Methomyl

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Study type:

direct photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

The 14C-test substance at 1 ppm in circulated river water was exposed to sunlight and ambient temperatures for 8 weeks. Two 50 µL aliquots were counted in Fluoralloy DXA® to determine total radioactivity.

GLP compliance:

no

Specific details on test material used for the study:

- Substance name: 14C-Methomyl
- Purity: Not reported

Radiolabelling:

yes

Analytical method:

other: thin layer chromatography

Light source:

sunlight

Duration:

8 wk

Initial conc. measured:

1 other: ppm

Reference substance:

yes

Dark controls:

no

Key result

DT50:

> 1 wk

Test condition:

Ambient temperature

Transformation products:

yes

Remarks:

S-methyl N-hydroxythioacetimidate (12%); CO2 (65%)

Conclusions:

The 14C-test substance at 1 ppm in circulated river water was exposed to sunlight and ambient temperatures for 8 weeks. The test substance degraded rapidly with a half-life of slightly more than 1 week.

Executive summary:

The 14C-test substance at 1 ppm in circulated river water was exposed to sunlight and ambient temperatures for 8 weeks. The test substance degraded rapidly with a half-life of slightly more than 1 week. The first degradation product was S-methyl N-hydroxythioacetimidate, followed by extensive breakdown to 14CO2 which accounted for 65% of the original test substance after 8 weeks. After 2 weeks, the S-oxide of S-hydroxythioacetimidate was also detected and small amounts were still present at the conclusion of the experiment. In addition, traces of a polar fraction appeared which has not been further characterized. At the conclusion of the experiment, 9% of the original treatment was recovered by combustion of the sediment and biological film found on the walls of the container.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Phototransformation in water	Exposure to artifical sunlight at 10 and 100 ppm	DT50 = 5.5 days at 10 ppm DT50 = 2 days at pH = 100 ppm	EPA 63-13	2

Key value for chemical safety assessment

Half-life in water:

2 d