Sodium acrylate

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:

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

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Disposition and metabolism of Acrylic acid (AA) in C3H mice after single cutaneous administration.

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)

Radiolabelling:

yes

Species:

mouse

Strain:

C3H

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: C3H/HeNCrlBR
- Age at study initiation: approx. 35 d old
- Weight at study initiation: 21 g
- Diet (ad libitum): Agway Prolab Diet Mouse, Agway Inc., Syracuse, NY
- Water (ad libitum)

Route of administration:

dermal

Vehicle:

acetone

Details on exposure:

TEST SITE
- Area of exposure: 1.0 X 1.0 cm
- Type of wrap if used: nonocclusive dose containment devices constructed from Stomahesive and cemented to the skin with Skin-Bond
- Time intervals for shavings or clipplings: prior to application


REMOVAL OF TEST SUBSTANCE
- Washing (if done): at the end of experiment to remove the unabsorbed portion of the dose


TEST MATERIAL
- concentration (if solution): 1 mL test AA/100 mL acetone


VEHICLE
- Amount(s) applied (volume or weight with unit): 0.95 and 3.8 mL/kg bw, respectively

Duration and frequency of treatment / exposure:

72 hrs

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose / concentration:

15

Control animals:

no

Details on study design:

- Dose selection rationale: The cutaneous dose levels were selected based on previous work on the cutaneous toxicity of AA in several strains of mice (DePass et al. 1984, Tegeris et al. 1988).

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 350 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps. In addition to the in-line volatile organics trap, the dose-containment device was modified by cementing activated charcoal-impregnated filter paper sheets to the top of the frame in order to trap the volatile fraction of the applied dose at the dosing site.

Details on absorption:

After cutaneous administration of single doses (40 or 10 mg/kg bw) to C3H mice, the processes of AA absorption and elimination were rapid and nearly complete within 8 h. Evaporation from the dosing site accounted for the largest fraction of the applied dose, although total recovery of the dose was variable. After 40 mg/kg bw, 11.4 ± 1.7% (mean t ± SD, n= 5) of the dose was absorbed (sum of cumulative proportions exhaled as 14CO2 or excreted in urine or faeces and the proportions found in dosing site skin, tissues, and carcass at 72 h), and after 10 mg/kg bw, 12.4 ± 3.3% was absorbed. Metabolism to 14CO2 was the major route of elimination, accounting for 83.5 ± 8.4% and 77.7 ± 10.4% of the absorbed dose after the high and low dose, respectively. Elimination via other routes was minor.

Details on distribution in tissues:

At the end of the experiment, 0.2-1.5% of the dose was found in the dosing site skin, and about 1% was found in tissues and carcass. Exhalation of volatile organic compounds other than 14CO2 was not quantified separately but was presumed to be negligible based on the results from orally dosed animals. Elimination of radioactivity from the dosing site skin, plasma, liver, and kidney was rapid. The concentration of radioactivity found in fat at 72 h was greater than that found at 1 or 8 h.

Metabolites identified:

no

Details on metabolites:

Neither AA nor its metabolites were detected in livers from mice at any time after cutaneous administration of 40 mg/kg bw.

Disposition of radioactivity in C3H mice after cutaneous administration of [1 -14C]AA:

	Dose
	40 mg/kg bw	10 mg/kg bw
14CO2	9.6 ± 2.2	9.3 ± 1.2
Volatilized dose	49.9 ± 12.6	70.9 ± 9.6
Urine	0.4 ± 0.1	0.3 ± 0.1
Faeces	0.2 ± 0.1	0.4 ± 0.1
Cage wash	0.2 ± 0.1	0.2 ± 0.1
Tissues	0.0 ± 0.0	0.2 ± 0.1
Carcass	0.8 ± 0.8	0.5 ± 0.1
Dosing-site skin	0.2 ± 0.1	1.5 ± 2.3
Skin rinse	0.2 ± 0.1	0.6 ± 0.3
Total recovery	61.5 ± 14.0	84.0 ± 10.5

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

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:

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

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Disposition and metabolism of Acrylic acid (AA) in Fischer 344 rats after single cutaneous administration.

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: F344/NHsd
- Age at study initiation: approx. 7 wk old
- Weight at study initiation: 210 g
- Diet (ad libitum): Agway Prolab Diet Rat, Agway Inc., Syracuse, NY
- Water (ad libitum)

Route of administration:

dermal

Vehicle:

acetone

Details on exposure:

TEST SITE
- Area of exposure: 2.5 X 4.0 cm (high dose), 1.0 X 2.5 cm (low dose)
- Type of wrap if used: nonocclusive dose containment devices constructed from Stomahesive and cemented to the skin with Skin-Bond
- Time intervals for shavings or clipplings: prior to application


REMOVAL OF TEST SUBSTANCE
- Washing (if done): at the end of experiment to remove the unabsorbed portion of the dose


TEST MATERIAL
- concentration (if solution): 1 mL test AA/100 mL acetone


VEHICLE
- Amount(s) applied (volume or weight with unit): 0.95 and 3.8 mL/kg bw, respectively

Duration and frequency of treatment / exposure:

72 hrs

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose / concentration:

15

Control animals:

no

Details on study design:

- Dose selection rationale: The cutaneous dose levels were selected based on previous work on the cutaneous toxicity of AA in several strains of mice (DePass et al. 1984, Tegeris et al. 1988).

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 500 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps. In addition to the in-line volatile organics trap, the dose-containment device of the low-dose animals was modified by cementing activated charcoal-impregnated filter paper sheets to the top of the frame in order to trap the volatile fraction of the applied dose at the dosing site.

Details on absorption:

After cutaneous administration of single doses (40 or 10 mg/kg bw) to Fischer 344 rats, AA absorption and elimination were rapid and nearly complete within 8 h after either dose. Evaporation accounted for the largest fraction of the applied dose, although total recovery of the applied dose was only about 50-60%. After application of 40 mg/kg, 25.6 ± 1.5% (mean ± SD, n= 5) of the dose was absorbed. After 10 mg/kg, 19.4 ± 1.3% of the dose was absorbed. The major route of elimination of the absorbed dose was via exhalation of 14CO2, which accounted for 77.0 ± 5.5 and 69.5 ± 1.3% of the absorbed dose after the 40 and 10 mg/kg doses, respectively. Approximately 1% of the dose remained in the dosing site skin after either dose.

