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EC number: 269-052-1
CAS number: 68186-90-3
This substance is identified in the Colour Index by Colour Index Constitution Number, C.I. 77310.
Most pigments behave like inert
dusts and thus oral, dermal and inhalative adsorption can be
considered as not very likely. This is also supported by the low water
solubility and the results of the leaching studies. The heavy metal
oxides are absorbed by the spinel lattice and thus lose their
chemical, physical, and physiological properties. If the substance is
inhaled, it will be cleared without being absorbed due to the
effective clearance capacity of the lung. Based on the low water
solubility and the results from the comprehensive toxicity testing, it
is unlikely that the test substance become systemically available. If
any, there might be only a very small proportion available for
metabolization and biotransformation. The practically insoluble
pigment is most likely be excreted via faeces. Bioaccumulation is
unlikely due to the neglible bioavailability of the test substance.
General background and toxicological
C.I. Pigment Brown 24 is a complex inorganic coloured pigment based
on titanium dioxide with the molecular formula (Ti, Cr, Sb) O2. In the
rutile lattice, titanium ions are partially replaced by chromium (III)
and antimony (V) ions. The substance has a very low water solubility of
<1 ug/l (loading 100mg/l, 28d, pH 8.5).
Toxicokinetic analysis of C.I. Pigment Brown 24
C.I Pigment Brown 24 is a yellow-orange powder at room temperature
with a molecular weight of 90.67 g/mol, a density 4-5 g/cm³ and a
melting point >1000 °C. The substance has a very low water solubility of
Following oral administration, the likelihood of systemic absorption
through the walls of the intestinal tract depends on several
physicochemical substance properties. Generally, the smaller the
molecule the more easily it may be absorbed through the walls of the
gastrointestinal tract. As the molecular weight of C.I. Pigment Brown 24
is 90.67 g/mol, an uptake of the compound into the systemic circulation
via the gastro-intestinal (GI) tract is likely (ECHA 2014). But C.I.
Pigment Brown 24 has a very low water solubility of <1 ug/L and
therefore, the pigment can be regarded as not bioavailable.
With regard to the toxicological data, no signs of systemic toxicity
were observed in the three acute oral toxicity studies (BASF 1978, Bayer
1972, Ishihara Sangyo Kaisha 1985) as well as in the repeated-dose study
(Bomhard et al. 1982). Administered to rats via gavage in the acute oral
toxicity studies, C.I. Pigment Brown 24 led to LD50 values of greater
than 5000 mg/kg bw and 10000 mg/kg bw, without any clinical signs or
mortality. Furthermore, the results of a long-term toxicity studies in
rats (90d: NOAEL = 500 mg/kg bw/d in male and female) confirmed the
results of the in vitro leaching studies that organ translocation of
ions from the crystal lattice could not be demonstrated.
Since no inhalation data are available for the test substance,
read-across with the rutile pigment C.I. Pigment Yellow 53 (Nickel
antimony titanate yellow) was performed. The available inhalation data
show that absorption via the inhalation route is not to be expected for
C.I. Pigment Yellow 53. In a subacute inhalation study, male Wistar rats
were exposed for 5 days to 60 mg/m³ of C.I. Pigment Yellow 53. The
observation period was 0, 3, 10, 31 and 60 d (BASF 1994). Nickel and
antimony levels in the lung declined following first-order kinetics with
a clearance of 50 d. In liver and kidneys, antimony and nickel were
present in the range of the limit of quantification or below. In
conclusion, study results indicate a negligible bioavailability of Ni
and Sb after inhalation of the test substance.
The dermal exposure pathway is assessed as not relevant, because no
relevant leaching of Sb and Cr ions in sweat simulated medium was
detected in a leaching study (BASF 2017). Furthermore, the substance
must be sufficiently soluble in water to partition from the stratum
corneum into the epidermis. Since the Pigment is nearly insoluble,
dermal uptake is likely to be low.
Based on the low water solubility and the results from the
comprehensive toxicity testing, it is unlikely that the test substance
becomes systemically available. If absorbed, the metal ions will most
likely be transported within the body via blood stream and gain access
to the body tissues potentially bound to macromolecules due to its low
water solubility. This only happens to a very small degree because organ
translocation of the ions from the crystal lattice could not be
demonstrated in the repeated-dose studies.
A leaching study was performed at different pH conditions (pH 1.5 and
6.5) and different media (artificial gastric fluid, artificial sweat
solution). The release of Sb was zero after substraction of the blanks.
The release of Cr was ~ 0.5 ug/l after 24h in GST and zero after 2h and
in AST. Since the test covers the pH extrema in the human organs and for
dermal contact, the leaching fraction of metals can be regarded as of no
concern for distribution.
As already described above, due to its insolubility in water and
inert character, if any, only very low amounts of the test substance may
be absorbed and become available for metabolisation. Metal ions are not
metabolised in the body but are bound to carrier proteins and are
transported to the target location. In addition, based on the results of
the Ames test (BASF 1995), Mouse lymphoma assay (BASF 1996) and
Micronucleus test (BASF 2001) it can be assumed that the test substance
is not enzymatically activated (toxified) during the metabolism as the
parent compound showed no higher toxicity compared to the metabolic
Chemicals can be excreted via various routes and mechanisms. The
excretion depends on the physical and chemical properties of the
compound. The inert pigment will most likely be excreted unchanged via
faeces. Due to the lack of adsorption, urinary excretion will not occur
and bioaccumulation can most likely be excluded due to the neglible
bioavailability of the test substance.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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