2,4,6-triisopropyl-m-phenylene diisocyanate

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to Read-across statement in section 13

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

2,4,6-triisopropyl-m-phenylene diisocyanate

EC Number:

218-485-4

EC Name:

2,4,6-triisopropyl-m-phenylene diisocyanate

Cas Number:

2162-73-4

Molecular formula:

C17H22N2O2

IUPAC Name:

2,4-diisocyanato-1,3,5-tris(propan-2-yl)benzene

Test material form:

liquid

Results and discussion

Results: maternal animals

Effect levels (maternal animals)

1

Dose descriptor:

NOAEL

Effect level:

0.1 ppm

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEL

Effect level:

0.1 ppm

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Fetal body weight changes:

no effects observed

Description (incidence and severity):

Fetal body weight per litter (males, females, or all fetuses) was unaffected by exposure.

Reduction in number of live offspring:

effects observed, treatment-related

Description (incidence and severity):

The number of nonviable implants per litter (total, early or late resorptions, or dead fetuses) and the percent live fetuses per litter were not significantly changed by treatment.

Changes in sex ratio:

no effects observed

Description (incidence and severity):

Sex ratio (% males) per litter was unchanged by exposures.

Changes in litter size and weights:

no effects observed

External malformations:

no effects observed

Description (incidence and severity):

There were no significant differences in the incidence of any individual malformation, of malformations by category (external, visceral, or skeletal), or of total malformations. There were no significant differences in the incidence of individual external or visceral variations, of variations by category, or of total variations.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Out of 111 skeletal variations observed in the present study, six exhibited statistically significant differences in incidence in one or more toluene diisocyanate-exposed groups relative to the incidence in the control group. Only one of these, poorly ossified cervical centrum 5, exhibited an increased incidence at 0.50 ppm relative to that in controls, indicative of possible minimal fetotoxicity. This finding was observed in the absence of any other indication of developmental toxicity. The five remaining significant findings did not indicate fetotoxicity and did not appear treatment related. They included reductions in the incidence of bilobed thoracic centra 11 and 13 and wavy rib at 0.50 ppm, and reductions in the incidence of some (1– 4) proximal phalanges of the forelimb unossified and of all proximal phalanges of the hindlimb unossified at 0.02 ppm.

Visceral malformations:

no effects observed

Description (incidence and severity):

There were no significant differences in the incidence of any individual malformation, of malformations by category (external, visceral, or skeletal), or of total malformations. There were no significant differences in the incidence of individual external or visceral variations, of variations by category, or of total variations.

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

0.1 ppm (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

skeletal malformations

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Table 2: Chamber analysis
Exposure Parameters
Target Concentration, ppm	0.00	0.02	0.10	0.50
Analytical Concentration, ppm ^a	< MDL b	0.021 ±0.0018	0.12 ± 0.017	0.48 ± 0.038
A/T Ratio ^c	-	1.05	1.20	0.96
Nominal Concentration, ppm ^a	-	0.049 ± 0.0038	0.18 ± 0.017	0.67 ± 0.025
A/N Ratio ^d	-	0.44	0.67	0.72
Temperature, °C ^a	22.6 ± 0.43	23.3 ± 0.44	23.5 ± 0.33	23.9 ± 0.19
Relative Humidity, %^a	54.4 ± 0.86	50.9 ± 1.65	52.1 ± 0.98	50.1 ± 1.41
^aGrand mean of daily means ± standard deviation.
^bLess than the minimum detection limit of 1 ppb.
^cAnalytical to target concentration ratio.
^dAnalytical to nominal concentration ratio.

