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Endpoint:
basic toxicokinetics in vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
No data
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Bioavailability of aluminium compounds including aluminium sulphate studied in rats; study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Objective of study:
absorption
Qualifier:
no guideline followed
Principles of method if other than guideline:
A bioavailability study is performed to measure the fraction of aluminium that leaves the gastrointestinal tract and enters the bloodstream following the ingestion of aluminium compounds.
GLP compliance:
yes
Radiolabelling:
yes
Remarks:
Al 26 - 26Al is as a carrier free solution was sourced from the PRIME Laboratory, Purdue University, Indiana, USA.
Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River (Canada).
- Age at receipt: 6 weeks
- Weight at receipt: Approximately 120 g
- Fasting period before study: Animals were fasted for 24 hours prior to test item administration.
- Housing: Animals were housed two per cage
- Individual metabolism cages: Yes
- Acclimation period:4-6 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 24 °C
- Humidity: 60%
- Photoperiod: 12 h dark / 12 h light
Route of administration:
other: oral: by gastric tube/in honey or intravenous
Vehicle:
other: insoluble powders - either as particulates suspended in water with added 1% carboxymethylcellulose or mixed with honey
Details on exposure:
Administration by gastric tube or honey: All test solutions were administered to the rats via a gastric feeding tube. Insoluble powders were administered either as particulates suspended in water with added 1% carboxymethylcellulose (to maintain a suspension) or added to the back of the rat tongue in honey – which experience has shown ensured that the particles were swallowed.
Administration by intravenous injection: 0.5 mL of aluminium citrate solution containing 0.19ng of 26Al was injected into the saphenous vein of rats under anaesthesia.

VEHICLE:
- Aluminium citrate injection: 1% citrate solution buffered at pH 6.5
- Solution for Ingestion: Aluminium citrate, Aluminium chloride, Aluminium nitrate and Aluminium sulphate
- Test Suspension: Aluminium hydroxide (1% carboxymethylcellulose in water); Aluminium oxide (2% carboxymethylcellulose in water); Aluminium Metal, Powdered pot electrolyte (honey); FD&C Red 40 aluminium lake (with added propylene glycol and 1% carboxymethylcellulose); SALP, KASAL and Sodium aluminium silicate
Duration and frequency of treatment / exposure:
Single administration
Remarks:
Doses / Concentrations:
Administered doses are as follows: 27Al dose per rat (mg); 26Al dose per Rat (ng)
Aluminium citrate injection: 0 mg, 0.19 ng
Aluminium chloride: 50 mg, 1.24 ng
Aluminium nitrate: 50 mg, 1.77 ng
Aluminium sulphate: 50 mg, 2.44 ng
Aluminium citrate: 50 mg, 1.47 ng
Aluminium hydroxide: 17 mg, 12.2 ng
Aluminium oxide: 23 mg, 17.9 ng
Aluminium metal: 6.9 mg, 1.2 ng
Powdered pot electrolyte: 26 mg, 2.40 ng
SALP: 10 mg, 0.46 ng
KASAL: 10 mg, 0.31 ng
Sodium aluminium silicate: 27 mg, 0.60 ng
FD&C Red 40 aluminium lake*: 414 mg, 0.96 ng
*: total mass of product
No. of animals per sex per dose / concentration:
12 females for aluminium citrate injection
6 females each for aluminium chloride, aluminium nitrate, aluminium sulphate, aluminium citrate, aluminium hydroxide, aluminium oxide, aluminium metal, powdered pot electrolyte, SALP, KASAL, sodium aluminium silicate and FD&C Red 40 aluminium lake
6 females for control group
Control animals:
other: received water without added 26Al
Positive control reference chemical:
Not applicable
Details on study design:
Intravenous injection: An initial experiment used 12 rats. This experiment was conducted in order to measure the fraction of bloodstream aluminium (i.e. uptake) that is retained by rats at 7 days post-injection. All rats were injected with an ultra-filtered aluminium citrate solution pH 6.5 prepared from 26Al in 0.02M nitric acid mixed with an equal volume of 2% trisodium citrate. After 7 days the animals were sacrificed and the fraction of the injected aluminium retained in the animal carcasses (less pelts) was determined. The fraction of 26Al intake was then determined by comparing the results for six rats where the short carcass was employed with the results for six carefully prepared entire rats.

Oral ingestion: Seventy-eight rats were then used for the subsequent ingestion study. Each test compound was administered to 6 rats. Test solutions / suspensions were prepared with the aim of administering ~ 1.4 ng of 26Al as citrate, nitrate, chloride and sulphate and >10 ng of 26Al as insoluble particulates and metal. (Note: these levels could not be achieved for the SALP, Kasal, sodium aluminium silicate, and FD&C red 40 aluminium lake and aluminium metal because the production method for these could not be scaled down sufficiently to produce small batch sizes. This resulted in the production of larger batches of test materials that contained much less 26Al/g than planned). These administered amounts were confirmed / adjusted by the analysis of triplicate doses. In addition, six control animals received water without added 26Al. After 7 days the rats were sacrificed and their pelts wetted to minimise dusting. The short carcass samples were ashed in a muffle furnace and white ash was produced. A known amount (typically 10 mg) of stable 27Al was added to each sample. The samples were then dissolved in acid and aluminium extracted by precipitation. Ion sources were prepared and the sample 26Al(ng): 27Al(g) ratio determined using AMS. The amount of 26Al present in each sample was then calculated from this ratio and then corrected to account for the radionuclide discarded with the unanalysed body parts. The fraction of aluminium absorbed was calculated by reference to the amount of 26Al administered and the fractional retention of injected aluminium at 7 days post-intake.
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption)
- Tissues and body fluids sampled: Full rat carcass (excluding the pelt and gastro-intestinal tract (GIT)) and short-carcass samples (which excluded the pelt, GIT, paws, tail and head – all of which were potentially contaminated by 26Al residues present in the bedding from urine and faeces)
- Time and frequency of sampling: Seven days after 26Al administration the control and experimental rats were euthanized (using carbon dioxide gas and cervical dislocation) and samples were collected.
Other:
- Carcass samples were kept in muffle furnace to 500 °C. After 12 hours at this temperature the ash was cooled, dissolved in 8 M nitric acid, dried and then re-ashed at 500 °C to produce a white ash for analysis.
- Measurement of 26A1 Content of Samples: The 26Al content of samples was analysed by using accelerator mass spectrometry (AMS).
- Determination of fractional GIT absorption: The amount of 26Al remaining in test rats at 7 days post-administration (after short-term clearance is completed) of the isotope by injection directly into the bloodstream and by gastric tube into the stomach were compared. The fractional bioavailability of each administered test compound was determined:
Bioavailability =Fraction administered dose in carcass at 7 days (by ingestion) / Fraction administered dose in carcass at 7 days (by injection)

