Sodium chlorate

Endpoint summary

Description of key information

In the sub-chronic studies performed in rats, the main target organ was the blood (with anaemia effects). The NOAEL obtained in the two studies is very similar. The GLP study reported in 1987 is more reliable as all the parameters required in Directive 2001/59/EC, Annex V, Method B.26 were evaluated and reported while in the non GLP study published in 1995 all these parameters were not reported (or incompletely reported). The thyroid effects described by McCauley et al.(1995) at levels above 100 mg/kg bw are of uncertain clinical significance and were not observed in the rat and dog GLP studies. An increased level of thyroid colloid depletion compared to control can be regarded the result of a physiological adaptation and not an adverse effect per se.

In the 90-day study performed in the dog, there were no significant toxic effects up to the highest dose level tested. Considering that dogs have lower levels of methaemoglobin reductase than humans and thus are more susceptible to methaemoglobin, the higher NOAEL level in this studies for dogs adds to the confidence of the reliability of the 100 mg/kg NOAEL obtained in rats. The overall lowest sub-chronic NOAEL is 100 mg/kg bw/day, based on effects on erythrocytes; and a No Observed Effect Level (NOEL) of 38 mg/kg in males and 55 mg/kg in females when considering the physiological colloid depletion observed at the dose of 128 mg/kg in males and 209 mg/kg in females in the McCauley study.

Effects on haematology and the thyroid were also observed in a three week study in rats (NOAEL 35 mg/kg bw males and 40 mg/kg bw females) and no effects were seen in mice (NOAEL 350 mg/kg  bw males and 365 mg/kg bw females) (NTP 2005).

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

March 1987 - July 1987

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study performed according to standard US EPA protocol and under GLP.

Qualifier:

according to guideline

Guideline:

EPA OPP 82-1 (90-Day Oral Toxicity)

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Deviations:

yes

Remarks:

- Haematology, clinical biochemistry and histopathology only in 10 animals/sex/group - humidity 23 - 86% in stead of 30 - 70%

Principles of method if other than guideline:

- Haematology, clinical biochemistry and histopathology only in 10 animals/sex/group
- humidity 23 - 86% in stead of 30 - 70%

GLP compliance:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., New York, USA
- Age at study initiation: 42 days old
- Weight at study initiation: males: mean 205 g, range 181-229 g; females: mean 143 g, range 129-168 g
- Fasting period before study: no info
- Housing: animals were doubly housed in elevated stainless steel wire mesh cages during the first week of the acclimatisation period and individually housed thereafter
- Diet (e.g. ad libitum): standard laboratory diet (Purina Certified Rodent Chow), ad lib
- Water (e.g. ad libitum): Elizabethtown Water Company, ad lib
- Acclimation period: 14 days (March 24 - April 6, 1987)


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24
- Humidity (%): 23 - 86
- Air changes (per hr): no info
- Photoperiod (hrs dark / hrs light): 12 h light/dark cycle (7 AM to 7 PM)


IN-LIFE DATES: From: April 7, 1987 (Pretest: March 31, 1987) To: July 6, 1987

Route of administration:

oral: gavage

Vehicle:

other: distilled water

Duration of treatment / exposure:

90 or 91 days depending on day of necropsy
(13 weeks)

Frequency of treatment:

daily (7/7)

Remarks:

Doses / Concentrations:
10 - 100 - 1000 mg/kg bw d
Basis:
actual ingested

No. of animals per sex per dose:

120 (60 males 60 females): 15 animals per sex per group (3 dose groups and 1 control group)

Control animals:

yes, concurrent vehicle

Details on study design:

Post-exposure period: No

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily; once in the morning and once in the afternoon


BODY WEIGHT: Yes
- Time schedule for examinations: twice pretest, weekly during treatment and terminally (after fasting)


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): not applicable (however, food intake is examined weekly, beginning one week prior to treatment)


FOOD EFFICIENCY: not applicable


WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): not applicable


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: pretest and termination


HAEMATOLOGY: Yes
- Time schedule for collection of blood: termination (week 13)


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: termination (week 13)


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

- Macroscopic: complete post mortem examinations were performed on all animals. External surface, all orifices, the cranial cavity, carcass, the external of the brain and spinal cord, nasal cavity and paranasal sinuses, the thoracic, abdominal and pelvic cavities and their viscera and cervical tissues and organs were examined.
- Microscopic: complete post mortem examinations were performed on all animals. Sectioned surfaces of the brain and spinal cord, nasal cavity and paranasal sinuses, the thoracic, abdominal and pelvic cavities and their viscera and cervical tissues and organs were examined.

