HDI oligomers, allophanate

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.5 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Dose descriptor:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

DNEL extrapolated from long term DNEL

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Most sensitive endpoint:

sensitisation (skin)

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Most sensitive endpoint:

sensitisation (skin)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

no hazard identified

Additional information - workers

For delineating occupational exposure limits a read across to a substance with a similar composition (HDI oligomerisation product, isocyanurate type, EC 931-274-8, CAS 28182 -81 -2) is applied. The read across is based on physicochemical and toxicological similarity of the two substances. Especially a recently conducted comparative pulmonary irritant potency study based on the recommendations of TRGS 430 (Technical Rule for Hazardous Substances 430; published by the German Federal Ministry of Labour and Social Affairs, last update 2009) confirmed for HDI oligomerisation product, allophanate-type the same toxicological mode of action (irritant portal of entry toxicity) with a similar potency (NOAECs: 3.4 mg/m³ for HDI oligomerisation product, allophanate-type versus 3.3 mg/m³ for HDI oligomerisation product, isocyanurate type). For further justification of the grouping and read-across according to regulation (EC) No 1907/2006, Annex XI, 1.5 see document attached to chapter "Assessment Reports".

 

The most relevant route for assessing risk in humans is via inhalation for HDI oligomerisation product, allophanate-type and also for the read-across substance HDI oligomerisation product, isocyanurate type. In rats effects from repeated aerosol exposure to the read-across substance caused by local irritation are limited to the respiratory tract (report nos 22725, 16070, and 13504, Bayer AG, 1993, 1987 and 1985, respectively). No indications of systemic toxicity were found in these subacute and subchronic inhalation studies. It was shown, that if a non-irritant threshold concentration is not exceeded, neither functional nor morphological indications of damage to the respiratory tract are observed.

For workers in industrial settings, which are exposed via inhalation, DNELs for local effects for acute and long-term inhalation exposure have to be derived. In addition, sensitisation after skin contact has to be assessed.

According to Guidance Document R.8 (ECHA, 2012) a national occupational exposure limit (OEL) could be used as a surrogate for a DNEL. The German Federal Ministry of Labour and Social Affairs (Bundesministerium für Arbeit und Soziales, BMAS) published the Technical Rule for Hazardous Substances 430 (TRGS 430, last updated in 2009) for regulating the workplace exposure of isocyanates. ”This technical rule describes procedures for the assessment and surveillance of workplaces involved in the handling and use of polyurethanes and requires the assessment of isocyanates present either in the form of vapour, aerosol or both” (Pauluhn, J. Appl. Toxicol. 24, 2004, 231-247). In contrast to commonly employed workplace standards that focus solely on monomeric (di)isocyanates, the common unifying concept of TRGS 430 is to consider separate hazard assessment for monomeric and polymeric isocyanates, present as vapour and/or aerosol.

The surrogate now used as DNEL for the HDI oligomerisation product, isocyanurate or allophanate-type is the exposure assessment value (Expositionsbeurteilungswert, EBW). The EBW is either derived from the acute pulmonary irritant threshold concentration using a benchmark extrapolation of the concentration dependence of protein in bronchoalveolar lavage fluid of an 1 x 6 hours inhalation study (study recommended in TRGS 430) or, alternatively, if available, from the NOAEC of a subchronic (13-week) inhalation study according to OECD 413 or OPPTS 870.3465. The approach suggested by TRGS 430 is inherently conservative, as a comparison of the irritant threshold concentration to the NOAEC from repeated inhalation studies shows (Pauluhn, J. Appl. Toxicol. 24, 2004, 231-247).

If the irritant threshold concentration/NOAEC of the polymeric diisocyante from either of the two studies is ≤10 * AGW (Arbeitsplatzgrenzwert = German national OEL) of the monomeric diisocyanate then EBW = AGW, if the threshold concentration is >10 * AGW then EBW = 10 * AGW.

For the monomeric hexamethylen-1,6-diisocyante (HDI) the AGW is 0.035 mg/m³.
Since for HDI oligomerisation product, allophanate-type pulmonary irritant threshold concentration (3.4 mg/m³, report AT06679, Bayer AG, 2014) is > 10 * AGW the EBW = 10 * AGW. The data for the read-across substance support this, as for HDI oligomerisation product, isocyanurate type both the pulmonary irritant threshold concentration as well as the derived no observed adverse effect concentration of the subchronic study are > 10 * AGW (3 mg/m³, report AT03922, Bayer AG, 2007, and 3.3 mg/m³, report 16070, Bayer AG, 1987, respectively).

According to TRGS 430 there is even an option to set the EBW > 10 * AGW. This was done for HDI oligomerisation product, allophanate-type and also for its read-across substance HDI oligomerisation product, isocyanurate type taking into account that there were data from the read-across substance on pulmonary irritation as well as on repeated (e.g. subchronic) inhalation exposure available, which clearly show that the respiratory damage is linked to the inhaled irritating concentration, and does not exacerbate during repeated exposure (Pauluhn, Inhal. Toxicol., 13, 2001, 513-532 and 14, 2002, 287-301).

Therefore the EBW = DNEL_{long-term local effects} for inhalation is set to 0.5 mg/m³.

This is in line with a published proposed TLV-TWA of 0.5 mg/m³ for HDI-derived polyisocyanates (Pauluhn and Mohr, Inhal. Toxicol., 13, 2001, 513-532). The value is further in the same order of magnitude compared to a DNEL delineated according to Guidance Document R.8 (ECHA, Nov. 2012).

AGWs are based on 8-hour time weighted average exposure. According to the German rule for OELs (Technical Rule for Hazardous Substances 900, German Federal ministry of Labour and Social Affairs, 2006/2013) an exposure limit for short-term ceiling concentrations could be established by multiplication to an exceeding factor (Überschreitungsfaktor), which is set per default 1 (could be adjusted to max. 8). Pauluhn and Mohr proposed a maximum concentration limit of 1.0 mg/m³ (exceeding factor 2) for HDI-derived polyisocyanates. This value was used as surrogate DNEL_{acute local effects} for inhalation for HDI oligomerisation product, allophanate-type, and the read-across substance HDI oligomerisation product, isocyanurate type. This procedure is in accordance to Guidance Document R.8 (ECHA, Nov. 2012), Appendix R. 8-8, Box 6.

 

For skin sensitization no DNEL is calculated as the relationsship between skin dose and response is not clear. Furthermore, there is no validated method of DNEL calculation for skin sensitizers, therefore a quantitative risk assessment for this endpoint is not possible and a qualitative risk assessment is applied. As the substance is classified with R43/Cat. 1 for skin sensitisation (without sub-categorisation), it has to be allocated to the high hazard category (Guidance Document - Part E: Risk characterization, ECHA, Nov. 2012). Consequently, the respective risk management measures (RMMs) at the workplaces have to be considered for risk assessment.

The DNEL acute/long-term for inhalation for workers covers also reproductive toxicity, as the local effects at the respiratory tract are the most sensitive effects.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

no hazard identified