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Repeated dose toxicity: inhalation

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short-term repeated dose toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comprehensive, well documented study comparable to guideline study. Restriction: heating the TS to 180-240°C may cause test substance degradation which was not examined in this study.

Data source

Referenceopen allclose all

Reference Type:
Inhalation toxicity study of formamide in rat.
Warheit DB, Kinney LA, Carakostas MC, and Ross PE
Bibliographic source:
Fund. Appl.Toxicol. 13, 702-713.
Report date:
Reference Type:
other: TSCATS
Report date:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)
GLP compliance:
not specified
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
purity >99 %, obtained from Aldrich Chem.

Test animals

other: Crl:CD BR

Administration / exposure

Route of administration:
Type of inhalation exposure:
nose only
other: air/nitrogen
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
The atmospheric concentration of formamide in each exposure chamber was determined at approximately 45-min intervals during each exposure. Samples of the chamber atmospheres were collected in duplicate from the rats' breathing zones with tandem midget impingers containing methanol as a trapping solvent. Each sample was injected into a Hewlett- Packard 5880 gas chromatograph equipped with a flame ionization detector. Samples were chromatographed isothermally at 70°C on a 30mx 0.53-mm i.d . poly dimethyl siloxane Megabore column. The atmospheric concentration of formamide was determined by comparing peak areas with standard curves calculated daily. Standard samples were prepared at least weekly by diluting a known amount of liquid formamide in a volumetric flask containing methanol.
Duration of treatment / exposure:
2 weeks
Frequency of treatment:
5 days/week; 6 hours/day
Doses / concentrations
Doses / Concentrations:
ca. 0.19, 0.93, 2.8 mg/l (100, 500, 1500 ppm)

No. of animals per sex per dose:
10 males/dose
Control animals:
yes, concurrent no treatment
Details on study design:
Post-exposure period: 2 weeks
Positive control:
not required


Observations and examinations performed and frequency:
- Time schedule: daily

- Time schedule: daily

- Time schedule for examinations: daily

- Time schedule for collection of blood: on day 12 after 10 exposures (5/sex/dose) or at the end of the 14-day recovery period (5 rats/sex/dose)
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: all
- Parameters examined: erythroctye count; kematokrit; hemnoglobin; platelet count; total and diffeerntial leucocyte count.

- Time schedule for collection of blood: on day 12 after 10 exposures (5/sex/dose) or at the end of the 14-day recovery period (5 rats/sex/dose)
- Animals fasted: No data
- How many animals: all
- Parameters examined: Serum samples were analyzed for alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase activity and for concentrations of urea nitrogen, creatinine, total protein, and cholesterol .

- Time schedule for collection of urine: 9th day of exposure, and 13th day of recovery
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters examined: Samples were analyzed for volume, osmolality, and standard biochemical parameters using a commercially available urine dipstick (Multistix, Ames Division, Miles Laboratories, Elkhart, IN) . The sediment from each sample was also examined microscopically .
Sacrifice and pathology:
Mean body weights and body weight gains for test rats were compared to controls during the exposure and recovery periods. Data were statistically analyzed by one-way analysis of variance (ANOVA). Exposure group values were compared to controls by the least significant difference test and Dunnett's test when the ratio of variance (F) indicated a significant among-to-within group variation . Significant differences were declared at the 0 .05 probability level .
For analysis of clinical measurements, ANOVA and Bartlett's test were calculated for each sampling time . When the F-test from ANOVA was significant, Dunnett's test was used to compare means from the control groups and each of the groups exposed to formamide.

Results and discussion

Results of examinations

Clinical signs:
effects observed, treatment-related
mortality observed, treatment-related
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
effects observed, treatment-related
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
effects observed, treatment-related
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
not examined

Effect levels

Dose descriptor:
Effect level:
0.19 other: mg/l
Basis for effect level:
other: hematologic and clinico-chemical parameters measured at 500 and 1500 ppm (in particular thrombocytopenia)

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables


The NOAEC for repeated inhalation of formamide in rats was considered to be 100 ppm, based on the hematologic and clinico-chemical parameters measured at 500 and 1500 ppm (in particular thrombocytopenia) [table 4, p. 707]. The biological relevance of this effect was considered equivocal, because histopathological examination of bone marrow in all groups  failed to demonstrate any alterations in megakaryocytopoiesis which might confirm TS-related, suppressive effects on platelet production.

