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Basic toxicokinetics

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Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
key study
Study period:
5 November 1986 to 27 April 1987
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
few details available on some parameters and on the substance identity (name). Due to the read-across purpose it was given a Klimisch 2 rating, in accordance with the ECHA Practical guide #6 on the reporting of read-across in IUCLID. The justification for read across is provided in the attached background material of the chapter summary.
Cross-reference
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
basic toxicokinetics
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See attached justification
Reason / purpose for cross-reference:
read-across source
Type:
excretion
Type:
distribution
Details on absorption:
after the 6-hour period, it was possible to remove a mean of 47.89% dose from the skin of the 6 rats. Means of 0.19% dose was measured in the treated skin of these 6 rats after removal of the excess dose.
Details on distribution in tissues:
Proportions of the applied dose in tissues were greatest at 3-6 hours in the gastro-intestinal tract GIT (2-7% dose), at 3 hours in liver and fat (0.6 - 0.9% dose) and at 3 hours in muscle (0.3-0.4% dose). Radioactivity in all other tissues measured was <0.1% dose at 3-6 hours except in the kidneys and plasma (<0.2% dose). At 12 hours, amounts of dosed radioactivity had decreased slightly in the GIT (2-4% dose), liver (0.08-0.2% dose) and fat (0.1-0.3% dose). At this time radioactivity in all other tissues measured was either Peak concentrations of radioactivity in tissues of the 12 rats were measured at 3-6 hours after dose application. At 24 hours, concentrations were not appreciably lower in the GIT but were substantially lower in liver, kidneys and fat. At 72 hours, concentrations had declined appreciably in the GIT, and had decreased further in liver, kidneys and fat.
The tissue:plasma concentration ratios showed higher concentrations than in plasma during 3-48 hours in the GIT, liver, kidneys, fat, lymph notes and pancreas.
Details on excretion:
Mean overall recovery of 76.4% attributed to the loss of some material by volatilisation during application of the dose to the skin.
Total urinary excretion until the time of sacrifice accounted for means of 8?04, 12.36 and 9.91% dose in the pairs of rats sacrificed at 24, 48 and 72 hours recpectively.
Total excretion of radioactivity in faeces accounted for 1.17, 2.29 and 2.42% dose in rats sacrificed at 24, 48 and 72 hours respectively.
Radioactivity in the expired air traps accounted for means of 17.55, 15.77 and 14.78% dose until the times of sacrifice at 24, 48 and 72 hours respectively. Most of this radioactivity was un the first expired trap (overall mean of 12.57% dose) with a smaller proportion in the second trap (overall mean of 3.47% dose). Radioactivity in the expired air traps may mostly be attributed to 14C-limonene volatilised directly from the site of application.
Metabolites identified:
not measured
Conclusions:
Interpretation of results: low bioaccumulation potential based on study results.
An appreciable proportion of the dermally applied dose (48%) was recovered in the dose washings. The radioactivity in urine (10% dose) and in faeces (2% dose) showed that these proportions were absorbed throught the skin. Radioactivity in the expired air traps may mostly be attributed to volatilisation from the site of application. However, there may also be a contribution of absorbed and exhaled air.
Renal excretion of limonene and/or its metabolite is expected to be the major route (as confirmed by studies using the oral route). The radioactivity in the faeces, gastro-intestinal tract and liver indicate some hepatic elimination.
Executive summary:

Twelve male rats received one dermal dose of 5 mg/kg bw for 6 hours (or 3 hours for those sacrificed at this time). Pairs of rats were sacrificed at 3, 6, 12, 24, 48 and 72 hours after dosing. Urine, faeces, plasma and various tissues were sampled and their radioactivity content measured.

Almost half the administered dose was removed by skin washing at the end of the application time. The renal route is the main one but faeces and exhaled air are also involved.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1990
Report date:
1990

Materials and methods

Objective of study:
toxicokinetics
Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
Deviations:
yes
Remarks:
one dose only; no identification/quantification of excreta; few details on husbandry and environmental conditions
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Reference substance name:
+[propene-1-14C]limonene
IUPAC Name:
+[propene-1-14C]limonene
Details on test material:
- Lot/batch No.: 80277
- Radiochemical purity (if radiolabelling): 96.8%
- Specific activity (if radiolabelling): 6.9 mCi/mmol; 50.7 µCi/mg
- Locations of the label (if radiolabelling): on the propene
- Storage condition of test material: -20°C away from light and moisture
Radiolabelling:
yes

Test animals

Species:
rat
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River, Margate, Kent
- Age at study initiation: 6 weeks
- Weight at study initiation: 200 to 208 g
- Fasting period before study: useless as dermal route
- Housing: not reported
- Individual metabolism cages: yes
- Acclimation period: 5 days

Administration / exposure

Route of administration:
dermal
Vehicle:
ethanol
Details on exposure:
TEST SITE
- Area of exposure: 9 cm²
- Type of wrap if used: aluminium foil secured with waterproof adhesive dressing

REMOVAL OF TEST SUBSTANCE
- Washing (if done): yes with cotton wool swabs moistened in ethanol
- Time after start of exposure: 6 hours (or 3 hours for animals to be sacrificed at this time)

