Perchloric acid

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:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Well conducted study performed according to OECD and EPA guidelines. The top-dose was not based on dose-limiting toxicity but on antithyroid effects, limiting the sensitivity of the study for classification for Developmental Effects classification. Justification for read-across : Perchloric acid, once absorbed in the general circulation is expected to be transformed into perchlorate moiety because of the blood buffering effect. Mammalian toxicity data of a perchlorate salt : ammonium perchlorate (CAS no. 7790-98-9), has been used for read across where data gaps for perchloric acid exist.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2003

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Deviations:

not specified

Test guideline 2

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

Highest dose chosen with the aim to induce antithyroid effects, but not based on dose-limiting toxicity.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Ammonium perchlorate

EC Number:

232-235-1

EC Name:

Ammonium perchlorate

Cas Number:

7790-98-9

Molecular formula:

ClHO4.H3N

IUPAC Name:

ammonium perchlorate

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Details on test material:

- Physical state: solid powder
- Nominal purity: 99.8%
- Lot/batch No.: 03907LF
- Stability under test conditions: Stability of formulations was established for up to 109 days.
- Storage condition of test material: at room temperature

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories (Raleigh, NC).
- Age at study initiation: Female rats were approximately 59 days old at arrivai and only female rats were treated; untreated male rats, approximately 73 days old at arrivai, were used only as breeders.
- Weight at study initiation: no data
- Fasting period before study: no
- Housing: stainless steel wire-bottomed cages, individual except during mating
- Diet (e.g. ad libitum): PMI Certified Rodent Diet, ad libitum
- Water (e.g. ad libitum): reverse osmosis water, ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2° C
- Humidity (%): 50 ± 15%
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 2000-01-25 To: 2000-03-15

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

Test formulations of ammonium perchlorate in deionized water were prepared at least weekly, stored refrigerated, and dosage solutions were brought to room temperature prior to use. Stability of formulations was established for up to 109 days. Test drinking solutions were adjusted to concentrations that yielded target doses of 0 (control), 0.01, 0.1, 1 and 30 mg/kg-day based on actual weekly water consumption.

Analytical verification of doses or concentrations:

yes

Details on mating procedure:

- Impregnation procedure: cohoused with treated males
- M/F ratio per cage: 1:1
- Length of cohabitation: 9 days
- No replacement of males or further mating, as only presumably pregnant females were assigned to gestation study.
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: vaginal plug or sperm in vaginal smear; referred to as day 0 of pregnancy

Duration of treatment / exposure:

36 to 44 days: 14 days prior to mating, 1-9 days of mating, and 21 days of gestation before sacrifice.

Frequency of treatment:

Continuous (treated water ad libitum)

Duration of test:

Approximately 50 days

No. of animals per sex per dose:

24 rats per exposure group.
Five dose groups of 24 satellite rats per exposure group were also housed in the same animal room and received the same regimen of treatment. Satellite rats were used for collection of blood and thyroid tissues to prevent interference with the fetal evaluations in the main study.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: 10 mg/kg/day resulted in antithyroid effects in pups in a neurobehavioral study, and in adults in a 90-day study (7.5.1)
- Rationale for animal assignment: random

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily for viability

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily during pregnancy only

BODY WEIGHT: Yes
- Time schedule for examinations: twice during acclimation and daily throughout exposure period

FOOD CONSUMPTION: Yes
- Time schedule: daily throughout exposure period

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
- Time schedule for examinations: weekly, individually
- Calculated as mg/kg/day from body weight data

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 21
- Organs examined: gross necropsy of all viscera.