In each case the carcass sample content was determined from the short-carcass sample content by multiplying the latter by a correction factor of 1.7 – derived from the comparison of the full carcass and short carcass results for the rats injected with 26Al-labelled citrate. For each material the mean bioavailability was calculated, ± the standard deviation of the mean (n = 5 or 6).
Statistics:
None
Preliminary studies:
Not applicable
Bioaccessibility (or Bioavailability) testing results:
- The results of the analysis of the six rats that received 26Al are shown in Table 7.1.1/1. It can be seen that the mean 26Al: 27Al ratio was 5.0 x 10^-13. This is ratio is about 500 times lower than that measured in the carcasses of rats that received aluminium citrate injections and about 7 times lower than the ratios measured following the administration of 26Al-labelled compounds. This background level is acceptable and was subtracted from all subsequent 26Al results prior to the calculation of 26Al sample content and absorbed fraction.
- At 7 days after injection 14.6% of the injected 26Al remained in the full rat carcass. In contrast only 8.6% of the injected 26Al remained in the short carcass samples that were used for the remainder of the study. It follows that a correction factor of 1.7 was used to estimate retention at 1 week for all experimental samples that employed the short carcass sample.
- AMS results of the analysis of administered doses showed that the mean amounts of 26Al administered were 1.6 ng for aluminium citrate, 1.1 ng for aluminium chloride, 1.9 ng for aluminium nitrate, 2.4 ng for aluminium sulphate, 12.2 ng for aluminium hydroxide, 17.9 ng for aluminium oxide, 1.3 - 1.5 ng for the aluminium metal, 2.4 ng for the powdered pot electrolyte, 0.46 ng for the SALP, 0.31 ng for the Kasal, 0.51 ng for the sodium aluminium silicate and 0.96 ng for the FD&C red 40 aluminium lake.
- Estimates of GI tract bioavailability were possible for all of the test materials except the aluminium metal, SALP and Kasal. In these cases the amount of 26Al present in the samples was insufficient to determine the 26Al: 27Al ratio. A reanalysis is expected. The calculated fractional uptake of 26Al for all the aluminium solutions was similar and ranged from a high uptake of 0.002 for aluminium sulphate to a low uptake of 0.0006 for aluminium chloride. The fractional uptake of 26Al administered as insoluble particulates was lower: 0.0003 for aluminium hydroxide; 0.0002 for aluminium oxide and 0.0003 for the 26Al administered as powdered pot electrolyte; 0.001 for the sodium aluminium silicate; 0.0009 for the FD&C red 40 aluminium lake. The results for aluminium metal, SALP and Kasal were <0.0003, <0.001 and <0.001, respectively.

Table 7.1.1/2: Mean measured fractional uptake of aluminium following gastric administration of 26Al – labelled compounds

 

Compound

Mean Fraction

SD

Upper 95% CI

Lower 95% CI

Aluminium Citrate

7.9 x 10-4

5.7 x 10-5

9.0 x 10-4

6.7 x 10-4

Aluminium Chloride

5.4 x 10-4

1.5 x 10-4

8.3 x 10-4

2.5 x 10 -4

Aluminium Nitrate*

4.5 x 10-4

1.3 x 10-4

7.0 x 10-4

2.0 x 10-4

Aluminium Sulphate

2.1x 10-3

7.9 x 10-4

3.7 x 10-3

5.6 x 10-4

Aluminium Hydroxide

2.5 x 10-4

4.1 x 10-4

1.1 x 10-3

-5.7 x 10-4

Aluminium Oxide

1.8 x 10-4

3.8 x 10-4

9.4 x 10-4

-5.9 x 10-4

Aluminium Metal

<6.0 x 10-4

 

 

 

Powdered Pot Electrolyte*

4.2 x 10-4

3.6 x 10-5

1.2 x 10-3

-3.1 x 10-4

SALP

<5.8 x 10-4

 

 

 

Kasal**

<7.7 x 10-4

 

 

 

Sodium Aluminium Silicate

1.2 x 10-3

1.1 x 10-4

1.5 x 10-3

1.0 x 10-3

FD&C Red 40 aluminium lake

9.3 x 10-4

2.0 x 10-4

1.3 x 10-3

5.4 x 10-4

*One outlier result censored **5 rats only The results of the present study in the rat confirm this expectation with the measured bioavailability decreasing in the order: aluminium sulphate (2.1 x 10-3); sodium aluminium silicate (1.2 x 10-3); FD&C red 40 aluminium lake (9.3 x 10-4); aluminium citrate (7.9 x 10-4); aluminium chloride (5.4 x 10-4); aluminium nitrate (4.5 x 10-4); aluminium in powdered pot electrolyte (4.2 x 10-4); aluminium hydroxide (2.5 x 10-4); aluminium oxide (1.8 x 10-4). The results for aluminium metal, SALP and Kasal were below the detection limit under the AMS conditions employed (<1.0 x 10-4, <5.8 x 10-4, and < 7.7 x 10-4, respectively), but are being reanalysed using different AMS conditions. Given the level of uncertainty in the mean (average SD ~13% of mean) bioavailability the ranked values given above should be treated with caution. However, it can be safely concluded that under the experimental conditions employed: the most bioavailable species was aluminium administered as aluminium sulphate: other soluble species, sodium aluminium silicate and FD&C red 40 aluminium lake have a similar bioavailability – within the range 5 x 10 -4 to 1 x 10-3; insoluble species were less bioavailable than soluble species with a bioavailability of about 2 x 10-4.

Conclusions:
Bioaccumulation potential cannot be judged based on study results.
Under the experimental conditions, the most bioavailable aluminium compound was aluminium sulphate with an oral absorption rate of 0.21%.
Executive summary:

A study was performed to determine the bioavailability of Aluminium compounds in Sprague-Dawley rats. Initially 12 rats intravenously injected with aluminium citrate (0.19 ng 26Al) and after 7 days the animals were sacrificed and the fraction of the injected aluminium retained in the animal carcasses was determined. Subsequent to intravenous injection study, the following substances (as 27Al dose per rat (mg) and 26Al dose per Rat (ng), respectively) were administered to 6 rats of each by oral administration:

Aluminium chloride: 50 mg, 1.24 ng; Aluminium nitrate: 50 mg, 1.77 ng; Aluminium sulphate: 50 mg, 2.44 ng; Aluminium citrate: 50 mg, 1.47 ng; Aluminium hydroxide: 17 mg, 12.2 ng; Aluminium oxide: 23 mg, 17.9 ng; Aluminium metal: 6.9 mg, 1.2 ng; Powdered pot electrolyte: 26 mg, 2.40 ng; SALP: 10 mg, 0.46 ng; KASAL: 10 mg, 0.31 ng; Sodium aluminium silicate: 27 mg, 0.60 ng; FD&C Red 40 aluminium lake*: 414 mg, 0.96 ng

Control rats received water without added 26Al. After 7 days the animals were sacrificed and the fraction of the injected aluminium retained in the animal carcasses was determined. The 26Al content of samples was analysed by using accelerator mass spectrometry (AMS). The fraction of aluminium absorbed was calculated by reference to the amount of 26Al administered and the fractional retention of injected aluminium at 7 days post-intake.

At 7 days after injection 14.6% of the injected 26Al remained in the full rat carcass. In contrast only 8.6% of the injected 26Al remained in the short carcass samples that were used for the remainder of the study.  AMS results of the analysis of administered doses showed that the mean amounts of 26Al administered were 1.6 ng for aluminium citrate, 1.1 ng for aluminium chloride, 1.9 ng for aluminium nitrate, 2.4 ng for aluminium sulphate, 12.2 ng for aluminium hydroxide, 17.9 ng for aluminium oxide, 1.3 - 1.5 ng for the aluminium metal, 2.4 ng for the powdered pot electrolyte, 0.46 ng for the SALP, 0.31 ng for the Kasal, 0.51 ng for the sodium aluminium silicate and 0.96 ng for the FD&C red 40 aluminium lake.

