Reaction mass of 2-methylbutyl acetate and pentyl acetate

Basic toxicokinetics

Administrative data

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:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Materials and methods

Objective of study:

absorption

metabolism

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Combined evaluation of gas uptake inhalation measurements, plethysmography and a blood sampling system (for analysis of each parent chemical and its alcohol or acid metabolites) developed to determine the respiratory bioavailability of a series of alcohols and acetate esters in rats.

Test material

Test material information

Constituent 1

Reference substance name:

Reaction mass of 2-methylbutyl acetate and pentyl acetate

EC Number:

908-918-1

Molecular formula:

Unspecified

IUPAC Name:

Reaction mass of 2-methylbutyl acetate and pentyl acetate

Details on test material:

- Name of test material (as cited in study report): amyl acetate mixture
- Analytical purity: see below for composition
- Composition of test material, percentage of components: 65% pentyl acetate, 35% 2-methyl butyl acetate and <0.1% isoamyl acetate content
- Lot/batch No.: no data (from Dow Chemical Co.)
- Other: the test substance was evaluated in paralell with ethyl Acetate, propyl acetate, n-propanol, sopropyl acetate, n-butanol, isobutyl acetate, isobutanol, isobutyl isobutyrate, n-pentanol, n-pentyl acetate, and amyl alcohol mixture

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: male SD rats with indwelling jugular cannulas from Hilltop Lab Animals, Inc. (Scottsdale, PA)
- Age at study initiation: no data
- Weight at study initiation: 270 - 350 g
- Fasting period before study: no data
- Housing: no data
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): PMI 5002 Cetified Rodent Diet (Animal D
- Water (e.g. ad libitum): deionised water (reverse osmosis)
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 72 ± 3
- Humidity (%): 50 ± 20
- Air changes (per hr): 15-20
- Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

unchanged (no vehicle)

Details on exposure:

TYPE OF INHALATION EXPOSURE: head only

GENERATION OF TEST ATMOSPHERE / CHAMPER DESCRIPTION
- Exposure apparatus: closed, 8-l gas uptake exposure chambre. The tubular shaped plethysmograph chamber was modified to be positioned inside the gas uptake chamber so that respiratory parameters (tidal volume, respiratory rate, and minute volume) could be measured concurrent with the gas uptake studies. The gas uptake exposure chamber was retrofitted to accommodate the plethysomgraph and intravenous jugular cannula without changing the existing chamber lid by fabricating a 1" thick Plexiglas ring positioned between the desiccator-style chamber and the chamber lid. Both the pneumotachograph tube and cannula were passed through ports attached to this ring.
- Method of holding animals in test chamber: a restrained whole-body plethysmograph from Buxco Electronics, Inc. (Sharon, CT) was used for non-invasive ventilatory measurements on conscious animals. The animals were restrained in a constant-pressure plethysmograph with an attached pneumotachograph. A neck seal separated the head of the animal from the body chamber and ventilatory parameters were computed from flow measurements through the pneumotrachograph from the body chamber. Total length of time that any given animal was restrained in the gas uptake chamber never exceeded 2.5 hours, in accordance with the Batelle ACC committee instructions.
- Source and rate of air: no data
- Method of conditioning air: no data
- System of generating particulates/aerosols: each test material was added through a heated injection port
- Composition of vehicle (if applicable): no data
- Concentration of test material in vehicle (if applicable): not applicable; the concentration in the chamber was monitored using gas chromatography at 7-9 min intervals (depending on the chemical) for up to 2 hours
- Method of particle size determination: no data
- Treatment of exhaust air: no data

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: no data
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): no data

Duration and frequency of treatment / exposure:

once for 2 hours

Doses / concentrations

Remarks:

Doses / Concentrations:
2000 ppm in normal air (corresponding to approx. 10.8 mg/L)

No. of animals per sex per dose / concentration:

6

Control animals:

other: same animals (pre-exposure values) and historical

Positive control reference chemical:

None specified; the test substance was evaluated together with 12 additional compounds and mixtures

Details on study design:

- Dose selection rationale: these studies were designed to determine the respiratory bioavailability of chemicals. They were not intended to determine metabolic rate constants. Therefore, animals were exposed to a single concentration/chemical. For chemicals for which this group has previous gas uptake data (ethyl acetate, butanol, propanol, propyl acetate, isobutanol) gas uptake parameters were linear for 200 and 2000 ppm exposures. Therefore, 2000 ppm exposures were utilized to maximize analytical quantification. For chemicals with which previous data is not available, 2000 ppm was also used.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled : blood
- Time and frequency of sampling: blood samples of about 0.1 ml each were drawn from the jugular cannula using a heparinised syringe prior to exposures and at 5, 10, 15, 20, 25, 30, 40, 50, 60, and 90 min after injection of test material into the chamber.

