Isocyanic acid, polymethylenepolyphenylene ester, 2-ethyl-1-hexanol-blocked

Endpoint summary

Description of key information

There are no sub-acute repeated dose toxicity studies available for MDI MT. A read across with data from the source substances 4,4’-MDI and pMDI is performed.  Inhalation is the most appropriate route of exposure for assessing occupational risk of substances of the MDI substances in humans. Reliable repeated dose inhalation toxicity studies are available for the two source substances 4,4’-MDI and pMDI.

Heinrich  et al. ( 1991)  evaluated the inhalation toxicity of 4,4’-MDI in a subchronic inhalation toxicity study. Wistar rats were exposed to concentrations of 0, 0.3, 1 or 3 mg 4,4’-MDI/m³ for 18 hours a day on 5 days a week for 13-weeks. Reduced body weight gains and an increase in relative lung weights were found at 1 mg/m³ and above. At and above this concentration infiltration of mononuclear cells, goblet cell hyperplasia, erosion of the respiratory epithelium in the upper respiratory tract, hyperplasia of the bronchus-associated lymphatic tissue and inflammatory changes of the lung were additionally observed. At 3 mg/m³ there was an increase in the total cell count and proportion of granulocytes and lymphocytes, a decrease in the proportion of macrophages in the bronchoalveolar lavage fluid, an increase in protein, β-glucuronides and lactate dehydrogenase, and changes in lung function. No effects were observed at 0.3 mg/m³ (Heinrich et al., 1991). Hoymann  (1995)  conducted a subsequent chronic inhalation study with 4,4’-MDI. Female Wistar rats were exposed to 0.23, 0.70 or 2.05 mg 4,4’-MDI/m³ aerosols for 17  hours/day, 5 days /week for up to 24 months. Essentially, a dose-dependent impairment of the lung function in terms of an obstructive-restrictive malfunction with diffusion disorder, increased lung weights, an inflammatory reaction with increased appearance of lymphocytes in the lung in the high dose group as a sign of specific stimulation of the immune system by MDI, an intermediately retarded lung clearance in the high dose group as well as dose-dependent interstitial and peribronchiolar fibrosis, alveolar bronchiolisation and a proliferation of the alveolar epithelium, which was classified as preneoplastic, as well as a bronchiolo-alveolar adenoma were identified. The LOAEC for the female rat was identified as 0.23 mg/m³ after long-term inhalation of 4,4'-MDI aerosols.

In a subchronic inhalation study by Reuzel et al. (1994b) Wistar rats were exposed to pMDI aerosol at concentrations of 0, 0.35, 1.4 and 7.2 mg pMDI/m³(analytical concentration), for 6 hours/day, 5 days/week over a period of 13 weeks. Transient slight growth retardation was observed in male rats exposed to 7.2 mg/m³ air. Haematology, blood chemistry and urinalysis did not show treatment-related effects. There were no significant differences in organ weights between the test and control groups. Gross examination at autopsy did not reveal changes which could be ascribed to the test substance. Histopathological examination revealed yellow material (possibly polyurea originated from test material) in the respiratory tract of rats exposed to 7.2 mg/m³. Under the conditions of this test a NOAEC of 1.4 mg/m³ was defined.

In an associated second subchronic study by Reuzel et al. (1994b) Wistar rats were exposed to higher aerosol concentrations of 4.07, 8.43 and 12.25 mg pMDI /m³ air (analytical concentration) for 3-months. Severe respiratory distress was observed in rats exposed to 12.25 mg/m³ with 11 males and 4 females dying during the exposure period. Significantly less severe signs were seen in rats exposed to 8.43 mg/m³. This study demonstrated adverse effects in the lungs and nasal cavity at levels of 4.07 mg/m³ and above and included histological effects in the lungs (increase in alveolar macrophages and interstitial macrophage infiltration) and in the mediastinal lymph nodes (macrophages with yellowish inclusions). At 8.43 mg/m³ and above increased relative lung weights, partially reversible damage to the olfactory epithelium and basal cell hyperplasia were observed.

In a combined chronic toxicity and carcinogenicity key study (Reuzel et al., 1990; Reuzel et al., 1994a) conducted according to OECD Guideline 453 rats were exposed for 6 hours/day, 5 days/week for one year (satellite groups) or two years (main groups) to aerosol concentrations of 0, 0.2, 1.0 or 6.0 mg pMDI /m³ (analytical concentrations: 0, 0.19, 0.98, 6.03 mg/m³). The effect of chronic exposure of rats to respirable pMDI aerosol was confined to the respiratory tract. The compound-related changes were found in the nasal cavity, the lungs and the mediastinal lymph nodes, and to some degree they were already present after one year of exposure. Histopathology of the organs/tissues investigated showed that exposure to 6.0 mg/m3 over two years was related to the occurrence of pulmonary tumours in males (6 adenomas and 1 adenocarcinoma) and females (2 adenomas). In this two-year rat study, the NOAEC was 0.2 mg/m3 for the repeated dose toxicity of pMDI. The LOAEC was set at 1.0 mg/m³.