 

Estimates of GI tract bioavailability were possible for all of the test materials except the aluminium metal, SALP and Kasal. The calculated fractional uptake of 26Al for all the aluminium solutions was similar and ranged from a high uptake of 0.002 for aluminium sulphate to a low uptake of 0.0006 for aluminium chloride. The fractional uptake of 26Al administered as insoluble particulates was lower: 0.0003 for aluminium hydroxide; 0.0002 for aluminium oxide and 0.0003 for the 26Al administered as powdered pot electrolyte; 0.001 for the sodium aluminium silicate; 0.0009 for the FD&C red 40 aluminium lake. The results for aluminium metal, SALP and Kasal were <0.0003, <0.001 and <0.001, respectively. It can be seen that highest fractional uptake 2.1 x 10 -3 (0.21%) was found following the ingestion of 26Al-labelled aluminium sulphate and the lowest uptake followed the administration of the aluminium oxide – 1.8 x 10-4 (0.02%). The results show that the compounds administered as suspensions (hydroxide, oxide, metal and powdered pot electrolyte) were less bioavailable than the soluble compounds (citrate, chloride, nitrate and sulphate).

 

Under the experimental conditions, the most bioavailable aluminium compound was aluminium sulphate with an oral absorption rate of 0.21%.

Endpoint:
basic toxicokinetics in 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: Non-guideline but well-documented GLP-compliant study conducted according to scientifically acceptable methods
Objective of study:
distribution
Qualifier:
no guideline followed
Principles of method if other than guideline:
The objective of the present study was to evaluate the relative biodistribution of aluminium following repeated, oral administration of various aluminium salts. Sprague Dawley rats were orally gavaged with formulations of aluminium citrate, sulfate, nitrate, chloride and hydroxide, each delivering a dosage of 30 mg/kg body weight elemental aluminium. Control animals were similarly dosed with deionized water. Animals were dosed daily for either 7 days or 14 days, followed by blood and organ collection. Blood/organs were analysed for aluminium, manganese, iron and copper concentrations. Animals were maintained on low aluminum feed (9 μg/kg) and water (2 ng/mL) for a 2 week period prior to and during dosing. In-life observations included body weights, food and water consumption and general health.
GLP compliance:
yes
Radiolabelling:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
SPECIES, STRAIN, SUPPLIER AND SPECIFICATIONS:
• Species/Strain: Rats, Sprague Dawley CD®
• Supplier: Charles River Canada Inc.
• Number of Animals in the Study: 120
• Age at Initiation of Treatment: 5 weeks
• Weight Range at Initiation of Treatment (grams): Females: 127.4 – 171.9; Males: 142.5 – 203.3

ENVIRONMENT AND HUSBANDRY:
The animal room environment was controlled with targeted conditions:
• Housing: individual
• Temperature: 18-26°C
• Relative Humidity: 30-70%
• Air Changes: ≥10 per hour in room. Within ventilated cages, animals are expected to experience approximately 50 air changes per hour using room air for intake and exhaust.
• Light Cycle: ~12 hours light
• Caging: Ventilated cages with environmental enrichment

DIET AND WATER:
• Diet: Purina AIN-093M – Irradiated, Lot #4475188. This diet was fed ad libitum to all animals from arrival until the end of the study. A sample of feed was collected and sent to the Test Site for analysis of Aluminum, iron, manganese, copper and zinc levels. This analysis was performed prior to study day 1.
• Water: ad libitum UV sterilized reverse osmosis water. A sample of drinking water was collected prior to arrival and sent to the Test Site for analysis of aluminum, iron, manganese, copper and zinc levels.
• Bedding: Anderson Bed-O’Cobs Lot # 103007; no contaminants found.


PRE-TREATMENT PROCEDURES:
• Animal Health Procedure: Rats were observed daily and body weights taken once during the acclimation period. A health status report was generated prior to animals being released to the study.
• Acclimation Period: 17 days
• Allocation to Treatment Group: Rats were randomly allocated to treatment groups and number of doses received with a computer generated randomization program using the SAS PROCPLAN procedure to minimize group differences in body weights between treatment .
• Selection Criteria: Only animals in apparent good health and within the specified age range were selected for randomization to treatment groups.
• Identification of the Animals: Double ear tags
• Identification Numbers: Rats were assigned a unique number upon arrival at the Facility.
• Identification of the Cages: Cage cards
Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS:

ALUMINIUM CITRATE:
• Preparation on study days -1 and 7: Aluminum citrate (30.61g) was weighed and placed into a beaker. A stir bar was added and then Nanopure water was added to the 400 ml mark, the beaker was then placed on a stir/hot plate, which allowed a vortex to form. The temperature was set at maximum. This was continued until the Aluminum citrate appeared to be dissolved; the solution was heated to a final temperature of 99°C. The solution was cooled to room temperature. The initial pH was between 2.49 (23.2°C, day -1) and 2.58 (21.6°C, day 7) and was a slightly cloudy solution. The pH was adjusted using 5N NaOH and 5N HCl to a pH of 6.74 (25.4°C, day -1) and 6.16 (23.7°C, day 7) and the final appearance was a slightly cloudy solution. The contents were transferred to a 1000 ml volumetric flask, the beaker rinsed 3 times with Nanopure water and the content added to the volumetric flask. The solution was made to volume with Nanopure water and mixed well by vigorous shaking. The solution was then filtered through a 45μm pore size filter using a peristaltic pump and speed controller and stainless steel pressure filter holder. The filtered solution was again mixed by vigorous shaking. The final pH was determined to be 6.99 (22.6°C, day -1) and 6.48 (22.5°C, day 7) and the final appearance was a clear, colorless solution.
• Storage following formulation: Room temperature
• Frequency of Preparations: Study day -1 and 7
• Disposition of dosing solutions: Discarded

ALUMINIUM SULFATE:
• Preparation on study day -1 and day 7: Aluminum sulfate (34.29g) was weighed and placed into a 600 ml beaker. A stir bar was added, and then Nanopure water was added to the 400 ml mark, the beaker placed on a stir plate, which allowed a vortex to form. This was continued until the Aluminum hydroxide appeared to be mixed. The initial pH was 3.27 (23.2°C, day -1) and 3.4 (22.9°C, day 7) and was a slightly milky, cloudy solution. The pH was adjusted using 5N NaOH to a pH of 6.24 (26.7°C, day -1) and 6.40 (25.5°C, day 7) and the final appearance was a milky cloudy solution. The
contents were transferred to a 1000 ml volumetric flask, the beaker rinsed 3 times with Nanopure water and the content added to the volumetric flask. The solution was made to volume with Nanopure water and mixed well by vigorous shaking. The final pH was determined to be 6.08 (24.6°C, day -1)and 6.72 (23.0°C, day 7) and the final appearance was milky, cloudy.
• Storage following formulation: 2 - 8°C
• Frequency of Preparations: Study day -1 and 7
• Disposition of dosing solutions: Discarded