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: blood
- Time and frequency of sampling: see above
- From how many animals: samples not pooled
- Method type(s) for identification: GC-FID; blood was placed in pre-weighed 4-ml screw cap vials containing 2 µg phenylmethylsulfonyl fluoride to stop any further hydrolysis. The vials were quickly sealed, weighed, and placed on dry ice. Samples were frozen at -80°C until analysis. The samples were analysed by gas chromatography using Stabilwax DA capillary column 2/FID as column/detector, 2-methyl butyl acetate, pentyl acetate, pentyl alcohol and valeric acid/butyl alcohol and 2-methyl butyric acid as internal standards with 2.4, 4.5 and 9.2/5.6, 6.3, and 13.1 min as respective retention time, and ethyl acetate as extracting solvent.

Statistics:

None

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

The alcohol metabolites exhibited the highest Cmax value, indicating a rapid conversion from the test substance parent to the alcohol. The acid metabolite was near limits of detection.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

n-Pentanol and valeric acid were identified, as well as 2-methyl butyl butanol and methyl butyric acid

Any other information on results incl. tables

Test substance loss

The non-specific loss (in the absence of animals) of test substance from the chamber was biphasic, showing an initial more rapid loss, and generally tended to be slightly greater for the acetates than for the alcohols.

The specific chamber loss rates were fairly high (up to 66% over the first hour). The additional loss of chemical from the chamber in the presence of a live rat was always substantially greater than non-specific chamber loss (Table 1).

 

Respiratory parameters

Minute volume and tidal volume decreased immediately after the introduction of chemical, resulting in a relatively stable respiratory rate

 

Table 1: n-Pentyl acetate/2 -Methylbuty acetate (average of all live rats)

Average time (hours)		n-Pentyl acetate/2 -Methylbuty acetate chamber concentration (ppm)
Mean	Standard deviation	Mean	Standard deviation
0.16	0.02	2012.01/1077.52	86.57/38.42
0.32	0.02	1503.43/819.98	95.99/47.20
0.48	0.03	1186.85/650.25	93.08/43.60
0.63	0.03	965.44/532.01	81.88/38.17
0.79	0.03	805.01/444.24	73.47/34.05
0.95	0.04	677.85/372.62	66.39/30.64
1.11	0.03	584.18/620.00	57.91/26.75
1.26	0.04	509.31/277.94	54.47/24.99
1.42	0.04	445.45/241.82	50.70/23.06
1.58	0.04	388.66/209.02	45.49/20.02
1.74	0.05	344.47/183.99	44.72/19.63
1.90	0.05	306.31/162.79	41.34/18.20
2.05	0.6	288.48/151.94	32.48/12.25

 

Table 2: Average blood n-pentyl acetate, n-pentanol and valeric acid concentrations from gas uptake exposures to n-pentyl acetate (at indicated average time period)

Time period (min)	Average concentrations (µM) of
	n-Pentyl acetate/2 -methyl butyl acetate		n-Pentanol/2 -methyl butanol		Valeric acid/methyl butyric acid
	Mean	SD	Mean	SD	Mean	SD
0.08	24.61/8.05	9.68/2.09	36.2/28.3	11.82/5.05	1.95/5.31	0.77/3.88
0.17	31.56/9.97	13.77/3.67	55.0/41.4	17.12/9.25	2.88/10.26	0.88/3.01
0.25	27.85/9.40	17.75/4.31	54.3/43.5	14.51/7.97	3.10/13.50	0.88/4.09
0.33	28.28/8.66	8.34/1.67	58.6/46.6	15.43/8.03	3.01/15.12	0.68/7.13
0.42	25.00/8.49	9.53/3.30	54.9/45.7	13.62/8.08	2.86/16.92	0.76/7.80
0.50	24.68/8.39	7.49/2.30	52.3/44.2	13.22/8.56	2.60/16.94	0.92/8.33
0.67	18.81/7.08	4.07/0.83	47.6/49.3	13.84/7.66	2.38/16.53	0.78/7.82
0.83	20.71/7.11	6.20/2.22	39.9/34.8	9.86/6.76	2.45/14.85	1.04/7.34
1.00	22.69/7.48	6.77/2.25	33.8/31.7	9.31/8.41	2.13/13.57	0.83/6.34
1.50	19.50/6.51	9.29/1.31	24.2/22.5	9.70/7.16	1.17/7.04	0.26/1.93