1,4-dioxane

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Objective of study:

absorption

excretion

metabolism

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

no

Radiolabelling:

yes

Remarks:

14C

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Route of administration:

inhalation: vapour

Vehicle:

unchanged (no vehicle)

Details on exposure:

TYPE OF INHALATION EXPOSURE:
head only

GENERATION OF TEST ATMOSPHERE / CHAMPER DESCRIPTION
The dioxane vapour was pumped from the a Saran bag (Anspec) to the chamber via the 3-way connector, where it was diluted with room air to a total flow rate of 8 liters/min. The flow rate was adjusted to give a chamber concentration of 50 ppm. The ai exiting was continously moonitored using Wilks Miran I infrared analyzer equipment.

Duration and frequency of treatment / exposure:

once for 6 hr

Dose / conc.:

50 ppm

No. of animals per sex per dose / concentration:

4

Control animals:

no

Details on study design:

Four male Sprague-Dawley rats with jugular vein cannulas were placed in a 1 litre “head-only” chamber under dynamic air flow conditions. The flow rate of 1,4-dioxane vapour was adjusted to give a chamber concentration of 180 mg/m3 (50 ppm).

Details on dosing and sampling:

During and after the 6-hour exposure urine was collected and analysed.

Details on absorption:

When estimated from the total 1,4-dioxane (6.8 μg) and 1,4-dioxane equivalents of HEAA (21271 μg [= ratio of molecular weights]) excreted in urine, the rats absorbed at least 72 mg 1,4-dioxane/kg bw during the 6-hour exposure period. Assuming a respiratory minute volume of 240 mL/min for rats, these data indicate complete absorption.

Details on excretion:

The radioactivity expressed as 1,4-dioxane in plasma at the end of exposure was 7.3 μg/mL. Thereafter, the plasma concentration of 1,4-dioxane decreased in a log-linear manner until it was not detectable (<0.3 μg/mL) at 11 hours after the start of the experiment. A t½ of 1.01 hours was calculated.

The amounts of 1,4-dioxane and β-hydroxyethoxyacetic acid (HEAA) in urine during exposure (0-6 h) were 5.1 and 7613 μg, respectively, and afterward (6-48 h) 1.7 and 13659 μg, respectively. Hence, more than 99.9% of the total urinary excretion of the inhaled 1,4-dioxane was HEAA.

Metabolites identified:

yes

Details on metabolites:

The amounts of 1,4-dioxane and β-hydroxyethoxyacetic acid (HEAA) in urine during exposure (0-6 h) were 5.1 and 7613 μg, respectively, and afterwards (6-48 h) 1.7 and 13659 μg, respectively. Hence, more than 99.9% of the total urinary excretion of the inhaled 1,4-dioxane was HEAA.

Pharmacokinetics of 50 ppm 1,4-dioxane vapour inhaled for 6 hr by 4 male rats.

	Amount excreted in urine (µg), mean ± SD
Time (hr)	Dioxane	HEAA
0-6	5.1 ± 1.9	7613 ± 3540
6-48	1.7 ± 1.3	13659 ± 7071
0-48	6.8 ± 3.14	21271 ± 4810

Time (hr)	Plasma concentration of dioxane (mg/mL), mean ± SD
6	7.3 ± 2.0
7	4.5 ± 1.2
8	2.2 ± 0.7
9	1.0 ± 0.2
10	0.48 ± 0.12
11	0.3

Parameter	Value mean ± SD
rat weight, kg	0.215 ± 0.011
dose, mgEq	15535 ± 3511
dose, mg/kg	71.9 ± 3.6
K. hr^-1	0.6838 ± 0.1040
t1/2	1.01 ± 0.15

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Objective of study:

absorption

excretion

metabolism

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

no

Radiolabelling:

yes

Remarks:

14C

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Duration and frequency of treatment / exposure:

single and repeated (17 daily doses) dosing

Dose / conc.:

10 mg/kg bw/day (actual dose received)

Remarks:

single and repeated dosing

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Remarks:

single dosing only

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

Remarks:

single and repeated dosing

No. of animals per sex per dose / concentration:

single dosing: 3
repeated dosing: 2

Control animals:

no

Details on dosing and sampling:

PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: urine, faeces, expired air/CO2, carcass.

- Time and frequency of sampling:
single dosing study: radioactivity in urine and expired air was determined at 8 hour intervals for 24 hours for rats treated once with 10 mg/kg bw and for 72 hours for rats given once 100 or 1000 mg/kg bw. Faeces were collected at 24 hour intervals.
repeated dosing study: excreta were collected at 24 hour intervals for 17 days and at 8 hour intervals for 3 additional days (total collection was for 20 days).

