Chlorpyrifos

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Objective of study:

metabolism

toxicokinetics

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Substance ID: Chlorpyrifos
Lot#: AGR 200341
Purity: 99.9%

Radiolabelled substance ID: 14C-labelled chlorpyrifos
Inventory#: 541
Radiochemical purity: >99%
Specific activity: 15.78 (45 µCi/mg)

Radiolabelling:

yes

Species:

rat

Strain:

other: CDF Fischer 344

Details on species / strain selection:

Rats were used because these are the preferred species for metabolism studies. The Fischer rat was selected because it is available from a reliable supplier, and it is the strain used in recent studies connucted on test substance in test facility.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, kingston, Newyork
- Age at study initiation: Not specified
- Weight at study initiation: Males: 173-250 g; Females: 128-170 g
- Housing: Animals were housed in pairs in suspended stainless steel cages with fronts and floors constructed of wire mesh. Cage board was placed under these cages and changed as required to control odor and maintain a clean environment.
- Diet: certified rodent chow (Ralston Purina #5002) ad libitum
- Water: Municipal tap water ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
The animals were housed in rooms designed to maintain adequate environmental conditions concerning temperature, humidity, air changes, and lighting for the species under test.

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Dose solutions containing 14C-labelled test substance: The 0.5 mg/kg dose solution was prepared by dissolving sufficient 14C-labeled test substance in USP corn oil to produce a solution containing approximately 0.27 mg test substance and 12 µCi/g of corn oil. The 25 mg/kg dose solution was prepared by dissolving sufficient analytical grade and 14C-labelled test substance in USP corn oil to produce a solution containing approximately 13.6 mg test substance and 12 µCi/g of corn oil. Concentrations of test substance and radioactivity in these solutions were determined by HPLC and 14C-analysis. These solutions were administered by gavage at a rate of 2 ml/kg of body weight using a syringe and stainless steel feeding needle. The quantity of dose solution actually administered was determined by weighing the syringe prior to and following administration of the dose.

Dose solution containing no radiolabelled test substance: The dose solution administered for 15 consecutive days was prepared by dissolving sufficient analytical grade chlorpyrifos in USP corn oil to produce a
solution containing about 0.27 mg test substance per g of corn oil. The concentration of test substance in this solution was determined to be 0.313 mg test substance/g when analyzed by HPLC. The concentration of test substance in a similarily prepared solution did not change when stored for up to two months at room temperature. This solution was administered by gavage at a rate of 2 ml/kg of body weight using a syringe and stainless steel feeding needle. The volume of dose solution administered was based on the animal's body weight taken at 3 to 4 day intervals.

Duration and frequency of treatment / exposure:

Radiolabelled test substance: Single dose
Non-radiolabelled test subsatnce: 15 days daily followed on 16th day by single dose of radiolabelled test sustance.

Dose / conc.:

0.5 mg/kg bw/day (nominal)

Remarks:

Radiolabelled and non-radiolabelled test susbtances are given at this dose

Dose / conc.:

25 mg/kg bw/day (nominal)

Remarks:

Radiolabelled test susbtance

No. of animals per sex per dose / concentration:

5/sex

Details on study design:

- Dose selection rationale: The lower dose level (0.5 mg/kg) was selected as one that would produce no adverse effects, and, based on the specific activity of the radiotracer, was the lowest dose level that could be given if each rat was to receive at least 3 µCi of radioactivity. The higher dose level (25 mg/kg) was selected as a dose level that should inhibit cholinesterase activity and that might produce some clinical signs of cholinesterase depression. A dose level higher than 25 mg/kg was not used because of concern it might cause diarrhea and depress the absorption of orally administered test substance.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: Urine, faeces, tissues (brain, gonads, heart, kidneys, liver, lungs and spleen), portions of the blood, bone, perirenal fat, skeletal muscle and skin.
- Time and frequency of sampling: Urine: 12-hr intervals for the first 72 hr. In-addition, urine was collected from female rats at 24-hr intervals between 72 and 144 hrs post-dosing. Feces were collected at 24-hr intervals for 72 hrs from the males and for 144 hrs from the females. The male and female rats were anesthetized with CO2 and exsanguinated 72 and 144 hr, respectively, after the 14C-labelled test substance was administered.
- Other: The charcoal and 14CO2 traps were changed 6, 12 and 24 hr after the 25 mg/kg dose was administered. Expired volatiles were not trapped following the single or multiple 0.5 mg/kg doses because no radioactivity was found in either the charcoal or 14CO2 traps following the 25 mg/kg dose

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: The urine specimens used for the metabolite identification were taken from animals given the single 25 mg/kg oral dose. 12-24 Hr urine for males and males and 24-36 Hr urine for femlales only.
- From how many animals: Both males and female urine samples were pooled.
- Method type(s) for identification: HPLC and mass spectroscopy
- Limits of detection and quantification: Nor specified.