In a subacute inhalation study by Kilgour et al. (2002), female Alpk:APfSD rats were exposed to pMDI aerosol at  concentrations of 0, 1.0, 4.0 and 10 mg pMDI/m³, for 6 hours/day, 5 days/week, for  28 days, a 30-day recovery group was included. No clinical signs were noted during exposure and recovery phase. An increase of  lung weights were seen in animals of the highest exposure group at the end of exposure  time, although that had returned to  control values at the end of the recovery period. Lung lavage parameter indicated an dose dependent inflammatory reaction of animals of the mid and high dose group at the end of the exposure period. Histopathology of the lung showed in animals exposed to 10 mg/m3 pMDI an increase in bronchiolitis and thickening of the centro-acinar region, interstitial thickening at the acinar junctions, and accumulations of alveolar macrophages containing yellow pigment in the cytoplasm. In animals exposed to 4 mg/m³ pMDI 1/5 animals showed thickening of the centro-acinar region and bronchiolitis and 1/5 animals exposed to 1 mg/m³ pMDI showed bronchiolitis. After the recovery phase, alveolar macrophages containing a yellow pigment were present in the interstitium in all animals that had been exposed to 10 mg//m³ pMDI but were absent in animals exposed to 1 or 4 mg/m³ pMDI. In addition, 1/5 animals exposed to 10 mg/m³ pMDI still had bronchiolitis and centro-acinar thickening, but at a reduced severity and distribution to that seen in the main study. Ultrastructural findings suggest a perturbation of surfactant homeostasis by exposure to pMDI. Based on findings of histopathology, bronchiolitis noted at 1 mg/m3 and evidence of effect on surfactant homeostasis at 1 mg/m³, NOAEC could not be defined and the LOAEC was set at 1 mg/m³ pMDI. In another subacute inhalation study Pauluhn et al. (1990) exposed Wistar rats to pMDI. Rats were exposed to to pMDI aerosol at  concentrations of 0, 1, 3 and 10 mg/m³ 6 hours/day, 5 or 7 days/week over a period of 2 weeks. The study results indicated that pMDI directly interacts with the pulmonary surfactant lining fluids. This assumption was corroborated further by increased levels of intracellular phospholipids - evidenced by three independent methods, i.e., visualization of phospholipids by polychrome stain, biochemical determination of phosphatidylcholine and electron microscopy - and increased activity of the lysosomal enzyme acid phosphatase. The findings obtained suggest that pMDI interacts with surfactant or surfactant constituents which eventually results to precipitation of surfactant which acts as chemotactic stimuli to alveolar macrophages. The lack of recycled phospholipids and alterations in surfactant activity might act as stimuli to pneumocytes type II to increase surfactant synthesis in an adaptive manner. Evidence of an inflammatory response appears to occur at exposure levels equal to 13.7 mg/m³. Taking all findings into account 1.1 mg/m³ constitutes the lowest-observable-effect concentration (LOEC) for effects in the lower respiratory tract and appears to be related to an adaptive rather than adverse response.

For the repeated dose toxicity endpoint, the observation in the respiratory tract, especially the lung noted in both source substances is consistent with the hypothesized MoA. As a MDI substance enters the lung, NCO groups react with biological nucleophiles at the MDI/lung fluid interface to form MDI-conjugates. Formation of these MDI-adducts depletes protective nucleophiles in the lung and results in pulmonary irritation and inflammatory cell influx. As these acute effects become chronic this result in histopathological changes characterized by interstitial fibrosis, hyperplasia of the alveolar epithelium and a low incidence of bronchiolo-alveolar adenoma, the latter occurring in the high exposure groups of both chronic source substance studies (Hoymann et al. 1995., Reuzel et al. 1994). The findings from the repeated dose Toxicity studies indicate portal of entry effects and lack of distal toxicity, which is in line with the hypothesized MoA

For the repeated dose toxicity endpoint, the observations in the respiratory tract, especially the lung noted for both source substances are consistent with the hypothesized MoA. as a MDI substance enters the lung, NCO groups react with biological nucleophiles at the MDI/lung fluid interface to form MDI-conjugates. formation of these MDI-adducts depletes protective nucleophiles in the lung and results in pulmonary irritation and inflammatory cell influx. As these acute effects become chronic this results in histopathological changes characterized by interstitial fibrosis, hyperplasia of the alveolar epithelium and a low incidence of bronchiolo-alveolar adenoma, latter occurring in the high exposure groups of both chronic source substance studies (Hoymann et al. 1995, Reuzel et al. 1994). The findings from the repeated dose toxicity studies indicate portal of entry effects and lack of  distal toxicity.

As the source substances 4,4'-MDI, pMDI and the target substance MDI MT contain sufficient monomeric MDI, the driver of toxicity, similarities in reactions leading to inflammation and irritation to the respiratory tract is predicted. In addition, as the higher molecular weight non-monomeric  content of the UVCB substance MDI MT do not contains reactive centres and is consequently inert and thus do not contribute to the expected toxicity, it is reasonable to assume that using read across to source substances 4,4'-MDI and pMDI is warranted. 

As the source substances are classified with STOT RE 2 (H373) using the read across approach, a similar classification for the target substance is followed and the target substance MDI MT is classified as STOT RE (H373) EU GHS 1272/2008 CLP.

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 1985 - June 1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

yes

Remarks:

- some omitted exposures; clinical chemistry, urinalysis and haematological samples only taken at the end of the study

Principles of method if other than guideline:

Details of deviations:
Omitted exposures due to public holidays or to technical maintenance or repair of inhalation equipment there were no exposures during 21 days. (day 45, 100, 119, 197-198, 204, 290, 293, 323, 326, 331, 342,562-563, 569, 675, 678, 688, 692-693, 716, 727).
Clinical chemistry, urinalysis samples and haematological examination samples only taken at the end of the study (1 yr satellite group, 2 yr main group).

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

- AGE: at the start of the study the animals were approximately 6 weeks old.
- WEIGHT AT STUDY INITIATION: mean weight of male rats was 179 g and of female rats 141 g. The rats were weighted just prior to the start of the study and then weekly during the first 13 weeks and every 4 weeks afterwards. At the end of the exposure time, surviving rats were killed and weighed at the day of scheduled autopsy.
- NUMBER OF ANIMALS: 280 males and 280 females randomly allocated to four groups. Each group, composed of 70 males and 70 females. Each group was subdivided into one satellite group of 10 rats/sex and a main group of 60 rats/sex.
- STRAIN: Cpb:WU Wistar

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: The mean mass median aerodynamic particle size during the study was 0.68, 0.70 and 0.74 µm with geometric standard deviation of 2.93, 2.46 and 2.31 at the level of 0.2, 1.0 and 6.0 mg/m3, respectively. On average the aerodynamic diameter was for at least 93.5 % of the particles smaller than 4.2 µm.

