Registration Dossier

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
70.61 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
DNEL derivation method:
other: ECHA REACH Guidance and the ECETOC approach.
Overall assessment factor (AF):
6
Dose descriptor starting point:
NOAEL
Value:
270 mg/m³
Modified dose descriptor starting point:
NOAEC
Value:
423.69 mg/m³
Explanation for the modification of the dose descriptor starting point:

Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cel ular membranes. General y, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. General y, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cel membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additional y, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either. Therefore a route to route extrapolation from oral to inhalation is scientifically justified. For oral absorption 89 % absorption is assumed, while for inhalation absorption 100 % is assumed.

AF for dose response relationship:
1
Justification:
The NOAEL of the 90 d study (oral, rat) is set at the highest dose group, as there only very slight effects had been seen, which were reversible. Accordingly a special dose response effect could not be detected.
AF for differences in duration of exposure:
2
Justification:
Standard factor for extrapolation from sub-chronic to chronic according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".
AF for interspecies differences (allometric scaling):
1
Justification:
No additional interspecies allometric factor is applied at this stage as allometric scaling has already been considered in the route to route extrapolation step above with the respiratory volume adjustments ("Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health", Appendix *.8-2, Example B.3).
AF for other interspecies differences:
1
Justification:
In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.
AF for intraspecies differences:
3
Justification:
Intraspecies factor for healthy workers according to "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for the quality of the whole database:
1
Justification:
The NOAEL on which the DNEL derivation is based was derived in a subchronic study conducted in full compliance with the OECD Principles of Good Laboratory Practice and OECD Guidelines for the Testing of Chemicals, No. 408, adopted 21 September 1998.
AF for remaining uncertainties:
1
Justification:
No indications for remaining uncertainties.
Acute/short term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
11.25 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
DNEL derivation method:
other: ECHA REACH Guidance and the ECETOC approach.
Overall assessment factor (AF):
24
Dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Modified dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:

Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cel ular membranes. General y, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. General y, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cel membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additional y, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either. Further according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health": On the assumption that, in general, dermal absorption will not be higher than oral absorption, no default factor (i.e. factor 1) should be introduced when performing oral-to-dermal extrapolation.

AF for dose response relationship:
1
Justification:
The NOAEL of the 90 d study (oral, rat) is set at the highest dose group, as there only very slight effects had been seen, which were reversible. Accordingly a special dose response effect could not be detected.
AF for differences in duration of exposure:
2
Justification:
Standard factor for extrapolation from sub-chronic to chronic according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".
AF for interspecies differences (allometric scaling):
4
Justification:
Standard factor for allometric scaling between rat and human according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health" and "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for other interspecies differences:
1
Justification:
In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.
AF for intraspecies differences:
3
Justification:
Intraspecies factor for healthy workers according to "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for the quality of the whole database:
1
Justification:
The NOAEL on which the DNEL derivation is based was derived in a subchronic study conducted in full compliance with the OECD Principles of Good Laboratory Practice and OECD Guidelines for the Testing of Chemicals, No. 408, adopted 21 September 1998.
AF for remaining uncertainties:
1
Justification:
No indications for remaining uncertainties.
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:
no hazard identified

Additional information - workers

Summary of Repeat Dose Studies

Three studies have been identified that may be used to provide information regarding the toxicity of 2,6 DTBP in rats following repeated dosing.

These are a 90 day oral dietary toxicity study in rats, a 28 day oral (gavage) toxicity study in rats and a preliminary reproduction toxicity screening toxicity (oral gavage dosing) study in rats. Whilst the 90 d toxicity study is the key study for the definition of the DNEL, the findings from the 28 day toxicity study and the reproduction toxicity screening study may be used to support the NOAEL from the 90 day toxicity study.

Subchronic 90 Day Oral Dietary Toxicity Study with 2,6-bis (1,1 dimethylethyl)-phenol in the rat, study number 525862, Robertson, B., 2014.

Groups of 10 male and 10 female Han Wistar Crl:WI(Han) rats were assigned to the study and fed diets containing 0, 150, 500, 1600 or 4000 ppm of 2,6-di-tert-butylphenol for a minimum period of up to 91 consecutive days. A further 5 male and 5 female animals were

assigned as a recovery group to those receiving 0 or 4000 ppm of 2,6-di-tert-butylphenol and were retained for a further 28 days after the end of the treatment period to evaluate reversibility of any findings.

The following observations and end points were assessed: viability, clinical observations, body weights, food consumption, achieved dosage, food utilisation, a visual assessment of water consumption and ophthalmoscopy examinations. All animals received a detailed functional observation battery (including motor activity) assessment during pretrial and Weeks 12 of treatment, as well as all designated recovery study animals during Week 17 (Week 4 of recovery period). Blood samples for haematology, coagulation and blood chemistry investigations and urine samples were collected from all animals towards the end of the treatment period and at the end the recovery period.