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 5 mg/kg bw
- concentration (if solution): 1 mg/mL

USE OF RESTRAINERS FOR PREVENTING INGESTION: no
Duration and frequency of treatment / exposure:
6 hours (or 3 hours for animals to be sacrificed at this time); one application
Doses / concentrations
Dose / conc.:
5 mg/kg bw (total dose)
No. of animals per sex per dose / concentration:
12 male rats at one dose level
Control animals:
no
Positive control reference chemical:
no
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled (delete / add / specify): urine, faeces, blood, plasma, serum or other tissues, cage washes, bile
- Time and frequency of sampling:
- Other:
Pairs of rats were at 3, 6, 12, 24, 48 or 72 hours after dosing.
Urine was collected at intervals 0-6, 6-24, 24-48 and 48-72 hours and faeces at 24-hour intervals, only from the rats to be sacrificed at 24, 48 and 72 hours.
Expired air was also collected, in traps containing ethanolamine : 2-ethoxyethanol (1:3, v/v) from the rats sacrificed at 24, 48 and 72 hours. Radioactivity in whole-blood and in plasma was measured at terminal sacrifice.

The following organs/tissues were sampled: liver, kidney, muscle, fat, testes, heart, eyes, brain, lungs, adrenals, bone marrow, lymph nodes, pancreas, spleen, thymus, thyroid, gastro-intestinal tract, treated skin and untreated skin
The dressing covering the treated skin and swabs used to removed unabsorbed dose were also taken for measurement of residual radioactivity.

Results and discussion

Main ADME resultsopen allclose all
Type:
excretion
Type:
distribution

Toxicokinetic / pharmacokinetic studies

Details on absorption:
after the 6-hour period, it was possible to remove a mean of 47.89% dose from the skin of the 6 rats. Means of 0.19% dose was measured in the treated skin of these 6 rats after removal of the excess dose.
Details on distribution in tissues:
Proportions of the applied dose in tissues were greatest at 3-6 hours in the gastro-intestinal tract GIT (2-7% dose), at 3 hours in liver and fat (0.6 - 0.9% dose) and at 3 hours in muscle (0.3-0.4% dose). Radioactivity in all other tissues measured was <0.1% dose at 3-6 hours except in the kidneys and plasma (<0.2% dose). At 12 hours, amounts of dosed radioactivity had decreased slightly in the GIT (2-4% dose), liver (0.08-0.2% dose) and fat (0.1-0.3% dose). At this time radioactivity in all other tissues measured was either Peak concentrations of radioactivity in tissues of the 12 rats were measured at 3-6 hours after dose application. At 24 hours, concentrations were not appreciably lower in the GIT but were substantially lower in liver, kidneys and fat. At 72 hours, concentrations had declined appreciably in the GIT, and had decreased further in liver, kidneys and fat.
The tissue:plasma concentration ratios showed higher concentrations than in plasma during 3-48 hours in the GIT, liver, kidneys, fat, lymph notes and pancreas.
Details on excretion:
Mean overall recovery of 76.4% attributed to the loss of some material by volatilisation during application of the dose to the skin.
Total urinary excretion until the time of sacrifice accounted for means of 8?04, 12.36 and 9.91% dose in the pairs of rats sacrificed at 24, 48 and 72 hours recpectively.
Total excretion of radioactivity in faeces accounted for 1.17, 2.29 and 2.42% dose in rats sacrificed at 24, 48 and 72 hours respectively.
Radioactivity in the expired air traps accounted for means of 17.55, 15.77 and 14.78% dose until the times of sacrifice at 24, 48 and 72 hours respectively. Most of this radioactivity was un the first expired trap (overall mean of 12.57% dose) with a smaller proportion in the second trap (overall mean of 3.47% dose). Radioactivity in the expired air traps may mostly be attributed to 14C-limonene volatilised directly from the site of application.

Metabolite characterisation studies

Metabolites identified:
not measured

Applicant's summary and conclusion

Conclusions:
Interpretation of results: low bioaccumulation potential based on study results.
An appreciable proportion of the dermally applied dose (48%) was recovered in the dose washings. The radioactivity in urine (10% dose) and in faeces (2% dose) showed that these proportions were absorbed throught the skin. Radioactivity in the expired air traps may mostly be attributed to volatilisation from the site of application. However, there may also be a contribution of absorbed and exhaled air.
Renal excretion of limonene and/or its metabolite is expected to be the major route (as confirmed by studies using the oral route). The radioactivity in the faeces, gastro-intestinal tract and liver indicate some hepatic elimination.
Executive summary:

Twelve male rats received one dermal dose of 5 mg/kg bw for 6 hours (or 3 hours for those sacrificed at this time). Pairs of rats were sacrificed at 3, 6, 12, 24, 48 and 72 hours after dosing. Urine, faeces, plasma and various tissues were sampled and their radioactivity content measured.

Almost half the administered dose was removed by skin washing at the end of the application time. The renal route is the main one but faeces and exhaled air are also involved.