Details on distribution in tissues:

Elimination of radioactivity from plasma and tissues was rapid except for fat, where concentrations measured at 72 h were higher than those measured at earlier times.

Details on excretion:

Urinary excretion accounted for 1-2% of the dose, with most occurring within the first 24 h. Excretion in faeces accounted for less than 1%, and approximately 2-3% of the dose was found in peripheral tissues and the carcass at the end of theexperiment.

Metabolites identified:

yes

Details on metabolites:

Urine collected from rats after the cutaneous routes was analyzed by HPLC for AA and metabolites. After cutaneous dosing, a peak that coeluted with AA was detected in urine along with the polar major metabolite which was also found after oral dosing. A trace amount of one other metabolite was detected in urine from the 40 mg/kg bw cutaneous dose group but not after 10 mg/kg bw.

Disposition of radioactivity in Fischer 344 rats after cutaneous administration of [1 -14C]AA:

	Dose
	40 mg/kg bw	10 mg/kg bw
14CO2	19.7 ± 2.2	13.5 ± 1.0
Volatilized dose	26.5 ± 6.9	41.3 ± 5.8
Urine	2.0 ± 0.7	0.8 ± 0.1
Faeces	0.8 ± 0.1	0.5 ± 0.2
Cage wash	0.5 ± 0.1	0.3 ± 0.0
Tissues	0.1 ± 0.0	0.2 ± 0.0
Carcass	1.7 ± 0.5	2.8 ± 0.9
Dosing-site skin	1.0 ± 0.3	1.4 ± 0.6
Skin rinse	0.2 ± 0.1	0.4 ± 0.1
Total recovery	52.2 ± 7.6	61.1 ± 5.3

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Reference 3

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Qualifier:

no guideline followed

Principles of method if other than guideline:

Absorption of [14C]-acrylic acid measured through human and mouse skin.

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: 99 %
- Supplier: Sigma Aldrich Chemical Co Ltd, Dorset, England

- Radiochemical purity (if radiolabelling): 98 %
- Specific activity (if radiolabelling): no data
- Locations of the label (if radiolabelling): no data
- Supplier: Sigma Aldrich Chemical Co Ltd, Dorset, England

Radiolabelling:

yes

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: 1. Mouse: Female Crl:CD-1(ICR)BR mice, 6-8 weeks old.
2. Human: Human abdominal whole skin was obtained post mortem.
- Ethical approval if human skin: yes
- Type of skin: back
- Preparative technique:
1. Mouse: After killing, the backs of the mice were clipped carefully, ensuring that the skin was not damaged. The clipped area of skin was excised and, after removal of any subcutaneous fat, stored in foil at 4°C until required for use (<1 week).
2. Human: Human abdominal whole skin (dermis + epidermis) was obtained post mortem from subjects of varying age. Surplus fat was removed from the abdominal skin samples leaving the dermis and epidermis intact. The samples were stored at 4°C in foil until required for use (<1 week).
- Thickness of skin (in mm): no data
- Membrane integrity check: by measurement of their permeability to tritiated water
- Storage conditions: 4°C

PRINCIPLES OF ASSAY
- Diffusion cell: glass diffusion cell
- Receptor fluid: saline (0.9%)
- Static system: yes
- Test temperature: 30°C± 1°C
- Occlusion: yes

Absorption in different matrices:

1) Absorption rates were influenced by the vehicle (acetone > water > phosphate buffer).
2) Absorption rates were proportional to the applied concentration in each vehicle.
3) The amount of acrylic acid in the skin membrane during the steady state absorption period was proportional to the steady state absorption rate (within each species).
4) Mouse skin was 3 times more permeable than human skin.

Remarks on result:

other:

Steady state absorption rates:

1. Absorption rates [in µg/cm2/hr] through human skin:

Solvent	Acetone	Water	Phosphate buffer
Concentration [%]
0.01	0.204 ± 0.136 *	0.037 ± 0.015 *	0.007 ± 0.003 *
0.1	3.18 ± 2.06 *	0.44 ± 0.165 *	0.047 ± 0.030 **
1.0	16.1 ± 2.66 *	5.16 ± 0.702 *	0.898 ± 0.787 **
4.0	99.9 ± 64.0 *	28.9 ± 6.25 *	7.23 ± 3.94 *

* (n=5); ** (n=4)

2. Absorption rates [in µg/cm2/hr] through mouse skin:

Solvent	Acetone	Water	Phosphate buffer
Concentration [%]
0.01	0.651 ± 0.144 *	0.101 ± 0.015 *	0.022 ± 0.003 *
0.1	6.93 ± 2.16 *	0.964 ± 0.113 *	0.191 ± 0.048 *
1.0	103 ± 15.4 *	15.0 ± 3.49 *	2.60 ± 1.17 *
4.0	201 ± 130 *	69.3 ± 12.5 *	12.4 ± 0.694 **

* (n=5); ** (n=4)

The calculated Damage Ratios showed that the vehicles (containing l% w/v acrylic acid) caused little, if any, change to the permeability characteristics of the membranes. Membranes which have been exposed only to water, in a similar manner, had Damage Ratios of between 0.8 -1.1 (Downes AM et al, 1967).

Different profiles of absorption were apparent from each vehicle. Four concentrations were studied (4%, 1%, 0.1% and 0.01% w/v acrylic acid and similar profiies were detected with each concentration in each vehicle. From the acetone vehicle there was a short period, a lag phase, following skin contact, before the steady state period of absorption. With the water vehicle there was a similar lag phase as seen from the acetone vehicle, but from the phosphate buffer vehicle a larger lag phase was apparent before the establishment of a steady state absorption phase. These patterns were seen with both the mouse and human skin, however, the lag phases were longer through human skin than mouse skin. The lag times through mouse skin from the acetone and water vehicles were 1-2 hours and 2-4 hours from the phosphate buffer vehicle. Through human skin the lag time values were 2-6 hours from the acetone and water vehicles and approximately 4-12 hours from the phosphate buffer vehicle.

It is apparent from the data that the steady state absorption rates were influenced by the applied concentration in the vehicle. The data also show that mouse skin is more permeable than human skin to acrylic acid. For both species the steady state absorption rates were highest from acetone > water > phosphate buffer.