All main study animals were euthanized after completion of at least 91 days of treatment with all recovery study animals euthanized after completion of a subsequent 28-day treatment-free period, and underwent a detailed necropsy examination with selected organs weighed.

Tissues from all control and high dose (4000 ppm) animals were subjected to a comprehensive histological examination, with gross lesions (where appropriate) examined from low and intermediate dose animals.

There were no unscheduled deaths, and no treatment-related clinical observations noted during the observation periods.

Lower body weight gain was observed in males that were treated with 4000 ppm. This was associated with slightly lower food consumption.

The overall mean achieved dosages were 0, 10, 33, 107 and 270 mg 2,6-di-tertbutylphenol/kg/day in males and 0, 11, 39, 124 and 298 mg 2,6-di-tert-butylphenol/kg/day for females corresponding to dietary inclusion levels of 0, 150, 500, 1600 and 4000 ppm.

There were no test substance-related effects on the movement, general behaviour or the physiology of the animals and haematology, coagulation and clinical chemistry were unaffected by treatment. There were no eye changes that were related to treatment.

Very slight differences were, however, observed during pretrial in landing foot splay (higher in males that received 150 or 1600 ppm) and hind grip strength (higher in females that received 1600 ppm) and during week 12 in females that received 500 ppm (lower foot splay, fore grip strength and tail flick) when compared with the controls. This was not considered to be of toxicological significance.

Urinary pH was lower in males that received 4000 ppm, while specific gravity was lower in females that received 4000 ppm.

Higher liver and kidney weights were noted in males and females that received 4000 ppm, while spleen weights were lower in males that received 4000 ppm. On completion of the treatment free period, higher relative liver weights were recorded in females that received

4000 ppm 2,6-di-tert-butylphenol.

There were no gross or microscopic findings that were considered related to treatment with 2,6-di-tert-butylphenol.

All findings observed throughout treatment generally recovered after a treatment-free period of 28 days which indicated all differences were adaptive and reversible and of no toxicological significance.

Under the conditions of this study, the daily oral (dietary) administration of 2,6-di-tertbutylphenol up to 91 consecutive days was associated with slightly lower body weights, body weight gain and food consumed for males that received 4000 ppm. These findings recovered after a 28-day treatment free period. Additionally, liver weight increases, in the absence of histopathological correlate were considered to be an adaptive change and of no toxicological significance and were reversible following a treatment-free period.

Based on these findings the no observed adverse effect level (NOAEL) was considered to be 4000 ppm for both males and females equating to 270 mg 2,6-di-tert-butylphenol/k/day in males and 298 mg 2,6-di-tert-butylphenol/kg/day for females.

Subacute 28 Day Oral Toxicity Study with 2,6-bis (1,1 dimethylethyl)-phenol by daily gavage in the rat, RCC Notox project 057454, Reijnders, J.B.J., 1992.

Dose levels were 0, 15, 100 and 600 mg/kg/day. Treatment related changes in the blood, liver and kidney were observed at 100 and 600 mg/kg/day. At 600 mg/kg/day male and females had around 30 to 40% heavier livers than control animals and these weight increases were accompanied by very slight centrilobular hepatocellular hypertrophy. Although relative liver weight (% of bodyweight) in males at 100 mg/kg/day was approximately 20% heavier than controls this was not accompanied by microscopic changes and liver weight in females was comparable to controls. The increased liver weight at 100 (males only) and 600 mg/kg/day accompanied by slight centrilobular hypertrophy at 600 mg/kg/day was considered to be an adaptive change and of no toxicological significance. Reduced serum urea (17%) was present in females at 100 mg/kg/day and also noted in females at 600 mg/kg/day (33%).This is not considered a toxicologically relevant finding as a pathological change is normally reflected by an increase in serum urea levels. 

The NOEL in this study was determined to be 15 mg/kg/day. However, it may be considered that the findings at 100 mg/kg/day were not adverse in that they would not be considered to affect the performance of the whole organism or the ability of the organism to respond to an additional environmental challenge. The NOAEL in this study was therefore, 100 mg/kg/day. Definitions on NOAEL and adverse effects are extracted from the Ecetoc technical report No 85, Recognition of, and Differentiation between, Adverse and Non-adverse Effects in Toxicology Studies.[i]This conclusion is supported by the results of the reproduction toxicity screening test discussed below.

