Bentonite, acid-leached

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

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

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well documented study

Data source

Reference

Reference Type:

publication

Title:

Toxicological evalution and metal bioavailibility in pregnant rats following exposure to clay minerals in the diet

Author:

Wiles MC, Huebner HJ, Afriyie-Gyawu E, Taylor RJ, Bratton GR & Phillips TD

Year:

2004

Bibliographic source:

Jounal of Toxicology and Environmental Health, Part A,67:863-874.

Materials and methods

Principles of method if other than guideline:

Calcium montmorillonite and sodium montmorillonite clays were supplemented in the balanced diet of rats during pregnancy at a level of 2% w/w. Evaluations of toxicity were performed on gestation d 16.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Calcium montmorillonite

IUPAC Name:

Calcium montmorillonite

Constituent 2

Reference substance name:

Sodium montmorillonite

IUPAC Name:

Sodium montmorillonite

Details on test material:

- Name of test material (as cited in study report): Calcium montmorillonite clay (Novasil plus,NSP) Sodium montmorillonite clay (sWY-2)
- Other:NSP was obtained from Engelhard Corporation(Cleveland, OH). Wyoming sodium montmorillonite (Swy-2) was obtained from the clay minerals respository( Univeristy of Missour, Columbia).

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague-Dawley, Inc., Houston, TX
- Age at study initiation: Ten week-old
- Housing: Filter-top polycarbonate cages housed in a temperature-controlled and artificially illuminated room free from any sources of chemical contamination
- Diet : ad libitum
- Water :ad libitum
- Acclimation period:3-4 days


ENVIRONMENTAL CONDITIONS
- Photoperiod (hrs dark / hrs light):12h dark/ 12h light cycle

Administration / exposure

Route of administration:

other: Oral feed and by gavage

Details on exposure:

Three diets were prepared from a balanced powdered rodent feed and included 1) basal feed, 2) basal feed with 2% NSP (w/w) and 3) basal feed with 2% Swy-2 (w/w). To ensure a continuous presence of clay in the stomach, animals maintained on diets containing clay were gavaged once per day midway through the fasting period with the respective clay between gestation d 1 and 15. The gavage dose (0.25%) aqueous suspension) was selected as the maxmium amount of clay that could be suspended in 1ml without increasing the viscosity beyond the ability to deliver the dose through the gavage needle. Stock clay suspensions were made by shaking 25 g clay in 400 ml UP-H2O overnight.

Analytical verification of doses or concentrations:

no

Details on analytical verification of doses or concentrations:

no data

Details on mating procedure:

After an acclimation period, females were paired with males overnight.

Duration of treatment / exposure:

Day 1 to 15 of pregnancy

Frequency of treatment:

Gavaged once per day midway through the fasting period( 12 h light cycle) with the respective clay between gestation day 1 and 15

Duration of test:

16 days

Doses / concentrations

Remarks:

Doses / Concentrations:
2% w/w (equivalent to 1000-1500 mg/kg bw/day)
Basis:
nominal in diet

No. of animals per sex per dose:

6 animals per treatment group

Control animals:

yes, plain diet

Details on study design:

no data

Examinations

Maternal examinations:

Maternal liver, kidneys, tiba, brain, uterus, pooled placentas, and pooled embryonic mass were collected, weighed, and frozen prior to metal analysis
BODY WEIGHT: Yes
- Time schedule for examinations:
Maternal body weight at day 1 and day 16
Litter weight




OTHER:

Total feed intake

Ovaries and uterine content:

no data

Fetal examinations:

The uterine wall was cut open and the number of implants, resorptions, and dead and live fetuses were counted.

