Hexamethylenediamine

Endpoint summary

Description of key information

The NOAEC/inhalation for rat = 10 mg/m3/day for upper respiratory tract local damage (larynx and nose), (kr: 2, OECD 413, NTP, 1993).
The NOAEL/oral for rabbits = 25 mg/kg bw/day (kr:1, prenatal developmental toxicity study, OECD 414, CiToxLab, 2017 )

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

25 mg/kg bw/day

Study duration:

subacute

Species:

rabbit

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

10 mg/m³

Study duration:

subchronic

Species:

rat

Additional information

Inhalation and dermal exposure were the most appropriate route for assessing occupational risk in the workers. Inhalation and oral exposure were the most appropriate route for assessing risk for humans exposed via the environment. The effects from repeated exposure of animals to HMD are limited to the upper respiratory tract (larynx and nasal passages) caused by important local irritation.

- No repeated toxicity study conducted by dermal route was available. However, the waiving is justified considering animal welfare since HMD is classified as corrosive (C, R34) and in category 1B in the Annex VI of the CLP regulation (1272/2008).

- Three subchronic (90-day exposure) studies performed by inhalation route were available for HMD.

The "13-week inhalation study in rat" conducted by Hébert (1993) was identified as the key study.

In this study, groups of Fischer 344/N rats (5/sex) were whole-body exposed to 0, 1.6, 5, 16, 50 and 160 mg HDDC/m³ for 6 hours plus T90/day, 5 days/week, corresponding to 0, 1.0, 3.1, 10, 31 and 100 mg /m³ of HMD aerosol using the molecular mass (189.2 g/mol). No mortality was observed, no clinical sign specific to HMD exposure was noted, no treatment related change in body weight, organ weight and clinical chemistry parameters were recorded. Histopathological examination revealed changes in the nasal cavity and larynx. The nasal lesions were considered moderate in the 100 mg/m³ group and mild at 31 mg HMD /m³ exposure.

Sperm morphology and vaginal cytology examinations did not reveal any compound-related abnormalities.

The NOAEC for these local histopathological changes was 10 mg HMD/m³ based on the changes both in the nose and in the larynx in males and females.

In the same NTP studies (Hébert, 1993), mice were exposed to HMD under similar conditions as the study in the rat, i.e. 0, 1.6, 5, 16, 50 and 160 mg HDDC/m3 for 6 hours/day, 5 days/week for 13 weeks, corresponding to 0, 1.0, 3.1, 10, 31 and 100 mg HMD /m3 6 hours/day, 5 days/week. This study is considered as supporting evidence (Kr: 2) because hematological and clinical chemistry examinations were not performed while the local effects of HMD exposure were observed. Hence, the NOAEC for respiratory local damage was 10 mg/m³ for both sexes even if the mice appeared to be more sensitive to the irritant properties of HMD than the rat. The severity of lesions, however, was similar in both species.

The study of Ben-Dyke, 1981 is considered as a supporting study (Kr:2). Four groups of CD rats (15/sex) were exposed to aqueous HMD aerosols for 6h/day, 5 days/week for 13 weeks at 0, 12.8, 51 and 215 mg/m3. The rate of mortality was higher at the highest concentration of exposure, therefore this group was terminated during the seventh week of the study. Signs of respiratory and conjunctival irritation were noted in the rats exposed at the two highest concentrations. A significant reduction in body weight gain and a slight hemopoietic stimulation of peripheral blood parameters were observed in both sexes at 215 mg/m³.

Treatment-related microscopic lesions (inflammation and squamous metaplasia) were noted only in rats exposed to 215 mg/m³ HMD and were confined to the trachea, nasal passages, and lungs. These lesions were generally more severe than those observed in the NTP study (see above). Exposure-related local irritation effects without corresponding pathological changes were also observed at 51 mg/m3. An exposure level of 12.8 mg/m³ HMD was considered without local adverse effect . Therefore the NOAEC was considered to be 12.8 mg/m³ of HMD.

