2,2,4-trimethylpentane

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study meets generally accepted scientific principles, acceptable for assessment.

Objective of study:

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

- Only male rats were used. It would have been useful to see if the excretion patterns differed in female rats for which kidney toxicity may not be of concern; limited documentation.

GLP compliance:

not specified

Radiolabelling:

yes

Species:

rat

Strain:

other: F344/N

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 9-15 weeks

Route of administration:

inhalation

Vehicle:

unchanged (no vehicle)

Details on exposure:

TYPE OF INHALATION EXPOSURE: nose only

Duration and frequency of treatment / exposure:

one single dose for 2 hours

Remarks:

Doses / Concentrations:
nominal: 1.0 and 350 ppm (corresponding to 0.00473 and 1.7 mg/L)
analytical: 0.79 ± 0.22 and 385 ± 56 ppm

No. of animals per sex per dose / concentration:

4

Control animals:

no

Positive control reference chemical:

no data

Details on study design:

no data

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, serum or other tissues, cage washes, bile
- Time and frequency of sampling: Urine and feces were collected at all times except 1 or 2 hours post-exposure.



METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled (delete / add / specify): urine, faeces, tissues, cage washes, bile
- Time and frequency of sampling:
- From how many animals: (samples pooled or not)
- Method type(s) for identification (e.g. GC-FID, GC-MS, HPLC-DAD, HPLC-MS-MS, HPLC-UV, Liquid scintillation counting, NMR, TLC)
- Limits of detection and quantification:
- Other:


TREATMENT FOR CLEAVAGE OF CONJUGATES (if applicable):

Statistics:

A Bonferroni correction was applied to each group of t-tests comparing high and low exposure groups.

Metabolites identified:

not specified

Uptake rates were 3.4 and 2.2 nmol/kg/min/ppm for low and high isooctane (2,2,4 -trimethylpentane) levels, respectively. The fraction of inhaled hydrocarbon that was metabolised [sum of excreta, exhaled CO2 and carbon-14 equivalents in the carcass] was higher at low inhaled concentrations than at high inhaled concentrations. Major route of elimination was urine, for low exposure concentration 14C in urine exceeded 11% of total inhaled isooctane. The amount of inhaled 14C in the carcass at 70 hours post-exposure was less than 2% of total inhaled for both low and high concentrations. The fraction of inhaled parent compound exhaled unchanged was approx. 2%. Half of isooctane (2,2,4 -trimethylpentane) 14C retained at the end of the 2 hour exposure was eliminated within 15 hours post-exposure but elimination continued primarily by the urinary route throughout 70 hours of observation. The almost exclusive elimination of metabolites of inhaled isooctane via the kidney with little production of 14CO2 suggests that kidneys may be exposed to a higher concentration of high molecular weight metabolites of isooctane.

Conclusions:

Interpretation of results: low bioaccumulation potential based on study results

Reference 2

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study meets generally accepted scientific principles, acceptable for assessment.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Principles of method if other than guideline:

Guidance for conduct of the in vitro dermal kinetic experiments was posted in the United States FR, April 26, 2004 (Volume 69, Number 80), pages 22402-22441, "In vitro dermal absorption rate testing of certain chemicals of interest to the occupational safety and health administration".

GLP compliance:

not specified

Radiolabelling:

yes

Species:

other: in vitro human skin model

Strain:

other: in vitro human skin model

Sex:

not specified

Details on test animals or test system and environmental conditions:

not applicable

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Duration of exposure:

up to 60 min

Doses:

infinite dose: 1200 µL/cm2
10 min: 20 µL
60 min: 20 µL

No. of animals per group:

in vitro human skin model

Control animals:

no

Details on in vitro test system (if applicable):

see "any other information on materials and methods"

Signs and symptoms of toxicity:

not examined

Dermal irritation:

yes

The flux values for Normal-Heptane and the 10 and 60 min short-term absorption values (the quantity of chemical remaining in the skin plus that portion that had penetrated the skin was detected in the receptor fluid) were 63.2 µg/cm2/h, 113 µg/cm2/h (for the 10 min flux) and 22.1 µg/cm2/h (for the 60 min flux). Therefore, 10 min flux value for Normal-Heptane (based on both the amount in the skin and the receptor solution) was greater than the flux measured in a similar manner over 60 min.