Details on inhalation exposure:

- EXPOSURE CHAMBERS-EXPOSURE CONDITIONS: Animals were exposed to the test atmospheres in H1000 multitiered inhalation chambers (capacity about 2.3 m3) manufactured by Hazleton Systems, Inc.. During exposure the rats were housed individually in wire mesh stainless-steel cages. Total airflow through the chambers was on average between 35 and 45 m3/hr depending on the volume of air needed to reach the required concentration of polymeric MDI in the atmosphere. The temperature and relative humidity in the chambers were generally between 20 and 25°C and between 40 and 70 %, respectively. Except for exposure to polymeric MDI, control rats were treated similarly to test animals including housing in an H1000 multitiered inhalation chamber.
- GENERATION OF TEST ATMOSPHERES: Test atmospheres were generated by atomizing polymeric MDI liquid into droplets by using compressed air in a nebulizer designed by TNO. The nebulizer consisted of an atomizer and a glass jar. The atomizer coded DR 0 11 was purchased from Lechler (Germany). Before use, the nozzle of the atomizer was slightly modified by reducing empirically the internal diameter of the nozzle orifice. The nebulizer was operated at a pressure of approximately 2.5 bar. A baffle was fitted approximately 4 cm below the nozzle orifice to remove the larger droplets from the spray The smaller droplets followed the upward airflow and were emitted through the outlet port and passed through a cyclone with a diameter of 9 cm. The remaining particles larger than 5 µm were impinged onto the wall of the cyclone to obtain an aerosol of which 95% of the particles were smaller than 5 µm. The aerosol was then passed through a manifold pipe system constructed of polyvinyl chloride tubing, having a length of approximately 10 in and an internal diameter of 4.5 cm. Air-operated vacuum pumps (air movers, AIRNAC, Milford, CT; TD series, 110 size) adjacent to the top of the respective inhalation chambers moved polymeric MDI aerosol from the delivery system to the inlet of the inhalation chamber, where it was diluted in air from the main air supply of the inhalation chamber. By varying the operating air pressure to the vacuum pump the amount of withdrawn aerosol could be adjusted to the desired concentration of test material within the chamber.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

- ANALYSIS OF POLYMERIC MDI IN THE TEST ATMOSPHERES: Gravimetry was used as primary standard for assessing the polymeric MDI aerosol concentration in the test atmospheres. Test atmosphere samples were collected using closed filter-type collectors provided with glass fiber filters (Sartorius SM 13430; diameter, 44 mm). The filters were weighed before and after sampling. From the increase in weight and the volume of test atmosphere drawn through the filter the time-weighted average concentration of polymeric MDI was calculated. Beta attenuation using attenuators from Verewa (Germany) were used in parallel with gravimetry during the first 3 months of the study, and the results were compared with those obtained from gravimetry. In view of the proven reliability of beta attenuation during this period gravimetric determinations were carried out only once every 2 weeks thereafter. The particle size distribution in each of the test atmospheres was determined at weekly intervals using a 10-stage Berkeley quartz crystal microbalance cascade impactor.

Duration of treatment / exposure:

main groups: 2 years; satellite groups: 1 year

Frequency of treatment:

6 hours/day; 5 days/week

Dose / conc.:

0 mg/m³ air

Remarks:

negative control

Dose / conc.:

0.2 mg/m³ air (nominal)

Dose / conc.:

1 mg/m³ air (nominal)

Dose / conc.:

6 mg/m³ air (nominal)

Dose / conc.:

0 mg/m³ air (analytical)

Remarks:

negative control

Dose / conc.:

0.19 mg/L air (analytical)

Dose / conc.:

0.98 mg/m³ air (analytical)

Dose / conc.:

6.03 mg/m³ air (analytical)

No. of animals per sex per dose:

60 (main groups); 10 (satellite groups)

Control animals:

yes, sham-exposed

Observations and examinations performed and frequency:

- HEMATOLOGICAL PARAMETERS (red and white blood cell counts, hemoglobin, packed cell volume, differential white blood cell count, prothrombin time) and urinary parameters (appearance, volume, density, pH, protein, occult blood, glucose, ketones, microscopy of the sediment) were measured in all rats of the satellite groups in week 52.
- BIOCHEMICAL BLOOD PARAMETERS (albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, urea nitrogen, total protein, creatinine, total bilirubin, Ca, K, Na, inorganic phosphate, cholesterol, triglycerides, and glucose) were measured in blood samples taken at euthanization from all rats of the satellite groups, except for glucose, which was determined in blood samples after overnight fasting in week 52.

Sacrifice and pathology:

- ORGANS EXAMINED AT NECROPSY (MACROSCOPIC AND MICROSCOPIC): All rats of the satellite groups were randomly killed on two successive days in week 53, and all survivors of the main groups were randomly euthanized on seven successive working days in weeks 105 and 106 by
exsanguination from the abdominal aorta under ether anesthesia, autopsied, and examined for gross pathological changes. Adrenals, brain,
heart, kidneys, Iiver, Iungs with mediastinal lymph nodes, trachea and larynx, spleen and testes of all rats of the satellite groups and of all survivors of the main groups were weighed. A wide range of organs or samples of organs or tissues were preserved in an aqueous neutral
phosphate-buffered 4% formaldehyde solution. The lungs were fixed by intratracheal infusion with the main groups, nose, lungs, mediastinal
lymph nodes, and all gross lesions fixative under 10 cm water pressure. The urinary bladder was fixed by infusion of the fixative through the
bladder wall in the neck of the bladder. The nose was fixed by infusion of the fixative through the pharyngeal duct. In the 1-year study (satellite
groups) histopathological examination was carried out of kidneys, liver, nose, larynx, trachea with bronchi, lungs, mediastinal lymph nodes, and
all gross lesions all rats. In the 2-year study (main groups) 43 different organs (**) or tissues and all grossly visible lesions were examined by light microscopy of the control and high-concentration animals and of the low- and mid-concentration decedents. Moreover, in the low- and
mid-concentration survivors of the main groups, nose, lungs, mediastinal lymph nodes, and all gross lesions were subjected to histopathologicaI examination.