Details on absorption:

After both single and repeated administration high absorption of 14C-1,4-dioxane occurs in rats, as demonstrated by urinary excretion of 75.74 - 98.74% of the applied dose and faecal excretion of only 0.46-2.05% of the applied dose.

Details on excretion:

After both single and repeated administration urinary excretion was 75.74-98.74% of the applied dose and faecal excretion was 0.46-2.05% of the applied dose.
The amount of expired 1,4-dioxane increases dose-relatedly from 0.43% of the administered dose at 10 mg/kg bw to 25.25% at 1000 mg/kg bw indicating saturation of urinary excretion/metabolism. Excretion in faeces and expired CO2 was not affected by dosage.
After multiple dosing, saturation also occurs, and, in addition, the amount of expired CO2 increases. When 1000 mg/kg bw/d was given repeatedly, expired 1,4-dioxane decreased and expired 14CO2 increased when compared with single dosing. This effect was not observed when 10 mg/kg bw was given repeatedly.

Metabolites identified:

yes

Details on metabolites:

β-hydroxyethoxyacetic acid (urine)
CO2 (expired air)

Cumulative excretion of radioactivity in rats after oral dosing

	percentage of the dose, mean± SD
	Single oral dose			Multiple oral dose
dose (mg/kg/bw)	10	100	100	10	1000
time (hr)	24	72	72	480	480
n	3	3	3	2	2
urine	98.74 ± 7.73	85.52± 7.11	75.74± 1.48	98.87± 0.33	82.32± 1.90
faeces	0.95 ± 0.73	1.95± 1.42	1.06± 0.41	0.46± 0.08	2.05± 0.19
expired 1,4-dioxane	0.43 ± 0.38	4.69± 0.40	25.25± 1.80	1.33± 0.04	8.86± 0.76
expired ^14CO2	3.07 ± 0.87	3.13± 0.21	2.39± 0.07	4.17± 0.20	6.95± 0.95
body	3.11 ± 0.18	1.47± 0.32	1.02 ± 0.10	0.63± 0.04	0.53± 0.01
total	106.3 ± 7.92	96.75± 7.85	105.46± 1.96	105.45± 0.29	100.7± 2.30

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1977

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Objective of study:

metabolism

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Spartan Research Animals, Inc , Haslett . Mich
- Weight at study initiation: about 250 g
- Individual metabolism cages: yes (in all-glass Rothtype metabolism chambers designed for the separate collection of urine and feces)
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 days

ENVIRONMENTAL CONDITIONS
No data.

Route of administration:

oral: gavage

Vehicle:

water

Duration and frequency of treatment / exposure:

single oral dose

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose / concentration:

2

Control animals:

no

Metabolites identified:

yes

Details on metabolites:

ß-hydroxyethoxyacetic acid

The major metabolite of dioxane in the urine of rats is ß-hydroxyethoxyacetic acid. In recent studies designed to compare the pharmacokinetics of high and low doses of dioxane in rats, the fate of dioxane was found to be dose-dependent (Young and Gehring, 1975). The dose dependency can result from saturation of a capacity-limited process by which dioxane is metabolized to HEAA . Indeed, it was observed that at low doses, dioxane was metabolized almost completely to HEAA.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Objective of study:

absorption

excretion

metabolism

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

no

Radiolabelling:

yes

Remarks:

14C

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 200 - 285 g

Route of administration:

intravenous

Vehicle:

unchanged (no vehicle)

Duration and frequency of treatment / exposure:

single application

Dose / conc.:

3 mg/kg bw/day (actual dose received)

Dose / conc.:

10 mg/kg bw/day (actual dose received)

Dose / conc.:

30 mg/kg bw/day (actual dose received)

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Dose / conc.:

300 mg/kg bw/day (actual dose received)

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

Control animals:

no

Details on excretion:

The plasma curves at low doses were linear with half‐life values of about 1 h.
As the dose was increased above 10 mg/kg the plasma clearance rate decreased, the fraction of the dose excreted as HEAA decreased, and the fraction of the dose excreted as dioxane per se in the urine and expired in the breath increased.
These data could be described by a one‐compartment open system model with parallel first‐order (urinary and pulmonary excretion) and Michaelis‐Menten (metabolism) elimination kinetics. At saturation, the maximum velocity of metabolism of dioxane to HEAA was about 18 mg/kg h.

Metabolites identified:

yes

Details on metabolites:

β-hydroxyethoxyacetic acid (HEAA) in urine.

