Chlorpyrifos

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Deviations:

no

GLP compliance:

no

Specific details on test material used for the study:

Test substance is radiolabelled with 14C in 2 and 6 positions of pyridine ring
Radiochemical purity: 97.9%
Specific activity: 14.2mCi/mmole

Radiolabelling:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals: Day 0, 2, 4, 7, 14, 21 and 35
- Sampling method: 1.1 mL of solution was removed from each hydrolysis sample for analysis
- Sampling intervals/times for pH measurements: Day 0, 2, 4, 7, 14, 21 and 35

Buffers:

Purified water was buffered at pH 5, 7, and 9 at 0.005M with phosphate buffers

Details on test conditions:

TEST SYSTEM
- Test flasks: 50 mL Kimax centrifuge tubes sealed with aluminum-lined caps
- Sterilisation method: Autoclaving for 30 min at 120°C
- Lighting: Dark incubation

TEST MEDIUM
- Volume used/treatment: 50 mL sterile buffer solution
- Kind and purity of water: Water purified with a Corning Mega-Pure water purification system
- Preparation of test medium: Samples were prepared at each pH by addition of 50 mL of the acetone stock solution of test substance to 50 mL of sterile buffer solution contained in 50 mL Kimax centrifuge tubes

Duration:

35 d

Temp.:

25 °C

Initial conc. measured:

0.6 other: ppm

Remarks:

pH: 5, 7 and 9

Negative controls:

yes

Transformation products:

yes

No.:

#1

No.:

#2

Details on hydrolysis and appearance of transformation product(s):

Two hydrolysis products formed in the study were identified by HPLC and by GC/MS to be 3,5,6-trichloro-2-pyridinol (I) and 0-ethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate (II). At pH 5 and 7 production of (II) was favored slightly over (I), while at pH 9 (I) was the predominant hydrolysis product.
Under conditions encountered in the environment, where other dissipative processes act on the chemical, hydrolysis will tend to be a minor route for dissipation of the chemical.

% Recovery:

78.7

pH:

5

Temp.:

25 °C

Duration:

35 d

Remarks on result:

other: Recovery was >89% in all other sampling times

% Recovery:

90

pH:

7

Temp.:

25 °C

Duration:

35 d

% Recovery:

91

pH:

9

Temp.:

25 °C

Duration:

35 d

Key result

pH:

5

Temp.:

25 °C

DT50:

72 d

Type:

other: first order

Remarks on result:

other: Hydrolysis rate constant: 0.00951±0.00086

Key result

pH:

7

Temp.:

25 °C

DT50:

72 d

Type:

other: first order

Remarks on result:

other: Hydrolysis rate constant: 0.00961±0.00085

Key result

pH:

9

Temp.:

25 °C

DT50:

16 d

Type:

other:

Remarks on result:

other: Hydrolysis rate constant: 0.044±0.015

Details on results:

Pathway: Under conditions encountered in the environment, where other dissipative processes act on the chemical, hydrolysis will tend to be a minor route for dissipation of the chemical.

Conclusions:

Half life (pH 5 and 7, 25°C): 72 days
Half life (pH 9, 25°C): 16 days

Executive summary:

The purpose of the study was to examine the hydrolysis kinetics and confirm the identity of the hydrolysis products formed to satisfy Section 161-1 of the US EPA Pesticide Assessment Guidelines, Subdivision N.

Hydrolysis of the test substance was studied at pH 5, 7, and 9 at 25°C in sterile buffered water. The rate of hydrolysis of the test substance has been found to be independent of pH below pH 7 with a half-life of approximately 72 days at both pH 5 and 7. The reaction was base catalyzed under alkaline conditions at pH 9 with a measured half-life of 16 days.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Hydrolysis	Tested at pH 5, pH 7 and pH 9	DT50 =72 days at pH = 5 and pH 7 DT50 = 16 days at pH = 9	EPA 161 -11	1

Key value for chemical safety assessment

Half-life for hydrolysis:

16 d

at the temperature of:

25 °C