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Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
December 1987 - March 1988
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
13-week inhalation toxicity study of formic acid in rats and mice.
Author:
Leach CL, Abdo KM, Chou BJ, Roycroft JH and Mellcik PW
Year:
1989
Bibliographic source:
The Toxicologist, 144. Society of Toxicology, abstract of the 28th meeting, abstract No. 575.
Reference Type:
publication
Title:
Unnamed
Year:
1992

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
Deviations:
no
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
95 % formic acid / 5 % water
- Name of test material (as cited in study report): formic acid
- Physical state: liquid
- Analytical purity: 95%
- Impurities (identity and concentrations): water. Formaldehyde: <0.1%
- Composition of test material, percentage of components: 95% formic acid, 5% water

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Taconic Farms, Inc., Germantown, NY
- Age at study initiation: 6 wks (7 weeks for mice in 13-week studies)
- Housing: individually
- Diet: standard NIH-07 diet ad libitum
- Water: tab water ad libitum
- Acclimation period: 12 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): temperature 75°F
- Humidity (%): rel. humidity 55+/-15%,
- air changes per hour: 15
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation
Type of inhalation exposure:
whole body
Vehicle:
other: air
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: commercial 1.7 m³ inhalation chambers
- Temperature, humidity, pressure in air chamber: temperature 75°F, rel. humidity 55+/-15%
- Vapor generation: liquid formic acid was pumped by a micrometer pump to a  vaporizer heated to 97.5°C. The vapor entered a distribution line  where a  constant 2300 ppm atmosphere was maintained. Dilution air (HEPA filtered,  rel. humidity 50%) carried a metered amount to the  individual exposure  chambers.

TEST ATMOSPHERE
- Brief description of analytical method used:  a Foxboro Mitran 980 infrared spectrometer at 9.050 microns was  used to monitor the exposure chambers, control chamber, exposure room, an  online standard of formic acid vapor, and a pure nitrogen source. All  locations were monitored every 40 min. In addition, formaldehyde  concentrations were monitored in the 8 ppm and 128 ppm exposure chambers,  and in the formic acid distribution line. Corrections were made for absorbance of water and for instrument drift.
The online monitor was calibrated with GC analyses of grab samples taken from the exposure chambers at the time of the readings.

The limit of detection and limit of quantification for the on-line monitor were determined at an average chamber relative humidity of 33-51%.
The practical detection limit was 0.36 ± 0.10 ppm, with a practical quantification limit of 0.68 ± 0.10 ppm.

- Samples taken from breathing zone: yes


Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
A Foxboro Mitran 980 infrared spectrometer at 9.050 microns was  used to monitor the exposure chambers, control chamber, exposure room, an  online standard of formic acid vapor, and a pure nitrogen source. All  locations were monitored every 40 min. In addition, formaldehyde  concentrations were monitored in the 8 ppm and 128 ppm exposure chambers,  and in the formic acid distribution line. Corrections were made for absorbance of water and for instrument drift. The online monitor was calibrated with GC analyses of grab samples taken from the exposure chambers at the time of the readings.
The limit of detection and limit of quantification for the on-line monitor were determined at an average chamber relative humidity of 33-51%. The practical detection limit was 0.36 ± 0.10 ppm, with a practical quantification limit of 0.68 ± 0.10 ppm.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
5 days/week, 6 hours/day
Doses / concentrations
Remarks:
Doses / Concentrations:
0, 0.015; 0.030; 0.061; 0.122; 0.244 mg/l (0, 8, 16, 32, 64, 128 ppm) as vapour
Basis:
analytical conc.
No. of animals per sex per dose:
20
(10 for core study and 10 for clinical pathological studies performed after 3, 23 and 90  days of the study)
Control animals:
yes, concurrent no treatment
Details on study design:
Post-exposure period: none
- Dose selection rationale: based on rangefinding study

Examinations

Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily


BODY WEIGHT: Yes
- Time schedule for examinations:  recorded on a weekly base


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood: additional rats on days 3 and 23, core study animals at termination in week 13
- Anaesthetic used for blood collection: Yes (70% CO2:30% O2)
- Animals fasted: No data
- How many animals: 10/sex/dose
- Parameters checked in table No. B1 (report, Appendix B) were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood:
- Animals fasted: No data
- How many animals: 10/sex/dose
- Parameters checked in table No. B1 (report, Appendix B) were examined.