Statistics:

Body weight, food consumption, hematology and clinical chemistry parameters, organs weights and organ/body weights ratios were analyzed. Mean values of all dose groups were compared to the control at each time interval. Statistical evaluation of equality of means was made by the appropriate one way analysis of variance technique, followed by a multiple comparison procedure if needed. First, Bartlett's test was performed to determine if groups had equal variance. If the variances were equal, parametric procedures were used; if not, nonparametric procedures were used. The parametric procedures were the standard one way ANOVA using the F distribution to assess significance. If significant differences among the means were indicated, Dunnett's test was used to determine which means were significantly different from the control. If a nonparametric procedure for testing equality of means was needed, the Kruskal-Wallis test was used, and if differences were indicated a summed rank test (Dunn) was used to determine which treatments differed from control. A statistical test for trend in the dose levels was also performed. In the parametric case (i .e., equal variance) standard regression techniques with a test for trend and lack of fit were used. In the nonparametric case Jonckheere's test for monotonic trend was used. The test for equal variance (Bartlett's) was conducted at the 1%, two-sided risk level. All other statistical tests were conducted at the 5% and I%, two-sided risk level.

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

See 'Details on results'

Mortality:

mortality observed, non-treatment-related

Description (incidence):

See 'Details on results'

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

See 'Details on results'

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

See 'Details on results'

Food efficiency:

not examined

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

effects observed, non-treatment-related

Description (incidence and severity):

See 'Details on results'

Ophthalmological findings:

no effects observed

Description (incidence and severity):

See 'Details on results'

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Normocytic, non regenerative anemia
See 'Details on results'

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

See 'Details on results'

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):

See 'Details on results'

Gross pathological findings:

no effects observed

Description (incidence and severity):

See 'Details on results'

Details on results:

CLINICAL SIGNS AND MORTALITY
Mortality:
- Time of death: day 69 and day 30
- Number of deaths at each dose: one 100 mg/kg bw d male and one 1000 mg/kg d female. No abnormaltities were found. (due to the lack of significant physical observations and histopathological lesions these deaths are not considered to be related to sodium chlorate administration).
Clinical signs: no sodium chlorate related clinical signs were observed

BODY WEIGHT AND WEIGHT GAIN
Body weight gain: All animals gained weight during the study. The body weights for the males did not differ from the control group body weights. Mean group body weights for 10 and 1000 mg/kg bw d females were significantly lower than for the control animals. From historical data it was shown that the body weight gain of the control animals was higher than expected. Also no dose related effect could be found. Therefore it is suggested that the observed effect is due to normal physiological variation and not related to sodium chlorate administration.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study) / WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study)
Food/water consumption: : Some increase of food consumption was seen (male 10 and 100 mg/kg bw/d week 6 and 7, male and female 100 mg/kg bw/d week 10) This effect was not sodium chlorate related.

OPHTHALMOSCOPIC EXAMINATION
Ophthalmoscopic examination: no sodium chlorate related ocular abnormalities were observed

HAEMATOLOGY
Haematology: The 1000 mg/kg d animals showed a statistically significant lower mean erythrocyte count, hemoglobin concentration and percent hematocrit as compared with the controls. Mean Cortpuscular Hemoglobin (MCH), Mean Corpuscular Volume (MCV), and Mean Corpuscular Hemoglobin Concentration (MCHC) as well as reticulocyte counts and percent haemoglobin for high-dose animals were comparable to control values. Females were more effected than males. These findings are consistent with a normocytic, non regenerative anemia and were considered related to sodium chlorate administration.

Mean values for each dose group per sex for every parameter measured are shown below (significant figures = *).