For transmission electron microscopic studies from selected paraffin blocks of the 13-week study, (Reuzel el aL, 1994), and the 1- and 2-year
studies, a portion of the block containing lung tissue was trimmed away and, deparaffinized in several changes of xylene over a 24-hr period. The
tissue was then rehydrated, and postfixed with 1% osmium Tetroxide in phosphate buffer, dehydrated using a graded series of alcohol, and then
infiltrated and embedded in Epon/Araldite. After polymerization overnight in a vacuum oven, sections were cut with a diamond knife, placed in of
copper grids, and stained with lead citrate and uranyl acetate. The sections were then examined and photomicrographs were taken using a Zeiss
EM-10 electron microscope.

** (Adrenals, aorta, axillary lymph nodes, brain-brainstem, cerebrum and cerebellum, caecum, coagulating glands, colon, epididymides, exorbital lachrymal glands, eyes, femur with joint and bone marrow, Harderian glands, heart, kidneys, larynx, liver, lungs, mammary glands, mediastinal lymph nodes, mesenteric lymph nodes, nerve-peripheral, nose oeasophagus, ovaries, pancreas, parathyroids, parotid salivary glands, pharynx, pituitary, preputial/clitoral glands, prostate, rectum, seminal vesicles, skeletal muscle, skin/subcutis-flank, small intestines (duodenum, ileum, jejunum), spinal cord, spleen, sternum with bone marrow, stoamch, sublingual salivary glands, submaxillary salivary glands, testes, thymus, thyroid, trachea/bronchi, urinary bladder, uterus, Zymbal glands)

Statistics:

Body weights were analyzed by an analysis of covariance (Cochran, 1957) followed by the Dunnett's multiple comparison test (Dunnett, 1955). Analysis of variance (Steel and Torrie, 1960) followed by the Dunnett's multiple comparison test was applied to hematological, biochemical, and organ weight data. Differential white blood cell count data were analyzed by the Mann-Whitney U test (Siegel, 1956a). Incidences of histopathological changes and numbers of deaths were analyzed by the Fisher exact probability test (Siegel, 1956b).

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

no effects observed

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:

effects observed, treatment-related

Key result

Dose descriptor:

NOAEC

Effect level:

0.2 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

NOAEC

Effect level:

0.19 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

LOAEC

Effect level:

1 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

LOAEC

Effect level:

0.98 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

1 mg/L air (nominal)

System:

respiratory system: lower respiratory tract

Organ:

lungs

Treatment related:

yes

Dose response relationship:

yes

Mortality incidences in males were comparable in all groups. Female rats showed negatively concentration-related mortality incidences. The number of animals with palpable masses did not differ between test and control animals. No treatment-related differences in body weights were observed between control and test groups.

Hematological examination of rats at day 357-358 revealed no exposure-related differences between the groups. Biochemical examination performed on days 360, 366 and/or 367 was essentially negative. No alterations were observed from parameters measured in urine of rats exposed to polymeric MDI aerosol for 360 days.

Lung weights were statistically significantly increased in both males and females exposed to 6.0 mg/m³ for 12 or 24 months as summarized in the following table 1:

Table 1: Mean absolute lung weights and lung-to-body weight ratios in rats exposed by inhalation to polymeric MDI aerosol for 1 year (satellite groups) or for up to 2 years (main groups)

Polymeric MDI (mg/m3)	Satellite groups (a)		Main groups (b)
	Absolute (g)	Relative (g/kg)	Absolute (g)	Relative (g/kg)
Males
0 0.2 1.0 6.0	2.30 ± 0.15 2.32 ± 0.09 2.44 ± 0.10 2.60 ± 0.06	4.29 ± 0.16 4.48 ± 0.22 4.48 ± 0.16 5.06 ± 0.08**	2.90 ± 0.06 2.88 ± 0.10 2.88 ± 0.08 3.28 ± 0.07**	5.04 ± 0.14 5.00 ± 0.15 5.19 ± 0.24 5.80 ± 0.16**
Females
0 0.2 1.0 6.0	1.67 ± 0.07 1.66 ± 0.05 1.69 ± 0.06 1.93 ± 0.09*	5.66 ± 0.29 5.63 ± 0.15 5.61 ± 0.21 6.51 ± 0.22*	2.10 ± 0.06 2.09 ± 0.04 2.06 ± 0.04 2.41 ± 0.05**	6.14 ± 0.28 5.87 ± 0.09 5.68 ± 0.11 6.68 ± 0.17

(a) Number of lungs weighed/sex/group was 10
(b) Number of lungs weighed/sex/group varied from 35 to 50

* p<0.05; ** p<0.01

No treatment-related gross changes were found in animals exposed for 12 months. Gross examination of animals exposed for 24 months revealed increased incidence of lungs with spotted surface and/or discoloured appearance in male rats exposed to 6.0 mg/m3.

Histopathology (main groups exposed over 2 years):

Nose: increased incidence of rats with a higher degree of basal cell hyperplasia frequently accompanied by hyperplasia of Bowman's glands in the olfactory epithelium in the nose at levels of 1.0 and 6.0 mg/m³. At 6.0 mg/m³ basal cell hyperplasia occurred in 32/60 males and 49/60 females against 14/60 and 4/60 for the corresponding controls.