URINALYSIS: No. Only in rangefinding study


NEUROBEHAVIOURAL EXAMINATION: No


- Gross pathology: YES
- Time schedule: at termination
- How many animals: 10/sex/dose

Histopathology: Yes
- Tssues examined: adrenal glands, brain, bronchial lymph nodes, cecum, colon, duodenum, epididymis/seminal vesicles/ prostate/testes or ovaries/uterus, esophagus, eyes (if grossly abnormal), femur (including marrow), gallbladder (mice), gross lesions and tissue masses with regional lymph nodes, heart, ileum, jejunum, kidneys, larynx, liver, lungs with mainstem bronchi, mammary gland and adjacent skin, mandibular and mesenteric lymph nodes, mediastinal lymph nodes, nasal cavity and turbinates, pancreas, parathyroid glands, pharynx (if grossly abnormal), pituitary gland, preputial /clitoral glands (rats), rectum, salivary glands, spinal cord and sciatic nerve (if neurologic signs present), spleen, stomach (including forestomach and glandular stomach), thigh muscle, thymus, thyroid gland, trachea, and urinary bladder. In addition to all gross lesions, the following tissues were examined in all other dose groups:
rats--nose (three transverse sections), lung, larynx, trachea, bronchial and mediastinal lymph nodes;
mice--nose (three transverse sections).
Organ weights (to the nearest mg) were obtained from all core study animals and include: liver, thymus, right kidney, right testis, heart
and lungs.

Other:
- sperm morphology and vaginal cytology were evaluated in rats and mice exposed to 0, 8, 32, and 128 ppm.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Other examinations:
Compared to OECD 423: additional examinations of effects on respiratory tract and  reproductive organs. Sperm morphology and vaginal cytology were evaluated in rats and mice exposed to 0, 8, 32, and 128 ppm.
Statistics:
Organ and body weight data: procedures by Williams (1971, 1972) and  Dunnett (1955).
Clinical chemistry and hematology data: nonparametric multiple  comparisons methods of Shirley (1977) and Dunn (1964).

Results and discussion

Results of examinations

Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
not specified
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
not examined
Details on results:
CLINICAL SIGNS AND MORTALITY
Mortality: none
Clinical signs of toxicity: no clinical signs that were clearly  treatment-related were noted. 

BODY WEIGHT AND WEIGHT GAIN
Body weights were not affected, terminal  body weights were all within +/- 5% compared to controls. 

Systemic toxicity: no systemic toxic effect occurred at any dose level.  Few changes compared to controls were noted (increase in body weight at  the low doses, isolated minor to mild changes in hematology and clinical  chemistry,) but were few and  generally minimal to mild in magnitude, and showed no dose-related  pattern.  


HAEMATOLOGY
Isolated minor to mild changes; few and  generally minimal to mild in magnitude, and showed no dose-related  pattern.

CLINICAL CHEMISTRY
Isolated minor to mild changes; few and  generally minimal to mild in magnitude, and showed no dose-related  pattern.


ORGAN WEIGHTS
No treatment-related effect  effects on absolute/relative organ weights.

GROSS PATHOLOGY
There were no unusual gross lesions. The occurrence of  variations in absolute or relative organs weights (liver: increased in  all treated male groups (p<0.05 at 8 and 16 ppm; p<0.01 at 32, 64, and  128 ppm); lung: decreased in all treated male and female groups, p as  much as p<0.01) was not dose-related, and there was no histopathological  correlate.

HISTOPATHOLOGY: NON-NEOPLASTIC
Increased incidences of histopathological changes were noted in the nose of animals at 128 ppm, substantiated by squamous metaplasia of the 
respirators epithelium and degeneration of the olfactory epithelium in most animals. The incidence was higher in males compared to females. The 
severity was generally minimal to mild. Lesions observed at 62.5 ppm in the preliminary 14-day exposure study in  this species/laboratory could not be reproduced in this more robust study  with longer exposure. For details see "Remarks on results" and "Overall Remarks"

OTHER FINDINGS
 Male and female reproductive organs:  Regarding the male and female reproductive organs, there were no effects  on sperm motility, density or testicular or epididymal weights, and no  changes were seen in the length of the estrous cycle.

