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Environmental fate & pathways

Phototransformation in water

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Reference
Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14 May 1990 - 27 February 1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP/Guideline study
Study type:
direct photolysis
Qualifier:
according to
Guideline:
EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)
Deviations:
not specified
GLP compliance:
yes
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable.
Radiolabelling:
yes
Analytical method:
other: HPLC and radioassay
Details on sampling:
Samples were taken for analysis by radioassay and by HPLC at Days 0, 4, 10, 16, 24, and 30.
Buffers:
pH 7 buffer solution prepared by adding 22.4 ml of KH2PO4 (0.1M) to 25.8 ml of Na2HPO4 (0.1M) then adding water to a final volume of one liter.

The solution was sterilized by filtering through a 0.22 micron filter. The pH was rechecked using an Orion 501 pH Meter.
Light source:
sunlight
Details on light source:
Natural sunlight
Details on test conditions:
14C RH-573 was exposed to natural sunlight at 10.8 ppm in sterile pH 7 aqueous buffer solution for up to 30 days, concurrent with an identical dark control system. Light exposed samples were contained in quartz tubes and dark controls were contained in Pyrex tubes wrapped with foil to prevent irradiation. Both samples were placed in a temperature controlled water bath at 24.9±0.8 °C.
Duration:
30 d
Temp.:
25 °C
Initial conc. measured:
10 mg/L
Reference substance:
not specified
Dark controls:
yes
Remarks:
Dark controls were contained in Pyrex tubes wrapped with foil to prevent irradiation
Computational methods:
Average (arithmetic mean), standard deviation, standard error and linear regression were the only statistical methods employed in the analysis of data.
Predicted environmental photolytic half-life:
The pseudo first-order calculated half-life of degradation was 266 hours (11 days) (R(2) = 0.86) for light exposed samples and 10191 hours (425 days) (R(2) = 0.11) for dark control samples. The low coefficient of correlation observed in the control samples reflects the minimal degradation which occurred in the dark during the sample period.
Transformation products:
yes
No.:
#1
No.:
#2
Details on results:
The recovery of applied radioactivity is 96.0±4.4% for the light exposed samples and 99.0±5.3% for the dark control samples. At the termination of the experiment (Day 30), parent comprised approximately 18% and 96% of the applied radiocarbon in the light exposed and dark controls, respectively. Half-life was calculated as 11 days for the light exposed samples and 425 days for the dark control samples. 14C CO2 accounted for 2.7% of the total applied activity and its presence demonstrated that the isothiazolone ring was cleaved. Two major photodegradates were detected in the light exposed samples. One, less polar than the parent accounted for 39.5% of the applied radiocarbon and was identified as 3-methyl-4-thiazolin-2-one, by mass spectroscopy and NMR. The other, accounted for 37.5%, was identified as N-methyl malonamic acid chromatographically.
Results with reference substance:
No data.

Radiochemical Purity of [14C]RH-573 used in this study was determined by HPLC to be 96.8%. Stability of the test substance under the conditions of administration was demonstrated by the HPLC analysis of the zero time samples which showed no degradation of RH-573.

Solution Stability (Sorption Test)

The average radiocarbon in solution at 10.3 ppm was 97.9 + 2.5% for the quartz sample holders. Similar results were obtained in pyrex containers in a hydrolysis study on RH-573. This [14C]RH-573 does not irreversibly adsorb to the glass sample tubes.

Material Balance of [14C]RH-573 throughout the Study Period

The material balance of [14C]RH-573 was determined by summing the radiocarbon remaining in solution and radiocarbon volatilized, and is expressed as percentages of radiocarbon applied (Table 2). Radiocarbon recoveries averaged 97.5 + 5.0% based on nominal applied radioactivity. No radiocarbon was detected in ethylene glycol traps at levels greater than 0.5%. The KOH traps contained 2.7% of the applied radiocarbon in light exposed samples which was confirmed as 14CO2 by precipitation as barium carbonate.

Table 2 Product Balance of [14C]RH-573 and its Degradates Expressed as Percent of Applied Radiocarbon

 Sample/Replicate  % RH-573  Degradate 11  Degradate 22  CO2  Unkown*  Total Recovery
 Hour 0            
 Irradiated (1)  100.9  -  -  -  -  100.9
 Irradiated (2)  100.8  0.1  -  -  -  100.9
 Dark Control (1)  100.8  -  -  -  -  100.8
 Dark Control (2)  100.8  -  -  -  -  100.8
 Day 4 (Hour 98.3)            
 Irradiated (1)  95.5  -  -  0.2  -  95.5
 Irradiated (2)  100.2  -  -  0.2  -  100.2
 Dark Control (1)  107.2  -  -  -  -  107.2
 Dark Control (2)  97.8  -  -  -  -  97.8
 Day 10 (Hour 242.5)            
 Irradiated (1)  50.9  23.5  18.4  0.6  0.1  93.5
 Irradiated (2)  54.3  24.6  19.0  0.6  0.1  98.6
 Dark Control (1)  92.9  -  -  -  0.8 [1]  93.7
 Dark Control (2)  96.3  -  -  -  -  96.3
 Day 16 (Hour 385)            
 Irradiated (1)  20.6  35.6  35.8  2.2  0.2  94.4
 Irradiated (2)  22.0  33.0  33.2  2.2  0.2  90.6
 Dark Control (1)  109.2  -  -  0.1  -  109.3
 Dark Control (2)  94.4  -  -  0.1  -  94.5
 Day 24 (Hour 575)            
 Irradiated (1)  48.4  7.4  30.1  2.3  0.2  88.4
 Irradiated (2)  26.8  24.7  36.8  2.3  0.2  90.8
 Dark Control (1)  102.0  -  -  0.1  0.2 [1]  102.3
 Dark Control (2)  92.7  -  -  0.1  -  92.8
 Day 30 (Hour 721)            
 Irradiated (1)  19.0  37.3  39.5  2.7  0.5  99.0
 Irradiated (2)  17.5  37.7  39.6  2.7  0.5  98.0
 Dark Control (1)  94.2  -  -  0.1  0.1  94.3
 Dark Control (2)  97.0  -  -  0.1  0.1  97.1

- Indicates none detected

* The % unknowns followed by the number identified by HPLC in brackets [ ].

1) Characterized as a mixture of N-methyl malonamic acid, N-methyl acetamide and N-methyl oxamic acid.

2) 3 -methyl-4 -thiazolin-2 -one

Solution Sterility

All buffer solution samples submitted for environmental cultures showed no growth of bacteria.

Sample Analysis and Storage Stability

Samples were analyzed by HPLC and LSC immediately following their removal from the water bath. Reanalysis of selected samples after 2 months under frozen storage conditions showed no detectable change in product distribution.

Validity criteria fulfilled:
yes
Conclusions:
Half-life was calculated as 11 days for the light exposed samples and 425 days for the dark control samples.
Executive summary:

The photodegradation capability of test material was determined in water. Half-life was calculated as 11 days for the light exposed samples and 425 days for the dark control samples.

Description of key information

The photodegradation capability of test material was determined in water. Half-life was calculated as 11 days for the light exposed samples and 425 days for the dark control samples

Key value for chemical safety assessment

Half-life in water:
11 d

Additional information