Calcium cyanamide

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water and sediment: simulation testing, other

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, fate in natural aquatic environments can be expressed in terms of cyanamide, irrespective of the substance constituting the exposure source. Thus, read-across from cyanamide to calcium cyanamide is justified for aquatic environmental endpoints.
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

Test performance:

No unusual observations during test and no other information affecting results.

Compartment:

other: water / sediment, material (mass) balance

Remarks on result:

other: For an appropriate detailed answer, see in fields: "Details on results" and "Remarks on results including table".

Key result

Compartment:

water

DT50:

ca. 2.3 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: in the river system

Key result

Compartment:

water

DT50:

ca. 4.3 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: in the pond system

Key result

Compartment:

entire system

DT50:

ca. 2.5 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: in the river system

Key result

Compartment:

entire system

DT50:

ca. 4.8 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: in the pond system

Key result

Compartment:

water

DT50:

ca. 7.7 d

Type:

other: DT90

Remarks on result:

other: in the river system

Key result

Compartment:

water

DT50:

ca. 14.4 d

Type:

other: DT90

Remarks on result:

other: in the pond system

Key result

Compartment:

entire system

DT50:

ca. 8.2 d

Type:

other: DT90

Remarks on result:

other: in the river system

Key result

Compartment:

entire system

DT50:

ca. 15.8 d

Type:

other: DT90

Remarks on result:

other: in the pond system

Transformation products:

yes

No.:

#1

Details on transformation products:

In the river system, cyanamide was degraded to 8 minor radioactive fractions. Two degradation products were identified as urea and dicyandiamide amounting to 6.7 % and 0.3 % of applied radioactivity, respectively. One degradation product, which accounted for 5.5 % of applied radioactivity, did not co-chromatograph with the available reference standards. All other degradation products present did not exceed a maximum level of 0.3 % of applied radioactivity. In the pond system, cyanamide was degraded to 4 components. Urea was the main degradation product amounting to a maximum of 13.4 % of applied radioactivity on day 1 and decreasing continuously thereafter to represent 1.2 % of the applied radioactivity on day 21. All other degradation products present did not exceed a maximum level of 5 % of applied radioactivity.
DT50 and DT90 values of urea:
The DT50 and DT90 values of urea were also calculated using first-order kinetics. The DT50 values in the water phase were calculated to be 2.7 and 7.5 days for the river and pond systems, respectively, and the DT90 values were determined to be 9.1 days and 11.6 days, respectively. In the total water sediment systems urea was degraded with half-lives of 2.9 days (river) and 8.0 days (pond). The DT90 values for the total systems were calculated to be 9.6 days in the river system and 26.7 days in the pond system.

Evaporation of parent compound:

no

Volatile metabolites:

yes

Residues:

yes

Details on results:

Mass balance:
Total mean recoveries obtained during the study were 95.4 ± 4.1 % and 95.7 ± 4.0 % of the applied radioactivity for the river and pond systems, respectively.
Distribution between water and sediment:
Radioactivity in the water phases of both test systems decreased continuously throughout the incubation period reaching 0.2 % (river) and 0.8 % (pond) after 28 days. The extractable radioactivity from sediments increased to maximum amounts of 4.9 % for river and 8.2 % for pond on days 2 and 6, respectively, and decreased thereafter to 0.7 % (river) and 1.2 % (pond) of the applied radioactivity on day 28.
Non-extractable residues:
Non-extractable residues in the sediment increased during the incubation period and peaked at 11.0 % and 7.8 % of the applied radioactivity on days 28 and 21 for the river and pond system, respectively.
Volatile degradation products:
The formation of CO2 was very high, accounting for a maximum of 86.1 % and 83.5 % of the applied radioactivity on day 28 for the river and pond systems, respectively. Other volatile compounds did not exceed 0.1 % of the applied radioactivity.
Cyanamide concentrations:
The amount of [14C]-cyanamide in the water phases decreased continuously to a minimum of 0.1 % of applied radioactivity on days 12 and 28 in the river and pond systems, respectively. In the sediment extracts of the river system, cyanamide was detected from day 1 to day 6 at a maximum concentration of 3.1 % of applied radioactivity. In pond sediment extracts cyanamide was detected from day 1 to day 12 amounting to a maximum of 4.7 % of applied radioactivity.
Principal degradation products:
In the river system, cyanamide was degraded to 8 minor radioactive fractions. Two degradation products were identified as urea and dicyandiamide amounting to 6.7 % and 0.3 % of applied radioactivity, respectively. One degradation product, which accounted for 5.5 % of applied radioactivity, did not co-chromatograph with the available reference standards. All other degradation products present did not exceed a maximum level of 0.3 % of applied radioactivity. In the pond system, cyanamide was degraded to 4 components. Urea was the main degradation product amounting to a maximum of 13.4 % of applied radioactivity on day 1 and decreasing continuously thereafter to represent 1.2 % of the applied radioactivity on day 21. All other degradation products present did not exceed a maximum level of 5 % of applied radioactivity.
DT50 and DT90 values of cyanamide:
The degradation of cyanamide in water/sediment systems was best described by first order degradation kinetics. The DT50 values in the water phase were calculated to be 2.3 and 4.3 days for the river and pond systems, respectively, and the DT90 values were determined to be 7.7 days and 14.4 days, respectively. In the total water sediment systems cyanamide was degraded with half-lives of 2.5 days (river) and 4.8 days (pond). The DT90 values for the total systems were calculated to be 8.2 days in the river system and 15.8 days in the pond system.
DT50 and DT90 values of urea:
The DT50 and DT90 values of urea were also calculated using first-order kinetics. The DT50 values in the water phase were calculated to be 2.7 and 7.5 days for the river and pond systems, respectively, and the DT90 values were determined to be 9.1 days and 11.6 days, respectively. In the total water sediment systems urea was degraded with half-lives of 2.9 days (river) and 8.0 days (pond). The DT90 values for the total systems were calculated to be 9.6 days in the river system and 26.7 days in the pond system

