p-phenylene diisocyanate

Endpoint summary

Description of key information

The read across for PPDI; is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of repeated dose toxicity.

The animals were whole body exposed to 0, 0.05 and 0.15 ppm of TDI (80/20) vapour for 6 hours/day, 5 days/week. In both species, body weight gain was reduced at 0.15 ppm over the first 12 weeks that persisted but did not worsen over the remaining period of the study. In rats, rhinitis was observed in males at 0.15 ppm and in females beginning at 0.05 ppm, generally characterized by squamous metaplasia/hyperplasia of the respiratory mucosa, with and without exudate in the lumen, and leucocyte infiltration in the lamina propria. This finding is considered to be due to local irritation of the anterior nasal cavity. In mice, histopathology revealed marked inflammatory processes in trachea, larynx, bronchi, lungs and predominantly in nasal turbinates (chronic and necrotic rhinitis) of male and female animals beginning at 0.05 ppm. Therefore, the LOAEC for rats and mice is 0.05 ppm (0.362 mg/m3) after long-term inhalation of TDI vapour.

Inhalation exposure is the most appropriate route for assessing occupational risk in humans. Effects from repeated exposure of animals to TDI are limited to effects on the respiratory tract caused by local irritation, no signs of systemic toxicity were observed.

Simultaneously, other studies show that nose is the targeted organ of the respiratory system. Thus, the assessment confirmed the legal classification of the substance as STOT Single Exp.3 (Hazard statement H335, May cause respiratory irritation).

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1976-10 to 1978-11

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

yes

Remarks:

2 doses investigated

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

As specified above.

Species:

rat

Strain:

Sprague-Dawley

Details on species / strain selection:

As per the guideline.

Sex:

male/female

Details on test animals or test system and environmental conditions:

- Age at study initiation: 8 - 9 weeks
- Housing: 6 ♂ / 6 ♀ per cage

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: Unchanged

Remarks:

No vehicle

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION:
- Method of holding animals in test chamber: Animals were housed 6 ♂ / 6 ♀ per cage and exposed in 9 m³ chambers.
- Method of conditioning air: Passage of dry nitrogen through liquid TDI maintained at 21°C. The vapour produced was then diluted with air in all-glass systems to produce the desired exposure concentration.

OTHER:
Because of the known chemical reactivity and thus its potential storage instability, TDI lots were renewed every three months and fresh TDI was placed in the respective vapour-generating apparatus at the beginning of each daily exposure period. The measured mean test concentrations of TDI were 0.052 ppm and 0.146 ppm over a period of up to 113 weeks, with standard deviations of 0.007 ppm and 0.014 ppm, respectively.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

5/day, each exposure group.
U.E.I. Model 7000 TDI tape monitor and the Marcali colorimetric method.

Duration of treatment / exposure:

6 h / day

Frequency of treatment:

daily, 5 days per week, up to 113 weeks. No post exposure period.

Dose / conc.:

0.05 ppm (nominal)

Dose / conc.:

0.15 ppm (nominal)

No. of animals per sex per dose:

126

Control animals:

yes, sham-exposed

Details on study design:

As per guideline.

Positive control:

None; not applicable.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
BODY WEIGHT: Yes
OPHTHALMOSCOPIC EXAMINATION: Yes
HAEMATOLOGY: Yes
CLINICAL CHEMISTRY: Yes
URINALYSIS: Yes

Interim sacrifices were performed after 6, 12, and 18 months of exposure consisting of 7 animals/sex/dose.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
ORGAN WEIGHTS: Yes
Other examinations: Special histopathology of the nasal cavity.

Statistics:

Survival probabilities for each group were calculated by the method of Kaplan and Meier (J. Am. Statist. Ass. 53: 457 (1958)). The survival of the individual treatment groups was compared using the log rank method of Peto and Pike (Biometrics 29: 579 (1973)).

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Compared to control rats, there were significantly reduced body weight gains in males and in females of the highest dose groups up to study week 12 that remained significantly reduced throughout the study for female rats.

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:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In rats sacrificed as scheduled (interim sacrifices after 6, 12 and 18 months + terminal sacrifice), lesions were localized primarily in the anterior respiratory mucosa of the nasal cavity. Rhinitis was increased in incidence and severity (grades1-4: minimal - marked rhinitis, generally characterized by squamous metaplasia and hyperplasia of the epithelium, leucocyte infiltration in the lamina propria and exudate in the lumen) in a dose-dependent manner and is considered to be due to local irritation.

