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Description of key information

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. The oral and dermal route of exposure are not relevant for assessment

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
LOAEC
0.362 mg/m³

Additional information

Since no data on repeated dose toxicity are available for TDI Biuret, such data have been 'read across' from TDI (justification of read-across see below).

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.

 

The most relevant evaluation of repeated dose toxicity comes from a 2-year chronic toxicity and carcinogenicity study with TDI in rats and mice (Owen, 1980 + 1986; Loeser, 1983). 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.

 

The findings of the key study were supported by subchronic studies in various strains and species (Henck, 1976). 30-day whole body exposure of SD- and Fischer-rats, hamsters and mice to vapors of 0.1 and 0.3 ppm resulted in repiratory irritation (LOAEL 0.1 ppm) but no signs of systemic toxicity.

Justification of read-across from supporting substance (2,4-/2,6-TDI to TDI Biuret)

The 80:20 mixture of 2,4-/2,6-TDI (CAS No. 26471-62-5) is the monomeric component of the oligomeric TDI Biuret. The examination of the material balance of Desmodur VP.PU 60WF14 (TDI Biuret) yielded amounts of 42 % 2,4-TDI, 13.7 % 2,6-TDI and ca. 44 % TDI Biuret (Currenta, 2009). Thus, TDI Biuret contains ca. 56 % of a 80:20 mixture of 2,4-/2,6-TDI.

 

With regard to the toxicological comparability of TDI Biuret and 2,4-/2,6-TDI acute inhalation toxicity studies in rats revealed 4-hour LC50 values (aerosol) of 112 mg/m3 for TDI Biuret (based on sum of TDI isomers) and 107 mg/m3 for 2,4-/2,6-TDI (Folkerts, 2010). All qualitative cornerstones of TDI-induced respiratory tract injury were essentially identical. This included the typical delayed-onset mortality, likely as a result of a bronchiolitis obliterans. Of note is the over-proportional presence of TDI vapor relative to the TDI Biuret after inhalation exposure. This is consistent with the higher vapor pressure of TDI. In summary, the similarities of LC50s in the presence of TDI Biuret up to analytically verified breathing zone concentrations of 112 mg TDI Biuret/m3 demonstrates that the inhalation toxicity of TDI per se isnot affected to any appreciable extent by the presence of TDI Biuret aerosol. This means, modulating factors due to physicochemical interactions (partitioning of the vapor phase with the liquid aerosol phase) were not apparent as this would have lead to a more immediate onset of mortality (immediate acute lung edema rather that delayed bronchiolitis obliterans). Overall, these data demonstrate that the acute inhalation toxicity of TDI Biuret is negligible relative to TDI and any dependence of acute hazards on specific use patterns (vapor vs. aerosol) cannot be envisaged(expert opinion of Prof. J. Pauluhn: Desmodur VP.PU 60 WF14 (TDI Biuret): Comparison of acute inhalation toxicities of TDI Biuret and TDI, dated Sep. 3, 2010; complete expert opinion attached in IUCLID chapter 7 “Endpoint summary: Toxicological information”).

In addition, the toxicity profiles of TDI Biuret and 2,4-/2,6-TDI also show a high degree of consistency regarding the endpoints acute oral toxicity, skin irritation, eye irritation, skin sensitization and genotoxicity in vitro.

Therefore, based on all available data the test results obtained for 2,4-/2,6-TDI can be transferred to TDI Biuret and based on such a read-across further testing of TDI Biuret is not required. This approach is in accordance with Annex XI, section 1.5 of the REACH Regulation (EC) No 1907/2006.

Justification for classification or non-classification

According to CLP Regulation (EC) No 1272/2008 the classification of 2,4-/2,6-TDI (CAS No 26471-62-5) was considered for the classification of TDI Biuret since TDI Biuret contains >= 50 % of 2,4-/2,6-TDI.

 

Repeated dose toxicity

2,4-/2,6-TDI is not classified under Annex I of Directive 67/548/EEC. According to Annex I of CLP Regulation (EC) No 1272/2008 no classification is required for repeated dose toxicity.