In addition to profiles and rates of absorption measured, the amount of [14C]acrylic acid in the skin membrane during the steady state absorption period was detemined following the 1% applications of each vehicle.

Concentration in Skin after 1% Application:

Skin type	Solvent	Amount in skin [µg/cm2]
	Acetone	49.1
Mouse	Water	26.8
	Phosphate buffer	4.04
	Acetone	95.8
Human	Water	58.1
	Phosphate buffer	9.34

Interestingly, more acrylic acid was found in human skin than in mouse skin. This might not have been expected since absorption rates were higher through the mouse skin. However, within a species and hence membrane-type, there was a proportionality between the amount in the membrane and the absorption rate. This is not believed to be due to the much thicker epidermis and dermis present in human skin acting as the diffusion barrier but due to differences in the structure and composition of the principal diffusion barrier, the stratum corneum, in both species.

Reference 4

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Principles of method if other than guideline:

Metabolic in-vitro studies on tissue slices and homogenates from rats (F344 and Sprague Dawley), using 1-14C-labelled AA. The rate of oxidation [expressed as nmol CO2/h per g tissue or mg protein and kinetic parameters (pseudo-Km and Vmax) were determined.

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: 98 %
- Supplier: Rohm and Haas Company

- Radiochemical purity (if radiolabelling): > 98 % and 95 %, respectively
- Specific activity (if radiolabelling): 0.1-0.5 mCi/mmol and 1.44 mCi/mmol, respectively
- Locations of the label (if radiolabelling): [1-14C]Acrylic acid
- Supplier: Sigma Chemical Co. (St. Louis, MO) and Chemsyn Science Laboratories (Lenexa, KS), respectively

Radiolabelling:

yes

Species:

rat

Strain:

other: Fischer 344 and Sprague Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Wilmington, MA)
- Weight at study initiation: 249 ± 50 g (Fischer 344); 386 ± 120 g (Sprague-Dawley)
- Housing: 1-2 per cage
- Diet (ad libitum): Purina Certified Lab Chow Checkers (Purina, St. Louis, MO)
- Water: ad libitum

Toxicokinetic parameters:

other: The kidney and liver were the organs showing the highest oxidation rates. All tissues were able to oxidize AA to a certain extent. Lung, glandular stomach, heart, spleen, small and large intestine oxidized AA at rates that were between 10 and 40 %.

Toxicokinetic parameters:

other: Oxidation of AA in Fischer 344 rat kidney and liver slices were described by pseudo MIchaelis-Menten kinetics. The pseudo Km value did not vary between kidney and liver: ca. 0.5 mM. However, the pseudo Vmax in kidney was approx. twice the value in liver.

The kidney and liver were the organs showing the highest oxidation rates, with maximal velocities of 4 and 2 µmol/h/g, respectively. The metabolic conversion rate was similar in both strains with no difference between slice model and homogenate. All tissues were able to oxidize AA to a certain extent, but with considerable variation. Lung, glandular stomach, heart, spleen, small intestine and large intestine oxidized AA at rates that were between 10 and 40 % of the rate measured in liver. The remaining tissues (forestomach, brain, skin, fat, and muscle) oxidized AA at less than 10 % of the rate observed in the liver.

Compared to the mouse (see Black et al., 1993), the absolute rates per g tissue in the rat are 2 - 3 x higher than in the mouse.

Oxidation of AA in Fischer 344 rat kidney and liver slices were described by pseudo MIchaelis-Menten kinetics. The pseudo Km value did not vary between kidney and liver: approx. 0.5 mM. However, the pseudo Vmax in kidney was approx. twice the value in liver. At relatively low concentrations, i.e. well below km, AA oxidation would follow apparent first-order kinetics, and the half-life of AA in liver and kidney would be approx. 10 min or less.

AA tissue-to-blood partition coefficients were measured in homogenates by micropartitioning. Relatively little variation between tissues in the partition coefficient was observed, with values ranging between 0.9 (fat) and 2.1 (brain).

Reference 5

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Qualifier:

no guideline followed

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Radiochemical purity (if radiolabelling): > 98 %
- Specific activity (if radiolabelling): 0.1 - 0.5 mCi/mmol
- Locations of the label (if radiolabelling): 1. [1-14C]AA; 2. [2,3-14C]AA (radiochemical purity and specific activity identical for both species)
- Supplier: Sigma Chemical Co., St. Louis, MO

Radiolabelling:

yes

Species:

mouse

Strain:

other: C3H/HeNCrlBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Wilmingtob, MA)
- Age at study initiation: 1.5 to 4.5 months
- Housing: 6/cage
- Diet (ad libitum): Purina certified Lab Chow Checkers
- Water (ad libitum): tap water

Metabolites identified:

yes

Details on metabolites:

HPLC analysis of incubation medium following metabolism of [1 -14C]AA by mouse kidney:
Kidney slices formed a metabolite that coeluted with a 3-hydroxypropionic acid standard. No other metabolites were found in this analysis. Samples from incubations of [1-14C]AA with either mouse liver, skin, or small intestine were also analyzed by HPLC, and a peak that coeluted with 3-hydroxypropionic acid was found in each.

Kinetic parameters for AA oxidation in mouse liver, kidney and skin were determined. Oxidation of [1-14C]AA to 14CO2 by liver, kidney and skin slices followed pseudo-Michaelis-Menten kinetics. Marked differences between these tissues in the pseudo-Vmax existed. The rate in the kidney was about 5-fold higher than the rate in the liver which, in turn, was about 12-fold higher than the rate in the skin.

Kinetic constants for acrylic acid metabolism in mouse tissue slices:

Tissue	Pseudo-Km [mM]	Pseudo-Vmax [nmol/hr/g]	Half-life [hr]
Kidney	0.558 ± 0.068	2890 ± 436	0.139 ± 0.026
Liver	0.759 ± 0.032	616 ± 62	0.867 ± 0.069
Skin	0.694 ± 0.058	47.9 ± 5.8	10.2 ± 0.6

The rate of AA oxidation in 10 additional tissues was measured at 1 and 5 mM AA. All tissues studied oxidized [1 -14C]AA; however, the rate varied considerably between tissues. The kidney, by far, was the most active tissue, oxidizing AA at a rate about five fold higher than in the liver, which was the next most active tissue. The other tissues oxidized AA at relatively low rates. Lung, glandular stomach, heart, spleen, fat, and large intestine oxidized AA at rates that were between 10 and 40 % of the rate measured in liver. The remaining tissues, forestomach, small intestine, brain, skin, and muscle oxidized AA at less than 10 % of the rates observed in liver. The rate of oxidation at 5 mM AA was l.5 to 3 times higher than the rate measured at 1 mM AA except for the fat, in which the rates were similar at these concentrations. Rates of AA oxidation in tissues from male and female mice were similar.

