A mixture of: N,N-diethylpropane-1,3-diamine 6-methyl-2-(4-(2,4,6-triaminopyrimidin-5-ylazo)phenyl)benzothiazole-7-sulfonate; 2,2-iminodiethanol 6-methyl-2-(4-(2,4,6-triaminopyrimidin-5-ylazo)phenyl)benzothiazole-7-sulfonate; 2-methylaminoethanol 6-methyl-2-(4-(2,4,6-triaminopyrimidin-5-ylazo)phenyl)benzothiazole-7-sulfonate

Endpoint summary

Additional information

Direct Yellow 166 is an orange powder with a density of 1.38 g/cm³at 23 °C, which decomposes before melting. The molecular weight is about 767 g/mol. The vapour pressure is <0.0019 Pa at 25°C (extrapolated), the substance is soluble in water, and the log Pow is 0.19 at 25 °C (pH 9.1).

Referring to acute toxicity, guideline studies are available for the oral and the dermal route of exposure; the LD50 for oral and dermal toxicity was > 5000 mg/kg bw and > 2000 mg/kg bw, respectively. In both cases, neither mortality nor clinical symptoms could be evidenced. Particulary the acute dermal toxicity study provides evidence that no significant dermal absorption of Direct Yellow 166 has to be expected.

No study is available for inhalation toxicity, however, it could be demonstrated that the conduct of such a study is scientifically unjustified, since (1) the determination of the vapour pressure for Direct Yellow 166 as liquid or in an amorphous form had revealed that percentage of compound volatiles is about 6% at 25 to 100 °C, and (2) particle size distribution analysis had resulted in a mass median diameter (MMD) of 23.4 µm, with 7.2% of particles having a diameter < 4 µm; therefore, the majority of generated particles will not penetrate into the broncho-alveolar tract. Thus, due to these physicochemical characteristics and taking into account the low acute toxic potential of the substance as shown by the oral and dermal studies, the conduct of an acute inhalation study was judged not necessary, also with respect to animal welfare.

With regard to long-term exposure, a subacute oral 28-day toxicity guideline study with Wistar rats of both sexes, was conducted. The substance was administered by gavage at dose levels of 0, 50 (low dose), 200 (mid dose) and 1000 mg/kg bw/day (high dose). In the control and the high dose groups, the rats were assigned to toxicity and recovery testing subgroups. No mortality occurred. Orange discoloured feces seen in all high dose animals during the test period and during the first 3 days of recovery implies that the substance is excreted via feces. The discolouration was considered to be due to the staining properties of the substance, and discoloured feces also were described within an OECD 421 reproduction and developmental toxicity screening test conducted with the same substance. In the 28 days repeated dose study, reversible changes in haematological data reflecting slight anaemia as well as changes in some clinical chemical parameters indicative of stress induced metabolic adaptation due to the treatment clearly indicate that the test substance was systemically available in the animals.

Thus, taken together, the physico-chemical properties of the substance and the available toxicological data provide evidence that no significant dermal absorption of Direct Yellow 166 has to be expected, and that, when systemically bioavailable, the substance would most likely be subjected to metabolism in the liver, and excretion, mainly via feces and urine. Bioaccumulation seems to be rather improbable.