In summary, the toxicity of HMD in rats and mice exposed by inhalation resulted from the irritant properties of the chemical. This toxicity was limited to the upper respiratory system. In the 13-week studies, the lowest NOAEC for respiratory local damage was 10 mg/m³ for rats and considered as a worst case.

- The prenatal developmental toxicity study in rabbits (CiToxLab 2017) was considered as key study for repeated dose toxicity by the oral route:

High toxicity (including mortality) was observed in dams of an OECD 414 prenatal developmental toxicity study in rabbits (see CiToxLab 2017) at 50 mg/kg bw/day (NOAEL for maternal toxicity: 25 mg/kg bw/day). In a mechanistic study (see repeated dose toxicity CiToxLab 2018) it was investigated whether use of PBS buffer had an influence on the toxicity observed in dams in this prenatal developmental toxicity in rabbits (CiToxLab 2017). With non-pregnant female rabbits receiving 75, 100, or 150 mg/kg bw/day by gavage for 7 days high toxicity (including mortality) was observed at the highest dose. Signs of (limited) toxicity in the lower doses were minimal histopathological changes in the GIT and urinary tract and haematuria. No marked difference was seen between using water or PBS buffer as vehicle. Urinary tract changes seem to be more likely linked to the high toxicity seen at the highest dose.

Further, in a subacute oral study (NTP dose-range finding study) (Hébert et al. 1993), male and female F344/N rats were exposed for 2 weeks to 1,6 -hexanediamine dihydrochloride (HDDC) in drinking water. Under the test conditions, no effects were observed at HDDC doses tested up to the highest dose (545 mg/kg b.w./d for males and 634 mg/kg b.w./d for females) corresponding to 335 mg HMD/kg bw/day in males and 390 mg HMD/kg bw/day in females. In the same NTP study (Hébert, 1993), B6C3F1 mice were exposed similarly to HDDC. Under the test conditions, no effects were observed at HDDC doses tested up to the highest dose (564 mg/kg b.w./d for males and 632 mg/kg b.w./d for females) corresponding to 347 mg HDA/kg bw/day in males and 388 mg HDA/kg bw/day in females. As a worst case the value of 335 mg/kg bw/day in the rats was used as the NOAEL for systemic and local effects.

Repeated dose toxicity: inhalation - (target organ) respiratory: larynx; respiratory: nose

Justification for classification or non-classification

For repeated toxicity by all routes, HMD is not classified in the Annex VI of the CLP Regulation (EC 1272/2008):

- Based on the results of the key and supporting studies the toxicity of HMD by inhalation was limited to upper respiratory tract irritation (nose/nasal passages and larynx) and the NOAEC/inhalation/rat and mice = 10 mg/m³. Therefore, no classification is required according to CLP Regulation (EC 1272/2008).

However, considering both the corrosive properties of HMD and the upper respiratory tract irritation (as specific non lethal target organ) in the absence of more severe organ effects including respiratory system observed in different species, HMD is classified as Category 3 for respiratory tract irritation - single exposure (irritation is driven mainly by concentration than by time of exposure): STOT SE3.

- Absence of toxicity of HMD by the oral route was observed up to approximately 390 mg/kg bw/d administered in drinking water to rats and mice after subacute exposure (2 weeks). Therefore, no classification is required according to CLP regulation (1272/2008). No clear mode of action could be identified for severe signs of toxicity in female rabbits in an OECD 414 study at 50 mg/kg bw/day (NOAEL: 25 mg/kg bw/day). When compared to the studies with dietary administration or via drinking water, gavage administration seems to lead to more pronounced toxicity. A special high susceptibility of rabbits also cannot be excluded.

- Based on the corrosive properties of HMD and its classification Skin Corrosive 1B, repeated dose toxicity study by dermal route is waived . Therefore, no classification is required according to CLP Regulation (EC 1272/2008).