Calcium cyanamide

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

form 2010-03-17 to 2010-08-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))

Version / remarks:

Regulation No 440/2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Version / remarks:

adopted 2001-01-22

Deviations:

no

GLP compliance:

yes

Type of method:

HPLC estimation method

Media:

soil

Radiolabelling:

no

Test temperature:

Column temperature: 35°C

Details on study design: HPLC method:

Selection of pH
According to the guideline two tests should be performed, for ionisable substances with both ionised and non-ionised forms but only in cases where at least 10 % of the test compound will be dissociated within pH 5.5 to 7.5. The test substance is a mixture of many components. The main component "Calcium cyanamide" is a salt. At any pH value the main component dissociates in water. The adsorption coefficient can therefore not be determined of the non-ionised form. Two tests were performed to determine the adsorption coefficient of the test substance at different pH values (5.5 and 7.5).

HPLC - system
System: Finnigan Surveyor
Column: LiChrospher 100 CN 5 μm 150*3 mm; Col. No. Q31021 ARC Seibersdorf
Column temperature: 35 °C
Mobile phase test 1 at pH 5.5: 40% methanol (Chromasolv, Sigma-Aldrich, Lot. No. SZBAO21S) 60% buffer* pH 5.5 in water
Mobile phase test 2 at pH 7.5: 40% methanol (Chromasolv, Sigma-Aldrich, Lot. No. SZBAO21S) 60% buffer* pH 7.5 in water
Flow: 0.5 mL/min
Injection volume: 10 μL
Detection: UV-absorption at 210 nm.
Buffer: 10 mMol/L potassiumdihydrogencitrate in water adjusted with sodium hydroxide to pH 5.5 respectively to pH 7.5.
The pH of the mobile phase was determined during the run with a pH-meter (InoLab pH Level 2; WTW, Germany).

Calculation of dead time
The dead time t0 was determined by an unretained compound (sodium nitrate; assay 99.6 %; Lot 50330; Riedel de Haen).

Calibration graph
According to the guidelines a minimum of six reference points, if possible at least one above and one below the expected value of the test substance should be used. Freshly prepared solutions of four reference compounds (see Table 1) in the mobile phase were injected individually to identify their peak in this HPLC-system. Then they were injected simultaneously (before and after the test substance) and the exact retention times were determined in duplicate. The corresponding capacity factors and logarithms of the capacity factors were calculated and plotted as a function of the log KOC.
A linear regression line was calculated from the data of this graph. The log KOC values of the reference compounds are described in the guidelines.

Determination of the adsorption coefficient of the test substance
The tests were performed with freshly prepared solutions of 39.0 mg respectively 41.4 mg of "Calcium cyanamide" per litre mobile phase. The retention time of the test substance was determined in duplicate and the capacity factor k was calculated.

Analytical monitoring:

not required

Details on sampling:

NA

Details on matrix:

NA

Details on test conditions:

NA

Computational methods:

Estimation of the log KOC
The adsorption coefficient KOC of "Calcium cyanamide" was estimated by an atom/fragment contribution method using the software KOCWIN Version v2.00, provided by the U.S. Environmental Protection Agency.
PCKOCWIN estimates Koc with two separate estimation methodologies:
(1) estimation using first-order Molecular Connectivity Index (MCI)
(2) estimation using log Kow (octanol-water partition coefficient)
The structure of the substance is entered into the program by SMILES (Simplified Molecular Input Line Entry System) notations.

Key result

Type:

log Koc

Value:

< 1.25

pH:

5.5

Temp.:

35 °C

Key result

Type:

log Koc

Value:

< 1.25

pH:

7.5

Temp.:

35 °C

Details on results (HPLC method):

Preliminary result
The calculated adsorption coefficients log KOC of "Calcium cyanamide" are: 0.9 (MCI) and 1.2 (log Kow)

Test 1 at pH 5.5:
The actual pH value of the mobile phase during the test was 5.5.
The temperature during the test was 35 °C.
The calibration curve of the reference substances was: log k' = 0.4148 x log KOC – 0.5753.
The adsorption coefficient log KOC of "Calcium cyanamide" is <1.25.
The experimentally determined log KOC is outside the range (1.5 to 5.0) for which the method is published in the guideline. The log KOC was therefore only determined with four reference substances and no further tests were performed.