Skin integrity measurements were taken before and after each experiment. All reporting laboratories (Normal-Heptane: Hask, DuPont Haskell Laboratory, USA) either used tritiated water permeability or electrical resistance (impedance) to confirm skin integrity; for consistency and to ease comparisons, all tritiated Kp values were converted to electrical impedance values expressed in kilo-ohms (k-ohms). A ratio of post- to pre-test impedance of "1" indicates that the skin barrier did not change over the course of the experiment. In the Kp experiments, skin exposed to Normal-Heptane had a damage ratio of 0.57, confirming that approx. 43% of the skin barrier function was lost due to exposure to Normal-Heptane. The barrier properties for the skin in the short-term experiments were given as the ratios of 0.90 for 10 min and 0.88 for 60 min.

Recovery of the applied dose, based on liquid scintillation count data when the radioactive chemical form was spiked into the non-radiolabeled chemical, was 95.5% (for the Kp experiment), 54.0% (for the 10 min experiment) and 110.0% (for the 60 min experiment).

At the end of the Kp experiment, the portion of Normal-Heptane in the skin (0.01%) was less than the portion in the receptor solution (0.12%). The portion of Normal-Heptane in the donor solution (wash) was 95.4%. In contrast to the Kp experiment, the skin (0.14%) retained a larger percentage of Normal-Heptane following a 10 min exposure. The portion of Normal-Heptane in the donor solution (wash) was 6.84% at 10 min. The greater portion of the applied dose remaining in the skin at 10 min suggests that partitioning into the skin from the donor solution is the driver of penetration with this brief exposure. After the 60 min experiments, there was also a larger percentage of n-heptane in the receptor solution (0.12%) than in the skin (0.06%). The increased proportion of Normal-Heptane detected in the receptor solution illustrates and confirms the movement of the chemical from the skin into the receptor solution.

Conclusions:

Under the test conditions, Normal-Heptane was able to penetrate the skin. During prolonged exposure, the penetration of the skin was aggravated, since the exposure to n-heptane simultaneously reduced skin barrier function.

Executive summary:

Under the test conditions, Normal-Heptane was able to penetrate the skin. During prolonged exposure, the penetration of the skin was aggravated, since the exposure to Normal-Heptane simultaneously reduced skin barrier function.

Description of key information

Short description of key information on bioaccumulation potential result: 

See toxicokinetics, metabolism and distribution.

Short description of key information on absorption rate: 

Under dermal in vitro test conditions, n-heptane was able to penetrate the skin. During prolonged exposure, the penetration of the skin was aggravated, since the exposure to n-heptane simultaneously reduced skin barrier function. Similar properties are expected for 2,2,4 -trimethylpentane.

Due to the experimental setup, e.g. undepletable reservoir of test substance and therefore absence of any evaporation, the dermal penetration factors reported by Fasano and McDougal (2008) are very conservative. In contrast, when using a diffusion cell, which is a more realistic setup for volatile subsances like hydrocarbon solvents, dermal penetration rates of 0.1 µg/cm2/h and 0.0005 µg/cm2/h were obtained for heptane and octane, respectively (Tsuruta, 1982).

