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Environmental fate & pathways

Phototransformation in water

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Link to relevant study record(s)

Reference
Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1991-06-26 until 1991-12-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
Qualifier:
according to guideline
Guideline:
EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)
Version / remarks:
October 1982
Deviations:
no
GLP compliance:
yes
Radiolabelling:
yes
Analytical method:
other: TLC
Details on sampling:
Non-exposed and exposed samples were analysed at 0, 1, 3, 7, 14, 21 and 30 days for total radioactivity by LSC.
Buffers:
The photolytic stability of [14C]-cyanamide was studied in aqueous solutions buffered at pH values of 5 and 7.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
290
Details on light source:
Test samples were installed in a photolysis chamber using a xenon arc lamp (290 - 400 nm). In addition dark controls, wrapped in foil, were incubated in the photolysis chamber.
Details on test conditions:
14C-cyanamide was dissolved in methanol (262 µg/mL) and a [12C]/[14C]-isotopic dilution was prepared by adding 924 mg of non-radiolabelled cyanamide to the stock solution in order to ensure an adequate amount of test material resulting in a concentration of 18.7 mg as/mL (radiochemical purity: 96.8 %). Aqueous solutions with [14C]-cyanamide were prepared at nominal concentrations of 20 µg/mL and were continuously irradiated under sterile conditions for up to 30 days at 25 ± 1 °C in a photolysis chamber using a xenon arc lamp. In addition dark controls, wrapped in foil, were incubated in the photolysis chamber.
Duration:
30 d
Temp.:
25 °C
Initial conc. measured:
20 other: µg/mL
Reference substance:
no
Dark controls:
yes
Computational methods:
The rate of degradation of cyanamide was determined using linear regression assuming first order reaction kinetics (DT50).
Preliminary study:
No
Test performance:
No special remarks
Key result
% Degr.:
48.2
Sampling time:
30 d
Test condition:
Light exposed samples at pH 5
Key result
% Degr.:
58.2
Sampling time:
30 d
Test condition:
Light exposed samples at pH 7
% Degr.:
80.5
Sampling time:
30 d
Test condition:
Dark control samples at pH 5
% Degr.:
86.6
Sampling time:
30 d
Test condition:
Dark control samples at pH 7
Key result
DT50:
28.9 d
Test condition:
Light exposed samples at pH 5
DT50:
116 d
Test condition:
Non-exposed samples at pH 5
Key result
DT50:
38.5 d
Test condition:
Light exposed samples at pH 7
DT50:
139 d
Test condition:
Non-exposed samples at pH 7
Predicted environmental photolytic half-life:
Under laboratory conditions (Xenon lamp 290 - 400 nm), cyanamide was moderately degraded. Quantum yield was not determined in the presented study, since the adsorption coefficient at 290 nm is below 10 in UV-VIS spectra. Therefore, it can be concluded that in contrary to the laboratory conditions natural irradiation in Central Europe does not cause relevant direct photolytic degradation.
Transformation products:
yes
No.:
#1
Details on results:
Degradation of the test substance cyanamide was observed in the exposed systems of both buffer solutions. The cyanamide concentration in the light exposed samples decreased after 30 days to 48.2 % of initial measured dose (IMD) and 58.2 % of IMD at pH 5 and pH 7, respectively. In the dark control samples the cyanamide concentration decreased to 80.5 % and 86.6 % of IMD at pH 5 and pH 7 after 30 days.

One major degradation product, identified as urea, was detected in the light exposed samples at maximum concentrations of 12.2 % of initial measured dose (IMD) at pH 7 and 42.4 % of IMD at pH 5. Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD.
Photolytic half-lives were calculated using first-order degradation kinetics and were determined to be 28.9 d and 38.5 d in the light exposed samples at pH 5 and pH 7, respectively. DT50 values of the dark control samples were calculated to be 116 d and 139 d at pH 5 and pH 7, respectively.
Results with reference substance:
No reference substance

- The mass balance in light exposed and dark control samples ranged from 89.1 to 103 % of applied radioactivity with mean recoveries of 98.3 % for light exposed samples and 96.1 % for dark control samples


- Quantum yield was not determined in the presented study, since the adsorption coefficient at 290 nm is below 10 in UV-VIS spectra


- Under laboratory conditions (Xenon lamp 290 - 400 nm), cyanamide was moderately degraded


Photochemical degradation of14C-Cyanamide in sterile buffers:


























































































Time



System



pH 5



pH 7



Total14C



Cyanamide



Urea



Total14C



Cyanamide



Urea



0





100



94.0



n.d.



100



96.7



n.d.



1



NON


EXP



99.5


100



95.1


96.3



n.d.


n.d.



103


102



99.8


95.6



n.d.


n.d.



3



NON


EXP



100


100



93.1


91.9



1.96


3.28



100


101



96.5


91.1



n.d.


1.78



7



NON


EXP



100


99.0



89.7


87.6



4.32


6.59



102


101



96.9


87.1



n.d.


3.49



14



NON


EXP



91.7


95.1



81.6


70.3



4.77


19.3



94.6


90.1



88.7


70.9



n.d.


6.57



21



NON


EXP



92.6


93.1



82.5


56.7



5.60


30.5



94.6


89.1



87.3


61.6



n.d.