Table 3:  Maternal Toxicity Parameters
	TDI vapour, ppm
	0.00	0.02	0.10	0.50
No. females on study	25	25	25	25
No. females at scheduled sacrifice^a	25 (100.0)	25 (100.0)	25 (100.0)	25 (100.0)
No. (%) gravid	22 (88.0)	21 (84.0)	23 (92.0)	23 (92.0)
No. (%) fully resorbed litters	0 (0.0)	1 (4.8)	0 (0.0)	0 (0.0)
No. (%) dams with viable fetuses	22 (100.0)	20 (95.2)	23 (100.0)	23 (100.0)
Maternal Body Weight Changes
Day 0 to 6 (pre-exposure period)	36.1±8.05^b	33.3 ± 7.98	33.7 ± 8.43	40.1 ± 8.29
Day 6 to 9	12.3 ± 3.90	9.2±3.76*	9.4 ± 2.89*	1.8 ± 5.31***
Day 9 to 12	16.7 ± 4.35	16.9 ± 4.74	17.7 ± 4.95	11.3 ± 8.23*
Day 12 to 16	24.1 ± 4.88	20.8 ± 7.10	22.5 ± 6.03	15.8 ± 8.23*
Day 6 to 16 (exposure period)	53.1 ± 7.37	46.4 ± 11.66	49.5 ± 9.96	28.9 ± 17.59***
Day 16 to 21 (post exposure period)	89.1 ± 11.63	76.3 ± 18.67*	88.4 ± 13.23	95.3 ± 18.07
Day 0 to 21 (gestation)	178.3 ± 20.25	156.0 ± 32.02*	171.5 ± 18.42	164.4 ± 28.79
Maternal Feed Consumption (g/animal/day)
Day 0 to 6 (pre-exposure period)	22.91± 3.434^b	21.44 ± 2.909	22.37 ± 4.045	22.28 ± 2.129
Day 6 to 15 (exposure period)	23.10±2.524	22.69 ± 2.123	23.17 ± 2.481	19.62 ± 2.006***
Day 15 to 21 (post exposure period)	26.64 ± 2.537	25.22 ± 2.009	26.60 ± 2.801	25.48 ± 3.267
Maternal Water Consumption (g/animal/day)
Day 0 to 6 (pre-exposure period)	36.45±7.331^b	34.88 ± 8.247	38.71 ± 12.623	41.67 ± 11.249
Day 6 to 15 (exposure period)	43.71 ± 9.743	42.03 ± 9.802	42.77 ± 11.509	39.14±10.374
Day 15 to 21 (post exposure period)	51.71 ± 8.897	54.91 ± 15.653	51.80±11.350	52.39 ± 11.772
^aNo females died, aborted, delivered early, or were removed from study.
^bData are presented as mean ± SD.
*p < 0.05 compared to control.
**p < 0.01 compared to control.
***p < 0.001 compared to control.

Table 4: Maternal Organ Weights
	TDI Vapour, ppm
	0.00	0.02	0.10	0.50
No. Dams	22	217	23	23
Initial body weight (g)	223.08 ± 10.89^a	220.65 ± 10.58	222.30 ± 9.05	224.16 ± 7.97
Body weight at sacrifice (g)	401.43 ± 24.34	376.63 ± 34.45*	393.80 ± 20.77	388.53 ± 31.40
Gravid uterine weight (g)	106.68 ± 12.22	92.50 ± 28.19	101.31 ± 18.21	101.25 ± 22.40
Corrected body weight (g)^b	294.74 ± 19.25	284.14 ± 16.41	292.49 ± 15.81	287.28 ± 21.82
Corrected body weight change (g)^c	71.66 ± 14.11	63.49 ± 14.55	70.20 ± 12.43	63.12 ± 17.90
Liver weight (g)	14.35 ± 1.58	13.34 ± 2.80	14.33 ± 1.37	13.98 ± 1.53
Relative liver weight (%)^d	4.86 ± 0.39	4.70 ± 0.5	4.90 ± 0.39	4.87 ± 0.48
^aData are presented as mean ± SD.
^bCorrected body weight = body weight at sacrifice minus gravid uterine weight.
^cCorrected body weight change = corrected body weight minus initial body weight.
^dCalculated as a percentage of the corrected body weight.
*p < 0.05 compared to control.

Table 5: Gestational Parameters
	TDI Vapour, ppm
	0.00	0.02	0.10	0.50
No. dams	22	21	23	23
Corpora lutea/dam	17.4±3.8^a	17.6±5.6	17.1±3.6	16.3±2.8
Total implants/litter	15.3±1.8	13.0±3.8*	14.3±3.0	14.3±3.4
% preimplantation loss/litter^b	10.2±14.0	18.6±19.0	14.6±18.8	12.1±19.01
Viable implants/litter	14.5±1.7	12.3±4.0*	13.5±2.8	14.0±3.5
Non-viable implants/litter	0.7±0.9	0.7±1.1	0.8±1.1	0.3±0.5
Early resorptions/litter	0.6±0.7	0.6±0.9	0.7±1.0	0.3±0.5
Late resorptions/litter	0.1±0.3	0.1±0.3	0.1±0.4	0.0±0.0
Dead fetuses/litter	0.0±0.0	0.0±0.0	0.0±0.2	0.0±0.0
% live fetuses/litter	95.4±5.4	89.1±23.6	94.6±6.7	97.1±5.7
No. litters	22	20^c	23	23
Sex ratio (% male fetuses)/litter	49.8±12.6	44.4±15.6	54.6±16.1	46.2±14.1
Fetal body weights per litter (g)
All fetuses	5.21±0.21	5.37±0.25	5.37±0.30	5.22±0.37
Male fetuses	5.32±0.23	5.51±0.37	5.51±0.36	5.37±0.39
Female fetuses	5.10±0.21	5.27±0.38	5.20±0.28	5.09±0.36
^aData are presented as mean±SD.
^bPercent preimplantation loss=[(corpora lutea - total implants)/corpora lutea]*100.
^cThe N is reduced because one dam was found to be pregnant by ammonium sulfide staining of the uterus (i.e., a fully resorbed litter).
*p<0.05compared to control.

