Di(µ-2,2´,2´´-nitrilotris(ethanol)-diperchlorato)dinatrium

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

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

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

Justification for type of information:

Justification for Read Across is given in section 13 of IUCLID.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2003

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Remarks:

in compliance with U.S. Environmental Protection Agency (TSCA/ FIFRA), the Organization for Economic Cooperation and Development (OECD), and the Japanese Ministry of Agriculture, Forestry, and Fisheries (MAFF)

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 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 arrival: 59 days old (females), 73 days old (males).
- Fasting period before study: no.
- Diet: feed (Certified Rodent Chow #5002 during the exposure periods (precohabitation and gestation), ad libitum.

ENVIRONMENTAL CONDITIONS: all cage sizes and housing conditions were in compliance with the Guide for the Care and Use of Laboratory Animals (Institute of Laboratory Animal Resources 1996).

RATIONALE FOR CHOICE OF ANIMALS: the Sprague-Dawley rat was selected because it has been demonstrated to be sensitive to developmental toxins and is widely used throughout the industry for nonclinical studies of developmental toxicity.

Institute of Laboratory Animal Resources. 1996. Guide for the care and use of laboratory animals. Washington, DC: National Academy Press.

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: test formulations of the substance 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.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The average actual consumed doses of ammonium perchlorate in the study were 0.0, 0.01, 0.08, 0.70, and 21.69 mg/kg-day during the 2-week precohabitation period and 0.00, 0.01, 0.10, 0.96, and 28.27 mg/kg-day during the 3-week gestation period.

Details on mating procedure:

- Proof of pregnancy: mated female rats (evidence of spermatozoa observed in a vaginal smear or a copulatory plug observed in situ) were considered to be day of gestation (DG) 0.

Duration of treatment / exposure:

14 days before cohabitation and continuing through sacrifice on Day 21 of gestation.

Frequency of treatment:

continual access through the drinking water

Duration of test:

From 14 days prior to cohabitation until the 21st day of gestation

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.01 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

0.1 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

1 mg/kg bw/day (nominal)

Doses / concentrations 4

Dose / conc.:

30 mg/kg bw/day (nominal)

No. of animals per sex per dose:

24 mated females

Control animals:

yes, concurrent vehicle

Details on study design:

- Satellite 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.

- Dose selection rationale: the doses were selected based on previous studies conducted with the test substance. In a developmental neurotoxicity (DNT) study (York 1998), thyroid effects (colloid depletion, hypertrophy, hormone level changes) were seen in pups on postpartum day 5 at 10.0 mg/kg/day. Furthermore, this dosage was clearly an effect level in a 90-day drinking water study conducted at another laboratory (Siglin et al. 2000).

- Study design rationale: as the exposure in the DNT study did not begin until after mating (confirmation of pregnancy), exposures for this study were started for both sexes, 2 weeks prior to the start of cohabitation to ensure a maternal hypothyroid state during all of gestation. The substance is readily absorbed from the intestinal tract, and oral uptake is considered to be the major route of human exposure, the substance in the drinking water was selected as the route of exposure. Thyroid hormone and thyroid-stimulating hormone (TSH) levels in circulating blood were assessed as a sensitive end point for the effect of the ion on a developing organism (Capen 1997).

York, R. G. 1998. A neurobehavioral developmental study of ammonium perchlorate administered orally in drinking water to rats [final report]. Sponsor’s study number 7757A210-1096-25F (Argus Protocol 1613–002).
Siglin J. C., D. R. Mattie, D. E. Dodd, P. K. Hildebrandt, and W. H. Baker. 2000. A 90-day drinking water toxicity study in rats of the environmental
contaminant ammonium perchlorate. Toxicol. Sci. 57:61–74.
Capen, C. C. 1997. Mechanistic data and risk assessment of selected toxic endpoints of the thyroid gland. Toxicol. Pathol. 25:39–48.

Examinations

Maternal examinations:

VIABILITY: Yes.
- Time schedule: at least twice daily.
- Groups tested: rats in the main study and satellite study.

GENERAL APPEARANCE: Yes.
- Time schedule: at least once during the preexposure period.
- Groups tested: rats in the main study and satellite study.

CLINICAL OBSERVATIONS: Yes.
- Time schedule: daily during the exposure period (14 days prior to cohabitation and through day of sacrifice).
- Groups tested: rats in the main study and satellite study.

BODY WEIGHT: Yes.
- Time schedule for examinations: daily throughout the exposure period.

