Propargite

Phototransformation in water

Link to relevant study record(s)

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.