Results with reference substance:

No reference substance

Percent distribution of applied radioactivity and mass balance in water/sediment systems treated with [¹⁴C]-Cyanamide:

Day	Organic volatiles	CO2	Radioactivity in water	Sediment extractable	Sediment unextractable	Total recovered
	[% of applied radioactivity]
	River
0	n.a.	n.a.	102.2	0.3	0.4	102.8
1	< 0.1	5.0	85.7	4.5	1.2	96.4
2	< 0.1	12.3	69.9	4.9	3.3	90.4
6	< 0.1	67.8	16.8	3.9	6.1	94.5
12	< 0.1	79.6	0.6	2.4	10.7	93.3
21	< 0.1	81.8	0.3	0.9	9.3	92.3
28	< 0.1	86.1	0.2	0.7	11.0	98.0
	Pond
0	n.a.	n.a.	98.5	0.5	0.2	99.2
1	< 0.1	5.3	86.1	6.3	1.5	99.1
2	< 0.1	7.7	83.1	7.2	2.1	100.1
6	< 0.1	28.6	53.3	8.2	3.9	94.0
12	< 0.1	66.4	13.3	5.0	5.4	90.1
21	< 0.1	81.9	4.0	2.2	7.8	95.9
28	< 0.1	83.5	0.8	1.2	6.0	91.6

n.a.: not analysed

Percent distribution of applied radioactivity and mass balance in water phase of an aerobic aquatic system treated with [¹⁴C]-Cyanamide:

Day	Cyanamide		Urea		Dicyandiamide
	water phase	sediment	water phase	sediment	water phase	sediment
	[% of applied radioactivity]
	River
0	101.2	n.a.	n.d.	n.a.	n.d.	n.a.
1	76.9	3.1	5.8	0.4	n.d.	n.d.
2	59.3	3.1	6.1	0.6	n.d.	n.d.
6	13.1	1.5	1.4	0.4	n.d.	0.3
12	0.1	n.a.	0.1	n.a.	n.d.	n.a.
21	n.d.	n.a.	n.d.	n.a.	n.d.	n.a.
28	n.d.	n.a.	n.d.	n.a.	n.d.	n.a.
	Pond
0	96.7	n.a.	n.d.	n.a.	n.d.	n.d.
1	72.0	4.0	11.8	1.6	n.d.	n.d.
2	72.0	4.7	8.6	1.6	n.d.	n.d.
6	43.3	4.7	5.3	1.1	n.d.	n.d.
12	6.9	2.0	5.5	1.4	n.d.	n.d.
21	1.3	n.a.	1.2	n.a.	n.d.	n.d.
28	0.1	n.a.	n.d.	n.a.	n.d.	n.d.

n.a.: not analysed due to the low amount extracted

n.d.: not detected or below limit of quantification

DT₅₀and DT₉₀values for cyanamide and urea in water/sediment systems:

	System	DT50(days)	DT90(days)	r^2
Cyanamide		River
	water	2.3	7.7	0.9969
	total system	2.5	8.2	0.9957
		Pond
	water	4.3	14.4	0.9898
	total system	4.8	15.8	0.9895
Urea		River
	water	2.7	9.1	0.966
	total system	2.9	9.6	0.965
		Pond
	water	7.5	11.6	0.939
	total system	8.0	26.7	0.935

