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EC number: 269-075-7
CAS number: 68187-15-5
An inorganic pigment that is the reaction product of high temperature calcination in which praseodymium (III) oxide, praseodymium (IV) oxide, silicon oxide, and zirconium (IV) oxide in varying amounts are homogeneously and ionically interdiffused to form a crystalline matrix of zircon. Its composition may include any one or a combination of the modifiers alkali or alkaline earth halides.
The in-vitro and in-vivo experiments described above are in very good agreement with regards to the negligible level of bioavailability of the elements Zr and Pr contained in the pigment.
(1) In in-vitro dissolution experiments in five different artificial physiological media, the highest dissolved Zr, Si and Pr concentrations were below 2.4 µg/L (24h, ALF), 62.7 µg/L (24h, ALF) and 574 µg/L (24h, GST), respectively, even at the highest loading of 0.1 g/L, referring to a solubility of 0.0024 %, 0.063 % and 0.574 %, respectively. Thus, the pigment is considered biologically inert. The dissolved Zr, Pr and Si concentrations from this pigment in GST, after 2h hours (2-hour gastric passage) were below LoD, 350 μg/L and 30 μg/L, respectively, even at the highest loading of 0.1g/L, corresponding to a solubility of less than 0.4 %.
(2) In a 28-day oral toxicity study with 1,000 mg/kg pigment no increase in Zr and Pr plasma and urine concentrations were observed when sampled at the end of the 28-day exposure period. From a final dose of 1,000 mg/kg of the pigment that the animals received on the last day of the study, only cumulated relative amounts of << 0.001 % (m/f) were found in the terminal 24-h urine collection period.
(3) In a mass balance study with a single oral dose of 1,000 mg/kg of the pigment, 102% Pr of the dose and 74.3% Zr were excreted via faeces within 3 days, with only <0.00001% Pr and < 0.002% Zr of the dose being excreted via urine at the same time.
(4) In a bioavailability study, the absolute (0.000055% (Pr)) and relative (0.000011% (Pr)) bioavailability of orally administered pigment was calculated in relation to a soluble Pr3+compound (PrCl3), injected i.v..
Comparing the findings ofin-vitrodissolution testing (1) within-vivoresults (2-4), thein-vivodata consistently demonstrates slightly lower bioavailability. This is in agreement with the general understanding thatin-vitroexperiments in simulated gastric juice provide a conservative estimate of actual (in-vivo) bioavailability.
In conclusion, the oral relative bioavailability of the pigment "Zirconium praseodymium yellow zircon" can be assumed to be negligible, as demonstrated in three independent in-vivo studies in rats yielding very comparably results supported by anin-vitrodissolution experiment in five different artificial physiological media.
A rounded value of <<0.01% for oral absorption can be taken forward from (i) terminal urine/plasma sampling in a study involving 28 repeated oral doses of 1,000 mg pigment/kg bw/d (<<0.001% for Pr) and (ii) a mass balance study involving a single dose of 1,000 mg pigment/kg bw (0.00003% for Pr and <<0.00001% for Zr).
Comparing the findings of in-vitro dissolution testing (1) with in-vivo results (2-4), the in-vivo data consistently demonstrates slightly lower bioavailability. This is in agreement with the general understanding that in-vitro experiments in simulated gastric juice provide a conservative estimate of actual (in-vivo) bioavailability.
In conclusion, the oral relative bioavailability of the pigment "Zirconium praseodymium yellow zircon" can be assumed to be negligible, as demonstrated in three independent in-vivo studies in rats yielding very comparably results supported by an in-vitro dissolution experiment in five different artificial physiological media.
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