9.0



30



NON


EXP



92.6


93.6



80.5


48.2



8.18


42.4



94.1


89.6



86.6


58.2



n.d.


12.2



 


Photochemical degradation of [14C]-Cyanamide in sterile buffers:


































pH



System



DT50[d]



R2



5



NON



116



0.9282



EXP



28.9



0.9924



7



NON



139



0.9293



EXP



38.5



0.9827



 

Validity criteria fulfilled:
yes
Conclusions:
The results show that photodegradation of cyanamide occurred in aqueous solution buffered at pH 5 and 7. Photolytic half-lives were calculated to be 28.9 d and 38.5 d in the light exposed samples at pH 5 and pH 7, respectively. Urea was detected as major degradation product in the light-exposed samples at maximum concentrations of 12.2 % of IMD at pH 7 and 42.4 % of IMD at pH 5. Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD. These data indicate that photolysis is a more significant degradation pathway at pH 5 and pH 7 (25 °C) than hydrolysis
2. Under laboratory conditions (Xenon lamp 290 - 400 nm), cyanamide was moderately degraded. Quantum yield was not determined in the presented study, since the adsorption coefficient at 290 nm is below 10 in UV-VIS spectra. Therefore, it can be concluded that in contrary to the laboratory conditions natural irradiation in Central Europe does not cause relevant direct photolytic degradation.
Executive summary:

The photolytic stability of [14C]-cyanamide was studied in aqueous solutions buffered at pH values of 5 and 7. For this purpose 14C-cyanamide was dissolved in methanol (262 µg/mL) and a [12C]/[14C]-isotopic dilution was prepared by adding 924 mg of non-radiolabelled cyanamide to the stock solution in order to ensure an adequate amount of test material resulting in a concentration of 18.7 mg as/mL (radiochemical purity: 96.8 %). Aqueous solutions with [14C]-cyanamide were prepared at nominal concentrations of 20 µg/mL and were continuously irradiated under sterile conditions for up to 30 days at 25 ± 1 °C in a photolysis chamber using a xenon arc lamp. In addition dark controls, wrapped in foil, were incubated in the photolysis chamber. Non-exposed and exposed samples were analysed at 0, 1, 3, 7, 14, 21 and 30 days for total radioactivity by LSC. For identification of parent compound and degradation products the samples were analysed by reversed-phase TLC. Selected samples were analysed by HPLC with UV detection to confirm the amounts and identities of the residues identified by TLC. The rate of degradation of cyanamide was determined using linear regression assuming first order reaction kinetics. The results show that photodegradation of cyanamide occurred in aqueous solution buffered at pH 5 and 7. The cyanamide concentration in the light exposed samples decreased after 30 days to 48.2 % of initial measured dose (IMD) and 58.2 % of IMD at pH 5 and pH 7, respectively. In the dark control samples the cyanamide concentration decreased to 80.5 % and 86.6 % of IMD at pH 5 and pH 7 after 30 days. Photolytic half-lives were calculated to be 28.9 d and 38.5 d in the light exposed samples at pH 5 and pH 7, respectively. Urea was detected as major degradation product in the light-exposed samples at maximum concentrations of 12.2 % of IMD at pH 7 and 42.4 % of IMD at pH 5. Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD. These data indicate that photolysis is a more significant degradation pathway at pH 5 and pH 7 (25 °C) than hydrolysis. Under laboratory conditions (Xenon lamp 290 - 400 nm), cyanamide was moderately degraded. Quantum yield was not determined in the presented study, since the adsorption coefficient at 290 nm is below 10 in UV-VIS spectra. Therefore, it can be concluded that in contrary to the laboratory conditions natural irradiation in Central Europe does not cause relevant direct photolytic degradation.

Description of key information

Photolysis of cyanamide is a more significant degradation pathway at pH 5 and pH 7 (25°C) than hydrolysis. The photolytical half-life of cyanamide in buffered aqueous solutions was calculated to be 28.9 days and 38.5 days at pH 5 and pH 7. Urea was detected as major degradation product in the light exposed samples.

Key value for chemical safety assessment

Half-life in water:
38.5 d

Additional information

The photolysis of cyanamide in water was examined in one study. The photolytical half-life of cyanamide in buffered aqueous solutions at 25°C was calculated to be 28.9 days and 38.5 days at pH 5 and pH 7 respectively. Urea was detected as major degradation product in the light exposed samples at maximum concentrations of 12.2 % of IMD (initial measured dose) at pH 7 and 42.4 % of IMD at pH 5. Urea was also detected in the pH 5 dark control samples at concentrations up to 8.18 % of IMD. Study details are summarized in the table below. The results indicate that photolysis is a more significant degradation pathway at pH 5 and pH 7 (25°C) than hydrolysis.


 


























Guideline /
Test method



Initial molar TS concen­tration



Total recovery of test substance
[% of appl. a.s.]



Photolysis rate constant (kcp)



Direct photolysis sunlight rate constant (kpE)



Reaction quantum yield (fcE)



Half-life (t1/2E)



Reference



EPA-FIFRA 161-2



18.7 mg ai/mL



98.3 %



nr



nr



nr



28.9 d (pH 5)


38.5 d (pH 7)



Schmidt, JM (1991)



nr = not reported