Table 6: Summarized Incidence and Frequency of Fetal Malformations and Variations
	TDI vapour, ppm
	0.00	0.02	0.10	0.50
Number examined externally^a
Fetuses	320	258	311	322
Litters	22	20	23	23
No significant malformation findings
Number examined viscerally'^b
Fetuses	164	134	162	168
Litters	22	20	23	23
No significant malformation findings
Number examined skeletally^c
Fetuses	156	124	149	154
Litters	22	20	23	23
No significant malformation findings
Significant variations
Cervical centrum no. 5 poorly ossified
No. (%) fetuses	13 (8.3)	18 (14.5)	29 (19.5)	36 (23.4)
No. (%) litters	8 (36.4)	12 (60.0)	14 (60.9)	18 (78.3)*
Wavy rib
No. (%) fetuses	45 (28.8)	27 (21.8)	16 (10.7)	11 (7.1)
No. (%) litters	11 (50.0)	9 (45.0)	8 (34.8)	4 (17.4)*
All proximal phalanges (hindlimb) unossified
No. (%) fetuses	61 (39.1)	23 (18.5)	57 (38.3)	58 (37.7)
No. (%) litters	19 (86.4)	9 (45.0)*	18 (78.3)	20 (87.0)
Summarized malformations
External
No. (%) fetuses	0 (0.0)	1 (0.4)^d	0 (0.0)	0 (0.0)
No. (%) litters	0 (0.0)	1 (5.0)	0 (0.0)	0 (0.0)
Visceral
No. (%) fetuses	7 (4.3)	7 (5.2)	9 (5.6)	8 (4.8)
No. (%) litters	5 (22.7)	5 (25.0)	6(26.1)	7 (30.4)
Skeletal
No. (%) fetuses	1 (0.7)	3 (2.4)	2(1.3)	1 (0.6)
No. (%) litters	1 (4.5)	3 (15.0)	2 (8.7)	1 (4.3)
Total malformations
No. (%) fetuses	8 (2.5)	10 (3.9)	11 (3.5)	9 (2.8)
No. (%) litters	6 (27.3)	7 (35.0)	8 (34.8)	8 (34.8)
Summarized variations
External
No. (%) fetuses	16 (5.0)	10 (3.9)	9 (2.9)	12 (3.7)
No. (%) litters	13 (59.1)	7 (35.0)	7 (30.4)	10 (43.5)
Visceral
No. (%) fetuses	106 (64.6)	93 (69.4)	99 (61.1)	86 (51.2)
No. (%) litters	20 (90.9)	20 (100.0)	22 (95.7)	22 (95.7)
Skeletal
No. (%) fetuses	156 (100.0)	124 (100.0)	149 (100.0)	154 (100.0)
No. (%) litters	22 (100.0)	20 (100.0)	23 (100.0)	23 (100.0)
Total variations
No. (%) fetuses	265 (82.8)	220 (85.3)	249 (80.1)	243 (75.5)
No. (%) litters	22 (100.0)	20 (100.0)	23 (100.0)	23 (100.0)
Note: A single fetus may be represented more than once in listing individual defects. Only live fetuses were examined.
^aAll fetuses were examined externally.
^bApproximately 50% of each litter were examined viscerally (Staples, 1974) and for soft tissue craniofacial defects (Wilson, 1965; van Julsingha and Bennett, 1977).
^cApproximately 50% of each litter were examined for skeletal defects after staining with alizarin red S.
^dOne fetus (in one litter) at 0.02 ppm exhibited multiple malformations and variations; all four of the external malformations observed (unilateral anophthalmia, cleft palate, unilateral microtia, parasitic twin on ventrum), and 11 of the 24 visceral malformations observed (it was not randomly selected for skeletal examination).
*p< 0.05 compared to control.

Applicant's summary and conclusion

Conclusions:

The study on toluene diisocyanate was performed according to EPA OTS 789.4350 (Inhalation Developmental Toxicity Screen), it is considered to be of high quality (reliability Klimisch 2). The criteria of validity of the test system are fulfilled. There was only one possible indication of minor fetotoxicity at 0.50 ppm with no other indications of developmental toxicity.The NOAEL for maternal and developmental toxicity was 0.1 ppm in this study. No embrytoxicity or teratogenicity was observed at any exposure concentrations employed.

