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Phototransformation in water

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Reference
Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13th November 2002 to 17th April 2003
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)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
yes
Analytical method:
high-performance liquid chromatography
Buffers:
The pH 5 buffer solution was prepared by transferring 14.6 mL of 0.1 M acetic acid solution and 10 mL of 0.1 M NaOH solution to a 100 mL volumetric flask and diluting to the mark with deionised water. The pH of the resulting solution was checked and then sterilised by filtration through a 0.22 µm filter.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
>= 300 - <= 800
Details on light source:
- Heraeus Suntest CPS+ unit equipped with a Xenon arc lamp with a radiation limit at approximately 290 nm corresponding to outdoor exposure.
- Light intensity: 506 W/m²
Duration:
10 d
Temp.:
20 °C
Initial conc. measured:
0.331 other: ppm
Key result
DT50:
3.9 d
Test condition:
or 93.6 hours
DT50:
10.4 d
Test condition:
predicted half-life at 40º N latitude during the summer season
No.:
#1
No.:
#2

Material balance

Radiocarbon recoveries averaged 95.2 ± 2.4 % in the study. Radiocarbon recovered in the aqueous test solutions increased from an average of 78.7 % at time zero to an average of 89 % after 10 days irradiation. Radiocarbon recovered in tube wall rinses decreased from an average of 13.9 % at time zero to an average of 5.6 % of the dose by the end of the study. Less than 1.5 % of the radiocarbon was recovered in the traps for volatiles at the end of the irradiation period.

Table 1: Product balance for [14C]-test material and degradates following aqueous photolysis at pH 5

 Sample  Test material  TBP  TBPC  U-1 (2.5 min)  Others  Organic volatiles  CO2  Total recovery
 Day 0
 T0 Rep A  89.7  0.0  2.2  0.0  2.6  NA  NA  94.5
 T0 Rep B  86.9  0.0  0.8  0.0  2.9  NA  NA  90.6
 Average  88.3  0.0  1.5  0.0  2.8  NA  NA  92.6
 Day 5
 T5day Rep A  36.9  8.0  28.9  8.9  13.7  0.0  0.4  96.8
 T5day Rep B  41.6  5.7  28.4  7.4  13.7  0.0  0.5  97.3
 Average  39.3  6.9  28.7  8.2  13.7  0.0  0.5  97.1
 Day 10
 T10day Rep A  14.5  14.0  31.6  16.4  18.2  0.0  1.1  95.8
 T10day Rep B  15.1  10.6  32.7  15.8  20.3  0.1  1.4  96.0
 Average  14.8  12.3  32.2  16.1  19.3  0.1  1.3  95.9

Photodegradation of [14C]-test material in aqueous pH 5 buffer solution

[14C]-test material degraded rapidly in pH 5 buffer after artificial light exposure and represented an average of 14.8 % of the dose after 10 days of continuous exposure. TBPC was the main degradate observed and represented an average of 32.2 % of the dose after 10 days of continuous light exposure. TBP represented an average of 12.3 % of the dose after 10 days continuous irradiation. A polar degradate peak eluting at 2.5 minutes by HPLC represented 16.1 % of the dose at the end of the study. Several minor peaks were observed with HPLC with no individual peak greater than 5 % of the dose.

Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the test, the half-life of the test material was calculated as 3.9 days using first-order kinetics. The predicted half-life for the test material at 40º N latitude during the summer season is 10.4 days. The mean degradates observed were TBPC (32 %), TBP (12 %) and a polar peak present in the solvent from by HPLC (16 %). Photolysis is a major mode of dissipation of the test material under the conditions of the test.
Executive summary:

[14C]-test material was exposed to artificial light in a sterile aqueous pH 5 buffer solution for up to 10 days of continuous irradiation at an application rate of 0.331 ppm. Quartz sample tubes were irradiated in a Suntest CPS+ apparatus equipped with a Xenon lamp with filters to block the infrared light and the irradiation below 290 nm. Light exposed samples were placed in a temperature controlled deionised water bath (20 ± 2 ºC) and the temperature monitored continuously. Volatiles were trapped at sampling using a series of traps containing ethylene glycol to trap organic volatiles, two 10 % aqueous NaOH solutions to trap CO2 and a charcoal trap.

Average radiocarbon recoveries were 95.2 ± 2.4 % based on the nominal applied radiocarbon. Analytical methods included LSC for quantitation of radiocarbon and HPLC for quantitation and co-chromatography of radioactive peaks with a mixed reference standards solution.

The test material degraded rapidly when exposed to artificial light and represented an average of 39.3 % of the dose after 5 days of irradiation. At the end of the exposure period, the test material represented an average of 14.8 % of the dose. Volatiles trapped in the caustic traps and traps for organic volatiles represented less than 1.5 % of the radiocarbon by the end of the study. The main degradates observed in the light exposed samples were TBPC and TBP representing an average of 32.2 and 12.3 % of the radiocarbon respectively by the end of the study period. A peak eluting at 2.5 minutes by HPLC was also present in 5 and 10 day samples and represented up to an average of 16.1 % of the dose at the end of the irradiation period.

The half-life of [14C]-test material in light exposed samples was calculated to be 3.9 days (r2 = 0.997) assuming single-exponential first order kinetics and based on experimental conditions of 24 hours of continuous irradiation. Using average solar light energy values, the half-life for the test material at 40º N latitude during summer seasons was calculated to be 10.4 days.

Description of key information

DT50 3.9 days; study was conducted in accordance with EPA Pesticide Assessment Guideline 161-2; Concha (2003)

Key value for chemical safety assessment

Half-life in water:
3.9 d

Additional information

Two photolysis studies have been submitted both conducted in accordance with accepted guidelines and to GLP. Both studies have been allocated a reliability score of 1 but as Concha (2003) has been conducted in accordance with a standardised guideline (EPA Pesticide Assessment Guidelines 161-2) and does not contain any deviations from the protocol, as is the case with McCorquodale and Paterson (2002), this study has been allocated as the key study.

[14C]-propargite was exposed to artificial light in a sterile aqueous pH 5 buffer solution for up to 10 days of continuous irradiation at an application rate of 0.331 ppm. Quartz sample tubes were irradiated in a Suntest CPS+ apparatus equipped with a Xenon lamp with filters to block the infrared light and the irradiation below 290 nm. Volatiles were trapped at sampling using a series of traps containing ethylene glycol to trap organic volatiles, two 10 % aqueous NaOH solutions to trap CO2 and a charcoal trap. Average radiocarbon recoveries were 95.2 ± 2.4 % based on the nominal applied radiocarbon. Propargite degraded rapidly when exposed to artificial light and represented an average of 39.3 % of the dose after 5 days of irradiation. At the end of the exposure period, propargite represented an average of 14.8 % of the dose. Volatiles trapped in the caustic traps and traps for organic volatiles represented less than 1.5 % of the radiocarbon by the end of the study. The main degradates observed in the light exposed samples were TBPC and TBP representing an average of 32.2 % and 12.3 % of the radiocarbon respectively by the end of the study period. A peak eluting at 2.5 minutes by HPLC was also present in 5 and 10 day samples and represented up to an average of 16.1 % of the dose at the end of the irradiation period. The half-life of [14C]-propargite in light exposed samples was calculated to be 3.9 days assuming single-exponential first order kinetics and based on experimental conditions of 24 hours of continuous irradiation. Using average solar light energy values, the half-life for propargite at 40º N latitude during summer seasons was calculated to be 10.4 days.

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