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Description of key information

The key physicochemical characteristics of the crystalline powder T001036 (CAS 62780-89-6) are: a moderate molecular weight (210.66 g/mol), a particle size of 86.556 µm (Mass Median Aerodynamic Diameter or MMAD), a moderate water solubility (0.194 g/L), a moderate partition coefficient (log Kow of 2.2) and a low volatility (vapour pressure of ≤1.7 E-5 kPa at 25°C). Furthermore, the substance is not irritating to the skin.

Based on its molecular weight is < 500 g/mol, its log Pow value between -1 and 4 and its moderate water solubility, oral absorption is expected. Based on the characteristics and test item-related clinical signs in a repeated dose oral toxicity study, the oral absorption factor of T001036 is set to 50%, the default absorption factor for oral intake.

The respiratory absorption factor is set to 100% due to its moderately water solubility and lipophilic character (logKow>0).

The dermal absorption factorfor T001036 is set to 50% based on the fact that the substance is a solid, its water solubility and logKow are moderate and an acute dermal toxicity study which showed no effects related to the test material (except for local clinical effects).

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
50
Absorption rate - dermal (%):
50
Absorption rate - inhalation (%):
100

Additional information

Toxicokinetic assessment of T001036

T001036 (CAS 62780-89-6) is a crystalline powder with a moderate molecular weight (210.66 g/mol), a particle size of 86.556 µm (Mass Median Aerodynamic Diameter or MMAD), a moderate water solubility (0.194 g/L), a moderate partition coefficient (log Kow of 2.2) and a low volatility (vapour pressure of ≤1.7 E-5 kPa at 25°C). Furthermore, the substance is not irritating to the skin.

The backbone of T001036 is a benzimidazolone group,with a chloropropyl group attached to it . The presence of nitrogen (amine functional group) within the benzimidazolone group can lead to a weak alkaline character. This would imply that the product has the potential to ionize to a small extent in an acidic environment. However, from the calculated pKa values based on the Perrin calculation method (Brekelmans, 2016) it can be confirmed that the test item is not ionized in environments between pH 1 and 14.

No toxicokinetic data (animal or human studies) are available on this substance. The data present in this dossier are based on physicochemical and toxicological parameters and will allow a qualitative assessment of the toxicokinetic behaviour of T001036.

Absorption

Oral/GI absorption:

T001036 is considered favourable for absorption since its molecular weight is < 500 g/mol, its log Pow value between -1 and 4 and its moderate water solubility which leads to dissolution of the substance into the gastrointestinal fluids and absorption through passive diffusion. It is generally assumed that the absorption along the gastrointestinal tract predominantly takes place in the small intestine.

A 28-day repeated dose oral toxicity study (Braun et al., 2008) has been performed by gavage with T001036 on Wistar rats applying following doses: 0, 30, 100 and 300 mg/kg bodyweight/day. During the study period, test item-related clinical signs were observed to be transient and noted only during daily observation and in rats treated at the highest dose level. The signs included slight sedation and ruffled fur. Ataxia was noted in some rats, but all findings were reversible within the first week of treatment, indicating an adaptive response. Histopathological observation of T001036 produced effects in the liver of males treated with 100 mg/kg/day and both sexes at 300 mg/kg/day which consisted of minimal to moderate hepatocellular, mainly centrilobular hypertrophy. This finding was not accompanied by increased incidence of inflammatory or degenerative lesions of the liver and resolved in the recovery groups. In the affected groups, the finding of hepatocellular hypertrophy correlated with an increased mean organ weight and organ weight ratios. In the thyroid glands of rats treated with 30, 100 and 300 mg/kg/day, activation of the follicles was recorded. The finding resolved in the recovery groups and was deemed to be of secondary nature due to hepatocellular hypertrophy leading to an increased turnover or hepatic uptake or thyroid hormones. In the kidneys of male animals treated with 100 and 300 mg/kg/day, increased severity of hyaline droplets was recorded. In males at 300 mg/kg/day, an increased mean severity of tubular basophilia was noted. In one animal at 300 mg/kg/day, focal tubular cell necrosis could be recorded at minimal severity. The latter findings partially resolved in the recovery group. Although these findings of increased hyaline droplets paralleled by increased tubular turnover resemble alpha-2-microglobulin nephropathy, they are considered adverse in rats.This is generally recognized as species- and gender-specific and presents no risk to humans. Based on this study, no NOEL could be determined. The NOAEL is considered to be 100 mg/kg/day. 

