Registration Dossier

Diss Factsheets

Environmental fate & pathways

Phototransformation in water

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Substance quantum yield of direct photolysis = 9.25*10-4. Direct photolysis half-life is between 164.1 days (at 40° N and mid-summertime) and 420.5 days (at 50° N and mid springtime). Under practical environmental conditions controlled by pathways of sensitised photolysis, a much faster photochemical degradation might take place. UBA Test Guideline "Phototransformation of Chemicals in Water, Part A, Direct Phototransformation", Phaff 1998
[phenyl-U-14C]substance was shown to degrade in a pH 5 buffer when exposed to artificial light at enhanced rate over unexposed controls. The calculated aqueous photolysis half-life (DT50) at pH 5 under irradiated conditions was approximately 30 days with a 1.622 days-1, rate constant. Incubation of test substance at pH 5 in the dark produced a calculated half-life (DT50 ) 208 days. The calculated DT90 values were 98 and 675 for irradiated and nonirradiated conditions. EPA N 161-2, Spare 1999a
[pyrimidinyl-5-14C] substance in the pH 5 buffer exposed to artificial sunlight with enhanced degradation rate over unexposed controls. The calculated aqueous photolysis half-life (DT50) at pH 5 under irradiated conditions was approximately 25 days with a 2.028 days-1 rate constant. Incubation of test substance at pH 5 in the dark produced a calculated half-life (DT50) of 326 days. Calculated DT90 values were approximately 82 and 1060 days for irradiated and nonirradiated conditions. EPA N 161-2, Spare 1999b

Key value for chemical safety assessment

Additional information

UBA Test Guideline Part A, Phaff 1998: The test substance phototransformation in water was investigated using UBA Test Guideline "Phototransformation of Chemicals in Water, Part A, Direct Phototransformation" Berlin, FRG, January 1990. The direct photolytic degradation of the test substance was studied using monochromatic light at 274nm of a xenon arc lamp operated at 800W. At a concentration of 2.18*10-6 mol/l or 1.03 ppm in 0.01 M aqueous phosphate buffer pH 7 containing 5% acetonitrile, photolysis of test substance followed first order kinetics. The mean rate constant and half-life of two independent experiments were 0.0152 h-1 and 45.6 hours, respectively. The incident light intensity was determined by chemical actinometry to be 7.89*10-4 Einstein*l-1*h-1. The quantum yield of direct photolysis was found to be 9.25*10-4. With the small overlap of the spectral absorption of test substance and the spectral irradiance of sunlight from 297.5nm to 400nm, test substance will be slowly degraded by direct photolysis. The photolytic half-life in shallow waters was estimated for mid-springtime and mid-summertime at geographical latitudes of 40°N and 50°N corresponding to locations such as Madrid or Denver and Frankfurt or Winnipeg, respectively. Under clear sky conditions, half-lives between 164.1 days (at 40° N and mid-summertime) and 420.5 days (at 50° N and mid-springtime) are to be expected for the case that direct photolysis represents the only photochemical pathway of degradation.

Under practical environmental conditions, however, where degradation is usually controlled by the more efficient pathways of sensitised photolysis, a much faster photochemical degradation might take place.

 

EPA N 161-2, Spare 1999a: The test substance photodegradation in water was investigated using EPA Guideline Subdivision N 161-2 (Photodegradation studies in water). The results demonstrated photolysis of [phenyl-U-14C]test substance in the pH 5 buffer exposed to artificial sunlight. Under irradiated conditions, the parent concentration degraded from an initial value of 99.0% to a value of 55.0% (mean) of applied dose at 30 days. The decline corresponded with a mean maximum concentration increase in a series of products: CGA-350426 (3.2% at 20 days), CGA-293731 (3.2% at 20 days), CGA- 293730 (3.9% at 28 days), CGA-98166 (4.2% at 28 days), CGA-368220 (1.7% at 28 days), CGA-364032 (2.1% at 24 days), five unknowns each less than 5% of dose, and one major product which attained 13.0% of dose at day 28. Isolation of the major product (A6) with mass spectral identification yielded a product with molecular ion of 474 which was a dechlorinated (OH exchanged) and hydroxylated version of test substance with the pyrimidinyl ring reduced. Another minor product (A12) was obtained during the isolation of A6. The molecular ion of A12 was 336 and was a dechlorinated and pyrimidinyl ring opened version of test substance .

Under non-irradiated conditions, the parent concentration did not significantly degrade from an initial value of 98.7% to a value of 98.0% (mean) of applied dose at 30 days. One unknown product was detected at days 7 and 10 up to a mean maximum of 5.5% of applied dose.

The calculated aqueous photolysis half-life (DT50) at pH 5 under irradiated conditions was approximately 30 days with a 1.622 days-1, rate constant. Incubation of test substance at pH 5 in the dark produced a calculated half-life (DT50 ) 208 days. The calculated DT90 values were 98 and 675 for irradiated and nonirradiated conditions, respectively. Photolytic exposure of test substance at pH 5 did enhance the degradation rate over unexposed controls.

 

EPA N 161-2, Spare 1999b: The test substance photodegradation in water was investigated using EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water). The results demonstrated photolysis of [pyrimidinyl-5-14C]test substance in the pH 5 buffer exposed to artificial sunlight. Under irradiated conditions, the parent mean concentration degraded from an initial mean value of 99.2% to a mean value of 37.9% of applied dose at 31 days. The decline corresponded with a mean concentration increase in a series of products: CGA-293731 (maximum 4.7% at 28 days), CGA-371902 (maximum 4.2% at 21 days), CGA-321432 (maximum 4.4% at 7 and 10 days), CGA- 293730 (maximum 2.1% at 28 days), CGA-368220 (maximum 3.1% at 24 days), 1,1,1- trifluoroacetone (maximum 0.3% at 31 days), a polar component (maximum 6.0% at 31 days), eight additional products each at 3.9% of dose or less, and one major product [Unknown #1 (A6)] which attained 19.9% of dose at day 31. This was identified as a molecular ion of 474 which was a dechlorinated (OH exchanged) and hydroxylated version of test substance with the pyrimidinyl ring reduced. Under non-irradiated conditions, the mean parent concentration did not significantly degrade from an initial mean value of 99.2% to a mean value of 94.7% of the applied dose at 31 days. Five degradates were detected occasionally in mean amounts up to 0.9% of applied dose. CGA-293731 was detected at up to 3.1% of applied dose at 21 and 31 days. The only detected volatile products were CO2 (maximum 2.8% at 31 days) and volatile organics (maximum 0.3% at 31 days) collected from continuously flushed irradiated samples.

The calculated aqueous photolysis half-life (DT50) at pH 5 under irradiated conditions was approximately 25 days with a 2.028 days-1 rate constant. Incubation of test substance at pH 5 in the dark produced a calculated half-life (DT50) of 326 days. Calculated DT90 values were approximately 82 and 1060 days for irradiated and nonirradiated conditions, respectively. Photolytic exposure of test substance at pH 5 did enhance the degradation rate over unexposed controls.

Categories Display