FOOD AND WATER CONSUMPTION: Yes.
- Time schedule: daily throughout the exposure period.

POST-MORTEM EXAMINATIONS: Yes.
- Sacrifice on gestation day 21.
- Organs examined (main study): uterus and placentae. Placentae was examined for abnormalities (size, color, or shape).
- Haematology examinations (satellite study): maternal blood collected from the inferior vena cava. Serum was aliquotted into three vials for TSH, T3 and T4 determinations. Radioimmunoassay (RIA) kits for the hormone measurements were all from the same batch number and with the same expiration date for all the standard and unknown samples. RIA T3 assay kits were purchased from Diagnostic Product (Los Angeles, CA) and canine T3 antibody–coated tubes were used. Likewise, RIA T4 assay kits were purchased from Diagnostic Product and T4 antibody–coated tubes were used. RIA TSH assay kits were purchased from Amersham (Arlington Heights, IL) and lyophilized rabbit anti-rat TSH serum and Amerlex-M second antibody (donkey anti-rabbit serum coated onto magnetized polymer particles containing sodium azide) were both used. All assays were performed in triplicate and according to the manufacturers’ recommended procedures.
- Gross necropsy (satellite study): thoracic, abdominal, and pelvic viscera of each dam was examined.
- Histological evaluation (satellite study): a section of the trachea containing the thyroids and parathyroids of all satellite dams were excised. Following fixation, the thyroid and parathyroid tissue samples were carefully trimmed and shipped to the laboratory for weighing and standard hematoxylin and eosin staining.
- Colloid depletion analysis (satellite study): it was scored as grade 0 (no depletion in the amount of colloid); grade 1 (1 % to 10 % follicles affected); grade 2 (11 % to 50 % follicles affected); or grade 3 (50 % to 100 % follicles affected). The grade was assigned based primarily on reduction in area of colloid in thyroid follicles, and secondarily on the tinctoral quality or staining characteristics of the colloid.
- Follicular cell hypertrophy analysis (satellite study): it was based on size of cell (cytoplasmic to nuclear ratio). Grade 0 (no hypertrophy); grade 1 (minimal) the follicular epithelium was taller than the normal cuboidal, approaching columnar; individual cells exhibiting increased height and width and was considered just above the limits of detection. Grade 2 (mild) was considered when the follicular epithelium cells were distinctly larger than normal; the follicular lumen was consistently obliterated by the hypertrophied cells.
- Follicular cell hyperplasia analysis (satellite study): it was only diagnosed when there was either stratification (multiple layers) or papillary infolding of single or multiple layers of follicular cells. Grade 1 (minimal) with 1 % to 10 % of follicles affected; grade 2 (mild) with 11 % to 50% of follicles affected; and grade 3 (moderate to severe) with 51 % to 100 % of follicles affected.

OTHER:
- Rats in the main and satellite study were examined daily during the exposure period (14 days prior to cohabitation and through day of sacrifice) for abortions, premature deliveries and deaths.
- Throughout the sacrifice procedures and sample collection, every effort was made to avoid inducing stress in the rats from excessive handling and noise, because this could affect scheduled hormone evaluations.
- Cesarean-sectioning observations on DG 21 were based on 19, 19, 17, 20, and 20 pregnant dams in the five respective exposure groups.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes.
Examinations included:
- Gravid uterus: the uterus was examined for pregnancy, number and distribution of implantations, early and late resorptions, and live and dead fetuses. Gravid uterine weights were recorded for rats of the main and satellite study.
- Number of corpora lutea: the number of corpora lutea in each ovary was recorded.

Fetal examinations:

- Gross external examinations: Yes.
- Soft tissue examinations: Yes. Approximately one half of the fetuses were examined for soft tissue alterations by the microdissection technique of Staples. Of the respective fetuses, 153, 131, 112, 158, and 137 fetuses were examined for soft tissue alterations.
- Skeletal examinations: Yes. The fetuses not examined for soft tissue alterations were examined for skeletal and cartilaginous development after staining with alizarin red S. 163, 140, 124, 167, and 145 fetuses were examined for skeletal alterations and fetal ossification sites.
- Head examinations: Yes. The heads of one half of the fetuses examined for soft tissue alterations were fixed in Bouin’s solution and subsequently examined by free hand sectioning.
- Weight: each cesarean-delivered fetus was weighed.
- Haematology and histological evaluation: fetal blood samples (T3, T4 and TSH evaluation) were collected following decapitation from fetuses not selected for histological evaluation and pooled by litter due to the small volumes of blood. A section of the trachea containing the thyroids and parathyroids of one male and one female fetus from each satellite litter were excised. Following fixation, the tissues were trimmed and examined for colloid depletion, follicular cell hypertrophy and follicular cell hyperplasia. Hormone analysis and histological evaluation was performed following the same procedures as the ones followed for the dams.
- Other: fetal alteration evaluations were based on 316, 271, 236, 325, and 282 live fetuses in the five exposure groups, respectively. Fetal alterations were defined as malformations (irreversible changes that spontaneously occur at low incidence) or variations (reversible delays or accelerations in development that commonly occur in this species/strain).

