[No public or meaningful name is available]

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics

Type of information:

other: Expert Statement

Adequacy of study:

key study

Study period:

2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Statement is based on valid study data.

Objective of study:

toxicokinetics

Principles of method if other than guideline:

The physicochemical properties of the test substance, and extensive toxicity studies in animals provide strong support in determining the ADME profile for this substance, and therefore may substitute for the experimentation of in vivo effects.

GLP compliance:

no

Radiolabelling:

no

Type:

absorption

Results:

Via GI-Tract and skin is possible; inhalation exposure is irrelevant and absorption is not applicable.

Type:

distribution

Results:

Via blood to target organs of toxicity

Type:

metabolism

Results:

Metabolic changes assumed

Type:

excretion

Results:

Elimination via urine or feces were supposed to be relevant

Metabolites identified:

yes

Details on metabolites:

Three representative chemical structures were selected to show function groups that are assumed to be candidate substrates for various enzymatic reactions. QSAR approach was used to predict the metabolism and kinetic profiles (OECD ToolBox version 1.1).

Function groups possibly involved in enzymatic metabolism – predicted by Skin Metabolism Simulator.
O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.
-CH2: Hydroxylation mediated by P450.

Function groups possibly involved in enzymatic metabolism – predicted by GI Metabolism Simulator.
O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.


Function groups possibly involved in enzymatic metabolism – predicted by Liver Metabolism Simulator.
O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.
-CH2: Hydroxylation mediated by P450.
-S-: oxidation (O=S=O)

Function groups possibly involved in enzymatic metabolism – predicted by Microbial Metabolism Simulator.
O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.
-CH-C: dealkylation (removed from the cyclic groups).
-CH-S: Hydroxylation mediated by P450 (COH-S)
-CH2: Hydroxylation mediated by P450 (CHOH).
-S-: oxidation (O=S=O)

The toxicokinetic profile of the registered substance was not determined by actual absorption, distribution, metabolism or excretion measurements. Rather, the physical chemical properties of this substance were integrated with data from acute and repeated-dose toxicity studies to create a prediction of toxicokinetic behavior.

 

Based on analytical characterizations, the substance meets the definition of a UVCB; the representative chemical structure of the registered substance is illustrated in Figure 1 (illustrated in section "Overall remarks, attachments"). 

 

This substance has an average molecular weight of 398, a water solubility of 0.105 mg/L, log Kow range from 3.7 to 7.8, vapor pressure of 1.6 Pa at 25 °C, and it is stable in neutral or acidic environment.

 

Significance of exposure route

Dermal route: is considered a principle route for occupational exposure.

Inhalation route: the test material has a vapor pressure of 1.6 Pa at 25 °C, OECD has indicated that inhalation exposure is negligible if the vapor pressure is less than 1. Therefore, under normal use and handling conditions, respiratory absorption of the test material in the form of vapors, gases, or mists is not expected to be significant, and no predictions on ADME were made.

 

Oral exposure: human exposure to this route is limited. It may occur following accidental spills at a manufacturing site and during transport and exposure via the environmental compartment, or deliberate misuse or accidental ingestion of the finished motor oil (< 1% of the test material).

 

Absorption

In the following sections, absorption after each exposure route was discussed individually. 

Oral Route: Absorption of a toxicant from the gastrointestinal (GI) tract depends on its physical properties, including lipid solubility and its dissolution rate. The test item has water solubility of 0.105 mg/L; log KOW range from 3.7 to 7.8 (values between 0 and 4 are the most suitable), and MW of 398 (values < 500 the most suitable). These data indicate that the substance is expected to participate in endogenous passive absorption within the mammalian GI tract. However, transported across cell membranes by forming a complex with carrier protein(s) is unlikely to occur, because the material is not expected to bind to a protein (computer modeling using OECD ToolBox version 1.1). Therefore, the overall absorption rate is estimated to be slow and inefficient.