Histopathological findings: neoplastic:

no effects observed

Key result

Dose descriptor:

NOAEC

Effect level:

0.15 ppm (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical signs

Key result

Dose descriptor:

NOAEC

Effect level:

< 0.05 ppm (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical signs

Key result

Dose descriptor:

LOAEC

Effect level:

0.15 ppm (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical signs

Key result

Dose descriptor:

LOAEC

Effect level:

0.05 ppm (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical signs

Key result

Critical effects observed:

no

Chronic Toxicity:

No exposure-related clinical signs of toxicity were observed during the study. No treatment-related changes in hematology, blood biochemistry, urinalyses, ophthalmoscopy or organ weights were recorded.

Compared to control rats, there were significantly reduced body weight gains in males and in females of the highest dose groups up to study week 12 that remained significantly reduced throughout the study for female rats. Mortality occurred in both test and control groups, with generally higher mortality rates at earlier time points in test groups than in the controls for males, providing additional supporting evidence indicating that MTD was reached.

Table 1: Body weight gain and mortality rate of rats during exposure

	Males			Females
	Control	Low dose	High dose	Control	Low dose	High dose
Group mean body weight gain (g): week 0 –12	298	296	275*	136	132	121*
Group mean body weight gain (g): week 0 - termination	554	579	525	395	378	345*
Mortality before interim sacrifice after 6 m	3/126	13/126	11/126	0/126	1/126	0/126
Mortality before interim sacrifice after 12 m	4/116	1/106	1/108	1/119	3/118	1/119
Mortality before interim sacrifice after 18 m	7/105	8/97	13/100	14/111	20/108	9/110
Mortality before terminal sacrifice	52/89	46/81	50/80	53/88	55/81	46/84

* P <0.01 when compared to the controls

In rats sacrificed as scheduled (interim sacrifices after 6, 12 and 18 months + terminal sacrifice), lesions were localized primarily in the anterior respiratory mucosa of the nasal cavity. Rhinitis was increased in incidence and severity (grades1-4: minimal - marked rhinitis, generally characterized by squamous metaplasia and hyperplasia of the epithelium, leucocyte infiltration in the lamina propria and exudate in the lumen) in a dose-dependent manner and is considered to be due to local irritation.

Table 2: Incidence of rhinitis in the anterior nasal cavity of rats

	Males			Females
	Control	Low dose	High dose	Control	Low dose	High dose
Grade 0*	30/58	30/55	6/51	46/56	27/47	17/57
Grade 1*	11/58	7/55(13 %)	5/51	7/56	8/47(17 %)	16/57(28 %)
Grade 2*	13/58	15/55 (27 %)	13/51(25 %)	3/56	9/47(19 %)	18/57(32 %)
Grade 3*	4/58	3/55	23/51 (45 %)	0	3/47(6 %)	5/57(9 %)
Grade 4*	0	0	4/51	0	0	0
No section	0	0		0	0	2
Percent rats with grade1- 4 rhinitis	48 %	45 %	88 %	18 %	43 %	70 %

* Grade 0 = unremarkable; Grade 1 = minimal rhinitis, Grade 2 = slight rhinitis, Grade 3 = moderate rhinitis, Grade 4 = marked rhinitis generally characterized by squamous metaplasia and hyperplasia of the epithelium, leucocyte infiltration in the lamina propria and exudate in the lumen

 

Carcinogenicity

With respect to the assessment of tumour formation, there were slight increases in the tumour incidence for some locations when compared to the incidence in the controls. In Table 1, specific tissues and the number of tumours in the various treatment and control groups are listed only if there were at least two more tumours in the groups treated with TDI than in the controls. The author concluded, that the type and incidence of tumours and the numbers of tumour-bearing rats were similar in both control and TDI treated groups.

A statistical analysis of the results was not carried out, but the tumour spectrum in all groups was in the range of the general experience (Loeser, 1983). A full assessment of the original tumour data by both the protocolled method and more current methodology has been reported by Müller (2008). Overall, and taking into account the statistical results, contemporary control animal data from the laboratory and the tumour profiles of the animal strain used, Müller concluded that there was no toxicologically significant increase in the tumour incidences of this long-term TDI rat study.    