Statistics:

Tissues in a group which did not contain sufficient radioactivity to quantify, the mean was calculated using half the limit of quantitation for those tissues which did not contain sufficient radioactivity to quantify. If the resulting mean was less than the limit of quantitation, the mean concentration was reported as being below the limit of quantitation. Slopes were calculated from the log transformed amounts of radioactivity excreted in the urine by the individual animals during the first 3 day post-dosing. Half-lives were obtained by dividing these slopes into the natural log of 2. These slopes and the cumulative amount of radioactivity excreted in the urine and feces were compared statistically using a 2-way analysis of variance with sex and dose as variables. Explicit comparisons were made using linear contrast statements in the analysis of variance procedure to test for differences between males and females at each dose level, between the single 0.5 and 25 mg/kg dose, and between the single and multiple 0.5 mg/kg dose.

Type:

absorption

Results:

84% of the orally administered test substance was absorbed.

Type:

distribution

Results:

No differences were observed in the distribution of radioactivity recovered between the sexes or between rats given the single 25 and 0.5 mg/kg doses.

Type:

metabolism

Results:

Urinary metabolites were identified by mass spectrometry to be 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) and the glucuronide and tenatively the sulfate conjugate of 3,5,6-TCP.

Type:

excretion

Results:

Radioactivity was eliminated in the urine with a half-life of 8 to 9 hr the first 3 days following the 0.5 mg/kg dose and with half-lives of 12.4 hr in males and 23.2 hr in females given the 25 mg/kg dose.

Details on absorption:

Orally administered 14C-labelled test substance was rapidly and extensively absorbed by fasted rats. A half-life for absorption cannot be calculated from these data. However, it is apparent that chlorpyrifos was rapidly absorbed since over half of the 0.5 mg/kg oral doses was excreted in the urine within 12 hr. Based on the fraction of the dose found in the urine, it can also be concluded that at least 84% of the orally administered 14C-labelled test substance was absorbed.

Details on distribution in tissues:

The tissues and carcass from the rats given the 25 mg/kg dose after 72 and 144 h contained 0.2% of the administered radioactivity, while those from the rats given the single or repeated 0.5 mg/kg dose contained less than 0.01% of the administered radioactivity. Small amounts of radioactivity (~0.14 % dose/g) were found in the fat from the males at all dose levels, and in the liver of males and the ovaries and fat of females given the 25 mg/kg dose level. The other tissues did not contain sufficient radioactivity to reliably quantify, i.e., ~0.01% dose/g.

Details on excretion:

The principal route of excretion was the urine which contained between 83.9 and 91.7% of the dose. The feces contained from 5.5 to 11.5% of the administered radioactivity, and another 0.5 to 2.0% of the dose was found in the final cage wash. Very little radioactivity remained in the rats when they were sacrificed 72 hr (males) or 144 hr (females) post-dosing. Rats given multiple oral doses of 0.5 mg/kg excreted a larger fraction of the dose in the urine and less in the feces than the rats given the single 0.5 mg/kg oral dose. No differences were found in the disposition of radioactivity recovered following the single 0.5 and 25 mg/kg oral doses or between male and female rats at any dose level.

Key result

Test no.:

#1

Toxicokinetic parameters:

other: Elimination Half life

Remarks:

Radioactivity was eliminated in the urine with a half-life of 8 to 9 hr the first 3 days following the 0.5 mg/kg dose and with half-lives of 12.4 hr in males and 23.2 hr in females given the 25 mg/kg dose.

Metabolites identified:

yes

Details on metabolites:

Urinary metabolites were identified by mass spectrometry to be 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) and the glucuronide and tenatively the sulfate conjugate of 3,5,6-TCP.

