1,3-bis(1-isocyanato-1-methylethyl)benzene

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

100

Absorption rate - inhalation (%):

100

Additional information

m-TMXDI is principally used to produce polyurethane (pre-polymer) dispersions that are later processed into a wide range of products. Since m-TMXDI is not sold directly to the consumer market, the general population will not be exposed, either directly or indirectly via the environment (m-TMXDI also has minor applications in the laboratory for analytical, QC or development activities. Typical quantities are small and the substance is handled only by technically qualified individuals in a laboratory hood so that risk of exposure is minimal). Exposure to m-TMXDI therefore occurs mainly in the industrial setting. Section 9 of the Chemical Safety Report details the lifecycle of m-TMXDI and indicates potential exposure routes for workers. Since m-TMXDI is used in liquid form, dermal or eye exposure may occur as a result of spills or splashes during transport, processing and handling. Because of its low vapour pressure, exposure via inhalation is expected to be minimal under ambient conditions but could occur in situations where the material volatilises during use or handling (e.g. spraying or exposure to elevated temperatures/pressures).

There is no published information on the toxicokinetics of m-TMXDI. However, indications on its likely absorption, distribution, metabolism and elimination after dermal or inhalation exposure can be derived from its structure and physico-chemical properties.

In the presence of water, m-TMXDI has been shown to hydrolyse and form a urea and/or polyurea, as well as potentially tetramethyl-m-xylylene diamine under specific conditions. Regardless of the exposure route, it is therefore possible that both the parent compound and its hydrolysis products are present in the organism.

m-TMXDI and the corresponding urea have low water solubility (<1 mg/L) and an estimated log Pow ≥4, suggesting that, despite their molecular weights ≤500, transfer into the epidermis from the stratum corneum of skin and direct uptake across the respiratory tract by passive diffusion would be limited (see Section R.7.12.2.1 of REACH Guidance R7.C). Inhalatory absorption via micellar solubilisation could nevertheless occur. Tetramethyl-m-xylylene diamine, on the other hand, has an estimated log Pow of 1.89, which suggests a higher direct absorption potential through both routes.

Once absorbed, neither m-TMXDI nor the hydrolysis products are expected to bioaccumulate significantly, based on the results of the fish bioconcentration study which yielded a BCF below 10. Other polyisocyanates such as MDI or TDI have been shown to conjugate with albumin in the circulatory system, with excretion via urine occurring within a few hours. Depending on exposure, a pool of isocyanate-conjugated albumin may persist in the circulatory system and reach a steady-state (Wisniewski et al., 2006).

As no specific information is available, the default oral, dermal and inhalation absorption values of 50, 100 and 100%, respectively, are considered for risk assessment purposes

References

Wisniewski AV, Redlich CA, Mapp CE and Bernstein DL (2006). Polyisocyanates and their pre-polymers. In: Asthma in the workplace, 3^rded. Bernstein et al. (eds). Taylor and, F rancis, NY: pp 486.