The overall evaluation of the study therefore led to the conclusion, that TDI is not carcinogenic in rats under the conditions described.

 

Table 1: Tumour incidences of the 2-year rat study with TDI (80/20)

TDI (ppm)	Sex	0	0.05	0.15
Number of animals investigated	M/F	104/104	104/105	104/105
Types of tumours for which there were at least 2 more tumours in the groups treated with than in the controls:
Adenomas (skin)	M	0	0	3
Papillomas (skin)	F	1	3	3
Benign tumours (mammary gland)	F	24	27	22
Carcinomas (mammary gland)	F	9	9	14
Fibromas (subcutis/muscle/bones)	M/F	29/1	22/1	35/4
Histiocytomas (subcutis/muscle/bones)	M	1	4	1
Malignant lymphomas (haematopoietic system)	F	1	1	3
Haemangiomas (haematopoietic system)	M	1	1	4
Islet cell adenomas (pancreas)	M	1	2	3
Adenomas (pituitary gland)	F	64	62	67
Meningiomas (brain)	M	0	0	2
Lipomatous tumours (kidney)	M	1	3	0

M = male; F = female

 

Conclusions:

The animals were whole body exposed to 0, 0.05 and 0.15 ppm of TDI (80/20) vapour for 6 hours/day, 5 days/week. In both species, body weight gain was reduced at 0.15 ppm over the first 12 weeks that persisted but did not worsen over the remaining period of the study. In rats, rhinitis was observed in males at 0.15 ppm and in females beginning at 0.05 ppm, generally characterized by squamous metaplasia/hyperplasia of the respiratory mucosa, with and without exudate in the lumen, and leucocyte infiltration in the lamina propria. This finding is considered to be due to local irritation of the anterior nasal cavity. In mice, histopathology revealed marked inflammatory processes in trachea, larynx, bronchi, lungs and predominantly in nasal turbinates (chronic and necrotic rhinitis) of male and female animals beginning at 0.05 ppm. Therefore, the LOAEC for rats and mice is 0.05 ppm (0.362 mg/m3) after long-term inhalation of TDI vapour.
Inhalation exposure is the most appropriate route for assessing occupational risk in humans. Effects from repeated exposure of animals to TDI are limited to effects on the respiratory tract caused by local irritation, no signs of systemic toxicity were observed.
Simultaneously, other studies show that nose is the targeted organ of the respiratory system. Thus, the assessment confirmed the legal classification of the substance as STOT Single Exp.3 (Hazard statement H335, May cause respiratory irritation).

Executive summary:

The animals were whole body exposed to 0, 0.05 and 0.15 ppm of TDI (80/20) vapour for 6 hours/day, 5 days/week. In both species, body weight gain was reduced at 0.15 ppm over the first 12 weeks that persisted but did not worsen over the remaining period of the study. In rats, rhinitis was observed in males at 0.15 ppm and in females beginning at 0.05 ppm, generally characterized by squamous metaplasia/hyperplasia of the respiratory mucosa, with and without exudate in the lumen, and leucocyte infiltration in the lamina propria. This finding is considered to be due to local irritation of the anterior nasal cavity. In mice, histopathology revealed marked inflammatory processes in trachea, larynx, bronchi, lungs and predominantly in nasal turbinates (chronic and necrotic rhinitis) of male and female animals beginning at 0.05 ppm. Therefore, the LOAEC for rats and mice is 0.05 ppm (0.362 mg/m3) after long-term inhalation of TDI vapour.

Inhalation exposure is the most appropriate route for assessing occupational risk in humans. Effects from repeated exposure of animals to TDI are limited to effects on the respiratory tract caused by local irritation, no signs of systemic toxicity were observed.

Simultaneously, other studies show that nose is the targeted organ of the respiratory system. Thus, the assessment confirmed the legal classification of the substance as STOT Single Exp.3 (Hazard statement H335, May cause respiratory irritation).