Statistics:

Clinical observation and other proportion data were analyzed using the variance test for homogeneity of the binomial distribution.
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 and the analysis of variance, when appropriate (i.e., Bartlett’s testwas not significant (p > 0.05). If the analysis of variance was significant (p ≤ .05), Dunnett’s test 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 ≤ 0.05), the Kruskal-Wallis test was used, when less than or equal to 75 % ties were present; and when more than 75 % ties were present, Fisher’s exact test was used. In cases in which the Kruskal-Wallis Test was statistically significant (p ≤ 0.05), Dunn’s method of multiple comparisons 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).
Sokal, R. R., and F. J. Rohlf. 1969. Bartlett’s test of homogeneity of variances. In Biometry, 370–371. San Francisco: W.H. Freeman and Co.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Localized alopecia, torn ear and red perivaginal substance. Localized alopecia on the limbs was observed for three dams (p ≤ 0.01) during mid-gestation in the 30 mg/kg-day exposure group. All these clinical observations were considered unrelated to the substance-treatment because the incidences were not dose dependent and/or the observation are commonly seen in rats in the laboratory environment. The maternal clinical observations for the 16 satellite dams in each of the five exposure groups during the precohabitation and gestation periods were comparable to the main study animals and did not differ significantly.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

All dams survived to scheduled sacrifice

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

The maternal body weights in the five exposure groups were comparable during the precohabitation and gestation periods. All increases or decreases in body changes were not considered exposure related because they were a singular occurrence and were transient. There were no statistically significant differences in average terminal body weights and corrected DG21 body weights (DG 21 body weight minus the gravid uterine weight) among exposure groups during gestation. The maternal body weights for the 16 satellite dams in each of the five exposure groups during the precohabitation and gestation periods were comparable to the main study animals and did not differ significantly.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Absolute (g/day) and relative (g/kg-day) feed consumption values were comparable among the five exposure groups. The maternal feed consumption values for the 16 satellite dams in each of the five exposure groups during the precohabitation and gestation periods were comparable to the main study animals and did not differ significantly.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Description (incidence and severity):

Absolute (g/day) and relative (g/kg-day) water consumption values were comparable among the five exposure groups.
The maternal water consumption values for the 16 satellite dams in each of the five exposure groups during the precohabitation and gestation periods were comparable to the main study animals and did not differ significantly.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Exposure to the substance in the drinking water up to 30.0 mg/kg-day had the expected effect of increasing serum TSH levels and decreasing serum T3 and T4 levels at all exposures tested. Serum TSH levels were significantly increased (p ≤ .001) and serum T4 levels were significantly decreased (p ≤ 0.001) at all exposure levels in an exposure-related manner. There was also a statistically significant decrease (p ≤ 0.01) in serum T3 levels at the 30.0 mg/kg-day target exposure, compared to the control carrier group values.

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

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.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

The only adverse necropsy observation was red substance in the stomach of the rat observed in the 0.1 mg/kg-day exposure group female rat with the clinical observation of red perivaginal substance.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Hypertrophy (grade 1) of the follicular epithelium and decreased colloid (grades 2 to 3) were observed in the dams in the 30.0 mg/kg-day exposure groups and was considered treatment related. Two dams in this exposure group were also observed to have thyroid hyperplasia. No treatment-related microscopic changes were observed in the thyroid gland of any dams offered 0.01, 0.1, or 1.0 mg/kg-day of substance.

Histopathological findings: neoplastic:

not examined

Maternal developmental toxicity

Number of abortions:

not specified

Pre- and post-implantation loss:

effects observed, non-treatment-related

Description (incidence and severity):

The preimplantation losses increased at each exposure level (12 %, 18 %, 20 %, 16 % and 25 %, respectively) but was not noted as biologically or statistically significant. Considering the 20 satellite dams per exposure group that were in the same animal rooms at the same time, preimplantation losses at DG 21 were 14 %, 11 %, 14 %, 15 % and 13 %, respectively.

