Methanesulphonic acid

Endpoint summary

Description of key information

Methane sulfonic acid (MSA) showed irritating effects on the respiratory system in the 28-days inhalation study. However, these effects were attributed to the corrosive nature of MSA. No adverse systemic toxicity effects were observed up to the highest dose tested (NOAEC for systemic effects >= 0.242 mg/l) .

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Qualifier:

according to guideline

Guideline:

EU Method B.8 (Subacute Inhalation Toxicity: 28-Day Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

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 (Portage, Michigan)
- Age at study initiation: 43 to 50 days
- Weight at study initiation: 235 ± 29.4 g (range 175 - 295 g) for males, 188 ± 16.9 g (range 155 - 235 g) for females
- Fasting period before study: no
- Housing: individually
- Diet: ad libitum, except during exposure period and period of fasting prior to blood collection (food withheld)
- Water: ad libitum, except during exposure period (water withheld)
- Acclimation period: 7 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.8 - 22.8°C
- Humidity (%): 28.8 - 66 %
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

other: unchanged (no vehicle); filtered air

Remarks on MMAD:

MMAD / GSD: 0.9 ± 1.7, 1.2 ± 1.9 and 1.2 ± 1.9 in the 0.026, 0.073 and 0.242 mg/L groups, respectively

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: In-Tox Products nose-only exposure units
- Method of holding animals in test chamber: exposure restraint tube
- Method of conditioning air: filtering
- System of generating particulates/aerosols: Inspiron Model 02305-A nebulizer (Intertech Resources, Inc.)
- Temperature, humidity, pressure in air chamber: 23 - 25°C, 27 - 49 %, pressure not reported
- Method of particle size determination: In-Tox Products particle size analyzer model 02-140/JB, Teflon 25 mm filter and Mettler AE240 electronic balance (for gravimetric determination)


TEST ATMOSPHERE
- Brief description of analytical method used: ion chromatographic analysis
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
0.026, 0.073 and 0.242 mg/L
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
0.025, 0.075 and 0.25 mg/L
Basis:
nominal conc.

No. of animals per sex per dose:

15

Control animals:

yes, sham-exposed

Details on study design:

- Post-exposure recovery period in satellite groups: 2 weeks (5 animals/sex/group)

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS/MORTALITY: Yes
- Time schedule: Twice daily on exposure days, once on non-exposure days incl. recovery period

BODY WEIGHT: Yes
- Time schedule for examinations: weekly, starting 1 wk prior to exposure until necropsy; exception: final week of recovery period (wk 6); final weight on day of necropsy

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/animal/day: Yes
- Time schedule for examinations: weekly, starting 1 wk prior to exposure; exception: final week of recovery period (wk 6)


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: at time of spontaneous death or at wk 4 and wk 6 necropsies
- Dose groups that were examined: all groups

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at wk 4 necropsies
- Anaesthetic used for blood collection: No
- Animals fasted: Yes, overnight
- How many animals: all surviving animals
- Parameters examined: total leukocyte count (white cell), erythrocyte count (red cells), hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC, also females at wk 6), platelet count, differential leukocyte count (neutrophil, lymphocyte, monocyte, eosinophil, basophil)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at wk 4 necropsies
- Animals fasted: Yes, overnight
- How many animals: all surviving animals
- Parameters examined: albumin, total protein, globulin, albumin/globulin ratio (A/G ratio), total bilirubin, urea nitrogen (also males at wk 6), creatinine, serum alkaline phosphatase, serum alanine aminotransferase, serum aspartate aminotransferase (also females at wk 6), gamma glutamyltransferase, glucose, total cholesterol, calcium, chloride, phosphorus, potassium, sodium, bile acids

URINALYSIS: Yes
- Time schedule for collection of urine: prior to wk 4 necropsy
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes, approximately 16 h
- Parameters examined: volume, urobilinogen, color, appearance, specific gravity, pH, protein, glucose, ketones, bilirubin, occult blood, nitrites, leukocytes, microscopy of sediment