ALUMINIUM NITRATE NONAHYDRATE:
• Preparation on study day -1 and 7: Aluminum nitrate (42.31g) was weighed and placed into a 600 ml beaker. A stir bar was added and then Nanopure water was added to the 400 ml mark, the beaker was then placed on a stir plate, which allowed a vortex to form. This was continued until the Aluminum nitrate appeared to be dissolved. The initial pH was 2.4 (29.6°C, day -1) and 2.54 (21.7°C, day 7) and was a clear, colorless solution. The pH was adjusted using 5N NaOH to a pH of 7.04 (30.2°C, day -1) and 6.98 (24.7°C, day 7) and the final appearance was a milky cloudy solution. This solution was placed on a stir/hot plate at a stir setting which allowed a vortex to form and the temperature set to maximum. The solution was allowed to come
to a boil and continue boiling for several minutes while stirring continuously. The contents were transferred to a 1000 ml volumetric flask, the beaker rinsed 3 times with Nanopure water and the content added to the volumetric flask. The solution was made to volume with Nanopure water and mixed well by vigorous shaking. The final pH was determined to be 5.07 (26.4°C, day -1) and 5.34 (22.4°C, day 7) and the final appearance was milky, cloudy.
• Storage following formulation: 2 - 8°C
• Frequency of Preparations: Study day -1 and 7
• Disposition of dosing solutions: Discarded

ALUMINIUM CHLORIDE:
• Preparation on study day -1 and 7: Aluminum chloride (27.27g) was weighed and placed into a 600 ml beaker. A stir bar was added, and then Nanopure water was added to the 400 ml mark, the beaker placed on a stir plate, which allowed a vortex to form. This was continued until the Aluminum chloride appeared to be dissolved. The initial pH was 2.45 (25.2°C, day -1) and 2.73 (22.3°C, day 7) and was a clear, colorless solution. The pH was adjusted using 5N NaOH to a pH of 6.59 (27.7°C, day -1) and 7.14 (24.7°C, day 7) and the final appearance was a milky cloudy solution. This solution
was placed on a stir/hot plate at a stir setting which allowed a vortex to form and the temperature set to maximum. The solution was allowed to come to a boil and continue boiling for several minutes while stirring continuously. The contents were cooled and transferred to a 1000 ml volumetric flask, the beaker rinsed 3 times with Nanopure water and the content added to the volumetric flask. The solution was made to volume with Nanopure
water and mixed well by vigorous shaking. The final pH was determined to be 6.20 (26.4°C, day -1) and 5.82 (22.7°C, day 7) and the final appearance was milky, cloudy.
• Storage following formulation: 2 - 8°C
• Frequency of Preparations: Study day -1 and 7
• Disposition of dosing solutions: Discarded

ALUMINIUM HYDROXIDE:
• Preparation on study days -1 and 7: Aluminum hydroxide (10.66g) was weighed and placed into a 600 ml beaker. A stir bar was added, then Nanopure water was added to the 400 ml mark, the beaker placed on a stir plate, which allowed a vortex to form. This was continued until the Aluminum hydroxide appeared to be dissolved. The initial pH was 8.69 (23.8°C, day -1) and 8.24 (22.5°C, day 7) and was a milky, cloudy solution. The pH was adjusted using 1N HCl to a pH of 6.87 (24.1°C, day -1) and 6.82 (22.5°C, day 7) and the final appearance was a milky cloudy solution. The contents
were transferred to a 1000 ml volumetric flask, the beaker rinsed 3 times with Nanopure water and the content added to the volumetric flask. The solution was made to volume with Nanopure water and mixed well by vigorous shaking. The final pH was determined to be 6.75 (24.8°C, day -1) and 6.79 (22.2°C, day 7) and the final appearance was milky, cloudy.
• Storage: 2 - 8°C
• Frequency of Preparations: Study day -1 and 7
• Disposition: Discarded

Duration and frequency of treatment / exposure:
• Method: Once daily oral bolus of formulated test or reference item gavaged with polypropylene gavage needles. Gavage was chosen as the method of administration due to the insolubility of some of the test items. Half of the animals (5/sex/group) received 7 doses and half (5/sex/group) received 14 doses.
• Volume Administered: 10 mL/kg. The body weight from study day 1 was used for dosing from study days 1 – 6; the body weight from study day 7 was used from study day 7 – 13 and the body weight from study day 14 was used for study day 14.
Dose / conc.:
30 mg/kg bw/day (nominal)
Remarks:
Doses / Concentrations:
Dosage level: 30 mg/kg body weight elemental aluminium
Dosage concentration of aluminium: 3 mg/ml
Dosage volume: 10 mg/kg
No. of animals per sex per dose / concentration:
5
Control animals:
yes
Statistics:
Statistical analyses were performed using SAS Release 9.1 for Windows XP. Statistical procedures were selected based on the distribution of the data and the validity of the assumptions. Statistical significance was declared when p ≤ 0.05.
Body weights for the 14 day Al exposure groups were analyzed using a repeated measures analysis of variance. The model included group (2, 4, 6, 8, 10 and 12), study day (7 and 14) and group by study day interaction as fixed effects as well as the body weights from study day 1 (predose) as a covariate. Body weights from study day 7 for the 7 day Al exposure groups were compared between groups (1, 3, 5, 7, 9 and 11) using an analysis of variance with the body weights from study day 1 (pre-dose) included as a covariate. Body weights on study day 1 (pre-dose) were compared between all groups (1-12) using an analysis of variance.
Average daily food and water consumption were analyzed using a repeated measures analysis of variance separately for the 7 and 14 day Al exposure groups. The model included group (1, 3, 5, 7, 9 and 11 for the 7 day Al exposure and 2, 4, 6, 8, 10 and 12 for the 14 day Al exposure), time period (study days -7 to 1 and 1 to 7 for the 7 day Al exposure groups and study days -7 to 1, 1 to 7 and 7 to 14 for the 14 day Al exposure groups), and group by time period interaction included as factors in the model.
For statistical analysis of body weight, food and water consumption, if the model revealed statistical significance (p≤0.05), Tukey-Kramer adjusted comparisons were used to determine if pairwise differences existed.
Since the aluminum concentrations in the tissues (blood, brain, liver, right kidney, spinal cord, spleen, and bone) were not normally distributed, Kruskal-Wallis and Wilcoxon non-parametric procedures were used to compare between treatments and the number of days of Al exposure (7 and 14). Concentrations below detection limit were assigned the value of 1/2 the detection limit.

ANALYTICAL - FEED/WATER:

In drinking water, the concentrations of all analytes were near to or below the limit of quantification For aluminum, the concentration was 2 ng/mL. All analytes in the Control dosing solutions were below the limits of quantification. The aluminum concentration in the diet was measured at 9 μg/g.

The nominal concentration of aluminum in the dosing solutions was 3 mg/mL. The relative error in the measured concentrations ranged from -7% to +12%. The aluminum citrate solutions were the only ones not within 10% of nominal concentration, at 11 and 12% over target, respectively for two different dosing solutions, however they were internally consistent for the test item.

MORTALITY:

All animals survived to scheduled euthanasia.