1 METHGB methemoglobin percent
2 HGB hemoglobin concentration g/dl
3 HCT Hematocrit percent
4 RBC erythrocyte count 10e6/microliter
5 PLAT platelet count 10e5/microliter
6 MCV mean corpuscular volume cubic u
7 MCH Mean Cortpuscular Hemoglobin uu g
8 MCHC Mean Corpuscular Hemoglobin Concentration g/dl
9 WBC Total leukocyte count 10e3/microliter
10 RETIC reticulocyte count % RBC

Males mg/kg bw
1 2 3 4 5 6 7 8 9 10
0 0.6 15.2 43 7.17 16.41 60 21.2 35.1 17.3 0
10 0.5 15.2 43 7.24 15.80 60 21.0 35.4 16.9 -
100 0.7 15.2 43 7.23 15.81 60 21.0 35.4 14.3 -
1000 0.5 14.6 41* 6.75 16.76 60 21.7 35.9 14.5 0

Females mg/kg bw
1 2 3 4 5 6 7 8 9 10
0 0.6 14.9 43 6.62 16.35 65 22.6 34.5 9.6 0
10 0.7 15.3 44 6.78 16.08 64 22.6 35.0 9.3 -
100 0.5 14.8 43 6.63 15.97 64 22.3 34.8 7.2 -
1000 0.6 13.9* 39* 6.24* 18.45 63 22.3 35.3 9.7 0.1


CLINICAL CHEMISTRY
Clinical chemistry: no sodium chlorate related abnormalities were observed

ORGAN WEIGHTS
Organ weights: 1000 mg/kg d males and females showed a significant slight decrease in absolute adrenal weights compared to the controls. Also in the 1000 mg/kg bw males a trend was seen towards a decrease in the adrenal to body weight ratio. Other effects were not attributed to sodium chlorate exposure. See Table 1.

GROSS PATHOLOGY
Gross pathology: no sodium chlorate related effects were observed

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

haematology

Dose descriptor:

LOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

haematology

Critical effects observed:

not specified

Table 1. Absolute and relative adrenal weight

 

Dose-level (mg/kg/day)	0		10		100		1000
Sex	M	F	M	F	M	F	M	F
Body weight (g)	519.0	308.5	548.4	278.0**	514.8	293.8	494.3	276.6**
Absolute adrenal weight (g)	0.0623	0.0655	0.0554	0.0620	0.0636	0.0702	0.0487*	0.0526*
Relative adrenal weight (g/g body weightх10000)	1.21	2.13	1.02	2.24	1.22	2.38	0.99	1.90

Conclusions:

Oral administration of Sodium Chlorate for 90 days resulted in no toxicologically significant effects at dose levels of 10 and 100 mg/kg bw/day. The NOAEL was 100 mg/kg bw/day and the LOAEL was 1000 mg/kg bw/day.

Executive summary:

The study was designed to investigate the systemic toxicity of the test material and complies the recommendations of the OECD Guidelines for Testing of Chemicals No. 408.

The test material was administered by gavage to three groups, each consisting of 15 male and 15 female Sprague-Dawley CD strain rats, for ninety consecutive days, at dose levels of 10, 100 and 1000 mg/kg/day. A control group of 15 males and 15 females was dosed with vehicle alone (distilled water). Clinical signs, bodyweight and food consumption were monitored during the study. Haematology and clinical chemistry were evaluated for 10 animals/sex/group at the end of the study. Ophthalmoscopic examination was also performed. All animals were subjected to a gross necropsy examination and a comprehensive histopathological evaluation of tissues from test and control groups was performed on 10 animals/sex/group. In addition, the lungs, liver, kidneys and spleen of 10 animals/sex/group from the low-dose and mid-dose group were examined microscopically.

One mid-dose male died on Day 69 and one high-dose female died on Day 30. These deaths were not considered due to the administration of sodium chlorate. Although mean group body weights for low- and high-dose females were statistically significantly lower than for control animals throughout most of the study, the absence of a similar finding in the mid-dose females and treated males coupled with historical control data which indicated control females gained more weight than normally expected suggests the lower body weights noted were not attributable to test material administration.

Abnormalities in haematology parameters related to administration of sodium chlorate were limited to a decrease in erythrocyte count, hemoglobin concentration, and percent hematocrit for high-dose animals, findings consistent with anemia. Examination of terminal organ and body weights and organ to body weight ratios revealed a number of statistically significant differences between control and treated groups.