Effect levels

open allclose all
Dose descriptor:
NOAEC
Remarks:
local
Effect level:
0.122 other: mg/l
Sex:
male/female
Basis for effect level:
other: microscopic examination of upper respiratory tract including olfactory epithelium: absence of / or minimal effects
Dose descriptor:
LOAEC
Remarks:
local
Effect level:
0.244 other: mg/l
Sex:
male/female
Basis for effect level:
other: increased incidences of squamous metaplasia of the respiratory epithelium and degeneration of the olfactory epithelium
Dose descriptor:
NOAEC
Remarks:
systemic
Effect level:
0.244 mg/L air
Sex:
male/female
Basis for effect level:
other: Absence of systemic effects. Histopathology: no effects except from nasal effects. Testicular and epididymal weight, sperm motility and sperm density: not affected. Female estrous cycle: not affected.

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

Exposure concentration: during the 2-week and the 13-week studies, at least 96% and 91%, respectively, of the measured concentrations for each chamber were within ± 10% of the target concentration.

Effects summary:

Species, strain, number, sex/group

Test substance

 

Duration, concentration

NOAEC/LOAEC, findings, remarks

Reliability

Reference

Inhalation

Rat

Fischer F344

10 m

10 f

Formic acid

 

13 weeks

 

0; 0.015; 0.030; 0.061; 0.122; 0.244 mg/L; (0, 8; 16; 32; 64; and 128 ppm) for 6 h/day, 5x/ week

 

(65 exposures). (whole body exposure)

NOAEC for local toxicity: 0.122 mg/(L*d) (64 ppm); based on upper respiratory tract irritation.

 

64 ppm: Nose; 1/20 mild degeneration olfactory epithelium.

 

LOAEC for local toxicity: 128 ppm: Nose; respiratory epithelium; squamousmetaplasiain 15/20 animals.Olfactoryepithelium degeneration in 14/20 animals.

NOAEC for systemic toxicity:128 ppm (0.244 mg/(L*d)

Systemic effects: 0/20; LOAEC not achieved at highest tested concentration (128 ppm)

Histopathology: no effects except from nasal effects.

Testicular andepididymalweight, sperm motility and sperm density: not affected.

Female estrous cycle: not affected.

1

NTP (1992)

 

Applicant's summary and conclusion

Executive summary:

In an OECD guideline No. 413 test conducted under GLP conditions, 10 rats per sex and dose were exposed to formic acid vapor at 0, 0.015, 0.030, 0.062, 0.122, or 0.244 mg/L (0, 8, 16, 32, 64, or 128 ppm; dose selection based on results of a range finding study) via whole-body inhalation 6 hours/day, 5 days/week for 13 weeks.

There were no mortalities nor clinical signs or systemic toxicity in male and female rats exposed to 8, 16, 32, 64, or 128 ppm for 13 weeks (5 days/week, 6 h/day). There were no unusual gross lesions noted during necropsy, organ weights were not affected by treatment. Male and female reproductive parameters (sperm motility, density, and testicular or epididymal weight; length of the estrous cycle) were not affected. Histopathology revealed increased incidences of squamous metaplasia of the respiratory epithelium and degeneration of the olfactory epithelium in the high-dose male and female rat groups where most of the animals were affected. However, the severity was generally minimal to mild.

A systemic LOAEC was not achieved. The authors suggested that the lack of systemic effects in both 2-week and 13-week NTP inhalation studies is possibly related to the rapid metabolizing capacity of formate to CO2, due to high tetrahydrofolate and 10-formyl tetrahydrofolate dehydrogenase levels in rodents. These levels are much lower in humans who are significantly more sensitive to the formate toxicity. Therefore, caution should be used in considering the results obtained with rodents in determining potential human risks associated with systemic exposure to formic acid. Nevertheless human experience does not indicate that formic acid represents a significant systemic thread to humans unless at high concentrations following intended or incidental ingestion or large scale skin contact, where the caustic effect also governs the toxic mode of action.

Based on the local histopathological changes in the respiratory tract the NOAEC in this study was determined to be 64 ppm (0.122 mg/l), and the LOAEC was 128 ppm (0.244 mg/l). The systemic NOAEC was 128 ppm (0.244 mg/l), the highest concentration tested.

Conclusion:

Increased absolute or relative liver weights and decreased lung weights were seen without histopathological correlation. Irritation of the upper respiratory tract was seen at 128 ppm (0.244 mg/L) along with degeneration of the olfactory epithelium and squamous metaplasia of the respiratory epithelium. The NOAEC and LOAEC were 0.122mg/L (i.e. 64 ppm) and 0.244mg/L (i.e. 128 ppm) based on respiratory effects.