Additional information

Differences in biological fate of inhaled nephrotoxic iso-octane and non-nephrotoxic n-octane were explored by Dahl (1989) in rats exposed to¹⁴C-labeled vapor by nose-only inhalation at concentrations of 0, 1.0, and 350 ppm for a single 2 hour exposure.Radioactivity of exhalant, urine, and feces was measured for 70 hours post-exposure after which residual radioactivity in the carcasses was determined. Inhaled uptake of n-octane was greater than iso-octane uptake at both concentrations. The uptake rates were 3.4 and 2.2 nmol/kg/min/ppm for low and high iso-octane levels, respectively. The fraction of inhaled hydrocarbon that was metabolised [sum of excreta, exhaled CO₂ and carbon-14 equivalents in the carcass] was higher at low inhaled concentrations than at high inhaled concentrations.The major route of elimination was urine, for low exposure concentration¹⁴C in urine exceeded 11% of total inhaled iso-octane.The amount of inhaled ¹⁴C in the carcass at 70 hours post-exposure was less than 2% of total inhaled for both low and high concentrations. The fraction of inhaled parent compound exhaled unchanged was approx. 2%. Half of iso-octane ¹⁴C retained at the end of the 2 hour exposure was eliminated within 15 hours post-exposure but elimination continued primarily by the urinary route throughout 70 hours of observation.The almost exclusive elimination of metabolites of inhaled iso-octane via the kidney with little production of ¹⁴CO₂ suggests that kidneys may be exposed to a higher concentration of potentially toxic high molecular weight metabolites of iso-octane.

In general, C₇-C9 alkanes are readily absorbed and distributed through the body. n-Alkanes are readily metabolized and excreted in urine and expired as CO₂. Iso-Alkanes are less readily metabolized to a range of metabolites that are excreted in the urine. Tissue/blood ratios are greater than unity, especially for iso-alkanes, but on prolonged administration, metabolizing enzymes appear to be induced and ratios decrease. For n-alkanes, there appears to be a very low rate of metabolism to potentially neurotoxic gamma diketones, and no such metabolism for the iso-alkanes.

Discussion on bioaccumulation potential result:

See toxicokinetics, metabolism and distribution.

Discussion on absorption rate:

There are no dermal absorption data available on iso-octane. However, there are reliable data available for a structural analogue. Thus, read-across was conducted based on an analogue approach.

Fasano and McDougal (2008) described the procedures for determination of a permeability coefficient (Kp) and two short-term dermal absorption rates at 10 and 60 min. The flux values for n-heptane and the 10 and 60 min short-term absorption values (the quantity of chemical remaining in the skin plus that portion that had penetrated the skin was detected in the receptor fluid) were 63.2 µg/cm2/h, 113 µg/cm2/h (for the 10 min flux) and 22.1 µg/cm2/h (for the 60 min flux). Therefore, the 10 min flux value for n-heptane (based on both the amount in the skin and the receptor solution) was greater than the flux measured in a similar manner over 60 min.

Skin integrity measurements were taken before and after each experiment. A ratio of post- to pre-test impedance of "1" indicates that the skin barrier did not change over the course of the experiment. In the Kp experiments, skin exposed to n-heptane had a damage ratio of 0.57, confirming that approx. 43% of the skin barrier function was lost due to exposure to n-heptane. The barrier properties for the skin in the short-term experiments were given as the ratios of 0.90 for 10 min and 0.88 for 60 min. At the end of the Kp experiment, the portion of n-heptane in the skin (0.01%) was less than the portion in the receptor solution (0.12%). The portion of n-heptane in the donor solution (wash) was 95.4%. In contrast to the Kp experiment, the skin (0.14%) retained a larger percentage of n-heptane following a 10 min exposure. The portion of n-heptane in the donor solution (wash) was 6.84% at 10 min. The greater portion of the applied dose remaining in the skin at 10 min suggests that partitioning into the skin from the donor solution is the driver of penetration with this brief exposure. After the 60 min experiments, there was also a larger percentage of n-heptane in the receptor solution (0.12%) than in the skin (0.06%). The increased proportion of n-heptane detected in the receptor solution illustrates and confirms the movement of the chemical from the skin into the receptor solution. Under the test conditions, n-heptane was able to penetrate the skin. During prolonged exposure, the penetration of the skin was aggravated, since the exposure to n-heptane simultaneously reduced skin barrier function.