However, with the exception of a slight decrease (p 0.05) in adrenal weight for high-dose animals when compared to controls, statistical differences noted were considered a result of differences in mean group body weights for low- and mid-dose females and not related to sodium chlorate administration.

It is noteworthy that in 1000 mg/kg/day males, only 2/15 absolute, 0/15 relative-to-brain and 3/15 relative-to-body weight values were lower than the lowest concurrent control value. In 1000 mg/kg/day females, only 2/14 absolute, 4/14 relative-to-brain, and 3/14 relative-to-body weights were lower than the lowest concurrent control value. No correlating gross observations (e.g. small, reduced in size) were recorded in adrenal glands.

There was no good correlation between the histopathological observation of vacuoles and the decreased adrenal weights observed in this study. Males had slightly greater decreases in adrenal weights than did females, but vacuoles were observed more frequently in females than in males. These histopathological findings were considered by the study pathologist to be not related to the administration of sodium chlorate.

In addition, no indication of decreased adrenal weights was mentioned in the carcinogenicity studies in both rats and mice, and no statistically significant adrenal weight changes were reported between treated groups (up to 500 mg/kg/day) and controls in the two-generation study, in both male and female rats.

Evaluation of physical observations, food consumption, ophthalmology, clinical chemistry values, and gross and microscopic pathology revealed no evidence of an effect of test material administration.

Oral administration of the test material, Sodium Chlorate, to rats for a period of ninety consecutive days at dose levels of up to 1000 mg/kg/day resulted in no toxicologically significant effects at dose levels of 10 and 100 mg/kg/day. The “No Observed Adverse Effect Level" (NOAEL) is considered to be 100 mg/kg/day and the “Lowest Observed Adverse Effect Level” (LOAEL) is considered to be 1000 mg/kg/day.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

100 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Concerns for subchronic and chronic chlorate exposures are related to its competitive inhibition of iodide transport through thyroid follicular cells, required for thyroid hormone synthesis. This results to an initial decrease in the T3 and T4 serum levels followed by a compensatory increase of TSH. This in turn results to an increase in thyroid cell proliferation with subsequent restored thyroid hormone production, and thus maintaining homeostasis. Thyroid effects were already visible after intake from 5 mg/kg/day in animal (rat) studies. These effects indicate a physiological compensatory mechanism to maintain homeostasis upon the presence of chlorate. For further details see Annex I on the MoA of the CSR for a position paper by Ledirac and Pontal 2008.

 

Sub-chronic and chronic studies do not show a high level of toxicity. A 90-day studies in rats resulted in a NOAEL of 100 mg/kg bw/day and a 90-day study in the dog resulted in a NOAEL of 360 mg/kg bw/day, the highest dose tested.

Available studies differ in their reported effects on thyroid. One study did not show any effect after 90-days up to 1000 mg/kg/day, whereas in NTP studies hypertrophy was observed from around 40 mg/kg/day. Another 90-day study in rats indicated possible effects of thyroid colloid depletion, and concluded to a NOAEL in rats of 38 (males) and 55 mg/kg bw/day (females). A two generation reproduction study on rats indicated a parental NOEL of 10 mg/kg bw/day for males and 70 mg/kg bw/day for females, based on slight to moderate follicular hyperplasia and signs of slight to moderate hyperactivity of the thyroid gland. The NOAEL for parental toxicity is 70 mg/kg bw/day for the females, based on signs of hyperactivity of the thyroid glands (grade 4) at the next highest dose level.

Justification for classification or non-classification

Concerns for subchronic and chronic chlorate exposures are related to its competitive inhibition of iodide transport through thyroid follicular cells, required for thyroid hormone synthesis. This results to an initial decrease in the T3 and T4 serum levels followed by a compensatory increase of TSH. This in turn results to an increase in thyroid cell proliferation with subsequent restored thyroid hormone production, and thus maintaining homeostasis. Thyroid effects were already visible after intake from 5 mg/kg/day in animal (rat) studies. These effects indicate a physiological compensatory mechanism to maintain homeostasis upon the presence of chlorate. This is an adaptive reponse to chlorate exposure. Furthermore a response to which rats are more sensitive than humans.

Therefore sodium chlorate is not classified for target organ specific toxicity.