Oxidation of [2,3 -14C]AA in kidney and liver slices:

Endproducts of acrylic acid metabolism are CO2 and Acetyl-CoA which is derived from carbons 2 and 3 of AA. Acetyl-CoA generated from AA in this manner could then enter the TCA cycle to provide for the complete oxidation of AA carbons to CO2. In both liver and kidney, the rate of 14CO2 formation from [2,3-14C]AA was about two-thirds of the rate from [1 -14C]AA.

Reference 6

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Principles of method if other than guideline:

Investigation of the pathway of acrylic acid metabolism to CO2 in rats.

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Radiochemical purity (if radiolabelling): > 95 %
- Supplier: Sigma Chemical Co.

- Locations of the label (if radiolabelling): [1-14C]AA
- Specific activity (if radiolabelling): 0.1 - 0.43 mCi/mmol

- Locations of the label (if radiolabelling): [2,3-14C]AA
- Specific activity (if radiolabelling): 0.4 - 1.0 mCi/mmol

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc. (Kingston, NY)
- Weight at study initiation: 150 - 300 g
- Housing: 2/cage
- Diet (ad libitum): Purina Mills Inc., St. Louis, MO
- Water: ad libitum

Metabolites identified:

yes

Details on metabolites:

Major intermediate: 3 -hydroxypropionic acid

The rate of 14CO2 formation from [14C]AA was measured in vitro with three different preparations from rat liver. Rat liver hepatocytes metabolized AA to CO2 at a rate of approximately 40 nmol/hr/mg protein. Disruption of the cells and reconstitution of the homogenate with buffers and cofactors resulted in a substantial loss of enzyme activity to approximately 5% of the whole cell rate. Isolation of the mitochondria from the tissue homogenate resulted in an 21 - fold increase in the specific enzyme activity responsible for 14CO2 production. These results suggest that the metabolism of AA to CO2 occurs primarily in the mitochondria. To determine if the mitochondrial oxidation of AA could be augmented by other hepatic fractions, [1 -14C]AA and mitochondria were incubated in the presence of various amounts of either 12500g supernatant (homogenate depleted of mitochondria), microsomes or cytosol. The rate of mitochondrial metabolism of AA was not affected by the addition of other subcellular fractions. In addition, neither 12500g supernatant, microsomes nor cytosol oxidized [1 -14C]AA significantly by themselves, further supporting the conclusion that the mitochondrion is the site of metabolism of AA.

The rate of 14CO2 formation by hepatic homogenates or mitochondria from AA radiolabeled at the olefinic carbons, [2,3 -14C]AA, was significantly less than AA radiolabeled at the carboxyl carbon, [1 -14C]AA, suggesting that not all the carbons of AA are metabolized to CO2 with equal efficiency and that the olefinic carbons may instead be bioincorporated into other molecules.

The metabolism of AA to CO2 was characterized further by examining the kinetics of the reaction. A plot of the rate of metabolism of [1 -14C]AA in liver homogenate versus AA concentration was consistent with apparent Michaelis-Menten kinetics. The metabolism observed with mitochondria and hepatocytes also followed apparent Michaelis-Menten kinetics. The apparent Km for AA metabolism in mitochondria and liver homogenates was about 0.1 mM, but this value was abaut 5 -fold higher in rat hepatocytes. The apparent Vmax was highest in mitochondria and was about 35 and 95% lower in isolated hepatocytes and liver homogenates, respectively.

HPLC analysis of [1-14C]AA metabolites following mitochondrial metabolism revealed the presence of a metabolite that coeluted with a synthetic standard of 3 -hydroxypropionic acid.

The presented results are consistent with the incorporation of AA into a secondary pathway for propionic acid metabolism in which 3 -hydroxypropionate is an intermediate. In this pathway, AA is first converted to acrylyl-CoA which is subsequently oxidized to 3 -hydroxypropionate. 3 -Hydroxypropionate is, in turn, metabolized to acetate and CO2 via malonic semialdehyde. The resultant acetate is then incorporated into intermediary metabolism. This pathway has been reported to be a major pathway for the metabolism of propionic acid in various insect and plant species, but is a secondary pathway in mammals. Identification of 3 -hydroxypropionate as a metabolite of AA in conjunction with the observed inhibition of the mitochondrial metabolism of AA by propionic acid indicates that AA is incorporated into this secondary pathway.

Reference 7

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Qualifier:

no guideline followed

Principles of method if other than guideline:

The reaction of acrylic acid with glutathione and nonprotein sulfhydryls of rat blood in vitro were measured by the methods of Nachtomi (1970) and Beutler et al. (1963), respectively.

Nachtomi (1970). Biochem. Pharmacol. 19: 2853-3860
Beutler et al. (1963). J. Lab. Clin. Med. 61 (5): 882-888

GLP compliance:

no

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 99 %
- Supplier: Celanese Chemical Company, Houston, Texas

Radiolabelling:

no

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Wilmington, Mass.
- Age at study initiation: 8 weeks for biotransformation studies and 4-8 months for non-protein sulfhydryl studies.
- Housing: 2/ cage in stainless steel cages with wire bottoms
- Diet: Purina Lab Chow, ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

Metabolites identified:

not measured

Reaction of acrylic acid with reduced glutathione in vitro:

Only a 6 % depletion of GSH occurred in 30 min after adding 4 mM acrylic acid to 2 mM GSH in phosphate buffer, indicating that there is only a minimal spontaneous reaction between acrylic acid and GSH. Addition of an aliquot of a soluble enzyme preparation (100000 x g fraction) did not increase the reaction between acrylic acid and GSH. In contrast, the addition of 2 mM and 4 mM ethylacrylate caused a 40 and 74 % depletion of GSH within 30 min, respectively.

Effects of acrylic acid on nonprotein sulfhydryls of rat blood in vitro:

8 mM acrylic acid had only a minimal effect on blood NPSH. By comparison, a pronounced depletion of NPSH occurred when ethyl acrylate was added to rat blood in vitro at final concentrations ranging from 1 to 8 mM.