OBSERVATIONS:

All animals were observed to be normal throughout the study period with the exception of one male rat in the control group. On study day -4, this animal was observed to have a small scab on the face.

BODY WEIGHTS:

There were no significant differences in body weights between groups for males and females in the 7 day exposure group (males p=0.9202; females p=0.4216). There were no significant differences between groups for the 14-day exposure females (p=0.6774) and males (p=0.1652). In both the males and females, the overall body weights on study day 14 were significantly higher than the overall body weights on study day 7 (p<0.0001 for both sexes).

It was concluded that daily administration of the test items did not adversely affect body weight under the conditions of the study. The increase in body weight over the course of the study is consistent with normal growth in all groups.

FOOD CONSUMPTION:

There were no significant differences in food consumption between groups for either males (p = 0.5577) or females (p = 0.5369) for the 7 day exposures. Food consumption for the males was significantly higher on study days 1 to 7 compared with study days -7 to 1 (p=0.0038) but not for the females (p=0.0918). There were no significant group differences in food consumption of 14 day exposure males (p = 0.1871). However, for the 14 day exposure females, there was a significant difference between groups (p=0.0543). Specifically, the females receiving aluminum nitrate had a significantly higher (+18%) daily food consumption compared with the control group (p=0.0262). While average daily food consumption in the males significantly increased over the time period between 7 and 14 days of exposure to treatments (p<0.0001), the females did not consume significantly more over the same interval (p=0.5920).

The discrepancy in food consumption between aluminum nitrate and control females (14 day exposures) was consistent throughout the study, including the predose period, and is not likely a test article-related effect.

Food consumption is normally correlated to growth rate, so the lack of increase in food consumption in the females as opposed to a significant increase in the males might be considered anomalous. These animals, at age 5-8 weeks during the study, are at peak growth rates, and during this period, the males are growing at approximately double the rate of the females. From the first week of dosing to the second week, the males gained on average, between 25 and 30% while the females gained less than 15%, and at the same time, food consumption in the males increased only about 10% and in the females, food consumption did not increase. Thus food consumption increased at a slower rate than weight in both sexes. This is a very short interval in which to evaluate the correlation between weight gain and food consumption, so in context, the lack of increase in food consumption in the females is not surprising. Undoubtedly, had the animals been followed for more than two weeks, a more definitive pattern would have emerged.

WATER CONSUMPTION:

There were no significant differences in water consumption between groups for either males (p = 0.4339) or females (p = 0.6709) for the 7 day exposures. Water consumption for the males was significantly higher during study days 1 to 7 compared with study days -7 to 1 (p<0.0001) but not for the females p=0.8713. There were no significant differences in water consumption between groups in either the males (p=0.6414) or females (p=0.8577) for the 14 day exposures. For females overall, water consumption was significantly lower during study days 7 to14 compared with study days -7 to 1 (p=0.0137) or 1 to 7 (p = 0.0182). For males overall, water consumption was significantly lower during study days -7 to 1 compared with study days 1 to 7 and 7 to 14 (p<0.001 for both). In conclusion, differences in water consumption between groups and study day periods are relatively small and do not appear to be test article-related.

MACROSCOPIC EXAMINATION:

There were no gross postmortem abnormalities under the conditions of the study.

BLOOD AND TISSUE ALUMINIUM LEVELS:

The ranking of treatment in terms of effect on aluminum concentration is summarized in Table 1 below. Median blood and tissue aluminum concentrations for each of the tissues, exposure times and treatments in females are shown in Figure 1 (for figure 1 and all other figures, see attached PDF in section "Attached background material"), and in males, are shown in Figure 2. Median blood and tissue aluminum concentrations in males and females for each treatment and exposure time are shown for blood and each of the tissues separately are shown in Figures 3-9. In essence, very few statistically significant differences in aluminum concentration existed between treatments for any tissue of either sex (see table 2 below).

The tissues where differences did exist included liver (day 14 males, figure 5), kidney (day 7 males and day 14 females, figure 6), and bone (day 7 males, figure 9), although for liver the difference is between treatments, not between controls and treated groups. The concentrations of aluminum were highest for the aluminum citrate treatment. For example, median concentration of aluminum in the bone of day 7 males (0.61 μg/g) was 239% above controls (figure 9), in the kidney of day 7 males (0.60 μg/g) it was 200% above (figure 6), and in the kidney of day 14 females (0.90 μg/g) it was 350% above controls (figure 6). Concentrations of aluminum in these tissues related to other treatments were much lower by comparison (figures 1 -9).

Interestingly, comparisons of aluminum concentrations at day 14 and 7 reveal that, for all treatments, most tissues exhibited a decrease in median aluminum concentration between day 7 and 14 (This pattern can be visualized by examining figures 1 -9). The majority of statistically significant differences in this regard are for bone and blood (18 of 24, figures 9 and 3). For blood, the ratio of aluminum concentrations of day 7 versus day 14 ranged from 1.5 to 2.5 (figure 3), while for bone the ratio ranged from 1.5 to 6.5 (Figure 9).

The only tissue that clearly showed an increase in aluminum concentration from day 7 to day 14 was spinal cord (figure 7). The spinal cord concentration was higher on day 14 in every group (including controls) and sex, with the majority (7 of 12) of the differences being statistically significant. The ratio of aluminum concentrations in spinal cord for day 14 versus day 7 ranged from 1.7 to 2.0 in all cases, except aluminum sulfate (females) which had a ratio of 1.25. The other neuronal tissue examined, brain, showed only a slight change between day 7 and 14 (figure 4). The ratio of aluminum concentrations in brain for day 14 versus day 7 ranged from 0.70 to 1.11.

In summary, there appears to be little influence of treatment on systemic aluminum concentration for the dosage used in this study. This is evidenced by the fact that most tissues differ little from controls in their aluminum levels, and aluminum concentration is decreasing with time. The decrease is likely the result of the animals being maintained on low aluminum feed and water, and the animals are simply clearing themselves of the metal previously accumulated from normal feed/water. Only bone and kidney seem to be influenced by treatment, particularly aluminum citrate, resulting in significantly higher aluminum in select groups, relative to controls. However, their aluminum concentrations are decreasing with time. The only tissue clearly showing an opposite trend from this is spinal cord, while brain appears to have little or no clearance. This suggests poor clearance of aluminum from neuronal tissue relative to other tissues, and perhaps even bioaccumulation in the case of spinal cord.

Table 1. Treatment rankings (from Highest to Lowest, based on Wilcoxon scores) by Sex and Days of Exposure in terms of Aluminum Concentrations for each Tissue.