Test 2 at pH 7.5:
The actual pH value of the mobile phase during the test was 7.5.
The temperature during the test was 35 °C.
The calibration curve of the reference substances was: log k' = 0.4105 x log KOC – 0.5538.
The adsorption coefficient log KOC of "Calcium cyanamide" is <1.25.
The experimentally determined log KOC is outside the range (1.5 to 5.0) for which the method is published in the guideline. The log KOC was therefore only determined with four reference substances and no further tests were performed.

Adsorption and desorption constants:

NA

Recovery of test material:

NA

Concentration of test substance at end of adsorption equilibration period:

NA

Concentration of test substance at end of desorption equilibration period:

NA

Details on results (Batch equilibrium method):

NA

Statistics:

NA

Validity criteria fulfilled:

yes

Conclusions:

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

Executive summary:

The adsorption/desorption characteristics of Calcium cyanamide, technical grade (Kalkstickstoff) was studied using the HPLC estimation method. The experiment was conducted in accordance with Regulation (EC) No 440/2008, Method C.19 and OECD Guideline No. 121 for the testing of chemicals, adopted on 22 January 2001, and in compliance with GLP.

According to the guideline, two tests should be performed for ionisable substances with both ionised and non-ionised forms but only in cases where at least 10 % of the test compound will be dissociated within pH 5.5 to 7.5. The test substance is a mixture of many components. The main component "Calcium cyanamide" is a salt. At any pH value the main component dissociates in water. The adsorption coefficient can therefore not be determined of the non-ionised form. Two tests were performed to determine the adsorption coefficient of the test substance at different pH values (5.5 and 7.5).

The log Koc of Calcium cyanamide, technical grade (Kalkstickstoff) was measured to be <1.25 at pH 5.5 and 7.5. The experimentally determined log KOC is outside the range (1.5 to 5.0) for which the method is published in the guideline. The log KOC was therefore only determined with four reference substances and no further tests were performed.

In addition, the log KOC of the main component Calcium cyanamide was estimated using an atom/fragment contribution method (Software KOCWIN© v 2.00) revealing a value of 0.9 respectively 1.2, which is in line with the measure values.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

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

Adequacy of study:

supporting study

Justification for type of information:

Information on the adsorption of cyanamide in soil 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 adsorption of cyanamide in soil are relevant in the 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

Type:

Koc

Value:

> 0 - < 6.8 L/kg

Adsorption and desorption constants:

Adsorption coefficients Koc: For the soil Hörstel adsorption coefficients, normalised to organic carbon Koc, of approximately 6.81 mL/g and 4.35 mL/g were calculated for the high (8.97 mg/L) and low (0.89 mg/L) test concentrations, respectively. For the soil Jülich the Koc value was calculated to be 6.34 mL/g, whereas with the soil Borstel Ap no adsorption was detectable.
The adsorption was measured as disappearance of the test substance from the aqueous phase. It was calculated as difference between the concentration of the test substance in a control solution and the concentration in the respective test solution (concentrations as determined by LSC). This difference was small in relation to the relatively high original LSC value and it was in the same order of magnitude as the standard deviation of the LSC results. Therefore, the error of determination is relatively high and the calculated distribution coefficients are scattering around the zero value.

Recovery of test material:

Not indicated

Concentration of test substance at end of adsorption equilibration period:

The results indicate that at the end of the adsorption kinetics the cyanamide concentration in the samples was only slightly decreased (< 10 %) in comparison to the controls (CaCl2-solution with test substance, but without soil).

Concentration of test substance at end of desorption equilibration period:

In compliance with the guideline, the desorption part of the study was not performed, because significant adsorption (approximately 25 % or less) had not occurred.

Sample no.:

#1

Duration:

48 h

% Adsorption:

< 2

Sample no.:

#2

Duration:

48 h

% Adsorption:

< 2

Sample no.:

#3

Duration:

48 h

% Adsorption:

< 2

Sample no.:

#4

Duration:

48 h

% Adsorption:

< 2

Transformation products:

not measured

Details on results (Batch equilibrium method):