The NOAEC based on histopathologic changes was 500 ppm.The study clearly showed that 10 repeated exposures to doses higher than 500 ppm produced nephrotoxicity and that the liver apparently was not affected (contrary to dimethyl formamide) [p. 713]. It was evident that the growth rate was normal up to 500 ppm, that, however, the high toxic dose of 1500 ppm markedly depressed body weight, which continuously decreased at about 20 % after 10 exposures and did not catch up until 6 d after termination of treatment, but then at a growth rate similar to that of the other groups [Plot p. 705].  

Mortality: During the study, two of the rats in the highest dose group died (on test days 3 and 9); another rat was sacrificed in extremis on test day 11.
Body weights: The body weights and body weight gains of rats exposed to 1500 ppm were statistically significantly depressed compared to controls. No differences in body weight and body weight gains were observed in the other treated groups.
Clinical signs of toxicity:weakness, hunched postures were observed in the 1500 ppm group only, while low incidences of diarrhea occurred in all groups.
Clinical pathologic examination revealed mild thrombocytopenia in rats exposed to 500 and 1500 ppm after 10 days of exposure and during the recovery period. Additionally, lymphopenia and slight hypocholesterolemia was observed in the high-dose group; lymphopenia was statistic- ally significant and persisted after 14 days of recovery.

Histopathology: In the high-dose rats only, pathological examinations revealed compound-related minimal to severe zonal nephrosis in the inner cortex and outer medulla, characterized by necrosis and regeneration of the renal tubular cells with all tubular segments affected in the deep cortical nephrons. After the 14-days recovery period, the mild renal lesions consisted of regeneration of the tubular epithelium with no necrosis present. Presumably due to the pronounced weight loss, kidney-to-body ratios were significantly elevated in the highest dosed  group. But absolute kidney weights were increased, too, but not statistically significant, at the end of the exposure period. After 14 days of recovery, absolute and relative kidney weights were statistically significantly elevated.

C.   Addendum PATHOLOGY:
Although apparently elevated as compared to the control and low-dose groups, a number of changes diagnosed microscopically in the 1500-ppm group were not considered to
  be compound-related

-  depletion of lymphocytes in spleen, thymus, lymph nodes;  
- gastric erosion;
- degeneration of seminiferous epithelium in the testes;
- atrophy in bone marrow.


3/5 animals of the 1500-ppm group vs. none or 1/5 in other groups exhibited degeneration in the testicular epithelium  [publication, Tab. 3, p. 707].

Applicant's summary and conclusion

Executive summary:

In an inhalation study that was conducted similar to OECD TG 412, three groups of 10 male CrLCD BR rats each were exposed nose-only for 6 hr/day, 5 days/week for 2 weeks to design concentrations of 100, 500, or 1500 ppm of formamide aerosol in air. A control group of 10 male rats was exposed simultaneously to air only. 50% of the animals were sacrificed on study day 12 after 10 exposures, the remaining animals were allowed a 14 day recovery. Statistically significantly reduced body weights, histopathological changes in the kidneys, and reduced platelet counts were seen in rats at 1500 ppm. Rats at 500 ppm showed reduced platelet counts only.


The NOAEC for repeated inhalation of formamide in rats was considered to be 100 ppm or 0.19 mg/kg bw/day, based on the hematologic and clinico-chemical parameters measured at 500 ppm (in particular thrombocytopenia). The biological relevance of this effect was considered equivocal. 100 ppm corresponds to 0.187 mg/L [which is far above the vapour saturation concentration of 0.055 mg/L], or 54 mg/kg bw/d, calculated on the basis of default physiological parameters [R8, page 26: rat body weight: 0.25 kg; rat respiratory volume, 6h: 0.29 m³).


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