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Key value for chemical safety assessment

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Since no toxicokinetic studies are available for 2-imidazolidone the following assessment is based on the available physicochemical properties and results from other toxicological studies.

 

The substance is a white/yellowish solid with faint specific odour and with a molecular weight of 86.0925 g/mol. The calculated log Pow value is -1.16 at 25 °C and the calculated solubility in water is 596 g/L at 20°C. High water solubility and low molecular weight (< 200 g/mol) suggest that the substance may readily dissolve into the gastrointestinal fluids. In case of low molecular weight substances (MW < 200 g/mol) the substance may also pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water. It is thus expected that the substance will be readily absorbed by gastrointestinal tract.

No experimental data is available concerning the respiratory hazard of 2-imidazolidone. Generally, water-soluble dusts would readily diffuse/dissolve into the mucus lining of the respiratory tract. Very hydrophilic substances may be absorbed through aqueous pores (for substances with molecular weights below around 200 g/mol) or be retained in the mucus and transported out of the respiratory tract. Overall it is therefore expected that the substance will be readily absorbed by inhalation.

According to Chapter R.8 of REACH Guidance on information requirements and chemical safety assessment, it is proposed in the absence of route-specific information on the starting route, to include a default factor of 2 in the case of oral-to-inhalation extrapolation. This approach will be taken forward to DNEL derivation.

The low log Pow (< -1) value and the high water solubility (> 10000 mg/L) suggest that the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum. Dermal uptake for these substances will be very low. This is supported by the estimated Kp value of 0.000167 cm/h using the Danish (Q)SAR Database (EPI Suite, DERMWIN V 2.01) indicative for a very low dermal penetration potential according to DK-EPA heuristics (User Manual for the Internet Version of the Danish (Q)SAR Database, Database Version 1, May 2005). In the available acute dermal study no effects were observed (Bioassay, 2012). In the absence of route-specific information and based on the available information a ratio of 0.1 for oral to dermal absorption is provisionally suggested for the risk assessment of the substance, based on its physico-chemical properties and (Q)SAR estimation.

In the key studies concerning repeated dose toxicity (BASF, 88R0054/08C017, 2013; BASF, 50C0054/08S034, 2018), target organ was the thyroid gland. The results of these studies provide evidence concerning distribution of the substance or metabolites thereof.

The results from several in vitro genotoxity studies with and without metabolic activation suggest that no genotoxic metabolite was formed after the addition of rat liver S9 mix. Furthermore, the results of an in vitro study indicate that under physiological conditions reactive metabolites from 2-imidazolidone generated by either flavin-containing monooxygenase (FMO) or cytochrom P-450 are preferentially trapped by endogenous GSH and do not interact with cellular targets (Decker et al., 1991).

No studies are available for the bioaccumulation assessment of the substance. However, based on the low log Pow of -1.18 accumulation of the substance in organisms is not to be expected.