Executive summary:

The developmental toxicity of toluene diisocyanate was investigated in Sprague Dawley rats according to EPA OTS 798.4350 (Inhalation Developmental Toxicity Screen) (Tyl, 1999). The test substance was administered to mated female rats via inhalation (0, 0.02, 0.1 or 0.5 ppm, 6 h/day, from gestation day 6 to 15). Maternal clinical signs, body weights, and feed and water consumption were recorded throughout gestation. At termination (gd 21), maternal body, gravid uterine, and liver weights were recorded. Corpora lutea were counted, and implantation sites were identified. In addition resorptions and dead and live fetuses were recorded. All live fetuses were examined for external alterations. One-half of the live fetuses/litter were examined for visceral (including craniofacial) alterations. The remaining intact fetuses/litter were stained with alizarin red S and examined for ossified skeletal alterations. The most plausible and appropriate interpretation of the initial, brief, minor, and transient decrements in weight gain at 0.02 and 0.10 ppm is that they were due to initial responses of the dams as they acclimated to exposure of an irritating vapour rather than to toxicity per se. There were also significant reductions at 0.02 ppm in maternal weight gain for gd 16–21 (p < 0.05; postexposure period), therefore, for gd 0–21 (p < 0.05, gestational period) and for body weight at sacrifice (p < 0.05; not observed at 0.10 or 0.50 ppm), accompanied by significant reductions in total implants per litter and in viable implants per litter (both p < 0.05) at 0.02 ppm. These effects at 0.02 ppm were due, at least partially, to the presence of a fully resorbed litter with one implant only in this group (the dam and her data were included in the summary tables because she was pregnant). When her data are deleted from the individual data and the revised data statistically compared to the control group values for gd 21 terminal body weight and viable implants per litter, the differences were still statistically significant but less so. It is unlikely that this cluster of interrelated effects is due to exposure to TDI for the following reasons: (1) none of the effects were observed at higher concentrations so it is not dose related; (2) the major effect, reduced body weight gain for gd 16–21, occurred after exposures were over (they ended on gd 15); (3) this last trimester is during the time of rapid fetal growth and weight gain, and so the reduced maternal weight gain was most likely due to the reduced number of fetuses per litter in this group (i.e., the fetuses grew normally but were fewer in number); and (4) the reduction in maternal weight gain for gd 16–21 for 0.02 ppm was enough to affect the gestational weight gain (gd 0–21) for maternal body weight on gd 21 but did not affect maternal weight gain during the exposure period (gd 6–16). The cause of the smaller litters at 0.02 ppm is most likely due to biologic variation, with the viable litter size (12.9) slightly below the current historical control values of 13.30 –16.24 live fetuses per litter. The maternal toxicity at 0.50 ppm consisted of reduced body weights, body weight gains, feed consumption, and clinical signs of toxicity. Water consumption was unaffected. Gestational parameters exhibited no significant treatment-related changes, including pre- and postimplantation loss, sex ratio/litter, or fetal body weights/litter. Incidences of individual malformations, malformations by category (external, visceral, and skeletal), total malformations, individual external and visceral variations, variations by category, and total variations were unaffected. Of 111 skeletal variants observed, only 1, incidence of poorly ossified cervical centrum 5, was increased at 0.50 ppm, indicating possible minimal fetotoxicity, although it occurred in the absence of any other indications of developmental toxicity. Therefore, exposure to TDI vapor by inhalation, during major organogenesis in CD rats, resulted in maternal toxicity and minimal fetotoxicity at 0.50 ppm. No treatment-related embryotoxicity or teratogenicity was observed. The A/D ratio (Fabro et al., 1982), the ratio of the lowest doses resulting in adult and developmental toxicity, is at most 1.0, indicating no preferential susceptibility to the conceptus.

This study confirmed effects of TDI on the maternal respiratory tract, with concomitant reductions in maternal body weight, weight gain, and feed consumption at 0.50 ppm. There was only one indication of possible minor fetotoxicity at 0.50 ppm (increased incidence of reduced ossification in cervical centrum no. 5), with no other indications of developmental toxicity. There was no evidence of maternal or developmental toxicity at 0.02 or 0.10 ppm, and no evidence of embryotoxicity or teratogenicity at any exposure concentration evaluated. The present study has shown that exposure to toluene diisocyanate vapour by inhalation during major organogenesis in CD (Sprague-Dawley) rats results in maternal toxicity and minimal indication of fetotoxicity at 0.50 ppm. The no observable adverse effect level (NOAEL) for maternal and developmental toxicity was 0.10 ppm in this study. No embryotoxicity or teratogenicity was observed at any exposure concentrations employed.