Lungs: incidences of non-neoplastic findings and tumors are summarized in the following table 2:

Table 2: Number of rats with non-neoplastic findings and tumors in lungs after 2-year exposure to polymeric MDI (main groups)

Polymeric MDI (mg/m3)		0	0.2	1.0	6.0
Animal number	M	60	60	60	60
	F	60	60	60	60
Surviving animals	M	38	38	42	36
	F	41	42	48	50
- Macrophages with yellow pigment	M	0	3	21**	60**
	F	0	1	23**	59**
- Localized fibrosis	M	1	0	9*	44**
	F	0	0	4	48**
- Alveolar duct epithelialization	M	1	0	8*	54**
	F	0	0	8*	57*
- Localized alveolar bronchiolization	M	1	1	2	12**
	F	2	3	3	14**
- Mineralized deposits in the bronchial and alveolar region	M	0	1	1	13**
	F	0	0	0	24**
- Pneumonitis	M	13	13	17	28
	F	3	4	3	2
- Adenoma	M	0	0	0	6*
	F	0	0	0	2
- Adenocarcinoma	M	0	0	0	1
	F	0	0	0	0

* p<0.05; ** p<0.01

Mediastinal lymph nodes: increased incidence of rats with an accumulation of macrophages with yellow pigment at levels of 1.0 and 6.0 mg/m³. At 6.0 mg/m³ this finding occurred in 50/60 males and 43/60 females against 0/60 for the corresponding controls.

Other organs: the incidence and distribution of other tumour types was not affected by treatment.

Histopathology (satellite groups exposed over 1 year):

Rats killed after 1 year of exposure had treatment-related histopathological changes in the nasal cavity, lungs, and mediastinal lymph nodes starting at 1.0 mg/m3, but to a lower degree of severity compared to animals exposed over 2 years. There was no microscopic evidence of lung tumors or any other tumors following exposure to polymeric MDI for 1 year.

Conclusions:

In a combined chronic toxicity and carcinogenicity key study (Reuzel et al., 1990; Reuzel et al., 1994a) conducted according to OECD Guideline 453 rats were exposed for 6 hours/day, 5 days/week for one year (satellite groups) or two years (main groups) to aerosol concentrations of 0, 0.2, 1.0 or 6.0 mg pMDI /m3 (analytical concentrations: 0, 0.19, 0.98, 6.03 mg/m3). The effect of chronic exposure of rats to respirable pMDI aerosol was confined to the respiratory tract. The compound-related changes were found in the nasal cavity, the lungs and the mediastinal lymph nodes, and to some degree they were already present after one year of exposure. Histopathology of the organs/tissues investigated showed that exposure to 6.0 mg/m3 over two years was related to the occurrence of pulmonary tumors in males (6 adenomas and 1 adenocarcinoma) and females (2 adenomas). In this two-year rat study, the NOAEC was 0.2 mg/m3 for the repeated dose toxicity of pMDI. The LOAEC was set at 1.0 mg/m3.

Executive summary:

In a combined chronic toxicity and carcinogenicity study rats were exposed for 6 hours/day, 5 days/week for 1 (satellite groups) or 2 years (main groups) to polymeric MDI aerosol concentrations of 0, 0.2, 1.0 or 6.0 mg/m³. The effect of chronic exposure of rats to respirable polymeric MDI aerosol was confined to the respiratory tract. The compound-related changes were found in the nasal cavity, the lungs and the mediastinal lymph nodes, and to some degree they were already present after 1 year of exposure. Histopathology of the organs/tissues investigated showed that exposure to 6.0 mg/m³ over 2 years was related to the occurence of pulmonary tumors in males (6 adenomas and 1 adenocarcinoma) and females (2 adenomas).

In this 2-year rat study the NOAEC was 0.2 mg/m³ for the repeated dose toxicity of polymeric MDI. The LOAEC was set on 1.0 mg/m³.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Study duration:

chronic

Experimental exposure time per week (hours/week):

30

Species:

rat

Quality of whole database:

reliable

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 1985 - June 1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

yes

Remarks:

- some omitted exposures; clinical chemistry, urinalysis and haematological samples only taken at the end of the study

Principles of method if other than guideline:

Details of deviations:
Omitted exposures due to public holidays or to technical maintenance or repair of inhalation equipment there were no exposures during 21 days. (day 45, 100, 119, 197-198, 204, 290, 293, 323, 326, 331, 342,562-563, 569, 675, 678, 688, 692-693, 716, 727).
Clinical chemistry, urinalysis samples and haematological examination samples only taken at the end of the study (1 yr satellite group, 2 yr main group).

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

- AGE: at the start of the study the animals were approximately 6 weeks old.
- WEIGHT AT STUDY INITIATION: mean weight of male rats was 179 g and of female rats 141 g. The rats were weighted just prior to the start of the study and then weekly during the first 13 weeks and every 4 weeks afterwards. At the end of the exposure time, surviving rats were killed and weighed at the day of scheduled autopsy.
- NUMBER OF ANIMALS: 280 males and 280 females randomly allocated to four groups. Each group, composed of 70 males and 70 females. Each group was subdivided into one satellite group of 10 rats/sex and a main group of 60 rats/sex.
- STRAIN: Cpb:WU Wistar

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: The mean mass median aerodynamic particle size during the study was 0.68, 0.70 and 0.74 µm with geometric standard deviation of 2.93, 2.46 and 2.31 at the level of 0.2, 1.0 and 6.0 mg/m3, respectively. On average the aerodynamic diameter was for at least 93.5 % of the particles smaller than 4.2 µm.

Details on inhalation exposure:

- EXPOSURE CHAMBERS-EXPOSURE CONDITIONS: Animals were exposed to the test atmospheres in H1000 multitiered inhalation chambers (capacity about 2.3 m3) manufactured by Hazleton Systems, Inc.. During exposure the rats were housed individually in wire mesh stainless-steel cages. Total airflow through the chambers was on average between 35 and 45 m3/hr depending on the volume of air needed to reach the required concentration of polymeric MDI in the atmosphere. The temperature and relative humidity in the chambers were generally between 20 and 25°C and between 40 and 70 %, respectively. Except for exposure to polymeric MDI, control rats were treated similarly to test animals including housing in an H1000 multitiered inhalation chamber.
- GENERATION OF TEST ATMOSPHERES: Test atmospheres were generated by atomizing polymeric MDI liquid into droplets by using compressed air in a nebulizer designed by TNO. The nebulizer consisted of an atomizer and a glass jar. The atomizer coded DR 0 11 was purchased from Lechler (Germany). Before use, the nozzle of the atomizer was slightly modified by reducing empirically the internal diameter of the nozzle orifice. The nebulizer was operated at a pressure of approximately 2.5 bar. A baffle was fitted approximately 4 cm below the nozzle orifice to remove the larger droplets from the spray The smaller droplets followed the upward airflow and were emitted through the outlet port and passed through a cyclone with a diameter of 9 cm. The remaining particles larger than 5 µm were impinged onto the wall of the cyclone to obtain an aerosol of which 95% of the particles were smaller than 5 µm. The aerosol was then passed through a manifold pipe system constructed of polyvinyl chloride tubing, having a length of approximately 10 in and an internal diameter of 4.5 cm. Air-operated vacuum pumps (air movers, AIRNAC, Milford, CT; TD series, 110 size) adjacent to the top of the respective inhalation chambers moved polymeric MDI aerosol from the delivery system to the inlet of the inhalation chamber, where it was diluted in air from the main air supply of the inhalation chamber. By varying the operating air pressure to the vacuum pump the amount of withdrawn aerosol could be adjusted to the desired concentration of test material within the chamber.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

- ANALYSIS OF POLYMERIC MDI IN THE TEST ATMOSPHERES: Gravimetry was used as primary standard for assessing the polymeric MDI aerosol concentration in the test atmospheres. Test atmosphere samples were collected using closed filter-type collectors provided with glass fiber filters (Sartorius SM 13430; diameter, 44 mm). The filters were weighed before and after sampling. From the increase in weight and the volume of test atmosphere drawn through the filter the time-weighted average concentration of polymeric MDI was calculated. Beta attenuation using attenuators from Verewa (Germany) were used in parallel with gravimetry during the first 3 months of the study, and the results were compared with those obtained from gravimetry. In view of the proven reliability of beta attenuation during this period gravimetric determinations were carried out only once every 2 weeks thereafter. The particle size distribution in each of the test atmospheres was determined at weekly intervals using a 10-stage Berkeley quartz crystal microbalance cascade impactor.

Duration of treatment / exposure:

main groups: 2 years; satellite groups: 1 year

Frequency of treatment:

6 hours/day; 5 days/week

Dose / conc.:

0 mg/m³ air

Remarks:

negative control

Dose / conc.:

0.2 mg/m³ air (nominal)

Dose / conc.:

1 mg/m³ air (nominal)

Dose / conc.:

6 mg/m³ air (nominal)

Dose / conc.:

0 mg/m³ air (analytical)

Remarks:

negative control

Dose / conc.:

0.19 mg/L air (analytical)

Dose / conc.:

0.98 mg/m³ air (analytical)

Dose / conc.:

6.03 mg/m³ air (analytical)

No. of animals per sex per dose:

60 (main groups); 10 (satellite groups)

Control animals:

yes, sham-exposed

Observations and examinations performed and frequency:

- HEMATOLOGICAL PARAMETERS (red and white blood cell counts, hemoglobin, packed cell volume, differential white blood cell count, prothrombin time) and urinary parameters (appearance, volume, density, pH, protein, occult blood, glucose, ketones, microscopy of the sediment) were measured in all rats of the satellite groups in week 52.
- BIOCHEMICAL BLOOD PARAMETERS (albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, urea nitrogen, total protein, creatinine, total bilirubin, Ca, K, Na, inorganic phosphate, cholesterol, triglycerides, and glucose) were measured in blood samples taken at euthanization from all rats of the satellite groups, except for glucose, which was determined in blood samples after overnight fasting in week 52.

Sacrifice and pathology:

- ORGANS EXAMINED AT NECROPSY (MACROSCOPIC AND MICROSCOPIC): All rats of the satellite groups were randomly killed on two successive days in week 53, and all survivors of the main groups were randomly euthanized on seven successive working days in weeks 105 and 106 by
exsanguination from the abdominal aorta under ether anesthesia, autopsied, and examined for gross pathological changes. Adrenals, brain,
heart, kidneys, Iiver, Iungs with mediastinal lymph nodes, trachea and larynx, spleen and testes of all rats of the satellite groups and of all survivors of the main groups were weighed. A wide range of organs or samples of organs or tissues were preserved in an aqueous neutral
phosphate-buffered 4% formaldehyde solution. The lungs were fixed by intratracheal infusion with the main groups, nose, lungs, mediastinal
lymph nodes, and all gross lesions fixative under 10 cm water pressure. The urinary bladder was fixed by infusion of the fixative through the
bladder wall in the neck of the bladder. The nose was fixed by infusion of the fixative through the pharyngeal duct. In the 1-year study (satellite
groups) histopathological examination was carried out of kidneys, liver, nose, larynx, trachea with bronchi, lungs, mediastinal lymph nodes, and
all gross lesions all rats. In the 2-year study (main groups) 43 different organs (**) or tissues and all grossly visible lesions were examined by light microscopy of the control and high-concentration animals and of the low- and mid-concentration decedents. Moreover, in the low- and
mid-concentration survivors of the main groups, nose, lungs, mediastinal lymph nodes, and all gross lesions were subjected to histopathologicaI examination.

For transmission electron microscopic studies from selected paraffin blocks of the 13-week study, (Reuzel el aL, 1994), and the 1- and 2-year
studies, a portion of the block containing lung tissue was trimmed away and, deparaffinized in several changes of xylene over a 24-hr period. The
tissue was then rehydrated, and postfixed with 1% osmium Tetroxide in phosphate buffer, dehydrated using a graded series of alcohol, and then
infiltrated and embedded in Epon/Araldite. After polymerization overnight in a vacuum oven, sections were cut with a diamond knife, placed in of
copper grids, and stained with lead citrate and uranyl acetate. The sections were then examined and photomicrographs were taken using a Zeiss
EM-10 electron microscope.

