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Description of key information

Toxicity (except dermal toxicity and skin/eye irritation) of SMCA (the sodium salt of MCAA) is identical to that of MCAA. Under physiological conditions both substances are completely ionised and the relevant moiety is the monochloroacetate ion.
Key study: 13-week study in rats according to OECD 408. Outcome LOAEL 15 mg/kg bw (not used in risk assessment or DNEL derivation; NOAEL from 2-year carcinogenicit study is used for risk assessment purposes)

Key value for chemical safety assessment

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:
Not specified; published in 1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Animals were approximately 12 weeks old at start of treatment. No platelet counts and blood clotting potential, sodium, potassium, urea, total protein and albumin, and only two enzymes indicative of hepatocellular effects measured. No results on clinical observations. No functional observation, arena or ophthalmoscopic tests included. No epididymides and uterus weight included. No spinal cord and eyes examined histopathologically.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents)
Deviations:
not applicable
Qualifier:
equivalent or similar to
Guideline:
EU Method B.26 (Sub-Chronic Oral Toxicity Test: Repeated Dose 90-Day Oral Toxicity Study in Rodents)
Deviations:
not applicable
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 870.3100 (90-Day Oral Toxicity in Rodents)
Deviations:
not applicable
Principles of method if other than guideline:
OECD/EC/OPPTS guideline compliant with exception of items specified under Rationale for reliability.
GLP compliance:
not specified
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories (Kingston, USA)
- Age at study initiation: approximately 12 weeks
- Weight at study initiation: males: 471-493 grams (mean), females: 275-288 grams (mean)
- Fasting period before study: no
- Housing: 2 per cage in elevated wire mesh cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: approximately 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-22
- Humidity (%): 40-60
- Air changes (per hr): not specified
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: Not specified
Route of administration:
oral: gavage
Vehicle:
other: distilled water
Details on oral exposure:
PREPARATION OF DOSING SOLUTIONS:
Monochloroacetic acid (MCA) was diluted in distilled water. The dosing solutions of sodium monochloroacetate (SMCA) were prepared weekly from a stock solution with dilution to the appropriate concentration with distilled water. The solutions were adjusted with 1.0 N sodium hydroxide in order to achieve a pH of 7.0-7.5.

Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Stability tests (gas chromatography) determined that the MCA in these preparations was stable at least for 10 days.
No details provided on accuracy and homogeneity of preparations.
Duration of treatment / exposure:
90 days
Frequency of treatment:
daily
Remarks:
Doses / Concentrations:
0-15-30-60-120 mg/kg
Basis:
actual ingested
No. of animals per sex per dose:
10
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: Not specified, but likely based on LD50 values of MCA.
Positive control:
Not applicable.
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS/DETAILED CLINICAL OBSERVATIONS: All rats were observed for physiological and behavioral responses and for mortality
or morbidity.

OPHTHALMOSCOPY: no

BODY WEIGHT: Body weights were recorded at the initiation of dosing, and twice weekly throughout the study. A final body weight, following an 18 h fast, was recorded at necropsy.

FOOD AND WATER CONSUMPTION: Water and food consumption was determined at the beginning, middle and end of each week.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: end of treatment
- Anaesthetic used for blood collection: Yes (identity): pentobarbital (60 mg/kg i.p.)
- Animals fasted: Yes
- How many animals: all surviving animals
- Parameters checked: red blood cell count (RBC), white blood cell count (WBC), hemoglobin, hematocrit, reticulocyte count, and mean corpuscular volume (MCV). A differential leukocyte count was performed for segmented neutrophils, lymphocytes, monocytes and eosinophils.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood:end of treatment
- Animals fasted: Yes
- How many animals: all surviving animals
- Parameters checked : blood urea nitrogen (BUN), blood calcium (BCAL), inorganic phosphorous (PO4), creatinine, total cholesterol, glucose, lactate dehydrogenase (LDH), alanine aminotransferase (AL T), and aspartate aminotransferase (AST).

URINALYSIS: No.