OTHER:
FUNCTIONAL OBSERVATIONAL BATTERY (FOB):
- Time schedule: weekly (starting 1 wk prior to exposure, until necropsy; exception: recovery period)
- Dose groups examined: all
- Battery of functions tested:
Handling observations (ease of removal from cage, lachrimation/chromodacryorrhea, piloerection, palpebral closure, red/crusty deposits, eye prominence, ease of handling, salivation, fur appearance, respiratory rate/character, mucous membranes/eye/skin colour, muscle tone)
Open field observations (over 2 min period):
Time to first step (sec), rearing, mobility, backing, grooming, gait, convulsions, tremors, gait score, arousal, bizarre/stereotypic behaviour, urination, defecation

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

Other examinations:

Gross Pathology (macroscopic): All animals dying spontaneously or at scheduled euthanization. After inspection of external surfaces, all orifices, cranial, thoracic, abdominal and pelvic cavities including viscera, the following tissues were collected and preserved in 10 % neutral buffered formalin: adrenals (2), aorta, bone with marrow (sternebrae), brain (forebrain, midbrain, hindbrain), eyes with optic nerve (2), gastrointestinal tract (esophagus, stomach, duodenum, jejunum, ileum, cecum, colon, rectum), heart, kidneys (2), liver (sections of two lobes), lungs (2, including bronchi fixed by inflation with fixative), lymph node (bronchial, mesenteric, suprapharyngeal), mammary gland (females only and males in control and high-exposure group at wk 4 and 6 necropsies), nasal turbinates, ovaries with oviducts (2), pancreas, parathyroids (if present), peripheral nerve (sciatic), pituitary, prostate, salivary glands (submaxillary, 2), seminal vesicles (2), skeletal muscle (vastus medialis), skin, spinal cord (cervical, midthoracic, lumbar), spleen, testes with epididymides (2), thymus, thyroids, trachea, urinary bladder, uterus with vagina, all gross lesions. Organ weights, obtained from all animals euthanized at wk 4 and wk 6 necropsies: Adrenals, brain, heart, kidneys, liver, lungs, ovaries, spleen, testes with epididymides, thymus. Paired organs were weighed together. Organ to final body weight ratios were calculated. Histopathology: Examination of 6 cross sections of nasal cavities of all animals; sections (5-8 microns) of all other tissues examined macroscopically were HE-stained, and those of the control and high-exposure groups at scheduled necropsies and those of all animals found dead were examined microscopically, as well. The nasal turbinates, lungs, trachea, kidneys, liver and gross lesions were examined from all animals in the low- and mid-exposure groups at the scheduled necropsies.

Statistics:

All analyses were conducted using two-tailed tests for minimum significance levels of 1 % and 5 % comparing the treatment groups to the control group by sex. All statistical tests were performed by a Digital MicroVAX3400 computer with appropriate programming. Body weight, body weight change, food consumption, clinical laboratory, continuous FOB and absolute and relative organ weight data were analyzed by one-way analysis of variance (ANOVA) followed by Dunnett's test to compare the control and treated groups. Discontinuous (ordinal or descriptive) functional observation battery data were analyzed using Fisher's Exact test. Clinical laboratory values for leukocytes that occur at a low incidence (monocytes, eosinophils, basophils, unsegmented neutrophils) were not subjected to statistical analysis.

Details on results:

CLINICAL SIGNS AND MORTALITY
0 mg/l: 2/15 males; 2/15 females
0.025 mg/l: 0/15 males; 1/15 females
0.075 mg/l: 0/15 males; 1/15 females
0.25 mg/l: 1/15 males; 4/14 females
The cause of death for 6 of these animals (4 controls, 1 low-dose female, 1 high-dose female) was attributed to mechanical trauma related to confinement in the nose-only restraint tubes. A cause of death for the remaining animals found dead could not be determined, however, a relationship to test substance exposure was not apparent. All other animals survived till the scheduled necropsies.
Clinical signs 1 hr following exposure: rales in high-dose animals, increased incidence of wet and dried yellow matting on various body surfaces in mid-dose males and high-dose animals. In general, males tended to be more affected than females. Low incidences of rales were observed in high-dose animals before daily exposure and on non-dosing days. No other test substance-related clinical findings were observed throughout the exposure phase of the study. Rales were observed sporadically in the low- and mid-dose males and/or females 1 hr following exposure and before daily exposure; however, due to a very low incidence and lack of dose-related response, this finding was not considered to be toxicologically significant in the low- and mid-dose groups. No clinical signs were noted in animals at any exposure level during the recovery period.


