.32, 1.0, 3.2, 10.0 and 32.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L.
Mean measured concentrations of the 51.1 % (w/w) aqueous solution of cyanamide were 0.31, 0.86, 2.95, 10.18 and 34.5 mg /L, corresponding to 0.16, 0.44, 1.51, 5.20 and 17.63 mg ai/L and ranged from 76 to 109 % of nominal concentrations.

Details on test conditions:

The effects of SKW Cyanamid L500 (a 51.1 % (w/w) aqueous solution of cyanamide) on Lemna gibba G3 was determined in 20XAAP nutrient medium. Three replicates at test concentrations of 0.32, 1.0, 3.2, 10.0 and 32.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L, were incubated for 7 days and frond counts were taken on days 3, 5 and 7, corresponding to 0.16, 0.51, 1.64, 5.11 and 16.35 mg ai/L. Additionally, a control was tested in parallel. The samples of the test medium were analysed by a HPLC method using an UV/VIS-detector.

Reference substance (positive control):

no

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

2.33 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

biomass

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

biomass

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

5.61 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

2.4 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: dry weight

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: dry weight

Details on results:

The doubling time of fronds in the controls was 1.7 d (39.5 h) and thus less than 2.5 d (60 h), corresponding to an approximately 19-fold increase in 7 days.The test item had a statistically significant inhibitory effect on the growth of Lemna gibba after the exposure of 7 days first at the nominal concentration of 3.2 mg test item/L, corresponding to 1.63 mg ai/L. The 7-day NOEC was determined at the nominal concentration of 1 mg test item/L, corresponding to 0.51 mg ai/L, since up to and including this test concentration the mean biomass, mean growth rates and the dry weight of Lemna gibba were not significantly lower than in the control. At the nominal test concentrations of 0.32 to 3.2 mg/L, corresponding to 0.163 to 1.63 mg ai/l, the shape of fronds and colonies after the test period of 7 days was not different to those in the control. However, at the two highest test concentrations of 10.0 and 32.0 mg/L (5.1 and 16.35 mg ai/L), the fronds were pale and small.

Results with reference substance (positive control):

No positive control

Reported statistics and error estimates:

The test groups were significantly different from controls according to the Dunnett-test criteria, p < 0.05.

In the test medium the test item was sufficiently stable during the test period of 7 days. Therefore, all reported biological results are related to the nominal concentrations of the test item.

Analytical determination of concentrations tested:

Nominal concentrations of a 51.1 % (w/w) aqueous solution of cyanamide (mg/L)	Test concentration (% of nominal) samples taken after
	0 d	7 d
0.32	100.0	90.6
1.0	92.0	79.0
3.2	93.8	90.6
10.0	102.5	101.0
32.0	107.3	108.6

Effect of a 51.1 % (w/w) aqueous solution of Cyanamide on the growth and reproduction of Lemna gibba:

Nominal concentrations of a 51.1 % (w/w) aqueous solution of cyanamide (mg /L)	7-day mean frond number	7-day mean dry weight (mg)	Inhibition (%)
			Frond number	Dry weight	Area under the growth rate curve	Growth rate
Control	227.7	25.67	---	---	---	---
0.32	218.3	26.20	4.1	-2.2	3.1	1.4
1.0	205.7	25.87	5.8	-0.8	11.0	3.5
3.2	105.3	17.03	48.8	35.0*	47.7*	26.3*
10.0	50.0	6.33	52.5	78.4*	71.7*	51.5*
32.0	28.3	3.25	43.4	90.9*	88.0*	70.9*

Acute toxicity (7 d) of Cyanamide to Lemna gibba–Summary of endpoints:

Endpoint	Nominal concentration of a 51.1 % (w/w) aqueous solution of cyanamide
Biomass (area under growth curve):
EC50	4.56 mg/L (2.33 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)
Growth rate:
EC50	10.98 mg/L (5.61 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)
Dry weight:
EC50 4.7 mg/L	(2.4 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)

Validity criteria fulfilled:

yes

Conclusions:

Growth inhibition values obtained with the 51.1 % (w/w) aqueous solution of cyanamide on Lemna gibba were as follows: Considering the area under the growth curve (biomass), a 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

Executive summary:

The effects of SKW Cyanamid L500 (a 51.1 % (w/w) aqueous solution of cyanamide) on Lemna gibba G3 was determined in 20XAAP nutrient medium. Three replicates at test concentrations of 0.32, 1.0, 3.2, 10.0 and 32.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L, were incubated for 7 days. All chemical and physical parameters (pH, temperature) in the definitive test were within expected ranges. In the test medium the test item was sufficiently stable during the test period of 7 days. Therefore, all reported biological results are related to the nominal concentrations of the test item. The test item had a statistically significant inhibitory effect on the growth of Lemna gibba after the exposure of 7 days first at the nominal concentration of 3.2 mg test item/L, corresponding to 1.63 mg ai/L. The 7-day NOEC was determined at the nominal concentration of 1 mg test item/L, corresponding to 0.51 mg ai/L, since up to and including this test concentration the mean biomass, mean growth rates and the dry weight of Lemna gibba were not significantly lower than in the control. At the nominal test concentrations of 0.32 to 3.2 mg/L, corresponding to 0.163 to 1.63 mg ai/l, the shape of fronds and colonies after the test period of 7 days was not different to those in the control. However, at the two highest test concentrations of 10.0 and 32.0 mg/L (5.1 and 16.35 mg ai/L), the fronds were pale and small. A 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of Cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