Preliminary reproduction toxicity screening test with 2,6-bis(1,1-dimethylethyl)-phenol, Becker H., Biedermann K. (1992), RCC, Research and Consulting Company Ltd. and RCC Umweltchemie AG, Itingen, Switzerland, SI Group, Report No. 321794)

In this study male and female rats were dosed during a preparing and pairing period and until the day before sacrifice (around 43 days) at 0, 30, 150 and 750 mg/kg/day in order to investigate the effects on male and female reproductive performance. Marked toxicity as manifested by clinical signs of sedation, ataxia, lateral/ventral recumbancy, tremors, clonic spasms and hunched posture were recorded in both sexes at 750 mg/kg/day. There were no effects on general tolerability (clinical signs, bodyweight change, food intake), reproduction parameters or pup viability at 150 mg/kg/day.

The 90 d study is the study with the highest relevance for this endpoint. In addition the results shown there are in line with the findings of the other two studies. In the 28 d study slight effects in the liver and the kidneys have been seen at 100 mg/kg bw/d which are comparable to those seen in the 90 d study at the highest dose. In the latter study it has been shown that these effects are reversible in a short recovery period and therefore are not adverse. The fact that the liver effects in the 28 d study are a bit more pronounced at 100 mg/kg bw/d as compared to those seen in the 90 d study at 270 mg/kg bw/d might very well be a result of the bolus dosing in the former study. The continous exposure dietary exposure of the latter is nevertheless a better mimic for the continous exposure of worker and especially the general public.

The findings in the reproduction toxicity screening test with an exposure period of at least 43 days on the other hand support the findings of the 90-day study. At the very high dose of 750 mg/kg there were notable symptoms in male and female rats (increased food consumption in the male rats and reduced food consumption in the female rats). These were acute effects after bolus administration of a very high dose. Further, marginally reduced body weight gain in the males and slightly reduced body weight gain in the females were noted. In summary the NOAEL of the 90-day study is deemed a valid point of departure for the determination of a DNEL.

ASSESSMENT FACTORS

Study duration: The standard factor for extrapolation from sub-chronic to chronic was used according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".

Oral absorption: Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cellular membranes. Generally, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. Generally, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cell membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additionally, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either.

According to the "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health", section 8.4.2 an oral absorption of 89 % was assumed and an inhalation absorption of 100% ("Note that if data on the starting route (oral) are available these should be used, but for the end route (inhalation), the worst case inhalation absorption should still be assumed (i.e. 100%)").

Interspecies Assessment factors: In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.

Intraspecies assessment factors: A factor for workers of 5 and for the general population of 10 has been suggested by the REACH guidance (8.4.3.1), however, based on several analyses of large data sets and in accordance with many workplace OEL setting practices an intraspecies factor for workers of 3 is considered appropriate for the worker population (ECETOC 2003 & 2010). Additionally following a review of human data which included both sexes and a variety of disease states and ages, the use of the 95thpercentile is considered sufficiently conservative to account for intraspecies variability in the general population and thus a default assessment factor of 5 is recommended (ECETOC, 2003 & 2010).

 

Conversion of oral NOAEL to inhalation DNEL, Workers.

REACH ECHA guidance Chapter R. 8: Characterisation of dose [concentration]-response for human health, R8.4.2 and using the example in Figure R. 8-3 Modification of a starting point.

For workers (in case of 8h exposure/d):

Corrected inhalatory N(L)OAEC

           =oral NOAEL * 1/sRVrat* ABSoral-rat/ABSinh-human* sRVhuman/wRV

           

sRVrat: standard respiratory volume (= 1/0.38);

ABS: absorption; ABS oral rat = 89%, ABS inhalation human = 100%

sRVhuman: standard respiratory volume 6.7 m3

wRV: worker respiratory volume 10 m3

oral NOAEL: 270 mg/kg/d

=oral NOAEL * 1/0.38 m3/kg/dt* 89/100* 6.7 m3(8h)/10 m3(8h)

= 423.69 mg/m3

 

For interspecies difference no additional interspecies allometric factor is applied at this stage as allometric scaling has already been considered in the route to route extrapolation step above with the respiratory volume adjustments (REACH ECHA guidance Chapter R. 8, Appendix *.8-2, Example B.3). An intraspecies assessment factor of 3 is applied.

           = 423.69 mg/m3/ 3

           = 141.23 mg/m3

Conversion from sub-chronic to chronic DNEL

           = 141.2 mg/m3/ 2

           = 70.61 mg/m3

Inhalation DNELlong-term(workers) = 70.61 mg/m3

 

Conversion of oral NOAEL to dermal DNEL, Workers.

REACH ECHA guidance Chapter R. 8: Characterisation of dose [concentration]-response for human health, Appendix R8-2, route to route extrapolation and allometric scaling, Part 2, Modification of starting point, Example B. 5.