Reference 8

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:

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

Objective of study:

metabolism

Qualifier:

no guideline followed

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: 99 %
- Supplier: Alfa Products (Danvers, MA)

- Radiochemical purity (if radiolabelling): 97 % (HPLC analysis)
- Specific activity (if radiolabelling): 2.43 mCi/mmol
- Locations of the label (if radiolabelling): [2,3-14C]AA
- Polymerisation inhibitor: 200 ppm hydroquinone monomethyl ether and dilution of the labeled monomer in toluene

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Stone Ridge, NY)
- Age at study initiation: 35 days old
- Weight at study initiation: 120 - 130 g

- Housing: Glass metabolism cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 3 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24
- Humidity (%): 40-65
- Photoperiod (hrs dark / hrs light): 12 h light/dark cycle

Route of administration:

oral: gavage

Vehicle:

other: 0.5 % aqueous methylcellulose

Duration and frequency of treatment / exposure:

72 hrs

Dose / conc.:

4 mg/kg bw/day

Remarks:

excretion and distribution study

Dose / conc.:

40 mg/kg bw/day

Remarks:

excretion and distribution study

Dose / conc.:

400 mg/kg bw/day

Remarks:

excretion and distribution study

Dose / conc.:

4 mg/kg bw/day

Remarks:

Glutathion depletion study

Dose / conc.:

40 mg/kg bw/day

Remarks:

Glutathion depletion study

Dose / conc.:

400 mg/kg bw/day

Remarks:

Glutathion depletion study

Dose / conc.:

1 000 mg/kg bw/day

Remarks:

Glutathion depletion study

No. of animals per sex per dose / concentration:

3 per dose for excretion and distribution studies
4 per dose for Glutathione Depletion Studies

Control animals:

other: Only for Glutathione Depletion Studies: Control animals received corn oil alone (2  mL/kg) with or without pretreatment with TOCP.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, tissues- liver, stomach (emptied of contents), gastrocnemius muscle and epididymal fat.
- Time and frequency of sampling: urine and faeces were collected at 6, 24, 48 and 72 h postdosing. Expired carbon dioxide was trapped in a solution of 30 % ethanolamine in 2-methoxyethanol and the trapping solution was collected at 0.25, 0.5, .075, 1.0, 1.5, 2.0, 4.0, 6.0, 8.0, 24, 48 and 72 h post dosing. Expired volatile organics were trapped with a synthetic activated charcoal (Rohm & Haas Ambersorb XE-348).

Statistics:

The significance of dose-related effects, the effect of the inhibitor, TOCP, and the interaction of these two treatment variables were determined by analysis of variance with Duncan's multiple range test for the comparison of means. The calculations were conducted on an IBM 3084 mainframe computer using SAS statistics, Version 5 (SAS Institute, Inc., Cary, NC).

Details on distribution in tissues:

The residual radioactivity remaining in representative major tissues examined after 72 hr was 19-25% for AA. Somewhat higher levels of residual
radioactivity were noted in adipose tissue, liver, and stomach (dosing site).

Details on excretion:

Following an oral dose of [14C]AA, a rapid elimination of the isotopic tracer was noted. Within 8 hr 35-60% of the dose was eliminated from the animals with most of the elimination occurring as expired carbon dioxide. By 24 hr 50-65% of the dosed radioactivity had been eliminated, and the excretion of radioactivity had virtually ceased.

Metabolites identified:

yes

Details on metabolites:

The primary excretory metabolite for acrylic acid was carbon dioxide, accounting for 44 - 65 % of the dose.
The HPLC profile of metabolites observed in the urine of rats following dosing with [14C]AA indicated the presence of 3-hydroxypropionic acid. The detection of this metabolite suggests the incorporation of AA into propionic acid metabolism and may explain the rapid evolution of carbon dioxide from AA. The main metabolite which eluted very near to the solution front could not be identified. The excretion of this metabolite decreased slightly with increasing dose from 3% of the dose at 40 mg/kg bw to 1% of the dose at 400 mg/kg bw. This metabolite accounted for the majority of the [14C]AA-derived radioactivity excreted in the urine over a 72-hr period. Radioactivity could not be detected at the retention times corresponding to that of 2,3-epoxypropionic acid or N-acetyl-S-(2-carboxy-2-hydroxyethyl)cysteine. Thus, epoxidation to 2,3-epoxypropionic acid was neither in vivo nor in vitro observed.

The distribution of dosed radioactivity in male rats following a single oral dose of AA:

Dose (mg/kg bw)	Urine	Faeces	CO2	Tissues	Total recovered
4	2.9 ± 0.6	2.4 ± 0.4	65.3 ± 1.1	18.9 ± 0.9	89.5 ± 0.3
40	2.7 ± 0.3	3.6 ± 0.1	58.5 ± 3.4	24.0 ± 8.4	88.8 ± 4.9
400	4.3 ± 1.6	2.6 ± 0.7	44.1 ± 14.9	24.6 ± 0.4	75.6 ± 16.2

All values are expressed as percentage of dosed radioactivity.

Tissues included liver and stomach, as well as estimates of the body burden of dosed radioactivity in blood, adipose, and muscle.

The tissue distribution of dosed radioactivity in male rats following a single oral dose of AA:

Dose (mg/kg bw)	Tissues (percentage of dose)
	Adipose	Blood	Plasma	Liver	Muscle	Stomach
4	9.14	0.87	0.35	1.68	6.99	0.19
40	13.43	1.10	0.30	1.71	7.54	0.18
400	15.24	0.83	0.21	2.23	6.54	0.18

The tissue burden of total radioactivity derived from the dosed compound was calculated from estimates of the fraction of body weight for adipose (11 %), muscle (50 %), blood (9 %), and plasma (4.5 %).

Each value is the mean of three rats.

Acrylic acid did not significantly decrease hepatic nonprotein sulfhydryl (NPSH) content in the liver, blood, or forestomach at oral doses of < 8 % AA in the dose solution (400 mg/kg bw), although a significant depletion of NPSH was observed in the glandular stomach at doses > 0.08 % (4 mg/kg bw). No conjugation involving the double bond of AA could be detected in in vitro reactions with glutathione or in the in vivo metabolites, suggesting a secondary effect of AA on NPSH content in these organs. The weights of the forestomach and glandular stomach increased with AA dose, reflecting gross edema and inflammation.