** (Adrenals, aorta, axillary lymph nodes, brain-brainstem, cerebrum and cerebellum, caecum, coagulating glands, colon, epididymides, exorbital lachrymal glands, eyes, femur with joint and bone marrow, Harderian glands, heart, kidneys, larynx, liver, lungs, mammary glands, mediastinal lymph nodes, mesenteric lymph nodes, nerve-peripheral, nose oeasophagus, ovaries, pancreas, parathyroids, parotid salivary glands, pharynx, pituitary, preputial/clitoral glands, prostate, rectum, seminal vesicles, skeletal muscle, skin/subcutis-flank, small intestines (duodenum, ileum, jejunum), spinal cord, spleen, sternum with bone marrow, stoamch, sublingual salivary glands, submaxillary salivary glands, testes, thymus, thyroid, trachea/bronchi, urinary bladder, uterus, Zymbal glands)

Statistics:

Body weights were analyzed by an analysis of covariance (Cochran, 1957) followed by the Dunnett's multiple comparison test (Dunnett, 1955). Analysis of variance (Steel and Torrie, 1960) followed by the Dunnett's multiple comparison test was applied to hematological, biochemical, and organ weight data. Differential white blood cell count data were analyzed by the Mann-Whitney U test (Siegel, 1956a). Incidences of histopathological changes and numbers of deaths were analyzed by the Fisher exact probability test (Siegel, 1956b).

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

no effects observed

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:

effects observed, treatment-related

Key result

Dose descriptor:

NOAEC

Effect level:

0.2 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

NOAEC

Effect level:

0.19 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

LOAEC

Effect level:

1 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Dose descriptor:

LOAEC

Effect level:

0.98 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

1 mg/L air (nominal)

System:

respiratory system: lower respiratory tract

Organ:

lungs

Treatment related:

yes

Dose response relationship:

yes

Mortality incidences in males were comparable in all groups. Female rats showed negatively concentration-related mortality incidences. The number of animals with palpable masses did not differ between test and control animals. No treatment-related differences in body weights were observed between control and test groups.

Hematological examination of rats at day 357-358 revealed no exposure-related differences between the groups. Biochemical examination performed on days 360, 366 and/or 367 was essentially negative. No alterations were observed from parameters measured in urine of rats exposed to polymeric MDI aerosol for 360 days.

Lung weights were statistically significantly increased in both males and females exposed to 6.0 mg/m³ for 12 or 24 months as summarized in the following table 1:

Table 1: Mean absolute lung weights and lung-to-body weight ratios in rats exposed by inhalation to polymeric MDI aerosol for 1 year (satellite groups) or for up to 2 years (main groups)

Polymeric MDI (mg/m3)	Satellite groups (a)		Main groups (b)
	Absolute (g)	Relative (g/kg)	Absolute (g)	Relative (g/kg)
Males
0 0.2 1.0 6.0	2.30 ± 0.15 2.32 ± 0.09 2.44 ± 0.10 2.60 ± 0.06	4.29 ± 0.16 4.48 ± 0.22 4.48 ± 0.16 5.06 ± 0.08**	2.90 ± 0.06 2.88 ± 0.10 2.88 ± 0.08 3.28 ± 0.07**	5.04 ± 0.14 5.00 ± 0.15 5.19 ± 0.24 5.80 ± 0.16**
Females
0 0.2 1.0 6.0	1.67 ± 0.07 1.66 ± 0.05 1.69 ± 0.06 1.93 ± 0.09*	5.66 ± 0.29 5.63 ± 0.15 5.61 ± 0.21 6.51 ± 0.22*	2.10 ± 0.06 2.09 ± 0.04 2.06 ± 0.04 2.41 ± 0.05**	6.14 ± 0.28 5.87 ± 0.09 5.68 ± 0.11 6.68 ± 0.17

(a) Number of lungs weighed/sex/group was 10
(b) Number of lungs weighed/sex/group varied from 35 to 50

* p<0.05; ** p<0.01

No treatment-related gross changes were found in animals exposed for 12 months. Gross examination of animals exposed for 24 months revealed increased incidence of lungs with spotted surface and/or discoloured appearance in male rats exposed to 6.0 mg/m3.

Histopathology (main groups exposed over 2 years):

Nose: increased incidence of rats with a higher degree of basal cell hyperplasia frequently accompanied by hyperplasia of Bowman's glands in the olfactory epithelium in the nose at levels of 1.0 and 6.0 mg/m³. At 6.0 mg/m³ basal cell hyperplasia occurred in 32/60 males and 49/60 females against 14/60 and 4/60 for the corresponding controls.

Lungs: incidences of non-neoplastic findings and tumors are summarized in the following table 2:

Table 2: Number of rats with non-neoplastic findings and tumors in lungs after 2-year exposure to polymeric MDI (main groups)

Polymeric MDI (mg/m3)		0	0.2	1.0	6.0
Animal number	M	60	60	60	60
	F	60	60	60	60
Surviving animals	M	38	38	42	36
	F	41	42	48	50
- Macrophages with yellow pigment	M	0	3	21**	60**
	F	0	1	23**	59**
- Localized fibrosis	M	1	0	9*	44**
	F	0	0	4	48**
- Alveolar duct epithelialization	M	1	0	8*	54**
	F	0	0	8*	57*
- Localized alveolar bronchiolization	M	1	1	2	12**
	F	2	3	3	14**
- Mineralized deposits in the bronchial and alveolar region	M	0	1	1	13**
	F	0	0	0	24**
- Pneumonitis	M	13	13	17	28
	F	3	4	3	2
- Adenoma	M	0	0	0	6*
	F	0	0	0	2
- Adenocarcinoma	M	0	0	0	1
	F	0	0	0	0

* p<0.05; ** p<0.01

Mediastinal lymph nodes: increased incidence of rats with an accumulation of macrophages with yellow pigment at levels of 1.0 and 6.0 mg/m³. At 6.0 mg/m³ this finding occurred in 50/60 males and 43/60 females against 0/60 for the corresponding controls.

Other organs: the incidence and distribution of other tumour types was not affected by treatment.