Validity criteria fulfilled:

yes

Conclusions:

It can be concluded that the elimination of [14C]-cyanamide from the water/sediment systems proceeded mainly via mineralisation to CO2. Degradation of cyanamide to other metabolites and incorporation into the organic matter of the sediment were of minor importance. The estimated half-life of cyanamide from the water phase of the aquatic systems was 2.3 days for the river system and 4.3 days for the pond system, respectively. One major metabolite was detected in the pond system (13.4 % of applied radioactivity) and identified as urea. The estimated DT50 value of urea was 7.6 days in the total pond system indicating a transient nature. In the river system no metabolite exceeded the 10 % level.

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide.
Therefore, fate in natural aquatic environments can be expressed in terms of cyanamide, irrespective of the substance constituting the exposure source. Thus, read-across from cyanamide to calcium cyanamide is justified for aquatic environmental endpoints.
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 aerobic aquatic degradation of [14C]-cyanamide was studied in two disparate water/sediment systems: pond and river system. After acclimatisation of the two systems the test solution was applied dropwise on the water surface of each test system at a nominal rate of 3.0 mg as/L corresponding to a field application rate of 30 kg as/ha. After treatment, the samples were connected to flow-through systems and incubated at 20 ± 1 °C in the dark for a period of 28 days. For the trapping of volatile degradation products the test vessels were connected to NaOH and ethylene glycol traps. Samples were taken immediate after application and after 1, 2, 6, 12, 21 and 28 days.

Results showed that the elimination of [14C]-cyanamide from the water/sediment systems proceeded mainly via mineralisation to CO2. Degradation of Cyanamide to other metabolites and incorporation into the organic matter of the sediment were of minor importance. The estimated half-life (TD50) of Cyanamide from the water phase of the aquatic systems was 2.3 days for the river system and 4.3 days for the pond system, respectively and the DT90 values were determined to be 7.7 days and 14.4 days, respectively. In the total water sediment systems Cyanamide was degraded with half-lives of 2.5 days (river) and 4.8 days (pond). The DT90 values for the total systems were calculated to be 8.2 days in the river system and 15.8 days in the pond system.

One major metabolite was detected in the pond system (13.4 % of applied radioactivity) and identified as urea. The DT50 and DT90 values of urea were also calculated using first-order kinetics. The DT50 values in the water phase were calculated to be 2.7 and 7.5 days for the river and pond systems, respectively, and the DT90 values were determined to be 9.1 days and 11.6 days, respectively. In the total water sediment systems urea was degraded with half-lives of 2.9 days (river) and 8.0 days (pond). The DT90 values for the total systems were calculated to be 9.6 days in the river system and 26.7 days in the pond system.

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

Read-across from hydrogen cyanamide to calcium cyanamide was performed to demonstrate biodegradation in water/sediment systems. Read-across is justified as calcium cyanamide is rapidly transformed to cyanamide in aqueous solution. For further information on read-across for environmental endpoints please refer to the document in IUCLID section 13.

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. 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 at significant amounts.

Key value for chemical safety assessment

Half-life in freshwater:

4.3 d

at the temperature of:

293 K

Additional information

Read-across from hydrogen cyanamide was performed to demonstrate biodegradation in water/sediment systems. Read-across is justified as calcium cyanamide is rapidly transformed cyanamide in aqueous solution. (For further information on read-across for environmental endpoints please refer to the document in IUCLID section 13.)

The aerobic aquatic degradation of [14C]-cyanamide was studied in two disparate water/sediment systems: pond and river system. After acclimatisation of the two systems the test solution was applied dropwise on the water surface of each test system at a nominal rate of 3.0 mg as/L corresponding to a field application rate of 30 kg as/ha. After treatment, the samples were connected to flow-through systems and incubated at 20 ± 1°C in the dark for a period of 28 days. For the trapping of volatile degradation products the test vessels were connected to NaOH and ethylene glycol traps. Samples were taken immediate after application and after 1, 2, 6, 12, 21 and 28 days.

Results showed that the elimination of [14C]-cyanamide from the water/sediment systems proceeded mainly via mineralisation to CO₂. 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 no longer detectable in both aquatic systems. In the sediments, neither the parent substance nor degradation products were detected in significant amounts.

Biological degradation in water/sediment i.e. in biologically active water systems plays the most important role for cyanamide dissipation in aquatic systems. Photolysis plays a minor role in the degradation of cyanamide in water.

In general for calcium cyanamide, a very fast degradation and mineralisation to CO₂ can be expected under environmental conditions.