Sex

Days of exposure

Blood

Brain

Liver

Kidney

Spinal cord

Spleen

Bone

Females

7

Water

Al nitrate

Al citrate

Al citrate

Water

Al sulfate

Al citrate

Al sulfate

Water

Al hydroxide

Al sulfate

Al sulfate

Water

Al nitrate

Al nitrate

Al citrate

Water

Al hydroxide

Al citrate

Al citrate

Al hydroxide

Al citrate

Al sulfate

Al chloride

Al nitrate

Al nitrate

Al chloride

Al sulfate

Al chloride

Al hydroxide

Al sulfate

Al chloride

Al hydroxide

Al hydroxide

Al chloride

Al hydroxide

Al chloride

Al nitrate

Water

Al chloride

Al nitrate

Water

Females

14

Water

Water

Water

Al citratea

Water

Al citrate

Water

Al sulfate

Al sulfate

Al citrate

Al sulfate

Al chloride

Water

Al hydroxide

Al nitrate

Al citrate

Al chloride

Al nitrateb

Al citrate

Al chloride

Al nitrate

Al citrate

Al nitrate

Al hydroxide

Al hydroxideb

Al sulfate

Al sulfate

Al citrate

Al hydroxide

Al chloride

Al sulfate

Al chlorideb

Al hydroxide

Al hydroxide

Al sulfate

Al chloride

Al hydroxide

Al nitrate

Waterb

Al nitrate

Al nitrate

Al chloride

Males

7

Al sulfate

Al nitrate

Al sulfate

Al citratea

Water

Al citrate

Al citratea

Water

Water

Al citrate

Al sulfateb

Al nitrate

Water

Al chlorideab

Al nitrate

Al chloride

Al hydroxide

Al nitrateb

Al citrate

Al nitrate

Al nitratebc

Al citrate

Al hydroxide

Water

Al hydroxideb

Al chloride

Al chloride

Al sulfatebc

Al hydroxide

Al citrate

Al chloride

Al chlordeb

Al sulfate

Al sulfate

Al hydroxidecd

Al chloride

Al sulfate

Al nitrate

Waterb

Al hydroxide

Al hydroxide

Waterd

Males

14

Al citrate

Water

Al citratea

Al sulfate

Al citrate

Al citrate

Al nitrate

Al citrate

Al nitrate

Al hydroxide

Al nitrate

Al nitrate

Al chloride

Al citrate

Al sulfate

Al citrate

Waterab

Al chloride

Water

Al hydroxide

Al chloride

Al chloride

Al sulfate

Al chloride

Al citrate

Al sulfate

Al nitrate

Water

Al hydroxide

Al hydroxide

Al sulfateb

Al hydroxide

Al chloride

Al sulfate

Al hydroxide

Al nitrate

Al chloride

Al nitrateb

Water

Al hydroxide

Water

Al sulfate

Note: Bolding indicates statistically significant differences existed (p<0.05). Groups with the same letter were not statistically significantly different.

Table 2. Median Aluminium Concentration (μg/g) Wet Weight vs. Treatment in Selected Tissues. 

 

Citrate

Sulfate

Nitrate

Chloride

Hydroxide

Control

Bone

(day 7males)

0.61*

0.28*

0.29*

0.30*

0.26

0.18

Kidney

(day 7males)

 

0.60*

 

0.20

 

0.20

 

0.20

 

0.20

 

0.20

Kidney

(day 14females)

 

0.90*

 

0.30

 

0.30

 

0.20

 

03.0

 

0.20

*denotes significantly different from controls (p<0.05)

Conclusions:
No appreciable biodistribution at dose level of 30 mg Al/kg bw.
To summarize, it appears that the dosage level of aluminum (30 mg/kg) via oral gavage was insufficient to lead to any appreciable biodistribution in Sprague Dawley rats of either sex, after 7 or 14 days of dosing, and for any of the salts examined. It appears instead that most tissues were clearing aluminum previously deposited, probably from feed and water not controlled for aluminum levels. The 2 week acclimation in which rats were maintained on low aluminum
feed/water was obviously not long enough for full clearance of these deposits or the detection of an influence of treatment. One exception to this may be aluminum citrate treated animals, with males exhibiting significantly higher levels of aluminum at 7 days in both bone and kidney compared with controls. However, after 14 days, the difference was only apparent in kidneys of both males and females. In contrast, spinal cord was unique in exhibiting a bioaccumulation of
aluminum, regardless of treatment. The other neuronal tissue, brain exhibited little difference in aluminum concentration between day 7 and 14.
Executive summary:

The objective of the present study was to characterize the relative biodistribution of aluminum in tissues following repeated, oral administration of various aluminum salts. Sprague Dawley rats (n = 5 per sex per group) were orally gavaged with formulations of aluminum citrate, sulfate, nitrate, chloride and hydroxide, each delivering a dosage of 30 mg/kg body weight of elemental aluminum. Control animals were similarly dosed with deionized water. Animals were dosed daily for either 7 days or 14 days, followed by blood and organ collection. Blood/organs were analysed for aluminum, manganese, iron and copper concentrations. Animals were maintained on low aluminum feed and water for a 2 week period prior to and during dosing. In-life observations included body weights, food and water consumption and general health.

All animals survived until their scheduled necropsies, and treatments did not result in any abnormal clinical observations during the in-life portion of the study. Treatments also had no biologically significant influence on food consumption, water consumption or body weights, and all animals showed normal growth patterns.

There appeared to be little influence of treatment on aluminum levels in most tissues for either sex. Significant differences did exist between controls and treated animals for bone (day 7 males) and kidney (day 7 males and day 14 females). For aluminum citrate treatment these differences were highest: concentration of aluminum in the bone (day 7 males) was 0.61 μg/g, 239% above controls, in kidney (day 7 males) it was 0.60 μg/g, (+200%), and in kidney (day 14 females) it was 0.90 μg/g, (+350%). Concentrations of aluminum in these tissues for other treatments were much lower by comparison.

A surprising result was that for most tissues, the concentration of aluminum was less after 14 days dosing than it was after just 7 days dosing, regardless of sex or treatment. The differences were statistically significant primarily in the case of blood and bone. This phenomenon occurred in controls as well. These results suggest that dosing had little influence on systemic levels of aluminum in most tissues, and the observed concentrations were likely the result of previous exposure to aluminum from regular feed and water (i.e., prior to the 2 week predose period). The decline in systemic concentrations likely reflected clearance of previously deposited aluminum, and that treatment had little effect (with the exception of bone and kidney).

The only tissue that had a pattern in which aluminum concentration was higher after 14 days compared with 7 days was spinal cord. This was true of every group (including controls) and sex, with the majority (7 of 12) of the differences being statistically significant. The other neuronal tissue examined, brain, was largely neutral, showing little change between day 7 and 14. This may suggest poor clearance in neuronal tissues and, in the case of spinal cord, bioaccumulation.

It is possible that if animals were maintained on the low aluminum feed/water for a longer pre-dose period, baseline levels in blood and tissue would be low enough to observe an influence from treatment. Obviously, higher dosing would have had a more observable effect on systemic aluminum, but the solubility of salts limited the ability to deliver a higher dosage of aluminum via a bolus administration.

Description of key information

Due to the available data, it is considered that the absorption and associated bioavailability of several soluble Aluminium salts are similar. Following absorption by any route of exposure, Aluminium is present in the body as the ionic species (Al3+) which is consequently the determining driver regarding the systemic effects of Aluminium salts, even including acute toxicity.

Hence, it can be assumed that Al3+ is the substance of biological interest and that the toxicological effects of Dialuminium chloride pentahydroxide can be attributed exclusively to Al3+.