Statistics:

Unless otherwise noted, all values are expressed as means ± standard error of the mean. Mean values for body and organ weights, feed intake, and developmental toxicity parameters were calculated from six rats in each treatment group. From those six rats, three were randomly selected for determination of metal content via neutron activation analysis. Data were compared statistically using the Gernal Linear Model procedure with Turkey's test and were considered significant if p< 0.05.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
no data

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

1 000 - 1 500 mg/kg bw/day (nominal)

Basis for effect level:

other: other:

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
no data

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Table 1: Effects of clay-based diets on implementations, resorptions, and embryos in the pregnant rat

 

	Control diet^a	2% Swy-2^a	2% NSP diet^a
Implantations	17±1	15±1	17±1
Embryos	15±1	14±1	15±1
Resorptions	1±1	1±0	2±1

 

Note. All data are expressed as mean values for 6 rats per treatment group ± SD. Mean values for rats maintained on Swy-2 and NSP diets were not statistically different (p≤0.05) from controls.

^aClays (NSP and Swy-2) were added to a powdered basal diet at a level of 2% (w/w) and fed to the rats between day 1 and 15 of pregnancy. Test animals were dosed orally with 0.25% clay in 1 ml aqueous suspension once per day (midway through the fasting period). Animals fed the control diets were dosed orally with 1ml aqueous vehicle alone

 

Table 2: Effects of Clay-based diets on tissue weights in the pregnant rat

 

Tissues^a	Weight of tissues from rats fed control diet^b(g)	Weight of tissues from rats fed 2% Swy-2 diet^b(g)	Weight of tissues from rats fed 2% NSP diet^b(g)
Liver	12.6±0.7	12.5±0.4	12.7±1.0
Right kidney	1.0±0.0	1.0±0.1	1.0±0.1
Left kidney	1.0±0.1	1.0±0.0	1.0±0.1
Brain	1.7±0.0	1.6±0.1	1.7±0.0
Right tibia	0.5±0.0	0.5±0.1	0.5±0.0
Left tiba	0.5±0.1	0.5±0.1	0.5±0.0
Uterus	4.6±0.4	4.4±0.6	4.7±0.3
Pooled placentas	5.1±0.8	4.8±1.1	5.0±0.8
Pooled embryonic mass	7.3±0.7	6.7±1.6	7.2±0.9

 

Note. All data are expressed as mean values for 6 rats per treatment group ± SD. Mean weights of tissues of rats maintained on Swy-2 and NSP diets were not statistically different (p≤0.05) from controls.

^aTissues were collected from pregnant rats at gestation day 16.

^bClays (NSP and Swy-2) were added to a powdered basal diet at a level of 2% (w/w) and fed to the rats between day 1 and 15 of pregnancy. Test animals were dosed orally with 0.25% clay in 1 ml aqueous suspension once per day (midway through the fasting period). Animals fed the control diets were dosed orally with 1ml aqueous vehicle alone

 

Table 3: Effects of Clay-based diets on gain in maternal body weight, Litter weight, and feed intake in the pregnant rat

 

Treatment^a	Maternal body weight at day 1 (g)	Maternal body weight at day 16 (g)	Gain in maternal body weight (g)	Litter weight (g)	Total feed intake (g)
Control diet	241±11.8	309±7.4	68.0±5.7	28.9±1.1	330±13
2% Swy-2 diet	237±9.1	308±8.7	71.0±3.5	27.0±2.1	352±7
2% NSP diet	240±7.4	309±8.1	69.3±3.5	29.2±1.4	345±7

 

Note. All data are expressed as mean values for 6 rats per treatment group ± SD. Mean values for rats maintained on Swy-2 and NSP diets were not statistically different (p≤0.05) from controls.

^aClays (NSP and Swy-2) were added to a powdered basal diet at a level of 2% (w/w) and fed to the rats between day 1 and 15 of pregnancy. Test animals were dosed orally with 0.25% clay in 1 ml aqueous suspension once per day (midway through the fasting period). Animals fed the control diets were dosed orally with 1ml aqueous vehicle alone

Applicant's summary and conclusion

Conclusions:

2% calcium montmorillonite or sodium montmorillonite in the diet had no effect on maternal weight or maternal organ weights, litter weight, embryonic implantations, or resorptions.