Reference 9

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:

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

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Disposition and metabolism of Acrylic acid (AA) in C3H mice after single oral administration.

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)

Radiolabelling:

yes

Species:

mouse

Strain:

C3H

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: C3H/HeNCrlBR
- Age at study initiation: approx. 35 d old
- Weight at study initiation: 21 g
- Diet (ad libitum): Agway Prolab Diet Mouse, Agway Inc., Syracuse, NY
- Water (ad libitum)

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

- Vehicle: Milli-Q filtered water at a final concentration of 4 or 15 mg/mL
- Dosing volume: 10 mL/kg bw

Duration and frequency of treatment / exposure:

once

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose / concentration:

15

Control animals:

no

Details on study design:

- Dose selection rationale: The oral dose of 40 mg/kg bw was selected for comparison to previous work on the disposition of [2,3-14C]AA in Sprague-Dawley rats (de Bethizy et al. 1987) and the 150 mg/kg bw dose was selected since a similar oral dose induced slight, acute gastric irritation in Fischer 344 rats (Ghanayem et al. 1985).

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 350 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps.

Details on absorption:

Absorption and elimination of AA were rapid and nearly complete within 24 h after administration of single oral doses of either 150 or 40 mg/kg bw to C3H mice. Metabolism to 14CO2 was the major route of elimination, accounting for about 80% of the administered dose (92% of recovered radioactivity).

Details on distribution in tissues:

Approximately 1% or less of the dose remained in the tissues and carcass at the end of the experiment. Elimination of radioactivity from stomach tissue, plasma, liver and kidney was rapid, but it was somewhat slower from fat.

Details on excretion:

Urinary excretion accounted for about 3% of the dose, with most occurring during the first 24 h. Excretion in faeces accounted for about 1% of the dose. Only trace amounts of exhaled volatiles other than 14CO2 were detected.

Metabolites identified:

yes

Details on metabolites:

Livers collected from orally dosed mice were analyzed by HPLC for AA and metabolites. Unchanged AA was not detected 1 h after oral administration; however, several metabolites that were more polar than AA were detected, including 3-hydroxypropionate and peak 1, the metabolite that was also the major urinary metabolite in rats. Neither AA nor its metabolites were detected at later times after oral administration.

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Disposition of radioactivity in C3H mice after oral administration of [1 -14C]AA:

	Dose
	150 mg/kg bw	40 mg/kg bw
Exhaled 14CO2	80.0 ± 4.1	76.8 ± 2.8
Exhaled volatiles	0.1 ± 0.0	0.1 ± 0.0
Urine	3.4 ± 1.3	3.0 ± 1.4
Faeces	1.2 ± 1.2	1.2 ± 0.4
Cage wash	1.9 ± 2.2	0.5 ± 0.3
Tissues	0.1 ± 0.1	0.3 ± 0.0
Carcass	0.3 ± 0.1	0.8 ± 0.1
Total recovery	86.9 ± 6.1	82.5 ± 2.1

Reference 10

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:

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

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Disposition and metabolism of Acrylic acid (AA) in Fischer 344 rats after single oral administration.

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material (as cited in study report): Acrylic acid
- Analytical purity: > 98 % (unlabeled AA)
- Supplier: Union Carbide Corporation

- Radiochemical purity (if radiolabelling): >= 98.6 %
- Specific activity (if radiolabelling): 0.14 - 0.4 mCi/mmol
- Locations of the label (if radiolabelling): [1-14C]AA
- Supplier: Sigma Chemical Co. (St. Louis, Mo.)

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY)
- Substrain: F344/NHsd
- Age at study initiation: approx. 7 wk old
- Weight at study initiation: 210 g
- Diet (ad libitum): Agway Prolab Diet Rat, Agway Inc., Syracuse, NY
- Water (ad libitum)

- Individual metabolism cages: no

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

- Vehicle: Milli-Q filtered water at a final concentration of 4 or 15 mg/mL
- Dosing volume: 10 mL/kg bw

Duration and frequency of treatment / exposure:

once

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose / concentration:

15

Control animals:

no

Details on study design:

- Dose selection rationale: The oral dose of 40 mg/kg bw was selected for comparison to previous work on the disposition of [2,3-14C]AA in Sprague-Dawley rats (de Bethizy et al. 1987) and the 150 mg/kg bw dose was selected since a similar oral dose induced slight, acute gastric irritation in Fischer 344 rats (Ghanayem et al. 1985).

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood, plasma, stomach contents (after sacrifice)
- Time and frequency of sampling: Urine was collected under dry ice and faeces were collected at room temperature at 8, 24, 48, and 72 h. At 1 and 8 hrs, 5 animals from ech group were sacrificed and blood samples collected. Tissues were sampled at termination (liver, kidney, fat, stomach).
- Traps for volatile compounds:
Room air was drawn through the metabolism cages at a rate of approximately 500 mL/min. Expired 14CO2 was collected in traps containing a solution of 2-methoxyethanol : ethanolamine (7:3, v/v), which was replaced with fresh solution at regular intervals. Other exhaled volatile 14C-labeled organic compounds were collected onto activated charcoal traps (approximately 4 g) placed in series ahead of the 14CO2 traps.

Details on absorption:

In Fischer 344 rats, AA was rapidly absorbed and eliminated after single oral doses of either 150 or 40 mg/kg bw. Exhalation of 14CO2 was the major route of elimination, accounting for approximately 80-90% of the administered dose (94% of recovered radioactivity) after either dose level. This process was rapid and nearly complete within 8 h after administration of 40 mg/kg and within 24 h after 150 mg/kg. The somewhat slower rate of 14CO2 exhalation after the latter dose appeared to reflect slower absorption of the bolus dose.

Details on distribution in tissues:

AA-derived radioactivity was rapidly eliminated from stomach tissue, plasma, liver, and kidney, while elimination of radioactivity from fat was somewhat slower. Less than 2% of the dose remained in tissues or carcass 72 h after dosing.

Details on excretion:

Urinary excretion accounted for about 3-4% of the dose, with most occurring over the first 24 h. Excretion in faeces accounted for less than 0.2% of the dose. Only trace amounts of exhaled organic volatile compounds other than 14CO2 were detected.