Reference 2

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

1. Source and target substances
The substances m-tolylidene diisocyanate (CAS No 26471-62-5, consisting of 80% tolylidene 2,4-
diisocyanate and 20% tolylidene 2.6-diisocyanate, hereafter referred to as TDI,source) and pphenylene
diisocyanate (CAS No 104-49-4, hereafter referred to as p-PDI, target) each consist of a
diisocyanate substituted benzene ring. The substituents on the phenyl ring are almost identical in
both cases, with the TDI being substituted in a meta-fashion with the two isocyanate groups, while
the p-PDI features the substituents in a para-fashion. Aside from this, the TDI features an additional
methyl substituent on the phenyl ring, which is absent in the p-PDI.
2. Description of the scenario
In the ECHA RAAF document 6 different read-across approaches are described in the form of
“scenarios”. The scenarios thereby categorize the type of read-across approach used to allow a
systematic assessment of the crucial scientific aspects. Each scenario comprises different
“assessment elements”, which address different scientific considerations deemed crucial to judge the
validity and the reliability of read-across.
In the present case, the read-across approach of m-tolylidene diisocyanate (TDI) and p-phenylene
diisocyanate (p-PDI) corresponds with scenario 2.
This scenario covers the analogue approach (read-across is employed between a small number of
structurally-similar substances; there is no trend or regular pattern on the properties) for which the
read-across hypothesis is based on qualitative similar properties of the compounds.

3. Read Across Hypothesis
The read-across approach should be used for data gap filling of p-phenylene diisocyanate (p-PDI)
using fate, ecotoxicitiy and human health toxicity studies of m-tolylidene diisocyanate (TDI). Based
on the similar chemical structure and the available experimental data both substances are highly
reactive diisocyanates. The chemical reactions known for the highly reactive diisocyanates (e.g. rapid
hydrolysis to the diamine in aqueous environments, polymerization reactions and reactions with
amines or hydroxyl groups in biological specimens) are reported for TDI (MAK 2003, ECHA 2013)
and can be assumed to take place also when p-PDI enters an organism. Both compounds consist of
a benzene ring and two isocyanate groups. TDI is substituted in a meta-fashion with the two
isocyanate groups, while the p-PDI features the substituents in a para-fashion. The differences in the
substitution pattern (meta versus para) do not lead to a difference in reactivity of the highly reactive
isocyanate groups.
It is reasonable to assume and experimentally verified that both compounds have nearly identical
behavior in physico-chemical and (eco)toxicological studies. Therefore there should be almost no
differentiation between effects of target and source substance.

4. Data Matrix
Please refer to Section 13.2 "Other Assessment reports" for full justification, reference "pPDI+TDI READ ACROSS JUSTIFICATION".

Reason / purpose for cross-reference:

read-across source

Key result

Dose descriptor:

NOAEC

Effect level:

0.15 ppm (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical signs

Key result

Dose descriptor:

NOAEC

Effect level:

< 0.05 ppm (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical signs

Key result

Dose descriptor:

LOAEC

Effect level:

0.15 ppm (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical signs

Key result

Dose descriptor:

LOAEC

Effect level:

0.05 ppm (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical signs

Key result

Critical effects observed:

no

Conclusions:

The read across for pPDI; is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of repeated dose toxicity.
Inhalation exposure is the most appropriate route for assessing occupational risk in humans. Effects from repeated exposure of animals to TDI are limited to effects on the respiratory tract caused by local irritation, no signs of systemic toxicity were observed.
Simultaneously, other studies show that nose is the targeted organ of the respiratory system. Thus, the assessment confirmed the legal classification of the substance as STOT Single Exp.3 (Hazard statement H335, May cause respiratory irritation).

Executive summary:

The read across for pPDI; is based upon the analogous substances to which basic form, degree of substitution of functional groups is not considered to effect the proposed read across for the endpoint of repeated dose toxicity.

Inhalation exposure is the most appropriate route for assessing occupational risk in humans. Effects from repeated exposure of animals to TDI are limited to effects on the respiratory tract caused by local irritation, no signs of systemic toxicity were observed.

Simultaneously, other studies show that nose is the targeted organ of the respiratory system. Thus, the assessment confirmed the legal classification of the substance as STOT Single Exp.3 (Hazard statement H335, May cause respiratory irritation).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

0.362 mg/m³

Study duration:

chronic

Experimental exposure time per week (hours/week):

113

Species:

rat

System:

other: chonic toxicity.

Justification for classification or non-classification

The substance has to be classified to hazard class STOT-SE3 according to CLP Regulation 1272/200.