Histopathology (satellite groups exposed over 1 year):

Rats killed after 1 year of exposure had treatment-related histopathological changes in the nasal cavity, lungs, and mediastinal lymph nodes starting at 1.0 mg/m3, but to a lower degree of severity compared to animals exposed over 2 years. There was no microscopic evidence of lung tumors or any other tumors following exposure to polymeric MDI for 1 year.

Conclusions:

In a combined chronic toxicity and carcinogenicity key study (Reuzel et al., 1990; Reuzel et al., 1994a) conducted according to OECD Guideline 453 rats were exposed for 6 hours/day, 5 days/week for one year (satellite groups) or two years (main groups) to aerosol concentrations of 0, 0.2, 1.0 or 6.0 mg pMDI /m3 (analytical concentrations: 0, 0.19, 0.98, 6.03 mg/m3). The effect of chronic exposure of rats to respirable pMDI aerosol was confined to the respiratory tract. The compound-related changes were found in the nasal cavity, the lungs and the mediastinal lymph nodes, and to some degree they were already present after one year of exposure. Histopathology of the organs/tissues investigated showed that exposure to 6.0 mg/m3 over two years was related to the occurrence of pulmonary tumors in males (6 adenomas and 1 adenocarcinoma) and females (2 adenomas). In this two-year rat study, the NOAEC was 0.2 mg/m3 for the repeated dose toxicity of pMDI. The LOAEC was set at 1.0 mg/m3.

Executive summary:

In a combined chronic toxicity and carcinogenicity study rats were exposed for 6 hours/day, 5 days/week for 1 (satellite groups) or 2 years (main groups) to polymeric MDI aerosol concentrations of 0, 0.2, 1.0 or 6.0 mg/m³. The effect of chronic exposure of rats to respirable polymeric MDI aerosol was confined to the respiratory tract. The compound-related changes were found in the nasal cavity, the lungs and the mediastinal lymph nodes, and to some degree they were already present after 1 year of exposure. Histopathology of the organs/tissues investigated showed that exposure to 6.0 mg/m³ over 2 years was related to the occurence of pulmonary tumors in males (6 adenomas and 1 adenocarcinoma) and females (2 adenomas).

In this 2-year rat study the NOAEC was 0.2 mg/m³ for the repeated dose toxicity of polymeric MDI. The LOAEC was set on 1.0 mg/m³.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

0.2 mg/m³

Study duration:

chronic

Species:

rat

Quality of whole database:

reliable

Mode of Action Analysis / Human Relevance Framework

Hypothesis: Similarly to the mechanism of acute toxicity, as a MDI substance enters the lung it is the reaction of the electrophilic NCO group with biological nucleophiles at the MDI/lung fluid interface which lead to formation of MDI-conjugates. Formation of these MDI-adducts depletes protective nucleophiles in the lung and results in pulmonary irritation and inflammatory cell influx. On a relatively short (acute) timescale, these effects can be seen as increases in lung weight as well as BALF levels of intracellular enzymes (LDH, γ-GT), plasma protein (ACE) and inflammatory cells. On a longer (chronic) timescale, when the acute effects become biologically significant, they can be seen as basal cell hyperplasia in the nasal cavity, pulmonary fibrosis, proliferation of the alveolar epithelium and bronchiolo-alveolar adenoma. In other words, chronic pathology following recurrent MDI inhalation is both dependent on the C x t and the degree of acute pulmonary irritation can be considered as an ‘acute-on-chronic’ effect (Pauluhn, 2011). This supports a simple, direct MoA at the site of contact in the lungs as described by the hypothesis. Based on the highly reactivity of the electrophilic NCO group with biological nucleophiles and subsequent MDI-conjugates formation MDI only enters the systemic circulation in the form of MDI-GSH or protein adducts. Consequently, there is no systemic exposure to the toxic NCO functional group which is consistent with the lack of distal toxicity in any study conducted.

The simple, direct MoA at the side of contact in the lungs and lack of systemic toxicity is clearly demonstrated in repeated inhalation toxicity studies of both source substances.

Additional information

There are no sub-acute repeated dose toxicity studies available for MDI MT. A read across with data from the source substances 4,4’-MDI and pMDI is performed.  Inhalation is the most appropriate route of exposure for assessing occupational risk of MDI substances in humans. Reliable repeated dose inhalation toxicity studies are available for the two source substances 4,4’-MDI and pMDI. Two chronic inhalation toxicity studies are available for the source substances, one for pMDI (Reuzel et al. 1994) and one for monomeric 4,4’-MDI (Hoymann et al., 1995). In the chronic rat study performed with polymeric MDI the NOAEC was 0.2 mg/m³ after aerosol exposure over 2 years (6 hours/day, 5 days/week) (Reuzel et al. (1990,1994). In a chronic inhalation toxicity study Hoymann et al. (1995) exposed rats daily 17 hours with 4,4'-MDI aerosols, the LOAEC set was 0.23 mg/m³ after long-term inhalation. A comparison of the both chronic rat studies with 4,4'-MDI and polymeric MDI has shown very good consistency across the studies with respect to gradation of inhaled dose and the observed histopathological changes. In this review it was concluded that a daily 17 hr-exposure of 0.23 mg/m³ 4,4'-MDI corresponds approximately to a daily 6 hr-exposure of 1 mg/m³ polymeric MDI (Feron et al. (2001), Arch. Toxicol. 75: 159-175).

In the 2-year rat study (Reuzel et al. 1990, 1994), used as key study, the NOAEC was 0.2 mg/m³ for the repeated dose toxicity of polymeric MDI. The LOAEC was set on 1.0 mg/m³.

 

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

Justification for classification or non-classification

According to CLP Regulation (EC) No.1272/2008 the classification of 4,4'-MDI (CAS No.101-68-8) is considered for the classification of MDI MT (CAS No.147993-65-5):

EU GHS 1272/2008 CLP: STOT Rep. Exp. 2 (H373: may cause damage to the respiratory system through prolonged or repeated exposures).