Chlorpyrifos

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:

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

Specific details on test material used for the study:

Batch 1: Lot # GHD-1348-31a, INV.751 with radiochemical purity of 99.8% (specific activity: 15.7 mCi/mmole)
Batch 2: Lot # GHD-1394-86a, INV.784 with radiochemical purity of 98.2% (specific activity: 25.6 mCi/mmole)

Radiolabelling:

yes

Analytical method:

gas chromatography

high-performance liquid chromatography

mass spectrometry

Light source:

other: Phosphor-coated mercury lamps, or natural sunlight

Duration:

30 d

Temp.:

25 °C

Initial conc. measured:

0.5 other: ppm (Rayonet experiments)

Duration:

30 d

Temp.:

20.9 °C

Initial conc. measured:

0.5 other: ppm (sunlight irridiated buffer solution)

Duration:

30 d

Temp.:

20.2 °C

Initial conc. measured:

0.5 other: ppm (sunlight irridiated natural water)

Dark controls:

yes

Key result

DT50:

30.7 d

Test condition:

buffered solutions of pH 7 at 25°C (Rayonet photolysis experiments)

Key result

DT50:

29.6 d

Test condition:

in buffered water of pH 7 exposed to sunlight

Key result

DT50:

39.9 d

Test condition:

in natural river water exposed to sunlight

DT50:

74 d

Test condition:

dark control at 25°C and pH 7

Transformation products:

yes

Remarks:

In buffered solutions, no single photoproduct obtained greater than 5% of applied. Three carboxylic acid peaks were detected in natural water with a range of 5.3 to 6.6% of the total applied.

Conclusions:

Photolytic half-life: 30.7 days (Rayonet experiments)
Photolytic half-life: 29.6 days (Sunlight irridiated buffer solution)
Photolytic half-life: 39.9 days (Sunlight irridiated natural river water)

Executive summary:

An aqueous photolysis study was conducted with 14C-test substance, in sterile pH 7 phosphate buffered solution as per the guideline EPA Guideline Subdivision N 161-2. These solutions were irradiated with either an artificial light source, a Rayonet equipped with phosphorcoated RPR-3500A lamps, or natural sunlight. The photolysis of the test substance was also carried out in natural river water to investigate photosensitization. Based on a mid-summer day at 40°N, test substance in sterile, buffered solutions had an average photolytic half-life of 30.7 days for the Rayonet photolysis experiments at 25°C. When exposed to sunlight, test substance decayed with an observed half-life of 29.6 and 39.9 days in buffered water and natural river water, respectively. The dark control for the buffered system gave a hydrolysis half-life of 74 days at 25°C and pH 7. The dark control for the natural river water system yielded a hydrolysis half-life of 25 days at 25°C and pH 7.6. The mass balance accountability for the photolysis experiments averaged 100.5% (range, 93.7% to 107.6%) in buffered solutions and was 95.3% in natural river water.

The photolytic decomposition of the test substance led to the formation of several photoproducts. In buffered solutions, no single photoproduct obtained greater than 5% of applied. The identities of some of these photoproducts from buffered solution were determined by GC/MS. In addition to the remaining test substance, two isomers of O,O-diethyl O-(dichloro-2-pyridinyl)phosphorothioate (~1%, buffered; 4% natural river water) were identified. After being derivatized as butyl esters, the following carboxylic acids were isolated and identified from a buffered solution by GCIMS and HPLC methods: oxamic acid, maleic acid, maleamic acid, succinic acid, malonic acid, 2-chlorosuccinic acid, E- and Z-2-chlorobut-2-enedioic acids, fumaric acid, succinamic acid, and fumaramic acid. Oxalic acid was identified by ion exclusion and ion pair chromatography. Derivatization with benzyl bromide made possible the identification of two more unknowns: glycolic acid and 3-hydroxypropionic acid. GC/MS analyses failed to detect 3,5,6-trichloro-2-pyridinol and O-ethyl O-(3,5,6-trichloro-2-pyridinyl)phosphorothioate in buffered solutions. HPLC analyses of the natural water solution showed that the photolysis of the test substance led to the formation of photoproducts of similar polarity as in the buffered solution. Three carboxylic acid peaks were detected in natural water with a range of 5.3 to 6.6% of the total applied as determined by ion exclusion chromatography.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Phototransformation in water	Exposure to Rayonet equipped with phosphorcoated RPR-3500A lamps; Sunlight irridiated buffer solution and Sunlight irridiated natural river water	DT50=30.7 days (Rayonet equipment) DT50=29.6 days (Sunlight irridiated buffer solution) DT50=39.9 days (Sunlight irridiated natural river water)	EPA 161 -2	1

Key value for chemical safety assessment

Half-life in water:

29.6 d