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EC number: 253-575-7
CAS number: 37640-57-6
The substance does not bioaccumulate in fat tissue. Exposure to doses exceeding the solubility limit in urine results in preciptiation in the kidneys. Melamine cyanurate crystals disappear upon cessation of treatment.
Melamine cyanurate is generally of low solubility, regardless of
whether the solvent is hydrophilic or lipophilic. Solubility in
distilled water is 2.7 mg/L. Solubility (dissociation to melamine and
cyanuric acid) increases if the solvent can disrupt the crystal lattice
(eg strong acids). In stomach acid (pH 1), melamine cyanurate (at a
loading rate of 100 mg/L) dissociates within 3 minutes whereas in lung,
intestinal and lysosomal fluid, between 7 and 12% dissociate within 2 or
3 hours (Weisbach 2015). A molecular weight is difficult to assign
because in the lattice, each melamine forms hydrogen bonds with six
cyanuric acid molecules and vice versa. It is non volatile. If heated
above 320°C, it decomposes with formation of nitrogen and carbon dioxide
and upon energy consumption, and this determines its technical function
of a flame retardent.
Melamine cyanurate is slightly hygroskopic. If bags containing milled
melamine cyanurate are left open, the upper layer of the material forms
Melamine cyanurate is taken up by the body after in ingestion as
indicated by the presence of crystals in the kidney after 7-day feeding
of rats (BASF 2010, Dobson 2008). Experimental data on the metabolism of
both melamine and cyanuric acid has been published reporting that both
melamine and cyanurate are eliminated without metabolism (Mast 1985,
Sugita 1991, Barbee 1983). If given alone, both melamine and cyanurate
are sufficiently soluble in water for renal elimination and eliminated
with half lives in the range of a few hours (Liu 2010, Barbee 1983).
Uptake and elimination from the blood over a period of 8h was
investigated for a single gavage exposure to either 2 mg/kg bw melamine
and cyanuric acid combined or to melamine cyanurate (Jacobs 2012).
Intravenous application of each 1 mg melamine or cyanuric acid was done
to allow determination of toxicokinetic properties. At this dose,
formation of precipitates in the kidney does not occur and elimination
is unperturbed. Individual concentration curves for melamine and
cyanuric acid in the combined treatment were almost indistinguishable
from those resulting from the individual administration of each
triazine. A detailed analysis of the main pharmacokinetic parameters
failed to reveal any noteworthy differences between the individual and
combined exposures, with bioavailabilities in the combined treatment
ranging from 0.83 to 0.91 for melamine and 0.66–0.78 for cyanuric acid.
In contrast, the administration of melamine cyanurate revealed
very substantial differences in the concentration curves in both sexes
for melamine and cyanuric acid. Treatment with preformed melamine
cyanurate led to lower bioavailabilities for both melamine (0.4 in males
and 0.49 in females) and cyanuric acid (0.26 in males and 0.4 in
females) and to substantially lower observed Cmax values, a later Tmax,
and prolonged elimination half lives. If given melamine
cyanurate, the maximum concentrations in plasma were reached after
1.5h (males) and 2h (females) for melamine and after 1h for cyanuric
acid. Elimination half-life of melamine was 3h and that of cyanuric acid
was 1.54h (males) and 1.88h (females).
Due to the low solubility of melamine cyanurate, the substance
precipitates in the kidney if a certain concentration is exceeded. This
is observed at the end of the 7-day feeding study at a dose level of 66
mg/kg bw melamine cyanurate (BASF 2010).
Melamine cyanurate is not bioaccumulating in the sense that it
accumulates in fat tissue. Below the threshold concentration that
results in precipitation in the kidneys, the substance is not
bioaccumulating. Applying the elimination half lives in rat (Jacobs
2012), complete elimination occurs within half a day.
In human urine, the pH-dependent solubility curve of combined melamine
and cyanuric acid shows a U-shape, with the lowest solubility of 15 mg/L
between pH 5 - 5.5. Solubility in human urine was in the range of 250
mg/L at pH 3 and 8.
If given in combination with each other by the oral route, the
kinetic behaviour depends the following parameters: gavage versus feed,
preformed melamine cyanurate versus melamine and cyanuric acid, delay
between dosing of melamine and cyanuric acid (Sprando et al). Effects
are least pronounced if preformed melamine cyanurate is given by feed.
From the mechanism of crystal formation upon concentration in the
kidney, high peak doses are more hazardous than chronic low doses.
Dermal and Inhalation routes of exposure
Uptake after ingestion is more efficient than uptake by inhalation or
the dermal exposure because the hydrogen bond lattice of the melamine
cyanurate complex rapidly dissociates in the highly acidic environment
of the stomach. Melamine cyanurate itself is of very low solubility (2.7
mg/L) in distilled water.
In the in-vitro skin permeability study with 14C-cyanuric labelled
melamine cyanurate (applied as a wet paste), the human skin permeation
rate for an aqueous suspension was extremely low (0.18 μg/cm2
For the single components, experimental data on skin permeability is
available for cyanuric acid, which is present in swimming pool water and
originates from the disinfectant trichloroisocyanurate. Continuous-dose
automated in vitro dermal absorption studies conducted with isocyanuric
acid demonstrated minimal absorption through rat, hairless guinea pig,
human and commercial test skin (Moody 1993). Total cumulative absorption
of isocyanuric acid from water containing 55 mg/L cyanuric acid during
24 h in test skin and human skin was 0.02 μg/cm2 in both cases.
Inhalation to vapour is not relevant since the substance is not
exposure to dusty material, the fraction dissolved in the lung
surfactant should be available for direct transport into the blood. In
Iung, intestinal and lysosomal fluid, between 7 and 12% dissociate
within 2 or 3 hours (Weisbach 2015). Insoluble particles that have
precipitated in the lung are eventually disposed off via the stomach so
that in general, systemic exposure via inhalation needs to be assumed.
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