Reference 2

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide.
Therefore, ecotoxicity in natural aquatic environments can be expressed in terms of cyanamide, irrespective of the substance constituting the exposure source. This is supported by experimental results: After stoichiometric correction of test concentrations, toxic effect values of cyanamide and calcium cyanamide are very similar in all standard test organisms. Thus, read-across from cyanamide to calcium cyanamide is justified for aquatic environmental endpoints.
For agricultural applications, calcium cyanamide is formulated as granules (PERLKA) that only slowly dissolve in a soil environment. Exposure of the aquatic environment will be exclusively due to runoff from agricultural fields. As above, cyanamide is the chemical moiety relevant for exposure due to rapid transformation from calcium cyanamide to cyanamide.
(Please note: direct release of the product to surface waters is strictly advised against, thus not a relevant exposure pathway.
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:

7 d

Dose descriptor:

EC50

Effect conc.:

2.33 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

biomass

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

biomass

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

5.61 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Duration:

7 d

Dose descriptor:

EC50

Effect conc.:

2.4 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: dry weight

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

0.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: dry weight

Details on results:

The doubling time of fronds in the controls was 1.7 d (39.5 h) and thus less than 2.5 d (60 h), corresponding to an approximately 19-fold increase in 7 days.The test item had a statistically significant inhibitory effect on the growth of Lemna gibba after the exposure of 7 days first at the nominal concentration of 3.2 mg test item/L, corresponding to 1.63 mg ai/L. The 7-day NOEC was determined at the nominal concentration of 1 mg test item/L, corresponding to 0.51 mg ai/L, since up to and including this test concentration the mean biomass, mean growth rates and the dry weight of Lemna gibba were not significantly lower than in the control. At the nominal test concentrations of 0.32 to 3.2 mg/L, corresponding to 0.163 to 1.63 mg ai/l, the shape of fronds and colonies after the test period of 7 days was not different to those in the control. However, at the two highest test concentrations of 10.0 and 32.0 mg/L (5.1 and 16.35 mg ai/L), the fronds were pale and small.

Results with reference substance (positive control):

No positive control

Reported statistics and error estimates:

The test groups were significantly different from controls according to the Dunnett-test criteria, p < 0.05.

In the test medium the test item was sufficiently stable during the test period of 7 days. Therefore, all reported biological results are related to the nominal concentrations of the test item.

Analytical determination of concentrations tested:

Nominal concentrations of a 51.1 % (w/w) aqueous solution of cyanamide (mg/L)	Test concentration (% of nominal) samples taken after
	0 d	7 d
0.32	100.0	90.6
1.0	92.0	79.0
3.2	93.8	90.6
10.0	102.5	101.0
32.0	107.3	108.6

Effect of a 51.1 % (w/w) aqueous solution of Cyanamide on the growth and reproduction of Lemna gibba:

Nominal concentrations of a 51.1 % (w/w) aqueous solution of cyanamide (mg /L)	7-day mean frond number	7-day mean dry weight (mg)	Inhibition (%)
			Frond number	Dry weight	Area under the growth rate curve	Growth rate
Control	227.7	25.67	---	---	---	---
0.32	218.3	26.20	4.1	-2.2	3.1	1.4
1.0	205.7	25.87	5.8	-0.8	11.0	3.5
3.2	105.3	17.03	48.8	35.0*	47.7*	26.3*
10.0	50.0	6.33	52.5	78.4*	71.7*	51.5*
32.0	28.3	3.25	43.4	90.9*	88.0*	70.9*

Acute toxicity (7 d) of Cyanamide to Lemna gibba–Summary of endpoints:

Endpoint	Nominal concentration of a 51.1 % (w/w) aqueous solution of cyanamide
Biomass (area under growth curve):
EC50	4.56 mg/L (2.33 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)
Growth rate:
EC50	10.98 mg/L (5.61 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)
Dry weight:
EC50 4.7 mg/L	(2.4 mg as/L)
No observed effect concentration (NOEC)	1.0 mg/L (0.5 mg as/L)

Validity criteria fulfilled:

yes

Conclusions:

Growth inhibition values obtained with the 51.1 % (w/w) aqueous solution of cyanamide on Lemna gibba were as follows: Considering the area under the growth curve (biomass), a 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide
Therefore, ecotoxicity in natural aquatic environments can be expressed in terms of cyanamide, irrespective of the substance constituting the exposure source. This is supported by experimental results: After stoichiometric correction of test concentrations, toxic effect values of cyanamide and calcium cyanamide are very similar in all standard test organisms. Thus, read-across from cyanamide to calcium cyanamide is justified for aquatic environmental endpoints.
For agricultural applications, calcium cyanamide is formulated as granules (PERLKA) that only slowly dissolve in a soil environment. Exposure of the aquatic environment will be exclusively due to runoff from agricultural fields. As above, cyanamide is the chemical moiety relevant for exposure due to rapid transformation from calcium cyanamide to cyanamide.
(Please note: direct release of the product to surface waters is strictly advised against, thus not a relevant exposure pathway.
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 SKW Cyanamid L500 (a 51.1 % (w/w) aqueous solution of cyanamide) on Lemna gibba G3 was determined in 20XAAP nutrient medium. Three replicates at test concentrations of 0.32, 1.0, 3.2, 10.0 and 32.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L, were incubated for 7 days. All chemical and physical parameters (pH, temperature) in the definitive test were within expected ranges. In the test medium the test item was sufficiently stable during the test period of 7 days. Therefore, all reported biological results are related to the nominal concentrations of the test item. The test item had a statistically significant inhibitory effect on the growth of Lemna gibba after the exposure of 7 days first at the nominal concentration of 3.2 mg test item/L, corresponding to 1.63 mg ai/L. The 7-day NOEC was determined at the nominal concentration of 1 mg test item/L, corresponding to 0.51 mg ai/L, since up to and including this test concentration the mean biomass, mean growth rates and the dry weight of Lemna gibba were not significantly lower than in the control. At the nominal test concentrations of 0.32 to 3.2 mg/L, corresponding to 0.163 to 1.63 mg ai/l, the shape of fronds and colonies after the test period of 7 days was not different to those in the control. However, at the two highest test concentrations of 10.0 and 32.0 mg/L (5.1 and 16.35 mg ai/L), the fronds were pale and small. A 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of Cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

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

In the absence of specific data for calcium cyanamide, information on the read-across substance cyanamide is used in the chemical safety assessment of calcium cyanamide:

Growth inhibition values obtained with the 51.1 % (w/w) aqueous solution of cyanamide on Lemna gibba were as follows:

Considering the area under the growth curve (biomass), a 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).

(No) observed effect values determined for the endpoint growth rate are carried forward in the chemical safety assessment.

Key value for chemical safety assessment

EC50 for freshwater plants:

5.61 mg/L

EC10 or NOEC for freshwater plants:

0.5 mg/L

Additional information

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide.

Therefore, ecotoxicity in natural aquatic environments can be expressed in terms of cyanamide, irrespective of the substance constituting the exposure source. This is supported by experimental results: After stoichiometric correction of test concentrations, toxic effect values of cyanamide and calcium cyanamide are very similar in all standard test organisms. Thus, read-across from cyanamide to calcium cyanamide is justified for aquatic environmental endpoints.

For agricultural applications, calcium cyanamide is formulated as granules (PERLKA) that only slowly degrade in a soil environment. Exposure of the aquatic environment will be exclusively due to runoff from agricultural fields. As above, cyanamide is the chemical moiety relevant for exposure due to rapid transformation from calcium cyanamide to cyanamide.

(Please note: direct release of the product to surface waters is strictly advised against, thus not a relevant exposure pathway.

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")

The effects of SKW Cyanamid L500 (a 51.1 % (w/w) aqueous solution of cyanamide) on Lemna gibba G3 was determined in 20XAAP nutrient medium. Three replicates at test concentrations of 0.32, 1.0, 3.2, 10.0 and 32.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L, were incubated for 7 days. All chemical and physical parameters (pH, temperature) in the definitive test were within expected ranges. In the test medium the test item was sufficiently stable during the test period of 7 days. Therefore, all reported biological results are related to the nominal concentrations of the test item. The test item had a statistically significant inhibitory effect on the growth of Lemna gibba after the exposure of 7 days first at the nominal concentration of 3.2 mg test item/L, corresponding to 1.63 mg ai/L. The 7-day NOEC was determined at the nominal concentration of 1 mg test item/L, corresponding to 0.51 mg ai/L, since up to and including this test concentration the mean biomass, mean growth rates and the dry weight of Lemna gibba were not significantly lower than in the control. At the nominal test concentrations of 0.32 to 3.2 mg/L, corresponding to 0.163 to 1.63 mg ai/l, the shape of fronds and colonies after the test period of 7 days was not different to those in the control. However, at the two highest test concentrations of 10.0 and 32.0 mg/L (5.1 and 16.35 mg ai/L), the fronds were pale and small. A 7-day EC50 of 4.56 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (2.33 mg as/L) was calculated, the corresponding NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). With respect to the growth rate, the 7-day EC50 was 10.98 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (5.61 mg as/L) and the respective NOEC was 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L). Finally, for the dry weight a 7-day EC50 of 4.7 mg of a 51.1 % (w/w) aqueous solution of Cyanamide/L (2.4 mg as/L) was determined with a corresponding NOEC of 1.0 mg of a 51.1 % (w/w) aqueous solution of cyanamide/L (0.5 mg as/L).