 

This argument is supported by the results obtained from animal toxicity tests administrated via oral gavage: (i) treatment with a single dose of test item did not result in mortality or abnormal necropsy in all treated animals (LD50> 5,000 mg/kg). (ii) An OECD 422 study was available for the substance. In this study, animals were treated at dose levels up to 1000 mg/kg/d, no treatment-related effects were observed in the clinical observations, behavioral parameters, functional performance, body weight, food/water consumption, hematology, blood chemistry, organ weights etc. NOAEL for systemic toxicity was determined to be 1000 mg/kg/day. Some treatment-related effects were also identified in this study, such as centrilobular hepatocyte enlargement in male rats treated with 1000 mg/kg/day, and the presence of hydrocarbon nephropathy in male rats from all treatment groups. These effects were generally considered to be adaptive in nature (liver), or species-specific effect (kidney). However, these treatment-related symptoms suggested the test substance was absorbed and became systemically available.

 

Taken together, substance absorption by the GI tract is expected, and mostly by simple diffusion. The relatively low toxicity observed in the animal studies indicated either low amount of test material was absorbed, and/or the test material has low inherent toxicity. 

 

Dermal Route: Physicochemical properties have a decisive influence on the penetration of molecules through the skin. The test item has Log Kow 3.7~7.8 (maximal absorption when Log Kow is between 1 and 2), MW of 398 (absorption decreased as MW > 500), [Guidance Document on Dermal Absorption, 2004], these parameters are not favorable for absorption when in contact with skin. This assumption was confirmed by a QSAR assay, which calculated dermal penetration coefficient (Kp) or Pd (the permeability of the skin) by using empirical formulas.

 

Relevant physicochemical properties: MW = 398, Log Kow = 3.7

Dermwin:

Log Kp = -2.72 + 0.71 log Kow - 0.0061 MW,

Log Kp = - 2.5

Kp =3.0x10-3cm/h

 

Empirical equation of skin permeability(Potts, R.O.,et al, 1992)

Log Kp = 0.71* LogKow- 0.0061 MW – 6.3,

Log Kp = -6.1

Kp = 7.9 x10-6cm/h

 

Human Health Evaluation Manual:

Log Kp = -2.80 + 0.66 logKow – 0.0056 MW,

Log kp = - 2.6

Kp = 2.6 x10-3cm/h             

                             

Equations on page 60 of ConsExpo Manual:(http://www.rivm.nl/en/healthanddisease/productsafety/ConsExpo.jsp):

Pd = 1/15 * (0.038 + 0.153 Kow) e-0.016 MW= 7.2 x10-5cm/h cm/hr

Pd = 0.0018 Kow0.71e-0.014MW= 1.8x10-5cm/hr

Log Pd = - 0.812 – 0.0104 MW + 0.616 log Kow; Pd = 2.1 x10-3cm/h

 

Relevant physicochemical properties: MW = 398, Log Kow = 7.8

Dermwin:

Log Kp = -2.72 + 0.71 log Kow - 0.0061 MW,

Log Kp = 0.4

Kp = 2.5 cm/h

 

Empirical equation of skin permeability(Potts, R.O.,et al, 1992)

Log Kp = 0.71* LogKow- 0.0061 MW – 6.3,

Log Kp = - 3.2

Kp = 6.4 x10-4cm/h

 

Human Health Evaluation Manual:

Log Kp = -2.80 + 0.66 logKow – 0.0056 MW,

Log kp = 0.12

Kp = 1.32 cm/h                

                          

Equations on page 60 of ConsExpo Manual:

(http://www.rivm.nl/en/healthanddisease/productsafety/ConsExpo.jsp):

Pd = 1/15 * (0.038 + 0.153 Kow) e-0.016 MW= 1.4 x10-4cm/h cm/hr

Pd = 0.0018 Kow0.71e-0.014MW= 3.1x10-5cm/hr

Log Pd = - 0.812 – 0.0104 MW + 0.616 log Kow; Pd = 0.7 cm/h

The Kp or Pd values range from 7.9 x 10-6to 2.5 cm/h. It has been suggested that if Kp < 10-3cm/hr low skin penetration will be assigned (Michael S. R., Kenneth A. W. 2007). Based on these calculations, this material was predicted to be absorbed very slowly and no significantly systemic uptake was expected; however, a value of 50% dermal absorption for this chemical was applied for a very conservative risk assessment.