OTHER:
Serum was aliquotted into three vials for TSH, triiodothyronine (T3), and T4 determinations and shipped (frozen on dry ice) to Air Force Research Laboratory (Wright Patterson Air Force Base, Dayton, Ohio; Meyer 1998) for determination of TSH, T3 , and T4 levels.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: placental abnormalities

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: half per litter

Statistics:

Clinical observation and other proportion data were analyzed using the variance test for homogeneity of the binomial distribution (Snedecor and Cochran 1967). Continuous data (e.g., maternal body weights, body weight changes, feed and water consumption values, and litter averages for percent male fetuses, percent resorbed conceptuses, fetal body weights, fetal anomaly data, fetal ossification site data, and thyroid hormone levels) were analyzed using Bartlett's test of homogeneity of variances (Sokal and Rohlf 1969) and the analysis of variance (Snedecor and Cochran 1967), when appropriate (i.e., Bartlett's test was not significant [p > .05]. If the analysis of variance was significant (p =< .05), Dunnett's test (Dunnett 1955) was used to identify the statistical significance of the individual groups.
If the analysis of variance was not appropriate (i.e., Bartlett's test was significant [p =< .05] , the Kruskal-Wallis test (Sokal and Rohlf 1969) was used, when less than or equal to 75% ties were present; and when more than 75% ties were present, Fisher's exact test (Siegel 1956) was used. In cases in which the Kruskal-Wallis Test was statistically significant (p =< .05),Dunn 's method of multiple comparisons (Dunn 1964) was used to identify the statistical significance of the individual groups. Count data obtained at cesarean-sectioning were evaluated using the procedures previously described for the Kruskal-Wallis test (Sokal and Rohlf 1969).

Indices:

% Pre-implantation loss and % Post-implantation loss were not calculated in the report. Recalculated by RSS author as:
% Pre-implantation loss = 100 * (Number of corpora lutea - Number of implantation sites) / Number of corpora lutea
% Post-implantation loss = 100 * (Number of implantation sites - Number of live fetuses) / Number of implantation sites

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Alopecia in 3 top-dose females, not toxicologically relevant.
Exposure to ammonium perchlorate in the drinking water up to 30 mg/kg-day had the expected effect of increasing serum TSH levels and decreasing serum T3 and T4 levels at all exposures tested based on the mechanism-of-action of perchlorate (USEPA 1998, 2002). Serum TSH levels were significantly increased (p =< .001) and serum T 4 levels were significantly decreased (p =< .001) at all exposure levels in an exposure-related manner. There was also a statistically significant decrease (p =< .01) in serum T3 levels at the 30 mg/kg-day target exposure, compared to the control carrier group values.

The absolute thyroid weights and ratios of thyroid weight to terminal body weight from the satellite dams in the 30.0 mg/kg/day exposure group were significantly increased (p =< .01) over the carrier control exposure group values. Microscopic examination of the thyroid glands for the satellite dams revealed hypertrophy (grade 1) of the follicular epithelium and decreased colloid (grades 2 to 3) in the dams in the 30.0 mg/kg-day exposure groups that was considered treatment related. Two dams in this exposure group were also observed to have thyroid hyperplasia. No treatment-related microscopie changes were observed in the thyroid gland of any dams offered 0.01, 0.1, or 1.0 mg/kg/day of ammonium perchlorate.

Effect levels (maternal animals)

1

Key result

Dose descriptor:

NOAEL

Effect level:

>= 1 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Key result

Dose descriptor:

NOAEL

Effect level:

>= 30 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes. Remark: minimal & non adverse

Details on embryotoxic / teratogenic effects:
There appeared to be an increase in % pre- and post-implantation losses* and a decrease in number of live fetuses, but dose-relationship was unclear and the number of implantation sites was unaffected by treatment. The effects are not considered as being toxicologically relevant. NB: an absence of impact on number of pups has been confirmed in a 2-generation study in rats treated at up to 30 mg/kg/day (see 7.8.1).
*: comparison with historical control impossible since these indices were not calculated in historical data.

There are 3% and 8% fewer ossification sites in sternum and forelimb phalanges, respectively, at 30 mg/kg/day vs. controls.** This effect is minimal, and not adverse: it represents a slight delay in development which is usually reversible.
**: the control group was already outside the historical range for sternal ossification sites: historical control data inadequate for interpretation.

No teratogenic effects.

