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EC number: 439-730-3 | CAS number: -
Toxicokinetic analysis of the test item
There are no experimental studies available on toxicokinetics of the test item. Therefore its toxicokinetic properties are assessed based on its physico-chemical properties as well as from data available from toxicity studies and in accordance with ECHA Guidance R .7c (2017).
The test substance is a crystalline white solid at room temperature and of low dustiness. The test item, being a mono-constituent substance, has a molecular weight of 282.47 g/mol and a relative density of 1.04. Its melting point was determined to be 66 °C and whereas the boiling point is at 190 °C at 1013 hPa. The substance is considered highly insoluble in water, as water solubility was found to be smaller than 0.005 mg/L. Partition coefficient (logPow) of the substance was estimated to be 8.6 being the highest calibration standard of the method applied. Vapor pressure of the substance was determined to be 1.95E-4 Pa at 25 °C.
Bioavailability via oral route is strongly linked to physico-chemical properties of the substance (ECHA Guidance, 2017). Generally, oral absorption is favored for molecular weights below 500 g/mol and with a logPow in the range of -1 to 4. Thus, with a logPow greater than 8.6 the substance would be expected to not passively pass biological membranes. In addition, the substance is highly insoluble in water. However, micellular formation in the gastrointestinal tract (GIT) could enable absorption processes. Moreover, the molecular weight of the substances is well below 500 g/mol and could thus contribute to a favored absorption. In addition, the substance is not expected to undergo hydrolysis based on its chemical structure. Abiotic degradation is thus not relevant for the oral route of exposure. Taken together, the physico-chemical properties of the substance indicate that intestinal absorption cannot be completely ruled out.
The above considerations are confirmed by findings of toxicity studies with the test substance. In an acute oral toxicity study with rats no mortality or other signs of toxicity were observed up to the limit dose of 2000 mg/kg bw.
However, a 28-day repeated dose toxicity study as well as a Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test revealed clear effects following oral administration at dose levels of above 15 mg/kg bw/d, including mortality at doses of 1000 mg/kg bw/d for up to 6 days. Based on the observed findings the test item is classified for specific target organ toxicity after repeated exposure (STOT RE) Cat. 2 (adrenal glands). Therefore, there is clear indication that the test item and/or its metabolites become systemically available via the oral route.
Regarding dermal exposure, the substance is considered to unlikely permeate the skin. According to ECHA guidance on toxicokinetics, there are no exclusion criteria for skin permeability, but a molecular weight of > 500 Da and a log Pow of > 4 are given as indicators for low absorption (10% or less). Considering the molecular weight, the test item would not be critical, however, its logPow of approx. 8.6 will probably not favor dermal permeation. Further, based on accepted calculation models and an expert statement provided in IUCLID Section 7.1.2 (reference 7.2.1-1), no or only very small amounts are expected to become systemically available upon dermal exposure.
The above considerations are in line with findings of an acute dermal toxicity study in rats (reference 7.2.3-1). No signs of toxicity were observed up to the limit dose of 2000 mg/kg bw. Moreover, it is noted that the test item is not classified for local effects such as skin or eye irritation and no skin sensitisation was observed in vivo (references 7.3.1-1, 7.3.2-1 and 7.4.1-1). Taken together, this indicates that the test item will not readily penetrate skin layers.
Due to a very low vapor pressure of 1.9E-4 Pa it is very unlikely that the substance becomes available as a vapor and the boiling point of the substance was determined to be 190 °C at 1013 hPa. The substance is a solid of very low dustiness. Therefore, exposure via inhalation is considered not relevant for the substance. However, in the unlikely case of inhalation, the substance would be expected to pass biological membranes taking into account same considerations as for the oral route.
As mentioned above, no or very poor bioavailability is expected for the test item via the dermal route, whereas absorption upon ingestion is considered to be likely based on physicochemical properties and as confirmed by in vivo toxicity studies. Repeated dose toxicity studies revealed specific effects in target organs adrenal glands, indicating that either the substance itself or one of its metabolites reached this tissue following oral administration. Based on its low water solubility and high logPow value the test item is expected to be absorbed by micellular formation and as such taken up and transported via the lymph system, similar to other lipophilic constituents of the diet. Further, protein binding is expected rather than dissolution in the plasma in terms of distribution via the blood stream.
Based on its low water solubility and high logPow value, bioaccumulating potential cannot completely be ruled out for the test item. However, based on a experimental study in fish, a steady state BCF mean value of 163 was determined, confirming that the test item is of no concern in regards to bioaccumulation (reference 5.3.1-1).
There is no experimental data available regarding potential metabolism of the test item.
Considering its chemical structure oxidation of the double bound of the aromatic ring or the vinyl group by phase I enzymes such as CYP 450 can be anticipated and will predominantly occur in the liver. Further, conjugation reactions by phase II enzymes such as glutathione-S-transferase in order to increase water solubility and thus facilitate excretion might occur. Nascent (cyclo-) alcohol groups might further represent a substrate for Alcohol as well as Aldehyde dehydrogenases.
Metabolism of the test item in the liver can be assumed, because the liver was found to be a target organ in both repeated dose toxicity studies as a result of metabolic adaptation (reference 7.5.1-1 and 7.5.1-2). Because of the reversibility of the observed effects (e.g. on liver), the substance is most likely eliminated from the organism.
Based on results of in vitro tests where experiments were conducted with as well as without exogenous metabolic activation it can be stated that adding rat liver S9 did not lead to an increased (cyto-) toxicity in any of the tests (reference 7.6.1-1 and 7.6.1-2). Therefore, activation of toxicity by metabolic transformation is considered unlikely to occur in the organism.
The based on its low water solubility test item is not expected to be eliminated via the urine unless it undergoes metabolic transformation increasing its hydrophilicity. Elimination via the bile would thus be more likely.
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