 

Distribution

With respect to MW, the lipophilic character, and water solubility, the test item may be transported through the circulatory system. This substance could potentially traverse cellular barriers and distribute to distant organs other than site of exposures. This argument is supported by (i) the observations of systemic toxicity (hepatocyte enlargement and hydrocarbon nephropathy) in the subacute oral study (OECD 422). Because no test article related histopathological lesions were observed, it suggested that there was no evidence of cumulative toxicity as would be manifested by an accumulation of this type of substances in tissues. 

Metabolism

Genotoxicity testing, acute and repeated-dose toxicity testing on the registration substance supported that the registered substance was not transformed to toxic metabolites.

QSAR approach (OECD ToolBox version 1.1) was used to simulate and predict substance metabolism, various option was selected: skin metabolism simulator, GI tract metabolism simulator, liver metabolism simulator, and microbial metabolism simulator (because intestinal microflora actively involved in metabolic processes).

The function groups in the representative chemical structure that likely to be candidate substrate(s) for various enzymatic reactions were illustrated, and potential transformation reactions via various metabolism simulators were present individually in the following sections. 

Skin Metabolism Simulator: by modeling assay, the test material was expected to be biotransformed in keratinocytes and fibroblasts, and 9 metabolites were predicted. The predicted breakdown products have function groups for phase II conjugation reactions.

Figure 2. Function groups possibly involved in enzymatic metabolism – predicted by Skin Metabolism Simulator.

O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.

-CH2: Hydroxylation mediated by P450.

GI Metabolism Simulator: by modeling assay, the test material was expected to be biotransformed in the GI tract, and 8 metabolites were predicted. The predicted breakdown products have function groups for phase II conjugation reactions.

Figure 3. Function groups possibly involved in enzymatic metabolism – predicted by GI Metabolism Simulator.

O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.

Liver Metabolism Simulator: by modeling assay, the test material was expected to be biotransformed in the liver, and 13 metabolites were predicted. The predicted breakdown products have function groups for phase II conjugation reactions.

Figure 4. Function groups possibly involved in enzymatic metabolism – predicted by Liver Metabolism Simulator.

O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.

-CH2: Hydroxylation mediated by P450.

-S-: oxidation (O=S=O)

 

Microbial Metabolism Simulator: by modeling assay, the test material was expected to be biotransformed in the liver, and 38 metabolites were predicted. The final products are small molecules, such as butanoic acid, acetoacetic acid etc, and have function groups for phase II conjugation reactions.

Figure 5. Function groups possibly involved in enzymatic metabolism – predicted by Microbial Metabolism Simulator.

O=C-O-: hydrolysis mediated by esterase; and the freed alcohol undergo series oxidation.

-CH-C: dealkylation (removed from the cyclic groups).

-CH-S: Hydroxylation mediated by P450 (COH-S)

-CH2: Hydroxylation mediated by P450 (CHOH).

-S-: oxidation (O=S=O)

Excretion

The metabolic assessment indicates that this substance will undergo biotransformation, and form breakdown products. If these metabolites were not assimilated into normal cellular metabolic pathways, they were expected to conjugate with phase II enzymes and readily undergo routine renal and/or biliary excretion based the predicted structures.

SUMMARY

The physicochemical properties and toxicity studies in animals provide sufficient supports in determining the ADME profile for the registered substance, and therefore may substitute for animal tests.

 

REFERENCE

 

1.     ConsExpo Manual (http://www.rivm.nl/en/healthanddisease/productsafety/ConsExpo.jsp)

2.     Derm Win (EPI Suite, version 4.0)

3.     Michael, S. R. and Kenneth, A. W. Dermal Absorption and Toxicity Assessment, Second Edition, Drugs and the Pharmaceutical Sciences, 2007

4.     Potts, R.O., Guy, R.H., “Predicting skin permeability”Pharm Res.(9): 663–91, Published by. The Chemical Daily Co. 1992. 