NEUROBEHAVIOURAL EXAMINATION: No
Sacrifice and pathology:
GROSS PATHOLOGY: Yes:
The necropsy included gross examination of the external surfaces, all orifices, external surface of the brain, cervical tissues, all organs,
and the cranial, thoracic, abdominal, and pelvic cavities. Tissues from selected organs, including the brain (with the stem), liver, spleen, lung with the lower half of the trachea, thymus, kidneys, adrenal glands, heart and gonads of each animal were weighed and grossly examined at necropsy.

HISTOPATHOLOGY: Yes:
In addition to tissues grossly examined at necropsy, skin, mandibular and mesenteric lymph nodes, mammary gland, thigh muscle, sciatic nerve, sternebrae, thymus, salivary gland, tongue, esophagus, stomach, duodenum, jejunum, ileum, colon, cecum, rectum, pancreas, urinary bladder, seminal vesicles, prostate, uterus, nasal cavity and turbinates, pituitary, preputial or clitoral gland, Zymbal's gland, aorta, thyroid, parathyroids and any gross lesions.
Other examinations:
None.
Statistics:
The standard statistical procedure was a one-factor analysis of variance (ANOVA) to analyze normally-distributed measures for a dose-related response (or effect). Males and females were considered separately in all statistical analyses and the parameters analyzed were: body weights, organ weights, organ-to-body weight ratios, water and food consumption, hematology, and clinical chemistry measurements. The differences between the control and treatment groups were analyzed pairwise using the Student t-test at an adjusted significance level to control the false positive rate (overall alpha = 0.05). Due to the high variability of some of the clinical chemistry measures, a non parametric analysis of variance, procedure i.e. the Kruskal-Wallis test, was also employed to determine differences among the dose groups and to pairwise compare each dose group to the control group. The incidence of microscopic lesions were tested for a dose related trend using the exact test for trend, which is a generalization of Fisher's Exact Test. Pairwise comparisons of each dose group vs. the control (one-tail test) were made using Fisher's Exact Test. Analysis of gross pathology diagnosis were limited to descriptive statistics.
Clinical signs:
effects observed, treatment-related
Mortality:
mortality observed, treatment-related
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
no effects observed
Ophthalmological findings:
not examined
Haematological findings:
effects observed, treatment-related
Clinical biochemistry findings:
effects observed, treatment-related
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
no effects observed
Details on results:
CLINICAL SIGNS AND MORTALITY
Thirteen (13) rats died during the study; all but two were in the high-dose group. The two deaths in the lower dose groups were both males, one at 15 and another at 60 mglkg per day. None of the control rats died during the experiment. It is apparent that 120 mg/kg per day is acutely toxic as over half of the deaths (7/11; 4 male and 3 female) occurred within the first 3 days of treatment. The other 4 deaths in the 120 mg/kg per day male group occurred between the 14th and 90th days of treatment. This may indicate a form of tolerance to continued treatment.
No details on clinical signs given.

HAEMATOLOGY
Significant increases were observed in WBC at dose levels of 30 mg/kg per day and higher and segmented neutrophils at 60 mg/kg per day and higher in females. Monocyte counts were significantly decreased in females at 15 mg/kg per day and increased in males at 15, 30 and 60 mg/kg per day.

CLINICAL CHEMISTRY
Statistically significant differences (significance not tested for male, 120 mg/kg per day group) were observed in the following clinical chemistry parameters indicating kidney damage: (a) increased BUN levels in females at 120 mg/kg per day and in males at 15 and 30 mg/kg per day; (b) increased creatinine levels in females at 30 and 60 mg/kg per day and in males at all dose-levels; (c) increased PO4 in females at 120 mg/kg per day; and (d) increases in BCAL in males at 15 and 30 mg/kg per day.
Liver damage was also suggested based on significant increases in serum ALT and AST in both females and males. The increases in ALT were observed in females at 120 mg/kg per day and in males at 15 and 30 mg/kg per day. Increases in AST were found in females at 120 mg/kg per day and both ALT and AST levels are substantially higher than controls at the high-dose level for males. The ALT and AST levels at 60 mg/kg per day were only slightly increased.

