1,3,5-tris(2,3-dibromopropyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Type of information:

other: Expert judgement

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Expert statement based on robust and valid data, no ADME study available

Justification for type of information:

No toxicokinetic tests have been conducted or proposed since the toxicokinetic behaviour of the substance can be derived from available data (i.e. physicochemical properties, in silico methods) and the in vivo toxicity studies performed on the test substance provide sufficient and robust supporting information.

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Expert judgement.
According to Annex VIII, Section 8.8.1, column 1, one should perform the "Assessment of the toxicokinetic behaviour of the substance to the extent that can be derived from the relevant available information."
The available data regarding physicochemical properties, environmental fate (e.g. hydrolysis) and in vivo toxicity studies performed on the test substance provide sufficient and robust supporting information to determine the ADME profile of the substance and therefore further testing is considered unnecessary.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,3,5-tris(2,3-dibromopropyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione

EC Number:

257-913-4

EC Name:

1,3,5-tris(2,3-dibromopropyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione

Cas Number:

52434-90-9

Molecular formula:

C12H15Br6N3O3

IUPAC Name:

tris(2,3-dibromopropyl)-1,3,5-triazinane-2,4,6-trione

impurity 1

Reference substance name:

unknown impurities

IUPAC Name:

unknown impurities

Test material form:

solid: particulate/powder

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Absorption of a substance via oral, dermal or inhalation routes depends on its physicochemical properties, in particular those related to its ability to cross biological membranes by passive diffusion, as this process requires a substance to be soluble both in lipid and water.


ORAL ABSORPTION:
Absorption of a solid substance in the gastrointestinal (GI) tract depends on its physicochemical properties, in particular those related to molecular weight, water and lipid solubility. Generally, substances with molecular weights above 500 have a limited oral absorption (AP 729 MW = 728.68 g/mol). Moreover, AP 729 has a log P of 4.31 and can be considered poorly water soluble (5.07 mg/L): the absorption of highly lipophilic substances (Log P of 4 or above) is limited by their ability to dissolve into the GI fluids.
The assumption that substance AP 729 should be considered as having low absorption through the GI tract is also supported by the fact that it is not stable in an aqueous environment. A hydrolysis test performed according to OECD Guideline 111 (Hydrolysis as a function of pH, Adopted: 13 April 2004) demonstrated that the substance is hydrolytically unstable due to 93.47% degradation in pH 4 buffer, 91.95% degradation in pH 7 buffer and 93.50% degradation in pH 9 buffer test solutions respectively and no formation of breakdown products was observed (results of the preliminary test conducted at 50°C for 5 days). In a Tier 2 test, the hydrolysis of the test item was investigated as a function of pH (4, 7 and 9) at three temperatures: 20 ± 0.5°C, 35 ± 0.5°C and 50 ± 0.5°C. At pH 4, 7 and 9, the total rate constant and half-life of the reactions at 25°C were calculated and found to be 0.2409 hour-1 and 2.88 hours, respectively.
The total rate constants and half-lifes of the reactions at 35°C were calculated and found to be:
• 0.1272 hour-1 and 5.45 hours at pH 4
• 0.0887 hour-1 and 7.81 hours at pH 7
• 0.1144 hour-1 and 6.06 hours at pH 9.
This gives an indication that the substance is present in the GI tract only for a limited time and since no degradation products are formed, there is no need to further assess their ADME pattern.
The prediction of limited bioavailability and low absorption is consistent with the absence of adverse effects observed in the tests performed, in which the substance was administered by oral gavage. The acute oral LD50 was found to be greater than 16 g/kg bw in both male and female CFY rats. There were also no treatment related effects on systemic, reproduction, fertility parameters and F1 generation pups up to and including the highest dose tested 1000 mg/kg/day, thus the No Observed Adverse Effect Level (NOAEL) for a Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test (OECD TG 422) in Wistar rats for the test item AP 729 was determined to be 1000 mg/kg/day.


RESPIRATORY ABSORPTION:
AP 729 has a very low vapour pressure (0.00005 Pa at 20°C), therefore cannot be inhaled as a vapour. However, the particle size distribution indicates the presence of inhalable and respirable particles having the potential to settle in the alveolar and nasopharyngeal regions. There is evidence that poorly water-soluble dusts depositing in the nasopharyngeal region could be coughed or sneezed out of the body or swallowed. Moreover, dusts depositing in the tracheo-bronchial region would mainly be cleared from the lungs by the mucocilliary mechanism and swallowed. However, a small amount may be taken up by phagocytosis and engulfed by alveolar macrophages. As for GI tract absorption, also if the substance deposits in the respiratory tract, the overall passive diffusion across membranes is to be considered of low entity as AP 729 has limited ability to dissolve into the fluids and is hydrolyzed.
The assumption of limited absorption is also consistent with the absence of adverse effects observed in the performed acute inhalation toxicity study, conducted on Wistar rats according to Annex 3d of OECD Guideline 436 (LC50 >5.03 mg/L). Moreover, if the substance were to be ingested, no adverse effects are neither expected as already mentioned for the oral route absorption.