In a reproduction/developmental toxicity screening test, the test substance was administered daily to rats by oral gavage (OECD guideline 421; Peter, 2016) at dose levels of 15, 50 and 150 mg/kg body weight/day. No parental, reproduction and developmental toxicity was observed up to 150 mg/kg/day (NOAEL at least 150 mg/kg body weight/day). 

Based on the physicochemical properties and the results of the toxicity studies, the absorption factor is set to 50%, the default for the oral route of exposure.

Respiratory absorption:

Given its low volatility, the availability of T001036 for inhalation as a vapour is limited. However, based on the fact that its aerodynamic diameter is larger than 50 µm but smaller than 100 µm, the solid particles have the potential to be inhaled and settle in the nasopharyngeal region.

T001036 can diffuse/dissolve into the mucus lining the respiratory tract, since it is a moderately water soluble powder. Its lipophilic character (logKow>0) implies that the product has the potential to be subsequently absorbed directly across the respiratory tract epithelium through passive diffusion. The portion of the product which is not dissolved into the mucus could be coughed or sneezed out of the body or swallowed. As described above, the product has the potential to be absorbed after oral intake.

Based on the physicochemical properties, the respiratory absorption factor is set to 100%.

Dermal absorption:

T001036 is a solid substance and therefore not readily taken up by the skin in comparison to liquid products. The product will have to dissolve into the surface moisture of the skin before uptake can take place. Based on its moderate water solubility (0.194 g/L), dermal uptake is expected to be moderate to high since the substance is sufficiently soluble in water to partition from the stratum corneum into the epidermis. The moderate logKow value of 2.2 indicates that the substance is lipophilic and therefore easily crosses the lipid rich environment of the stratum corneum leading to dermal uptake.

An acute dermal toxicity study (Latour, 2016) with Wistar rats to which a single dose of 2000 mg/kg was applied, showed no effects related to the test material except for local clinical effects at the treated skin area such as general erythema, scales and scabs. Based on an in vivo skin irritation test with New Zealand White rabbits (Sanders, 2004) T001036 was classified as non-irritant which implies that no enhanced penetration can be caused by damage to the skin. The fact that the substance is identified as a skin sensitizer (classification H314 Cat. 1) based on a study (Sanders, 2004) with a positive result at a 50% concentration and an EC3 value of 40.63%, suggests that a fraction of the applied dose has been taken up.  

As a result, the dermal absorption factor for T001036 is set to 50%.

Distribution

The moderate water solubility and moderate molecular weight predict that T001036 will probably distribute through the body due to diffusion through aqueous channels and pores. Since the substance is lipophilic (logKow>0), the substance is likely to distribute into cells leading to a higher intracellular concentration in comparison to the extracellular concentration particularly in fatty tissues. The conclusions of the oral toxicity study indicate that the target organs are mainly the kidneys and liver.However, the adverse effects observed in the kidneys are assumed to be observed in rats only and not in humans.

Accumulation

Since T001036 has a Log Kow of 2.2, accumulation is considered unlikely.

Metabolism

Based on the structure, T001036 might undergo phase I biotransformation such as hydroxylation followed by conjugation reactions (phase II) such as glucuronidation (by the enzyme glucuronosyltransferase) and sulfation (by the enzyme sulfotransferase. The Phase II conjugation reactions largely increase the hydrophilic character of the product. Metabolism mainly takes place in the liver, causing route specific presystemic (or first pass) effects, especially after oral intake. Other metabolic changes may take place in the gastrointestinal (GI) flora or within the GI tract epithelia (mainly in the small intestine), respiratory tract epithelia (in the nasal cavity, trachea-bronchial mucosa and alveoli and skin), etc.

Excretion

Given its moderate water solubility and molecular weight <300, a possible route of excretion of T001036 from the systemic circulation is the urine. In general, conjugated metabolites such as glucuronides and sulfates from phase II biotransformation reactions are excreted in the urine. Most of them will have been filtered out from the blood by the kidneys, though a small amount can enter the urine directly by passive diffusion. There is also the potential for re-absorption into the systemic circulation across the tubular epithelium. Another route of excretion of conjugated derivatives (such as glucuronides) is the bile. The excretion via the bile is highly influenced by hepatic function since metabolites formed in the liver may be excreted directly into the bile without entering the bloodstream. Products in the bile pass through the intestine before excretion in the faeces and can thus undergo enterohepatic recycling which will prolong their half-life. Furthermore, T001036 can be excreted in the saliva (where in can be swallowed again) or in the sweat since it is non-ionized and lipid soluble.