ORGAN WEIGHTS
A significant increase in liver and kidney weights for the 120 mg/kg per day female group was recorded.
Statistically significant increases were seen in the liver and kidney weight ratios in both females and males at 60 mg/kg per day and in females at 120 mg/kg per day. Statistical analyses were not performed in the high-dose male group because of the poor survival but the liver and kidney weight ratios rats were higher than the average ratios for males at 60 mg/kg per day.

GROSS PATHOLOGY
Reddened lungs (possibly a postmortem effect) in animals that died early (days 1-3) in the study. Pale, yellow-colored livers were seen in male rats at all dose levels and in female rats at the two highest dose levels. This change was particularly evident in the high-dose male group as well as
in two animals that died at 18 and 53 days. In contrast, only 2 out of the 7 surviving females at 120 mg/kg per day showed these liver colorations. The 3 females that died before day 3 were not examined.

HISTOPATHOLOGY: NON-NEOPLASTIC
Increases were observed in the incidences of lesions in the heart, kidneys, liver, and spleen in treated rats compared to controls. The incidences and severity of the microscopic lesions were greater in males than females. Due to low survival rates, the animals in the high dose group (120 mg/kg per day) were excluded from the statistical analyses of the microscopic lesions data. Chronic inflammation of the heart, a commonly seen incidental lesion in rats at this age, was increased in males at all levels of SMCA-treatment and in females given doses greater than 30 mg/kg per day. The incidence of heart inflammation was not significantly increased in either sex although the trend analysis (lesions vs. dose) for the pooled data from both sexes was significant (P = 0.035). The increase in kidney lesions was restricted to male rats. Chronic nephropathy in male rats was increased in a dose-related manner, (trend test, P :5 0.001) reaching statistical significance at 60 mg/kg per day (P = 0.002). Likewise, hepatocytic vacuolated foci (lipidosis) at the base of the liver lobes and in the subcapsular region were observed in several treated male rats. The trend analysis indicated a significant increase in the incidence of hepatocytic vacuolated foci with increasing dose (P = 0.013) in male rats, but no significant increase was found at any individual dose level (P > 0.05). Some other liver lesions (fatty changes and necrosis) were also observed in animals in the high-dose group that died during the experiment. Since the livers of the animals that died early in the study are not routinely examined, the true incidence of liver lesions in the high-dose group cannot be ascertained. Chronic inflammation of lung interstitium and perivascular areas was seen in both
treated and control male and female rats and was considered to be an incidental finding not related to SMCA. However, congestion and hemorrhage was consistently noted in animals that were found dead during the course of the experiment. This is especially true in the two highest dose male and high-dose female groups. While this was not observed in the controls, neither was it observed in the treated animals that survived the 90-day period and were then sacrificed. The incidence of splenic pigments, brown and localized in splenic macrophages, was significantly increased with dose (trend test, P < 0.001) in males. Pairwise comparisons versus the controls indicated that the increase was statistically significant at the 60 mg/kg per day dose (P < 0.001).
Dose descriptor:
LOAEL
Effect level:
15 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: see 'Remark'
Critical effects observed:
not specified

See also attached background material on tables with results.

Conclusions:
Rats were exposed to MCA for 90-days by oral gavage. The observation of one early death, the yellow color observed in SMCA-treated male liver, in addition to the altered serum biochemistry (BUN, ALT, BCAL and creatinine), and significant trends in the incidence of microscopic lesions in the males leads to the author's conclusion that 15 mg/kg per day is the lowest observed adverse effect level for a 90-day oral exposure. Thus, a no effect level was not found in this study.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LOAEL
30 mg/kg bw/day
Study duration:
subchronic
Species:
rat

Additional information

The study provided a LOAEL of 15 mg/kg bw, based on liver abnormalities. However, since a NOAEL of 3.5 mg for systemic effects is availabe from a 2 -year carcinogenicity study with MCAA, the latter value is used for risk assessment , C&L and DNEL derivation


Repeated dose toxicity: via oral route - systemic effects (target organ) other: all gross lesions and masses

Justification for classification or non-classification

the study provoded a LOAEL of 30 mg/kg bw. However, a two-year carcinogenicity stuy provided a NOAEL of 3.5 mg/kg bw, which justifies a Cat 1 for chronic toxicity.