Oral absorption is lower to 1% as confirmed in the key study Priest, 2010 (0.054% for aluminium chloride basic, 0.21% for aluminium sulphate and 0.018% for aluminium hydroxide). Therefore, dermal and inhaled aborption are assumed to be lower to 1%  for Dialuminium chloride pentahydroxide. Consequently, as soluble aluminium salt, it is likely that Dialuminium chloride pentahydroxide exhibits similar bioavailability regarding absorption by oral and dermal route, by inhalation.

None aluminium salts (sulfate, nitrate, chloride and hydroxide) accumulate in significant amount in any organs as demonstrated in the bioavailability study.

Key value for chemical safety assessment

Bioaccumulation potential:
low bioaccumulation potential
Absorption rate - oral (%):
1
Absorption rate - dermal (%):
1
Absorption rate - inhalation (%):
1

Additional information

In general, the toxicokinetic behaviour of substances is based on physico-chemical characteristics and the bioavailability.Due to the available data it is considered that the absorption and associated bioavailability of Dialuminium chloride pentahydroxide and of other soluble Aluminium salts (e.g. Aluminium sulphate, Aluminium chloride basic, Dialuminium chloride pentahydroxide, Aluminium citrate and Aluminium hydroxide, etc) are similar. Following absorption by any route of exposure, Aluminium is present in the body as the ionic species (Al3+) which is consequently the determining driver regarding the systemic effects of Aluminium salts, even including acute toxicity.Hence, it can be assumed that Al3+ is the substance of biological interest and that the toxicological effects of Dialuminium chloride pentahydroxidecane be attributed exclusively to Al3+.

Based on this similar behaviour, data from the different soluble Aluminium salts (e.g., Aluminium citrate, Aluminium chloride basic, Aluminium sulphate, Aluminium hydroxide, etc.), are used for read-across to assess the toxicokinetic properties. Moreover, it is reasonable to consider data obtained from the other soluble Aluminium salts, as a starting point in the hazard identification of Dialuminium chloride pentahydroxideand taking into account differences in bioavailability using available toxicokinetic information. Target ACHS contains several counter ions: chloride, hydroxide and sulphate; the inorganic analogues were selected having at least one common anion, possibly with varying ratio, but no additional different anion.

Regarding chloride ions (Cl-), only few data are available (WHO, 2003). The toxicity of chloride itself is largely unknown, as the behaviour of the salts depends in general on the associated cation. However, 88% of chloride in humans is extracellular and contributes to the osmotic activity of body fluids. The electrolyte balance in the body is maintained by adjusting total dietary/drinking water intake and by excretion via the kidneys and gastrointestinal tract. Chloride is almost completely absorbed from drinking water in normal individuals, mostly from the proximal half of the small intestine. Normal fluid loss amounts to about 1.5 -2 L/day, together with about 4g of chloride/d. Most (90-95%) is excreted in the urine, with minor amounts in faeces (4-8%) and sweat (2%). Finally, no more information is available about absorption, distribution, metabolism and excretion of chloride ions as it has only little toxicological interest.

 

ABSORPTION

Oral absorption

Absorption is a function of the potential for a substance to diffuse across biological membranes. In addition to molecular weight the most useful parameters providing information on this potential are the octanol/water partition coefficient (log Kow) value (not relevant for a inorganic substance) and the water solubility. Indeed, the main identified factors influencing absorption of Aluminium are solubility, pH and the chemical species (ATSDR, 2008; PHG, 2001; WHO, 1997; JECFA, 2001, 1989).

Following ingestion, the Dialuminium chloride pentahydroxide is quickly and completely hydrolysed into the Aluminium (Al3+), chloride (Cl-), sulphate (SO4)- and hydroxide (OH)- ions in the acidic aqueous conditions of the stomach (pH≈2) and gut. In aqueous solution Al3+does not occur as the free ion but is surrounded by six molecules of water to form (Al(H2O)6)3+. As the pH increases, protons are removed from the co-ordinated waters to give various hydolysis products. Progressive hydrolysis leads to the formation of Aluminium hydroxide which is less water soluble and therefore less absorbed. Therefore, the toxicological properties of Dialuminium chloride pentahydroxide after oral uptake can be assessed by the effects of its dissociation products and thus mainly by the Aluminium ion, as explained above.

Human studies indicate that only a small percentage of Aluminium that is normally ingested via the diet and drinking water is absorbed. Most estimates of average gastrointestinal absorption of Aluminium under normal dietary conditions are in the range of 0.1 - 0.6 %, although some human studies indicate that absorption of the more bioavailable forms. These forms are particularly complexes of Aluminium with particular carboxylic acids, (e.g. Aluminium citrate) which may be absorbed in the order of 0.5 - 5 % (ATSDR, 2008; PHG, 2001).

Animal studies showed that Aluminium absorption via the gastrointestinal tract is usually less than 1%.

The recent study of Priest (2010) investigated the bioavailability of several Aluminium salts (Aluminium sulphate, Aluminium citrate, Aluminium hydroxide as well as Aluminium chloride. The results performed showed that the measured mean bioavailability in rat for some of soluble Aluminium salts of interest in this dossier decreased in the order: Aluminium sulphate (0.21%), Aluminium citrate (0.079%), Aluminium chloride (0.054%), Aluminium hydroxide (0.025%).Although the result for Aluminium sulphate was unexpectedly higher than for other mineral acid salts tested, it corresponds closely with the uptake levels measured in two human volunteers that swallowed drinking water that contained 26Al introduced as Aluminium sulphate (0.20%).Due to the use of the same experimental methods for the different substances, the results from the human study can be quantitatively compared to the data from the animal study as both test substances were administered without co-exposures to ligands that may influence the bioavailability. The human result for Aluminium hydroxide (0.01%) was similar to that obtained using the rat model. Additionally, the measured bioavailability of the Aluminium citrate in the rat was well within the range of measured/estimated values of 0.047% to 1% in man for citrate (and orange juice).

The study of Wenker (2007) determined that the average oral absorption for Aluminium chloride basic as 0.028% for males and 0.026% for females, respectively. This also indicating, that oral absorption is very low which concurs with the results of Priest (2010) for Aluminium salts (<<1%).

Therefore, the results of both studies contribute to the overall evidence that Aluminium and its salts show low bioavailability after oral uptake.

 

Dermal absorption

While Aluminium compounds such as Dialuminium chloride pentahydroxide are a common additive for some cosmetics, there are only limited human data on the dermal absorption of Aluminium available. Indeed, aluminium salts are used in underarm antiperspirants where the Aluminium is soluble at low pH in the formulation, before being rendered insoluble as it is neutralised by the sweat on the skin’s surface and within sweat ducts (SCCS, 2014). This behaviour limits the bioaccessibility of Aluminium on living skin. In the form of an ionic Aluminium complex, the Aluminium salts will exhibit only shallow penetration of the skin, due to binding in the upper layers of the stratum corneum. The results of a non GCP guideline preliminary study of the dermal absorption of antiperspirants using labelled Aluminium estimated that the proportion of Aluminium that is absorbed averaged 0.012% using only two volunteers (Flareng et al.,2001). However, SCCS (2014) considers that Aluminium absorption after dermal exposure to cosmetics is still poorly understood based on the poor quality available studies, which have not been carried out according to the current requirements.