BODY WEIGHT AND WEIGHT GAIN
Significantly reduced mean body weight (p<0.01) of high-dose males during wk 0-1. During the rest of the exposure period, mean body weight gains of the high-dose males was comparable or slightly lower than control group values, but differences were not significant. By the end of the exposure period (wk 4), the mean body weight in the high dose males was 12 % lower than the control group value (p<0.01). During the first week of the recovery period mean body weight gain of high-dose males was comparable to that in the control group, and mean body weight was within 8 % of the control group value. Mean body weights and body weight gains in the low- and mid-dose males and females and high-dose females were not affected by exposure to the test substance


FOOD CONSUMPTION
Slightly decreased in the high-dose males throughout the exposure phase, differences were statistically significant during wks 0-1 and 3-4 (p<0.01 and p<0.05, respectively). During the recovery period, food consumption of high dose males was similar to the control group. Low- and mid-dose males and females and high-dose females were comparable to the control group throughout the study.


HAEMATOLOGY
No test article-related effects were observed at any exposure level. The only statistically significant (p<0.05) difference was a decreased MCHC value in mid-dose females at wk 4. However, the difference was slight and not dose-dependent, therefore it was not considered to be test substance-related.


CLINICAL CHEMISTRY
Blood urea nitrogen (BUN) mean was increased (20 vs. 16.2 mg/dl, p<0.05) in high-dose males, and aspartate aminotransferase mean was increased in high-dose females (148 vs. 116 U/l, p<0.05) at wk 4. No other differences in blood chemistry parameters were observed at any exposure level at wk 4. Both values had returned to levels similar to control groups at wk 6 recovery evaluation.


URINALYSIS
No test substance-related changes in urinalysis parameters were noted at any exposure level.


NEUROBEHAVIOUR (FUNCTIONAL OBSERVATIONAL BATTERY)
HANDLING OBSERVATIONS: no test substance-related findings during wks 0-3. Observations in treated groups were similar to those in the control group or occured infrequently, generally in single animals.
OPEN FIELD OBSERVATIONS: no test substance-related findings during wks 0-3. Observations in treated groups were similar to those in the control group or occured infrequently, generally in single animals.
The only statistically significant (p<0.05) differences from the control group were an increase in the time to first step in the mid-dose females in wk 2 and an increase in urination in the low-dose females in wk 3. These differences were considered to be due to biological variation, not the test substance, as similar differences were not observed in males, a dose-related response was not apparent, and the differences were not large.


ORGAN WEIGHTS
No test substance-related changes were noted in organ weight data at either necropsy. However, some statistically significant (p<0.05 or p<0.01) differences were observed between the control and the high-dose group. At wk 4 the high-dose males had decreased mean absolute liver, kidney and testicular/epididymal weights and an increased heart weight relative to final body weight. However, the respective mean absolute (for heart) and relative to final body weight( for liver, kidney and testes/epididymides) organ weights were comparable to control group values. Therefore, these differences were considered by the authors to be functions of the decreased final body weight in this group and not-related to the test substance. No exposure-related changes in organ weight data were observed at wk 6 recovery necropsy.


GROSS PATHOLOGY
No test substance-related findings were noted in animals found dead during the study (dark red contents of the ileum, dark red lungs, reddened and/or enlarged lymph nodes, etc. were also found at a similar incidence in the control group).
At wk 4 primary necropsy, no exposure-related internal findings were observed. Dark red and/or mottled lungs were observed in various animals at all exposure levels; however, these findings were not dose-related and observed at a comparable incidence in the control group, as well. Other changes observed in the treated groups (red fluid contents in the trachea, clear fluid contents in the uterus, reddened and/or enlarged lymph nodes, etc.) were commonly seen in laboratory rats and/or occured infrequently. No test substance-related findings were observed at wk 6 (reddened and/or enlarged lymph nodes, epididymal abscess, dark red lungs, etc.) were not noted in an an exposure-related manner and/or were observed similarly in the control group.