Conclusions:

- Test substance was rapidly absorbed with over 84% of orally adminstered dose abosorbed.
- No differences were observed in the distribution of radioactivity recovered between the sexes or between rats given the single 25 and 0.5 mg/kg doses.
- Test substance was rapidly metabolized and eliminated in the urine as 3,5,6-TCP and the glucuronide and tentatively the sulfate conjugates of 3,5,6-TCP.
- Due to their rapid elimination, test substance and its metabolites have little potential to accumulate in the rat upon repeated administration.

Executive summary:

The study was conducted according to the EPA guideline 85-1 to evaluate the tissue distribution and metabolism of orally administered¹⁴C-labelled test substance in rats. Five rats/sex were given single oral doses of 0.5 or 25 mg ¹⁴C- labelled test substance/kg body weight, or 15 daily oral doses of 0.5 mg non-labelled test substance/kg followed on the 16^thday by a single oral dose of 0.5 mg¹⁴C- labelled test substance/kg. Between 96.8 and 98.5% of the administered radioactivity was recovered. Most of the dose (83.9 to 91.7%) was excreted in the urine. Another 5.5 to 11.5% of the dose was eliminated in the feces. No radioactivity was found in the expired air. Only a small fraction of the administered radioactivity (≤0.2% of the dose) remained in the tissues and carcass of male and female rats terminated 72 and 144-hr post-dosing, respectively. A larger fraction of the repeated versus the single 0.5 mg/kg dose was excreted in the urine and less was eliminated in the feces; otherwise, the disposition of test substance was not altered by prior exposure to test substance. No differences were observed in the distribution of radioactivity recovered between the sexes or between rats given the single 25 and 0.5 mg/kg doses.

Radioactivity was eliminated in the urine with a half-life of 8 to 9-hr the first 3 days following the 0.5 mg/kg dose and with half-lives of 12.4-hr in males and 23.2-hr in females given the 25 mg/kg dose. The difference in elimination rates may have been secondary to differences in rates of absorption. No unchanged test substance was found in the urine. Urinary metabolites were identified by mass spectrometry to be 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) and the glucuronide and tentatively the sulfate conjugate of 3,5,6-TCP.

These data indicate that over 84% of the orally administered test substance was absorbed. Test substance was rapidly metabolized and eliminated in the urine as 3,5,6-TCP and conjugates of 3,5,6-TCP. Due to their rapid elimination, test substance and its metabolites have little potential to accumulate in the rat upon repeated administration.

Key value for chemical safety assessment

Absorption rate - oral (%):

84

Additional information

The study was conducted according to the EPA guideline 85-1 to evaluate the tissue distribution and metabolism of orally administered14C-labelled test substance in rats. Five rats/sex were given single oral doses of 0.5 or 25 mg 14C- labelled test substance/kg body weight, or 15 daily oral doses of 0.5 mg non-labelled test substance/kg followed on the 16thday by a single oral dose of 0.5 mg14C- labelled test substance/kg. Between 96.8 and 98.5% of the administered radioactivity was recovered. Most of the dose (83.9 to 91.7%) was excreted in the urine. Another 5.5 to 11.5% of the dose was eliminated in the feces. No radioactivity was found in the expired air. Only a small fraction of the administered radioactivity (≤0.2% of the dose) remained in the tissues and carcass of male and female rats terminated 72 and 144-hr post-dosing, respectively. A larger fraction of the repeated versus the single 0.5 mg/kg dose was excreted in the urine and less was eliminated in the feces; otherwise, the disposition of test substance was not altered by prior exposure to test substance. No differences were observed in the distribution of radioactivity recovered between the sexes or between rats given the single 25 and 0.5 mg/kg doses.

Radioactivity was eliminated in the urine with a half-life of 8 to 9-hr the first 3 days following the 0.5 mg/kg dose and with half-lives of 12.4-hr in males and 23.2-hr in females given the 25 mg/kg dose. The difference in elimination rates may have been secondary to differences in rates of absorption. No unchanged test substance was found in the urine. Urinary metabolites were identified by mass spectrometry to be 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) and the glucuronide and tentatively the sulfate conjugate of 3,5,6-TCP.

These data indicate that over 84% of the orally administered test substance was absorbed. Test substance was rapidly metabolized and eliminated in the urine as 3,5,6-TCP and conjugates of 3,5,6-TCP. Due to their rapid elimination, test substance and its metabolites have little potential to accumulate in the rat upon repeated administration.