Adsorption coefficients Koc:
In all samples the adsorption of cyanamide to soil was low. After 48 hour, the adsorption was less than 2 % for all soils and both concentrations. The highest adsorption was measured for the soil Hörstel (1.88 % after 52 hours). For the soil Hörstel adsorption coefficients, normalised to organic carbon Koc, of approximately 6.81 mL/g and 4.35 mL/g were calculated for the high (8.97 mg/L) and low (0.89 mg/L) test concentrations, respectively. For the soil Jülich the Koc value was calculated to be 6.34 mL/g, whereas with the soil Borstel Ap no adsorption was detectable.
The adsorption was measured as disappearance of the test substance from the aqueous phase. It was calculated as difference between the concentration of the test substance in a control solution and the concentration in the respective test solution (concentrations as determined by LSC). This difference was small in relation to the relatively high original LSC value and it was in the same order of magnitude as the standard deviation of the LSC results. Therefore, the error of determination is relatively high and the calculated distribution coefficients are scattering around the zero value.
Stability of cyanamide:
At the end of the adsorption kinetic TLC analyses were performed in order to check if a degradation of the test substance had occurred. The results indicate that at the end of the adsorption kinetics the cyanamide concentration in the samples was only slightly decreased (< 10 %) in comparison to the controls (CaCl2-solution with test substance, but without soil).
Desorption:
In compliance with the guideline, the desorption part of the study was not performed, because significant adsorption (approximately 25 % or less) had not occurred.

Statistics:

Not indicated

Adsorption of¹⁴C-hydrogen cyanamide in three soils:

	Soil Type	pH (H2O)	Organic Carbon (%)	Kd (mL/g)	Koc (mL/g)
Hörstel (8.97 mg/L)	acidic sand	5.3	1.35	0.092	6.81
Hörstel (0.89 mg/L)	acidic sand	5.3	1.35	0.059	4.35
Jülich	loamy silt	7.1	0.95	0.060	6.34
Borstel Ap	slightly acidic silty sand	5.8	1.35	0	0
arithmetic mean					4.38

Validity criteria fulfilled:

yes

Conclusions:

The derived Koc-values (0- 6.81 mL/g) indicate that cyanamide will not be adsorbed in soils and point towards a high mobility potential of cyanamide in soil.
Information on the adsorption of cyanamide in soil 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 slowly 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 adsorption of cyanamide in soil are relevant in the 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:

Test system

The adsorption/desorption characteristics of cyanamide on three soils were investigated: acidic sand (Hörstel), loamy silt (Jülich), and slightly acidic silty sand (Borstel Ap). The air-dried soil samples were equilibrated by shaking with 0.01 M CaCl2 solution (1:2.5, w/w) for 6 hours. Afterwards the samples were sterilised because cyanamide is suspected to be liable to biotic breakdown during the test. The samples were centrifuged and the CaCl2 solution decanted. Fresh CaCl2 solution was added to yield a soil/aqueous phase ration of 1:5 (w/w). [14C]-cyanamide dissolved in methanol was added to the soil suspensions in the CaCl2 solution to give a nominal concentration of 8.97 mg cyanamide/L. For the soil “Hörstel” an additional adsorption kinetic was performed with an initial concentration of 0.89 mg cyanamide/L. Samples were shaken at 20–25 °C and at each sampling point an aliquot of the supernatant was sampled and the tubes shaken again.

The following sampling points were chosen:

Hörstel (8.97 mg/L): 0.5, 2, 4, 9, 27 and 52 h

Hörstel (0.89 mg/L): 0.5, 1, 2, 6, 24 and 48 h

Jülich (8.97 mg/L): 0.8, 1.5, 2, 6, 30 and 96 h

Borstel Ap (8.97 mg/L): 0.8, 1.5, 2, 6, 24 and 48 h

Analytical method

At the end of the adsorption kinetics (after 48–96 hours) the supernatants were analysed by LSC and TLC using a linear analyser for the radioactive spots and UV detection for the nonlabelled reference substances.

Linear distribution coefficients (Kd) were calculated from the mean ratios of test substance adsorbed to test substance in the aqueous phase. In addition, the distribution coefficients Kd were related to the content of organic carbon of the soil sample and expressed as Koc.

Adsorption coefficients Koc

In all samples the adsorption of cyanamide to soil was low. After 48 hour, the adsorption was less than 2 % for all soils and both concentrations. The highest adsorption was measured for the soil Hörstel (1.88 % after 52 hours). For the soil Hörstel adsorption coefficients, normalised to organic carbon Koc, of approximately 6.81 mL/g and 4.35 mL/g were calculated for the high (8.97 mg/L) and low (0.89 mg/L) test concentrations, respectively. For the soil Jülich the Koc value was calculated to be 6.34 mL/g, whereas with the soil Borstel Ap no adsorption was detectable.