HISTOPATHOLOGY: NON-NEOPLASTIC
In animals found dead test substance-related lesions were observed in nasal turbinates of the high-dose animals. Degeneration of the olfactory epithelium was observed in a single female. Three females had goblet cell hyperplasia, and a single male had goblet cell hyperplasia and squamous metaplasia. Neutrophilic inflammation was noted in two females. Other micrsocopic findings in animals found dead (cytoplasmic vacuolation of the liver, histiocytosis and/or plasmacytosis of various lymph nodes, renal tubular degeneration, etc.) were observed at a similar incidence in the control group, as well, and are not uncommon findings in laboratory rats, according to the authors, and/or were typically seen in single animals.
Microscopic evaluation at wk 4 primary necropsy revealed exposure-related findings in the nasal turbinates of all treated groups. Degeneration of the olfactory epithelium was observed in 2/10, 4/10 and 2/9 males and 1/9, 2/9 and 3/6 females in the low-, mid- and high-dose groups, respectively. Goblet cell hyperplasia was noted in 5/10, 5/10 and 7/9 males and 5/9, 4/9 and 6/6 females in the same groups, respectively. Squamous metaplasia occured in 5/9 males and 1/6 females in the high-dose group, and respiratory metaplasia was seen in one female in each of the low-, mid- and high-dose groups. Dysplasia was observed in 1/10 and 3/9 males in the mid- and high-dose groups, respectively. Various forms of inflammation (neutrophilic, nonsuppurative, etc.) were noted in the nasal cavities of many treated animals and suggested a response to the mucosal irritation/degeneration caused by the test-substance. No similar findings were observed in the control group. No other test substance-related findings were observed at the wk 4 evaluation.
Glandular hyperplasia of the mammary gland was observed in 5/9 males and 1/6 females in the high-dose group; however, as this finding was also observed in the control group males at the wk 6 recovery evaluation, this finding was not considered to be test substance-related. Other effects in the treated animals (non-suppurative inflammation of various organs, centrolobular hepatic necrosis, renal tubular mineralization, histiocytosis and/or plasmacytosis of various lymph nodes, etc.) were observed at a similar incidence in the control group, as well. They were considered to be probably related to abdominal compression during the confinement in the nose-only tubes and were not dose-dependent.
Microscopic findings at wk 6 recovery evaluation were similar to those observed at wk 4. Degeneration of the olfactory epithelium was only observed in 2/5 low-dose males and 1/5 mid-dose females, indicating at least partial recovery from the effects of the test substance. Goblet cell hyperplasia was noted in 3/5, 3/5 and 4/5 males and 1/5, 4/5 and 2/5 females in the low-, mid- and high-dose groups, respectively. Squamous metaplasia was seen in 1/5 low-dose females, 2/5 males and 1/5 females in the mid-dose group, and 4/5 males and females each in the high-dose group. Respiratory epithelial metaplasia was observed in a single high-dose male. Various forms of inflammation were noted in the nasal cavities of many of the treated animals, indicating continued response to the mucosal irritation/degeneration caused by the test substance. No other test substance-related findings were observed at wk 6 recovery evaluation. The only other histopathological finding, glandular hyperplasia of the mammary glands in high-dose males, was observed at a similar incidence in the control group, as well.

Dose descriptor:

NOAEC

Remarks:

local effects

Effect level:

< 0.026 mg/L air (analytical)

Sex:

male/female

Basis for effect level:

other: Local irritation in the nasal turbinates

Dose descriptor:

LOAEC

Remarks:

local effects

Effect level:

0.026 mg/L air (analytical)

Sex:

male/female

Dose descriptor:

NOAEC

Remarks:

Systemic effects

Effect level:

0.242 mg/L air (analytical)

Sex:

male/female

Basis for effect level:

other: no adverse effects up to the highest dose level

Dose descriptor:

NOEC

Effect level:

0.026 mg/L air (analytical)

Sex:

male/female

Basis for effect level:

other: Histopathological lesions in the nasal turbinates, e.g. degeneration of the olfactory epithelium, goblet cell hyperplasia.