Metabolites identified:

yes

Details on metabolites:

Urine collected from rats after the oral route was analyzed by HPLC for AA and metabolites. Several peaks of radioactivity were detected by HPLC and were designated according to their order of elution in urine samples from rats dosed orally with 40 mg/kg bw. Trace amounts of material that coeluted with AA were detected in urine of orally dosed rats. The major metabolite eluted early in the gradient and accounted for about 2-3% of the oral dose (identy unknown). A metabolite that coeluted with 3-hydroxypropionic acid was also detected. Small amounts of several other metabolites more polar than AA were detected, as well as small amounts of two metabolites that were less polar than AA.
Plasma and liver from orally dosed rats were also analyzed for AA and metabolites by HPLC. One hour after dosing, a metabolite in plasma that coeluted with 3-hydroxypropionic acid accounted for about 0.5% of the dose after 40 mg/kg. This metabolite was also detected in plasma after the high dose, but the levels were variable. The polar metabolite, which was also the major urinary metabolite, was the major metabolite found in the liver 1 h after 150 mg/kg and was the only metabolite in liver after 40 mg/kg. After the high dose, peaks corresponding to 3-hydroxypropionate and a small amount of AA were detected. Neither AA nor metabolites were detected in plasma or liver at times later than 1 h, nor were they detected in kidney at any time after administration.

Disposition of radioactivity in Fischer 344 rats after oral administration of [1 -14C]AA:

	Dose
	150 mg/kg bw	40 mg/kg bw
Exhaled 14CO2	81.6 ± 1.8	90.3 ± 1.0
Exhaled volatiles	0.2 ± 0.4	0.1 ± 0.2
Urine	4.2 ± 1.0	2.9 ± 0.2
Faeces	0.6 ± 0.1	0.7 ± 0.0
Cage wash	0.2 ± 0.2	0.2 ± 0.1
Tissues	0.3 ± 0.1	0.3 ± 0.2
Carcass	1.0 ± 0.2	0.8 ± 0.1
Total recovery	88.1 ± 2.0	95.2 ± 0.9

The less than complete recovery of the administered doses is probably explained by the volatile nature of acrylic acid and its propensity to bind to materials such as plastic and glass, properties that may also be shared by some of the metabolites of acrylic acid.

Description of key information

Sodium acrylate is the sodium salt of acrylic acid. Only the proton of the hydroxy group has been replaced by a sodium ion in NaA. Both are equally charged ions.pH dependent sodium acrylate dissociates into acrylic acid and sodium hydroxid in aqueous media.

According to Henderson-Hasselbalch: pH = pKs + lg (c(NaAcrylate) / c(Acrylic acid))

With the pKa-value of acylic acid = 4.25.

The ratio c(NaAcrylate) / c(Acrylic acid) was caluclated according to the Henderson-Hasselbalch equation: c(NaAcrylate) / c(Acrylic acid)) = 10 pH - pKs

pH 1 : c(NaAcrylate) / c(Acrylic acid)) = 10 1 – 4,25 = 0,00056; ~ 99,94 % as acrylic acid

pH 3 : c(NaAcrylate) / c(Acrylic acid)) = 10 3 – 4,25 = 0,056; t ~ 94,7 % as acrylic acid

pH 5 : c(NaAcrylate) / c(Acrylic acid) = 10 5 – 4,25 = 5,62; ~ 15,1 % as acrylic acid

pH 7 : c(NaAcrylate) / c(Acrylic acid) = 10 7 – 4,25 = 562,3; ~ 0,2 % as acrylic acid

Especially after oral uptake in the acidic environment in the stomach sodium acrylate is nearly completely dissociated to acrylic acid. Therefore, it is appropriate to use the human health hazard data of acrylic acid for the assessment of sodium acrylate. In respect to the hazard data on ecotoxicity, using the acrylic acid data assuming a complete dissociation reflects the worst case.

No experimental data on the test substance is available. Data on the structural analogue acrylic acid which has been extensively studied using in-vitro and in-vivo tests, is included. Due to the differing vapour pressure of the two substances, only studies by the oral route can be considered for the assessment of the toxicokinetic behaviour and metabolism of sodium acrylate in mammals. These data consistenly show the absence of potential for bioaccumulation for acrylic acid which is assumed for the test substance, too.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

No experimental data on the test substance is available. Therefore, the evaluation is based on a weight of evidence approach using the toxicological data of the structural analogue acrylic acid (CAS 79-10-7) (for WoE information, see chapter 13.2). Due to the differing vapour pressure of the two substances, only studies by the oral route can be considered for the assessment of the toxicokinetic behaviour and metabolism of sodium acrylate in mammals.

Following oral administration of [¹⁴C]-Acrylic acid in rats and mice, a high percentage of the radiolabel (60 – 80 %) was rapidly absorbed and eliminated as¹⁴CO₂ within 24 hours by both species. Excretion in urine and faeces accounted for 1-4 %, respectively. In rats, about 19-25 % of the acrylic acid-derived radioactivity remained in the tissues examined after 72 hr, mostly in adipose tissue and muscle. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the ß-oxidation pathway of propionate catabolism. No unchanged AA was detected; however, several metabolites that were more polar than AA were measured, including 3-hydroxypropionate.

 

The presented results are consistent with the incorporation of AA into a secondary pathway for propionic acid metabolism in which 3 -hydroxypropionate is an intermediate. In this pathway, AA is first converted to acrylyl-CoA which is subsequently oxidized to 3 -hydroxypropionate. 3 -Hydroxypropionate is, in turn, metabolized to acetate and CO₂via malonic semialdehyde. The resultant acetate is then incorporated into intermediary metabolism. This pathway has been reported to be a major pathway for the metabolism of propionic acid in various insect and plant species, but is a secondary pathway in mammals.

On the other hand, reaction with reduced glutathion does not play a major role in the detoxification and metabolism of acrylic acid.

