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EC number: 214-014-1
CAS number: 1072-71-5
See attached expert statement.
order to assess the toxicokinetic behaviour of
2,5-Dimercapto-1,3,4-thiadiazole (DMTD), the available toxicological,
ecotoxicological and physico-chemical data were evaluated, also derived
from a suitable read-across substance, NATD, as toxicokinetic test data
molecular weight of 150.2457 g/mol, a LogPow of <0.0, and a water
solubility of 25.9 g/L at 20°C, a high potential for oral absorption is
given. The substance is not ready biodegradable and hydrolytically
stable, so degradation products do not need to be considered. Taking
into account the oral OECD 422 study, a certain absorption of the test
compounds is evident. Hence, a preliminary occurrence of oral absorption
of the test item after gavage can reasonably be deducted. DMTD is a high
melting solid with very low vapour pressure, and max. 5.17% of the
particles would reach the body via inhalation as they are otherwise too
large to be respirable, which is a rather negligible amount. Hence,
inhalative absorption is not relevant. In case of DMTD, an evaporation
after skin contact does not need to be regarded, and it will remain on
the skin until mechanical removal. Since the substance is not a skin
irritant, but effects on the skin were noted in the OECD 402 study,
additional absorption-enhancing effects cannot be assessed. With the
above-mentioned molecular weight, logPow and water solubility, a nearly
non-hindered dermal absorption can be assumed.
in summary, the absorption rates may be estimated to:
via oral route: 100%
via inhalative route: 10%
via dermal route: 50%
into account DMTD’s rather low molecular weight and its sufficient water
solubility, the absolute systemic bioavailability is very high. Similar
distribution patterns can be expected for its metabolites and a possible
accumulation can be neglected. A high peak exposure to the compound(s)
and hence high systemic bioavailability can be expected, but not a very
relevant AUC. This is supported by the results of the OECD 422 study, in
which systemic effects indicate a wide distribution of the test item
throughout the body.
low logPow and sufficient water solubility are clearly indicating that
for DMTD a certain potential for accumulation in the body can be
excluded and a rather fast excretion can be expected. So, the potential
of DMTD for bioaccumulation in its classic sense is virtually not
its metabolic fate, S-oxidation was identified as the only mode of
action during Phase-I-metabolism. The metabolite formed is not expected
to modify essentially the molecular weight, physico-chemical properties
and hence ADME behaviour of DMTD. This metabolite is expected to be
either excreted directly or to react in Phase II of the
biotransformation with different molecules, leading to the formation of
conjugations. Hence, it is unlikely that DMTD will be excreted
unchanged. DMTD and its estimated metabolite are small and hydrophilic
and very soluble in water. So a very fast excretion of the compounds via
the kidneys and so urine can be expected.
conclusion, DMTD has a minor potential for bioaccumulation, and will be
excreted rapidly after metabolism.
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