Critical effects observed:

not specified

Exposure of rats to an aerosol of MSA resulted in changes in the clinical conditions and body weight changes of the animals at exposure levels of 0.073 and 0.242 mg/L, and histopathologic lesions in the nasal turbinates of of all exposed groups. During the 2 -weeks recovery period, the effects on the clinical conditions and body weight gains were completely reversible. Histopathological changes in the nasal turbinates were observed in all groups at the end of the observation period. Based on the lesions in the nasal turbinates, the NOAEC/NOEC for local irritation was considered to be less than 0.026 mg/L. The NOEC (no observed effects level) was considered to be 0.026 mg/L. No adverse systemic toxicity effects were observed up to the highest dose tested (NOAEC for systemic effects >= 0.242 mg/l).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

26 mg/m³

Study duration:

subacute

Species:

rat

Additional information

Inhalation route:

In the key study (ElfAtochem 1996) performed according to OECD Guideline 412 (Repeated Dose Inhalation Toxicity: 28/14-Day), male and female rats were exposed to methane sulfonic acid aerosol at concentrations of 0.026, 0.073 or 0.242 mg/l for 6 hours/day, 5 days/week for 4 weeks. A 2-week recovery period followed exposure. A transient reduced body weight gain and slightly reduced food consumption were observed in 0.242 mg/l exposure level males. Exposure-related clinical signs included rales at 0.242 mg/l in both sexes and increased incidence of yellow matting on body surfaces at 0.242 mg/l in both sexes and at 0.073 mg/l in males. 11 animals were found dead during the exposure; the cause of death for 6 of these animals (2 control-males and females each, 1 low-dose female, 1 high-dose female) was attributed to mechanical trauma related to confinement in the nose-only restraint tubes. However, the cause of death for the remaining animals found dead could not be related to test substance exposure. All other animals survived till the scheduled necropsies. Histopathology revealed lesions in the nasal turbinates of variable strength and manifestation in all exposure groups; these included degeneration of the olfactory epithelium, goblet cell hyperplasia, squamous metaplasia, dysplasia and various forms of inflammation. During the two-week recovery (non-exposure) period the clinical signs and body weight gains were completely reversed; a variety of histopathological lesions in the nasal turbinates was observed in all groups at the end of the recovery period. Based on the lesions in the nasal turbinates, the NOAEC/NOEC for local irritation was considered to be less than 0.026 mg/L (LOAEC = 0.026 mg/L). No signs of adverse systemic toxicity were observed. The NOEC (no observed effects level) for systemic toxicity was considered to be 0.026 mg/L. No adverse systemic toxicity effects were observed up to the highest dose tested (NOAEC for systemic effects >= 0.242 mg/l). The result indicates irritating potential to respiratory system, however the test substance is corrosive, thus does not require further classification as irritant.

Oral route:

There is only one 7-days repeated dose study available (US EPA, HPV Data set, 2006). Four groups of 3-5 rats were fed diet containing Methanesulphonic acid (MSA) for 7 days at target dose levels of 50, 200, 500 and 2000 mg/kg bw. Control animals received normal diet. Clinical signs, body weight and food consumption was determined. The compound intakes for males were 51, 185, 420, 1805 mg/kg bw/d, respectively, and for females were 55, 201, 551, 2122 mg/kg bw/d, respectively. None of the rats orally exposed to MSA (up to 2122 mg/kg bw/day) died during this 7-day study. Furthermore, none of the measured parameters was affected by the exposure. Absence of mortalities or or othe effects might be due to mixing of MSA in diet that leads to formation of potassium salts of MSA, which are not toxic.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Methane sulfonic acid (MSA) showed irritating effects on the respiratory system in the 28-days inhalation study. However, these effects were attributed to the corrosive nature of MSA. No adverse systemic toxicity effects were observed up to the highest dose tested. NOAEC for systemic effects >= 0.242 mg/l

Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: nose

Justification for classification or non-classification

The sub-chronic study need not to be conducted as no systemic effects are foreseen because the available information from the 28-days study indicates no evidence of absorption or systemic toxicity.

EU classification according to Annex I of Directive 67/548/EEC: no classification required

GHS classification (GHS UN rev.3, 2009): no classification required

MSA is already classified as "Corrosive", nevertheless due to irritative effects observed in the inhalation study MSA is further classified as STOT SE 3, H335: May cause respiratory irritation.