Early or late resorptions:

no effects observed

Description (incidence and severity):

All placentae appeared normal and no dam had a litter consisting of only resorbed conceptuses.

Dead fetuses:

effects observed, non-treatment-related

Description (incidence and severity):

The averages for the number of live fetuses, were significantly reduced (p ≤ .05) in the 30.0 mg/kg-day exposure group. These reductions were not considered treatment-related because (1) the values were within the ranges observed historically at the testing facility; and (2) the values were not toxicologically important because there were no significant increases in fetal deaths or resorptions nor significant reductions in number of implantations. There was no decrease in the total number of live fetuses 237, 244, 254, 251, and 247, respectively, for the satellite dams.

Details on maternal toxic effects:

- Exposures to the substance as high as 30.0 mg/kg-day in the drinking water did not affect any DG 21 cesarean-sectioning parameters and all values were within the historical control range of the testing facility.

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

ca. 1 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Results (fetuses)

Fetal body weight changes:

not specified

Reduction in number of live offspring:

not specified

Changes in sex ratio:

not specified

Changes in litter size and weights:

effects observed, non-treatment-related

Description (incidence and severity):

The averages for litter size were significantly reduced (p ≤ .05) in the 30.0 mg/kg-day exposure group; non treatment-related. There was also no decrease in litter size (14.8, 15.2, 15.9, 15.7 and 15.4) in the satellite study.

Changes in postnatal survival:

not specified

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Fetal gross external alterations were rarely observed and were comparable between control and treated groups. Only one fetus from one 0.01 mg/kg-day group had gross external alterations: a cleft snout and palate.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

The only skeletal malformation observed was the incompletely ossified palate in the 0.01 mg/kg-day exposure group dam with the cleft snout/palate identified at gross external examination. There were no significant increases in skeletal alterations among the fetuses in the five exposure groups. Minor variations observed included incomplete ossifications; bifid, asymmetric or fused centra; and cervical or wavy ribs.
The average number of ossification sites in the hyoid, vertebrae (cervical, thoracic, lumbar, and sacral), sternum (manubrium and xiphoid), forelimbs (carpals and metacarpals), and hindlimbs (tarsals, metatarsals, and phalanges) occurred at similar incidences in all exposure groups and did not significantly differ.
The average number of ossification sites per litter for sternal centers (3.88) and for forelimb phalanges (6.43) were significantly reduced (p ≤ .05 or p ≤ .01) in the 30.0 mg/kg-day exposure group and below the historical control-range observed at the testing facility (3.96 to 4.00; and 6.97 to 8.77, respectively). The average number of ossification sites per litter for the caudal vertebrae (6.19) and ribs (13.01) were also reduced below historical values observed at the testing facility (6.47 to 7.99; and 13.02 to 13.12) but did not reach statistical significance.
These reductions were considered evidence of developmental retardation caused by maternal exposure to the substance but may be reversible developmental delays that will resolve with time. Most importantly there were no skeletal malformations of the caudal vertebrae, ribs, sternum, or phalanges at this exposure level, where the significant reductions in ossification sites occurred.

Other effects:

effects observed, treatment-related

Description (incidence and severity):

- Two male fetuses in the 0.01 mg/kg-day exposure group had grade 2 decreased colloid. An exposure-related increase in the incidence and severity of decreased colloid was present in male fetuses from the satellite litters in the 1.0 and 30.0 mg/kg-day exposure groups. 11 male fetuses in the 1.0 mg/kg-day exposure group had grade 1 decreased colloid and one 1.0 mg/kg-day exposure group had grade 2 decreased colloid. All male fetuses in the 30.0 mg/kg-day exposure group had grade 3 decreased colloid. Grade 2 decreased colloid was present in one female fetus in the 0.01 mg/kg-day exposure group and grade 1 decreased colloid was present in one female fetus in the 0.1 mg/kg-day exposure group. An exposure-related increase in the incidence and severity of decreased colloid was present in female fetuses from the satellite litters in the 1.0 and 30.0 mg/kg-day exposure groups. 12 female fetuses in the 0.1 mg/kg-day exposure group had grade 1 decreased colloid and one female fetus in the 1.0 mg/kg-day exposure group had grade 2 decreased colloid. All female fetuses in the 30.0 mg/kg-day exposure group had grade 3 decreased colloid.
- No follicular hypertrophy was observed in the male and female DG 21 fetuses at any exposures. Follicular cell hyperplasia was observed in only one 1.0 mg/kg-day exposure group male fetus and one 1.0 mg/kg-day exposure group female fetus.
- The serum levels of fetal TSH in the 1.0 and 30.0 mg/kg-day exposure groups from the satellite litters were significantly increased (p ≤ 0.01 or p ≤ 0.001), 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 ≤ 0.01 or p ≤ 0.001) at all exposure levels in an exposure-dependent manner.