 

Discussion on bioaccumulation potential result: 

In Vivo Studies:

 

C3H mice and Fischer 344 rats, respectively, were treated by gavage (40 or 150 mg/kg bw) with [1-¹⁴C]-acrylic acid. Mice rapidly absorbed and metabolised orally administered acrylic acid, with about 80% of the dose exhaled as¹⁴CO₂within 24 h. Excretion in urine and faeces accounted for approximately 3% and 1% of the dose, respectively. Elimination of the¹⁴C radiolabel from plasma, liver and kidney was rapid but it was slower from fat. The disposition of orally administered acrylic acid in rats was similar to the results obtained from mice. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the ß-oxidation pathway of propionate catabolism. No unchanged AA was detected 1 h after oral administration; however, several metabolites that were more polar than AA were measured, including 3-hydroxypropionate. Neither AA nor its metabolites were detected at later times after oral administration (Black et al., 1995).

 

Sprague-Dawley rats received single oral doses of [2,3-¹⁴C]-acrylic acid (4, 40 or 400 mg/kg bw in a 0.5 % aqueous methylcellulose solution). Within 8 hours, 35-60% of the dose was eliminated from the animal, mostly as expired CO₂. After 72 hours, 44-65% of the radioactivity had been eliminated via expired air, while 2.9-4.3% remained in urine, 2.4-3.6% in faeces and 18.9-24.6% in tissues examined (adipose tissue 9-15%, liver 1.7-2.2%, muscle 6.5-7.5% and blood 0.8-1.1%) (De Bethizy et al., 1987).

The HPLC profile of metabolites observed in the urine of rats indicated two major metabolites. One of the major metabolites co-eluted with 3-hydroxypropionic acid. Radioactivity could not be detected at the retention times corresponding to that of 2,3-epoxypropionic acid or N-acetyl-S-(2-carboxy-2-hydroxyethyl)cysteine leading to the conclusion that AA is not epoxidized to 2,3-epoxypropionic acid in vivo. This result was supported by an in vitro study. Hepatic microsomes were prepared using conventional methods from rats and incubations were started by the addition of 10 µL of [2,3-¹⁴C]-acrylic acid. No epoxidized metabolites could be detected and the parent compound was recovered from the incubation mixture unchanged (DeBethizy et al., 1987).

In addition, Glutathione Depletion Studies were conducted in rats that were administered doses of 4, 40, 400 or 1000 mg/kg bw AA by gavage. One hour following oral administration of acrylic acid in rats a significant depletion of NPSH in the glandular stomach was reported at doses above 4 mg/kg bw. In the forestomach NPSH depletion occurred at a dose of 1000 mg/kg bw. No significant effect of acrylic acid on NPSH in the blood or liver was observed (DeBethizy et al., 1987).

 

In Vitro Studies:

 

Dow Chemical (1979) have studied the metabolism of acrylic acid in rat tissue homogenates. Acrylic acid did not react with reduced glutathione either in the presence or absence of the soluble enzyme fraction. Non-protein sulfhydryl concentrations were not appreciably lower in blood after addition of acrylic acid in vitro (Dow Chemical, 1979).

 

The rate of¹⁴CO₂formation from [¹⁴C]-acrylic acid was measured in vitro with preparations from rat liver hepatocytes. Rapid oxidation of acrylic acid to CO₂was observed. Mitochondria isolated from the liver homogenates were incubated with acrylic acid under the same conditions and yielded higher rates of acrylic acid-oxidation than homogenates. HPLC analysis of the mitochondrial incubation mixtures indicated 3-hydroxypropionic acid as a major metabolite of AA (Finch & Frederick, 1992).

 

Black et al. (1993) determined the rate of the in vitro oxidation of acrylic acid in 13 tissues of mice. The maximal rate of acrylic acid oxidation in kidney, liver and skin was 2890, 616 and 48 nmol/h/g, respectively. In remaining organs acrylic acid was oxidized at rates less than 40% of the rate in liver. 3-Hydroxypropionic acid was the only metabolite detected by HPLC analysis.

Acrylic acid oxidation rates and blood tissue partition coefficients were studied in slices of rat tissue using [1-¹⁴C]-acrylic acid. Acrylic acid oxidation in rat kidney and liver slices was described by saturable kinetics with maximal rates of about 4 and 2 μmol/h/g, respectively. Acrylic acid oxidation rates in 11 additional tissues were 40% or less than that in liver (Black & Finch, 1995).

 

Discussion on absorption rate:

No experimental data on the test substance is available. Data on the structural analogue acrylic acid is included. Dermal absorption of sodium acrylate will probably be comparable or lower than absorption of acrylic acid. Thus, the read across represents a worst case scenario and is therefore acceptable for the hazard assessment of the substance.

The absorption of [¹⁴C]-acrylic acid from acetone, water, and phosphate buffer was measured through human and mouse skin in vitro. Membranes were mounted in glass diffusion cells and acrylic acid was applied in each solvent at 0.01 %, 0.1 %, 1 %, and 4 %, respectively (100 µL/cm²) under occlusive conditions. Samples were taken from the receptor solutions at recorded times, between 0 and 32 hr, and assayed for 14C content which was regarded as equivalent to acrylic acid. Steady state absorption rates were calculated to be between 0.007 µg/cm²/hr (human, 0.01 % AA in phosphate buffer) and 201 µg/cm²/hr (mouse, 4 % AA in acetone). Thus, absorption rates were influenced by the vehicle (acetone > water > phosphate buffer) and were proportional to the applied concentration in each vehicle. Mouse skin was 3 times more permeable than human skin under the conditions of the in vitro study (BAMM, 1988).

 

C3H mice and Fischer 344 rats, respectively, were treated dermally (10 or 40 mg/kg bw in acetone) with [1-¹⁴C]-acrylic acid. After cutaneous application to mice, about 12% of the dose was absorbed, while the remainder was apparently evaporated. Approximately 80% of the absorbed fraction of the dose was metabolised to¹⁴CO₂within 24 h. Excretion in urine and faeces each accounted for less than 0.5% of the dose. Elimination of radioactivity from plasma, liver, and kidney was rapid; however, levels in fat were higher at 72 h (0.5% of the higher dose) than at 8 h (0.1% of the higher dose). After cutaneous administration to rats, 19-26% of the dose was absorbed. Disposition of the absorbed fraction of the dose was similar to results found in mice. Results from an in vitro experiment with rat skin (Frantz cell) showed that at least 60 % of the applied dose evaporated and about 25% was absorbed, confirming the in vivo results. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the ß-oxidation pathway of propionate catabolism (Black et al., 1995).

 

No evaporation of dermally applied sodium acrylate from the skin is expected, but the absorbed fraction will be rapidly metabolised by the same pathway as described for acrylic acid.