 

 

 

Conclusions:

Interpretation of results (migrated information): other: Bioaccumulation in exposed organisms is predicted to be unlikely.
The toxicokinetic profile of the test substance was not determined by actual absorption, distribution, metabolism or excretion measurements. Rather, the physical chemical properties of this substance were integrated with data from acute and repeated-dose toxicity studies to create a prediction of toxicokinetic behavior. And it is concluded that: Absorption in GI-Tract is relevant, dermal absorption is very low, and inhalation irrelevant
Distribution via blood to target organs of toxicity
Metabolic changes assumed
Elimination is assumed, bioaccumulation supposed to be irrelevant.

Executive summary:

With respect to molecular weight (398 for the representative strucutre), low water solubility (0.105 ppm), and Log Kow (range from 3.7 to 7.8), it is concluded that the test material is absorbed in the gastro-intestinal tract after oral administration.

Absorption via skin is expected to be low based on QSAR analyses.

 

Inhalative exposure is of no relevance due to the low vapor pressure.

 

Extensive distribution can be assumed from the target tissues identified in a subacute toxicological study. After oral exposure to high doses, kidneys, and liver have been identified as target organs for systemic effects.

The test material is assumed to be object to hydroxylation, oxidation and reduction mediated by variousenzymes present in skin, liver, GI tract, or intestinal microflora. The metabolites have function groups suitable for conjugation reaction with phase II enzymes.

 

It can be assumed that elimination of the substance is relevent. Based on the results from the subacute study, bioaccumulation in exposed organisms is not expected.

Discussion on bioaccumulation potential result:

This substance is virtually insoluble in aqueous milieu (water solubility 0.105 ppm), and has a high Kow (range from 3.7 to 7.8, and 50% of the species > 5.89), both are outside the optimal window for intestinal/dermal absorption.The lack of adverse findings following oral dosing (LD50 > 5000 mg/kg for acute toxicity; or NOAEL 1000 mg/kg/d for repeat dose toxicity may be at least partially due to limited gastrointestinal/dermal absorption of the test substance after treatment, and/or a very low index of inherent toxicity for this substance, and/or its metabolite(s).

 

 

Description of key information

Short description of key information on bioaccumulation potential result: 
The physicochemical properties of the test substance, and extensive toxicity studies in animals provide strong support in determining the ADME profile for this substance, and therefore may substitute for the experimentation of in vivo effects.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

With respect to molecular weight (398 for the representative strucutre), low water solubility (0.105 ppm), and Log Kow (range from 3.7 to 7.8), it is concluded that the test material is absorbed in the gastro-intestinal tract after oral administration.

Absorption via skin is expected to be low based on QSAR analyses.

 

Inhalative exposure is of no relevance due to the low vapor pressure.

 

Extensive distribution can be assumed from the target tissues identified in a subacute toxicological study. After oral exposure to high doses, kidneys, and liver have been identified as target organs for systemic effects.

The test material is assumed to be object to hydroxylation, oxidation and reduction mediated by variousenzymes present in skin, liver, GI tract, or intestinal microflora. The metabolites have function groups suitable for conjugation reaction with phase II enzymes.

 

It can be assumed that elimination of the substance is relevent. Based on the results from the subacute study, bioaccumulation in exposed organisms is not expected.

Discussion on bioaccumulation potential result:

This substance is virtually insoluble in aqueous milieu (water solubility 0.105 ppm), and has a high Kow (range from 3.7 to 7.8, and 50% of the species > 5.89), both are outside the optimal window for intestinal/dermal absorption.The lack of adverse findings following oral dosing (LD50 > 5000 mg/kg for acute toxicity; or NOAEL 1000 mg/kg/d for repeat dose toxicity may be at least partially due to limited gastrointestinal/dermal absorption of the test substance after treatment, and/or a very low index of inherent toxicity for this substance, and/or its metabolite(s).