Details on embryotoxic / teratogenic effects:

No fetal alterations were attributable to exposure to the substance at exposures up to 30.0 mg/kg-day. The incidences were not exposure dependent; the observation occurred in only one or two high-exposure group fetuses; or the incidences are within the averages observed historically at the laboratory. The control and treated groups were comparable for the number of litters that had at least one fetus with any alteration, the number of fetuses with any alteration, or the percent of fetuses with any alteration/litter.
Fetal soft tissue alterations were sporadic among the five exposure groups. One carrier group fetus had a bifurcated aortic arch and absent innominate vessel as the only malformation. Seven other fetuses had minor variations. There was no significant difference in incidence of soft tissue alterations between the carrier control group and exposure groups.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

ca. 1 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

skeletal malformations

Remarks on result:

other: developmental

Fetal abnormalities

Abnormalities:

effects observed, treatment-related

Localisation:

skeletal: forelimb

skeletal: sternum

skeletal: rib

skeletal: vertebra

skeletal: hindlimb

visceral/soft tissue: cardiovascular

Overall developmental toxicity

Developmental effects observed:

yes

Lowest effective dose / conc.:

30 mg/kg bw/day (nominal)

Treatment related:

yes

Relation to maternal toxicity:

not specified

Dose response relationship:

not specified

Relevant for humans:

not specified

Any other information on results incl. tables

There were no adverse effects on embryo-fetal development at exposure that did not cause maternal toxicity and the substance should not be identified as a selective developmental toxicant at doses as high as 30 mg/kg-day of substance in the drinking water.

In fetuses, the increased serum TSH levels and decreased T3 and T4 hormone levels at exposure levels lower than 30 mg/kg-day were considered adaptive perturbation in the hypothalamic-pituitary-thyroid axis and not adverse. In dams, the increased serum TSH levels and decreased T3 and T4 hormone levels at exposure levels lower than 30 mg/kg-day were considered adaptive perturbation in the hypothalamic-pituitary-thyroid axis and not adverse. The authors suggest that a decrease in serum T4 would not be adverse until there is a 60 % decrease from normal. Dams demonstrated a 54 % decrease in T4 at the 30 mg/kg-day dose level while fetuses demonstrated a 13 % decrease in T4 at the same dose level.

Applicant's summary and conclusion

Conclusions:

NOAEL (maternal toxicity) = 1 mg/kg/bw/day (nominal)
NOAEL (developmental toxicity) = 1 mg/kg/bw/day (nominal)
No adverse effects on development occurred at levels that did not cause maternal toxicity. The substance is not a selective developmental toxicant.

Executive summary:

The developmental toxicity of the substance to Sprague-Dawley rats was evaluated by the administration of the substance in the drinking water at doses of 0.0, 0.01, 0.1, 1.0, and 30.0 mg/kg-day beginning 14 days before cohabitation and continuing through sacrifice. Twenty-four rats/group were cesarean sectioned on day of gestation (DG) 21 and fetuses examined for visceral and skeletal alterations. An additional 16 litters/group were sacrificed on DG 21 for maternal and fetal serum TSH, T3, and T4 levels and thyroid histopathology.

Clinical and necropsy observations, body weights, feed and water consumption, and cesarean sectioning 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. Maternal TSH was increased and T4 was decreased at all levels, and T3 was reduced at 30.0 mg/kg-day.

Decreased colloid was present in male and female fetal thyroids in the 1.0 and 30.0 mg/kg-day groups. 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 average number of ossification sites per litter for sternal centers and for forelimb phalanges were significantly reduced in the 30.0 mg/kg-day exposure group, these reductions were considered reversible developmental delays and were not considered teratologically important because there were no skeletal malformations of the sternum or phalanges at this exposure level.

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 1.0 mg/kg-day; developmental delays in ossification occurred in the 30.0 mg/kg-day group. The colloid depletion in the thyroids, the increased TSH and decreased T3 and T4 levels at lower exposures were considered adaptive and not adverse. No adverse effects on development occured at levels that did not cause maternal toxicity. The substance is not a selective developmental toxicant.