Chlorpyrifos

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

[14C]Test substance labeled at the 2 and 6 position of the pyridine ring (Ref. No.: GHD-1394-86a, 25.6 mCi/mmol, 1.62 x 10e5 dpm/µg)
Radiochemical purity: 98.2%

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

other: Thin layer chromatography, radioassay

Light source:

sunlight

Duration:

30 d

Temp.:

24 °C

Initial conc. measured:

33.3 other: ppm or µg/g

Reference substance:

no

Dark controls:

yes

Key result

DT50:

30 h

Test condition:

light sample

Key result

DT50:

28.5 h

Test condition:

dark sample

Transformation products:

yes

Remarks:

6-trichloropyridinol (TCP)

Conclusions:

The half-life of degradation was calculated to be 30 hours (R² = 0.94) and 28.5 hours (R² = 0.96) for light and dark, respectively indicating that photolysis is not a significant degradation process for the test substance.

Executive summary:

The photochemical degradation of [14C]test substance in natural sunlight was examined on a thin silt loam soil surface according to EPA guideline subdivision N-161-3, for up to 30 days. The application rate was 33.3 µg test substance per gram of soil. Temperature was controlled throughout the study and the average was 24.0 ± 0.4°C in the light exposed soils and 24.1 ± 0.2°C in the dark controls. Average radiocarbon recoveries were 93.3 ± 13.0% and 112.6 ± 7.6% in the light and dark samples, respectively. Extracts were analyzed using HPLC and TLC. The [14C]test substance degraded rapidly to its hydrolysis product, 3,5,6-trichloropyridinol (TCP) in both light exposed and dark controls with less than 10.0% of parent material remaining intact after 309 hours. The half-life of degradation was calculated to be 30 hours (R² = 0.94) and 28.5 hours (R² = 0.96) for light and dark, respectively indicating that photolysis is not a significant degradation process for the test substance. During the 30 day study course, TCP was observed to degrade primarily to non-extractable residues on the soil and 14CO2 (4.6%) on irradiated soils. Less than 0.1% of applied radiocarbon was detected in ethylene glycol traps.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Phototransformation in soil	Applied evenly to thin silt loam soil surface	DT50 = 30 hours (light) DT50 = 28.5 hours (dark)	EPA 161-3	1

Key value for chemical safety assessment

Half-life in soil:

28.5 h