The serum levels of fetal TSH in the 1 and 30 mg/kg-day exposure groups from the satellite litters were significantly increased (p =< .01 or p =< .001), and the serum T4 level were significantly decreased (p =< .01) at the 30 mg/kg-day exposure level, and fetal T3 levels were significantly decreased (p =< .01
or p =< .001) at all exposure levels in an exposure-dependent manner.
Decreased colloid was observed since the 0.01 mg/kg/day group (3/32) to reach a 25/32 and a 32/32 incidence in the 1.0 mg/kg/day and 30 mg/kg/day respectively. However, in the 0.1 mg/kg/day group, only one female fetuses presented decreased colloid.
No follicular hypertrophy or hyperplasia was observed in the 30 mg/kg/day group. Only one male and one female featuses presented hyperplasia in the 1 mg/kg/day group.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

>= 30 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Developmental toxicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Reproductive indices and ossification sites in rats treated with ammonium perchlorate

Dose (mg/kg/day)	0	0.01	0.1	1	30
Corpora lutea	19.3	17.9	18.1	19.8	19.8
Implantations	17.0	14.7	14.4	16.6	14.8
Live fetuses	16.6	14.3	13.9	16.2	14.1*
% Pre-implantation loss @	11.9	17.9	20.4	16.2	25.3
% Post-implantation loss @	2.4	2.7	3.5	2.4	4.7
Ossification sites (per fetus per litter):
- Sternal center	4.00	3.93	3.97	3.96	3.88**
- Forelimb phalanges	6.97	6.78	6.68	7.01	6.43*

@: no statistical analysis performed since these data were not in the original report

*: p<0.05; **: p<0.01

Applicant's summary and conclusion

Conclusions:

Maternal general NOAEL is 30 mg/kg/day in the absence of relevant general toxicity maternal effects. However, because of thyroid follicular cells hypertrophy/hyperplasia, maternal NOAEL is set at 1 mg/kg/day.
Developmental NOAEL set at 30 mg/kg/day in the absence of adverse developmental abnormalities and thyroid follicular cells hypertrophy/hyperplasia.
The top-dose was not based on dose-limiting toxicity but on antithyroid effects, limiting the sensitivity of the study for Developmental Effects classification.

Executive summary:

Ammonium perchlorate was provided to groups of 24 female rats via drinking water, at dose-levels of 0 (control), 0.01, 0.1, 1 and 30 mg/kg/day before (2 weeks before mating, complete mating) and during gestation (21 days).

At 30 mg/kg/day, there was no maternal toxicity. Pre- and Post-implantation loss indices were higher than in controls but this was not considered to represent relevant resorptions when considering the number of resorptions, implantation sites, live and dead fetuses. There was a minor indication of delayed ossification (fewer ossification sites) but this effect is minimal, and not adverse: it represents a slight delay in development which is usually reversible. No developmental abnormalities were noted. At 0.01 to 1 mg/kg/day, neither maternal nor embryo-/feto- or developmental toxicities were noted. 

An additional 16 Iitters/group were sacrificed on DG 21 for maternal and fetal serum TSH, T3, and T4 levels and thyroid histopathology. General and reproductive toxicology parameters were comparable among the groups with only delays in ossification observed in the 30 mg/kg-day group.

Maternal thyroid weights were increased in the 30.0 mg/kg-day group. Decreased colloid was present in male and female fetal thyroids in the 1.0 and 30.0 mg/kg-day groups. Maternal TSH was increased and T 4 was decreased at all levels, and T 3 was reduced at 30.0 mg/kg-day. Fetal TSH was increased at 1.0 and 30.0 mg/kg-day, T4 was reduced at 30.0 mg/kg-day, and T3 was decreased at all levels.

The maternal no-observable-adverse-effect level (NOAEL) was 1.0 mg/kg-day; exposures of 30.0 mg/kg-day increased absolute and relative maternal thyroid weights and histopathology findings.

The developmental NOAEL was 30.0 mg/kg-day. The colloid depletion in the thyroids and increased TSH and decreased T3 and T4 levels at lower exposures were considered adaptive and not adverse.

No adverse effects on development occurred at levels that did not cause maternal toxicity, therefore ammonium perchlorate is not a selective developmental toxicant.