Finally, following the results of the acute dermal studies from this dossier, neither systemic effect nor local effects are observed during the acute dermal testing and skin irritation studies. Moreover, no sensitisation potential of Dialuminium chloride pentahydroxide was observed in a relevant study which only would become apparent when some absorption via the skin is anticipated. Therefore, local toxicity is not expected after Dialuminium chloride pentahydroxide exposure by dermal contact. Moreover, considering the absence of systemic effects during testing by the dermal route, the high water solubility of Dialuminium chloride pentahydroxide that induces rapid hydrolysis of the substance into the Al3+, chloride ion at the surface of skin, very low absorption (<1%) is expected to occur during dermal exposure to Dialuminium chloride pentahydroxide.

This is corroborated by the study performed with three different formulations of alumniumchlorohydrate (antitranspirant Roll-on, an aqueous-ethanolic solution with 8% content of active ingredient; Deo Creme, an emulsion with 10% contect of active ingredient; Deo Roll-on, an emulsion with 7.5% active ingredient) which were tested for cutaneous penetration and absorption through pig skin in vitro (Grötsch, 1997). It is concluded that the cutaneous permeation of Aluminium was in each case less than 0.022% of the applied dose.

 

Inhalation absorption

The amount and location of deposition in the respiratory tract depend on respiratory tract architecture, breathing pattern and the droplet size distribution if the substance could occur as a solution for Dialuminium chloride pentahydroxide.

The acute toxicity study included in this dossier (NOTOX 2010) performed with polyaluminum chloride hydroxide sulphate delivered as fine droplet aerosol, did not show any clinical and macroscopic effects.

No chronic toxicity by inhalation data is available for the solution of Dialuminium chloride pentahydroxide. However, following chronic exposure, Dialuminium chloride pentahydroxide could reach the alveolar system if it occurred as a fine droplet aerosol (< 10 µm diameter) and then might pass cross the respiratory epithelium into the blood. Therefore, it could be assumed that following exposure by inhalation, Aluminium contained in the fine droplets (<10 µm diameter) might be absorbed across at the same magnitude as by the oral route, i.e. <1%. For larger droplets of Dialuminium chloride pentahydroxide (i.e.droplets < 100 µm but > 10 µm), they may be captured in the nasopharyngeal and upper respiratory areas and then transferred in the gastrointestinal tract by mucosal movement and mucocilliary action. Consequently, the toxicity of Dialuminium chloride pentahydroxide via inhalation exposure is primarily determined by its potential for toxicity via the oral route by which absorption is below 1% as determined in Priest's study (2010).

 

METABOLISM AND DISTRIBUTION

Aluminium is not metabolised in the liver. Once in the blood A3+is believed to be present almost exclusively in the plasma where it is bound mainly to transferrin and to a lesser extent to albumin. It was observed that 89% of the Aluminium in serum is bound to citrate and transferrin which may play a significant role in the distribution of Aluminium (ATSDR, 2008; PHG, 2001; WHO, 1997). Normal physiological levels of Aluminium in serum are approximately 1 – 3 μg/L (ATSDR, 2008).

There are limited data on distribution of Aluminium in humans, but the distribution of Aluminium in animals after oral exposure has been evaluated in a number of studies (ATSDR, 2008). These studies are particularly informative because they provide information on distribution of Aluminium in various tissues and demonstrate that Aluminium concentration in different tissue can increase substantially following oral exposure despite the low bioavailability of Aluminium. Evidence from animal studies suggests that Aluminium might accumulate in the brain (grey matter) where it distributed preferentially to the hippocampus. As it can be also anticipated for metals, Aluminium can interact with ions in the matrix of bone where it displaces the normal constituents of the bone, leading to retention of the metal, which determines to a large extent the total Aluminium body burden. In addition to the distribution of Aluminium to the brain, bone, muscle and kidneys of orally exposed animals, there is limited animal evidence indicating that Aluminium has the potential to cross the placenta (which may serve as a partial barrier during in utero development) and to accumulate in the foetus and be distributed to some extent to the milk of lactating mothers (ATSDR, 2008; PHG, 2001). This is corroborated by the results observed in in the developmental and one-year chronic neurotoxicity study performed in rats exposed to Aluminium citrate via drinking water (ToxTest. Alberta Research Council Inc., 2010). Whole body Aluminium levels in neonatal pups from high dose females and males were greater than those in the control groups, without significant sex differences. These results suggest transfer of Aluminium from dams to pups in utero, although a contribution from breast milk PND 0 to 4 is also possible. Aluminium levels were assayed in several tissues in the pup cohorts. Levels of Aluminium in whole blood were highest in the Day 23 cohort animals and declined with time, possibly due to the lower amounts of test substance containing water consumed once the pups matured. Although during the lactation period pups may have consumed some water/test solution, the results suggest that transfer of Aluminium from dams to pups can occur through breast milk. Concentrations of Aluminium in bone showed the strongest association with Aluminium dose and some evidence of accumulation over time in all of the Aluminium-treated groups. Of the central nervous system tissues, Aluminium levels were highest in the brainstem.  Although levels of Aluminium were relatively low in the cortex (< 1µg/g), they were positively associated with Aluminium levels in the liver and femur. In females, Aluminium levels in the high dose group remained elevated relative to the other groups at all time-points suggesting that accumulation might have occurred (ToxTest. Alberta Research Council Inc., 2010).

However, at lower dose of Al3+(30 mg/kg bw/d), none aluminium salts (sulphate, nitrate, chloride and hydroxide) accumulate in significant amount in any organs as demonstrated in the bioavailability stud of Semple (2010).

EXCRETION

Excretion data collected in animal studies are consistent with the results from human studies where the difference in the excretion rates most likely reflects differences in gastrointestinal absorption following oral exposure. There is insufficient information to comment on biliary excretion of Aluminium in humans (WHO, 1997).

From human dietary balance studies, it is clear that most of the ingested Aluminium is unabsorbed: Aluminium levels determined in faeces ranged from 76 to 98 % of the oral dose (ATSDR, 2008; PHG, 2001). Following ingestion in humans, absorbed Aluminium from the blood is eliminated in the kidney and excreted in the urine (ATSDR, 2008; PHG, 2001; WHO, 1997).

 

REVIEW REFERENCES:

-Agency for Toxic Substances and Disease Registry / ATSDR (2008) Toxicological profile for Aluminium, U. S. Department of Health and Human services, Public Health Service, September 2008, 357 p.

- Joint FAO/WHO Expert Committee on Food Additives / JECFA (2001) JECFA / IPCS, INCHEM. Aluminium, 1 p.

- JECFA (1989) JECFA / IPCS, INCHEM. Aluminium, 28 p.

- Public Health Goal / PHG (2001) Aluminium in Drinking Water, April 2001, 74 p.

- SCCS (2014) Opinion on the safety of Aluminium in cosmetic products. SCCS/1525/14.

-World Health Organisation / WHO (1997), Environmental Health Criteria n°194 - Aluminium. International Programme on Chemical Safety.

- World Health Organisation / WHO (2003), Chloride in drinking water. WHO/SDE/WSH03.04/03

In conclusion, the soluble aluminium salts considered for the hazard assessment of Dialuminium chloride pentahydroxide are:

Aluminium citrate: CAS# 31142-56-0

Aluminium chloride basic: 1327 -41 -9

Aluminium hydroxide: CAS# 21645-51-2