DERMAL ABSORPTION:
The physicochemical properties of a substance are crucial to determine the potential of skin penetration. It has to be borne in mind that dry particulates will have to dissolve into the surface moisture of the skin before uptake can begin. Considering the hydrolytically behaviour of the substance, it can be predicted that the dissolved substance will not remain in contact with the skin for a long time.
Substances with molecular weight above 500 may be too large to be absorbed. For substances with a water solubility between 1-100 mg/l absorption is anticipated to be low to moderate and moreover a Log P above 4 indicates that the rate of penetration may be limited by the rate of transfer between the stratum corneum and the epidermis, but uptake into the stratum corneum will be high.
Therefore, the absorption potential of AP 729 through skin is predicted to be low.
In addition, as a result of binding to skin components, the uptake of substances with halotriazines groups can be slowed further.
The above assumptions are confirmed by the prediction of the absorption potential of AP 729 through skin using EPI-Suite (v4.11) DERMWIN (v2.0), which resulted in a Kp = 9.33x10-5 cm/hr. It has been suggested that if Kp is below 10-3 cm/hr then low skin penetration is predicted. Based on the above, it can be concluded that AP 729 is absorbed very slowly and inefficiently by skin and that no significant systemic uptake can be expected, thus less than 10% absorption of the applied dose will be used in the risk assessment.
These results are consistent with the conclusions of the in vivo skin irritation test performed, where no adverse effects were detected, and with the QSAR predictions of skin sensitization potential.

Details on distribution in tissues:

Assuming that AP 729 was absorbed via oral, inhalation or dermal route, then its transport and distribution would be limited due to the high molecular weight and lipophilic behaviour, as it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration. However, it is not expected that AP 729 will reach the blood circulation without starting to hydrolyze.
Chapter R.7c: Endpoint specific guidance state that polar non-volatile (i.e. low log Kow and high log Koa, where estimated log Koa for AP 729 is 20.62) substances have a low bioaccumulation potential in aquatic organisms but a high bioaccumulation potential in air-breathing organisms (unless they are rapidly metabolised). Based on the performed testing on rats (acute toxicity tests via oral and inhalation routes and repeated dose test via oral route), adverse effects are not expected if the substance is ingested or inhaled. Moreover, the substance is hydrolytically unstable, and no formation of breakdown products is observed so it is predicted that AP 729 has a limited bioavailability and is present within the organism only for a limited time.
Moreover, as the Log P is below 4.5, then the substance is considered to have no bioaccumulation potential.
As reported in section "Details on absorption", it may be predicted that uptake of AP 729 into the stratum corneum will be high, but it won’t be well absorbed systemically: although it may persist in the stratum corneum, it will eventually be cleared as the stratum corneum is sloughed off and therefore no bioaccumulation can be expected.

Metabolite characterisation studies

Details on metabolites:

A QSAR approach using OECD QSAR Toolbox (version 4.5 SP1) was adopted to determine the possible formation of metabolism both after ingestion (both via oral route and as a consequence of inhalation) and after skin contact. The rat liver S9 metabolism simulator predicted 2 metabolites, the in vivo rat metabolism simulator identified 12 metabolites and the microbial metabolism simulator predicted 23 metabolites. The skin metabolism simulator predicted 1 metabolite. All the details are presented in the attached justification.

Applicant's summary and conclusion

Conclusions:

According to Annex VIII, Section 8.8.1, column 1, one should perform the "Assessment of the toxicokinetic behaviour of the substance to the extent that can be derived from the relevant available information."
The available data regarding physicochemical properties, environmental fate (e.g. hydrolysis) and in vivo toxicity studies performed on the test substance provide sufficient and robust supporting information to determine the ADME profile of the substance and therefore further testing is considered unnecessary.
According to the physicochemical properties and in silico modeling tools, the substance is considered to have limited bioavailability and low absorption rate by oral route (and when swallowed as a consequence of inhalation). Moreover, the substance is predicted to have a very low potential to bioaccumulate whether absorbed, as its transport and distribution would be limited, and it is not expected that AP 729 will reach the blood circulation without starting to hydrolyze.
The prediction of limited bioavailability and low absorption leads to predict that whether ingested or inhaled the substance is excreted in the faeces. Moreover, whether the substance undergo biotransformation in the GI tract, such considerations can also be made for those possible metabolites that show a structure similar to that of the parent compound while smaller and polar metabolites can be excreted with urine.
Absorption by dermal route can also be excluded and regarded as very low and inefficient.
The results obtained from in vivo testing led to the conclusion that AP 729 has no toxic effects if ingested, inhaled or placed in contact with the skin.