- plasma clearance was clearly dose-dependent

- area under the curve (AUC) of plasma concentration to time curve increased disproportionally with increasing doses

- at normalisation of dose to AUC for 3 mg/kg the following relations are obtained:

Dose actual received	Dose normalised	AUC
3 mg/kg bw	1.0	1.0
10 mg/kg bw	3.3	3.9
100 mg/kg bw	33.3	128.5
1000 mg/kg bw	333.3	4438.7

t1/2 was determined to be approx. 1 – 1.5 h for doses of 3 and 10 mg/kg bw.

At 100 mg/kg bw the Cmax was observed after 4 hours after injection and at 1000 mg/kg bw a cmax remained for 35 hours after injection (followed by a linear decrease).

Plasma clearance was determined to be:

- 3.33 mL/min at 3 mg/kg bw

- 2.88 mL/min at 10 mg/kg bw

- 0.25 mL/min at 1000 mg/kg

Metabolic clearance was determined to be:

- 2.82 mL/min at 10 mg/kg bw

- 0.17 mL/min at 1000 mg/kg bw

Maximum metabolism rate was 18 mg/kg h

 

Excretion via urine (as % of applied dose):

- at dose of 10 mg/kg bw: 4 % dioxane and 92 % HEAA

- at dose of 1000 mg/kg bw: 10.8 % dioxane and 60 % HEAA

Description of key information

Based on experimental data, the test item is expected to be rapidly absorbed via the oral and inhalation route, whereas a low absorption by the dermal route is expected. Once bioavailable, the test item is almost completely metabolised to beta-hydroxyethoxy acetic acid (HEAA) and predominantly excreted via the urine. There are indications that this metabolic pathway becomes saturated at high doses and other metabolites are formed and excreted as CO₂ via exhalation.

There are no indications for a bioaccumulation potential of the test item.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

100

Absorption rate - inhalation (%):

100

Additional information

Radiolabelled 1,4-dioxane was rapidly and almost completely absorbed after oral and inhalation exposure by rats (Young et al., 1978).

 

After inhalation exposure by humans, 1,4-dioxane was also rapidly and for at least 50% absorbed (Young et al. 1977; IUCLID Section 7.10.5).

 

For dermal absorption no quantitative conclusions can be drawn. However, based on the study of Marzulli et al. (1981), it can be concluded that skin absorption occurs.

In an in vitro study it was demonstrated that 1,4-dioxane can penetrate human skin when occluded even though to a small extend, but rapidly evaporates from human skin when not occluded (Bronaugh, 1982).

 

However, for the risk assessment, 100% absorption is chosen for the oral, dermal and inhalation route as a worst case scenario.

 

Both ß-hydroxyethoxyacetic acid (HEAA) and 1,4-dioxan-2-one were identified as metabolite in rat urine (Braun and Young, 1977). Identification of these metabolites is pH-dependent. At a high pH, HEAA will be detected and at a low pH, HEAA will be converted to 1,4-dioxan-2-one. These two metabolites are in chemical equilibrium. At low pH the equilibrium is more shifted to 1,4-dioxan-2-one.

 

In human urine, the major metabolite was β-hydroxyethoxyacetic acid (HEAA; Young et al., 1977). In rats and humans the pharmacokinetic and metabolic fate of 1,4-dioxane is rather comparable.

 

The fate of dioxane was found to be dose-dependent in rats (Young et al. 1978). Dose dependency can result from saturation of a capacity-limited process by which dioxane is metabolized to HEAA. At low doses, dioxane was metabolized almost completely to HEAA.

A single oral dose of 10 mg/kg bw to rats was rapidly metabolised and excreted via the urine, while a single oral dose of 1000 mg 1,4-dioxane/kg bw saturated the metabolism of 1,4-dioxane to HEAA, resulting in decreased urinary excretion of HEAA and increased 1,4-dioxane in the expired air (Braun & Young, 1977).

In toxicity studies, morphological and biochemical changes were seen at exposure concentrations which lead to this saturation of metabolism (IUCLID Section 7.5 and 7.7).

 

2-Hydroxyethoxyacetaldehyde is believed to be the reactive metabolite responsible for some of the principal expressions of toxicity seen with 1,4-dioxane.

 

In rats, 1,4-dioxane was eliminated from the plasma by linear kinetics with a t½ of 1 hour after i. v. doses up to 10 mg/kg bw and after inhalation exposure to 180 mg/m³ (Young et al., 1978). At higher i. v. doses (≥100 mg/kg bw) elimination occurred progressively more slowly until plasma peak levels of 100 μg/mL were reached, where after elimination occurred with the same t½ of lower doses. Hence, saturation of metabolism occurs at 1,4-dioxane doses resulting in plasma levels above 100 μg/mL.

After inhalation exposure of humans to 180 mg/m³ 1,4-dioxane, 1,4-dioxane was rapidly eliminated from plasma (t½ of 1 h) and excreted via urine. Saturation did not occur (Young et al., 1977).