The adsorption was measured as disappearance of the test substance from the aqueous phase. It was calculated as difference between the concentration of the test substance in a control solution and the concentration in the respective test solution (concentrations as determined by LSC). This difference was small in relation to the relatively high original LSC value and it was in the same order of magnitude as the standard deviation of the LSC results. Therefore, the error of determination is relatively high and the calculated distribution coefficients are scattering around the zero value.

Stability of cyanamide

At the end of the adsorption kinetic TLC analyses were performed in order to check if a degradation of the test substance had occurred. The results indicate that at the end of the adsorption kinetics the cyanamide concentration in the samples was only slightly decreased (< 10 %) in comparison to the controls (CaCl2-solution with test substance, but without soil).

Desorption

In compliance with the guideline, the desorption part of the study was not performed, because significant adsorption (approximately 25 % or less) had not occurred.

Conclusion

The derived Koc-values (0–6.81 mL/g) indicate that cyanamide will not be adsorbed in soils and point towards a high mobility potential of cyanamide in soil.

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

For justification of read-across for environmental endpoints please refer to the section "conclusion".

Description of key information

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

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.

For the purpose of exposure scenario building, the arithmetic mean value of Koc = 4.38 mL/g for cyanamide is included as key value for chemical safety assessment.

Key value for chemical safety assessment

Koc at 20 °C:

4.38

Additional information

The adsorption/desorption characteristics of calcium cyanamide, technical grade (Kalkstickstoff) was studied using the HPLC estimation method. The experiment was conducted in accordance with Regulation (EC) No 440/2008, method C.19 and OECD guideline no. 121 for the testing of chemicals, adopted on 22 January 2001, and in compliance with GLP.

According to the guideline, two tests should be performed for ionisable substances with both ionised and non-ionised forms but only in cases where at least 10 % of the test compound will be dissociated within pH 5.5 to 7.5. The test substance is a mixture of many components. The main component "Calcium cyanamide" is a salt. At any pH value the main component dissociates in water. The adsorption coefficient can therefore not be determined of the non-ionised form. Two tests were performed to determine the adsorption coefficient of the test substance at different pH values (5.5 and 7.5).

The log Koc of Calcium cyanamide, technical grade (Kalkstickstoff) was measured to be < 1.25 at pH 5.5 and 7.5. The experimentally determined log KOC is outside the range (1.5 to 5.0) for which the method is published in the guideline. The log KOC was therefore only determined with four reference substances and no further tests were performed.

In addition, the log KOC of the main component Calcium cyanamide was estimated using an atom/fragment contribution method (Software KOCWIN© v 2.00) revealing a value of 0.9 respectively 1.2, which is in line with the measure values.

In addition, information on the structural analogue hydrogen cyanamide is taken into account in a read-across approach:

The adsorption/desorption characteristics of cyanamide was investigated in three different soils: acidic sand (Hörstel), loamy silt (Jülich), and slightly acidic silty sand (Borstel Ap). The samples were sterilised because cyanamide is suspected to be liable to biotic breakdown during the test. Nominal concentration of 8.97 mg cyanamide/L was applied. For the soil ”Hörstel” an additional adsorption kinetic was performed with an initial concentration of 0.89 mg cyanamide/L. Samples were shaken at 20 - 25°C and at each sampling point (until 96 h) an aliquot of the supernatant was sampled and the tubes shaken again.

In all samples the adsorption of cyanamide to soil was low. After 48 hour, the adsorption was less than 2% for all soils and both concentrations. The highest adsorption was measured for the soil Hörstel (1.88% after 52 hours). For the soil Hörstel adsorption coefficients, normalised to organic carbon Koc, of approximately 6.81 mL/g and 4.35 mL/g were calculated for the high (8.97 mg/L) and low (0.89 mg/L) test concentrations, respectively. For the soil Jülich the Koc value was calculated to be 6.34 mL/g, whereas with the soil Borstel Ap no adsorption was detectable.

In compliance with the guideline, the desorption part of the study was not performed, because significant adsorption (approximately 25% or less) had not occurred.

The derived Koc-values (0- 6.81 mL/g) and Kd (0 -0.09 mL/g) indicate that cyanamide will not be adsorbed in soils and point towards a high mobility potential of cyanamide in soil.

Read-across is justified, as calcium cyanamide is in water 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 adsorption of cyanamide in soil are relevant in the 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"