Correct oral NOAEL rat (in mg/kg bw/d) into dermal NOAEL rat (in mg/kg bw/d) by correcting for differences in absorption between routes (if the case) as well as for differences in dermal absorption between rats and humans (if the case):

Corrected dermal NOAEL = oral NOAEL * ABSoral-rat/ABSdermal-rat* ABSdermal-rat/ ABSderm-human

           = oral NOAEL * ABSoral-rat/ ABSderm-human

(note - on the assumption that, in general, dermal absorption will not be higher than oral absorption, no default factor (i.e. factor 1) should be introduced when performing oral-to-dermal extrapolation (chapter R8.4.2).

For interspecies differences, apply factor for allometric scaling (4 for rat).

           = 270/4 mg/kg bw/d

           = 67.5 mg/kg bw/d

For intraspecies differences apply factor of 3.

= 67.5 mg/kg bw/d / 3

           = 22.5 mg/kg bw/d

Conversion from sub-chronic to chronic DNEL

           = 22.5 mg/kg bw/d / 2

           = 11.25 mg/kg bw/d

Dermal DNELlong-term(workers) = 11.25 mg/kg bw/d

1)     Batke M, et al. Poster presentation at the Eurotox conference, Dresden, 2009

2)     ECETOC, 2003, Technical Report No. 86, "Derivation of Assessment Factors for Human Health Risk Assessment."

3) ECETOC, 2010, Technical Report No. 110 "Guidance on Assessment Factors to Derive a DNEL”

4) Sietsma WK, J Pharm Sci. 1993 Jun;82(6):610-2. Absorption, bioavailability, and pharmacokinetics of tebufelone in the rat.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
20.9 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
DNEL derivation method:
other: ECHA REACH Guidance and the ECETOC approach.
Overall assessment factor (AF):
10
Dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Modified dose descriptor starting point:
NOAEC
Value:
208.96 mg/m³
Explanation for the modification of the dose descriptor starting point:

Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cel ular membranes. General y, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. General y, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cel membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additional y, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either. Therefore a route to route extrapolation from oral to inhalation is scientifically justified. For oral absorption 89 % absorption is assumed, while for inhalation absorption 100 % is assumed.

AF for dose response relationship:
1
Justification:
The NOAEL of the 90 d study (oral, rat) is set at the highest dose group, as there only very slight effects had been seen, which were reversible. Accordingly a special dose response effect could not be detected.
AF for differences in duration of exposure:
2
Justification:
Standard factor for extrapolation from sub-chronic to chronic according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".
AF for interspecies differences (allometric scaling):
1
Justification:
No additional interspecies allometric factor is applied at this stage as allometric scaling has already been considered in the route to route extrapolation step above with the respiratory volume adjustments ("Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health", Appendix *.8-2, Example B.3).
AF for other interspecies differences:
1
Justification:
In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.
AF for intraspecies differences:
5
Justification:
Intraspecies factor for general public according to "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for the quality of the whole database:
1
Justification:
The NOAEL on which the DNEL derivation is based was derived in a subchronic study conducted in full compliance with the OECD Principles of Good Laboratory Practice and OECD Guidelines for the Testing of Chemicals, No. 408, adopted 21 September 1998.
AF for remaining uncertainties:
1
Justification:
No indications for remaining uncertainties.
Acute/short term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
6.75 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
DNEL derivation method:
other: ECHA REACH Guidance and the ECETOC approach.
Overall assessment factor (AF):
40
Dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Modified dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:

Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cel ular membranes. Generally, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. Generally, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cel membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additional y, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either. Further according to “Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health”: On the assumption that, in general, dermal absorption will not be higher than oral absorption, no default factor (i.e. factor 1) should be introduced when performing oral-to-dermal extrapolation.

AF for dose response relationship:
1
Justification:
The NOAEL of the 90 d study (oral, rat) is set at the highest dose group, as there only very slight effects had been seen, which were reversible. Accordingly a special dose response effect could not be detected.
AF for differences in duration of exposure:
2
Justification:
Standard factor for extrapolation from sub-chronic to chronic according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".
AF for interspecies differences (allometric scaling):
4
Justification:
Standard factor for allometric scaling between rat and human according to "Guidance on information r
equirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health" and "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010).
AF for other interspecies differences:
1
Justification:
emaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.
AF for intraspecies differences:
5
Justification:
Intraspecies factor for general public according to "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for the quality of the whole database:
1
Justification:
The NOAEL on which the DNEL derivation is based was derived in a subchronic study conducted in full compliance with the OECD Principles of Good Laboratory Practice and OECD Guidelines for the Testing of Chemicals, No. 408, adopted 21 September 1998.
AF for remaining uncertainties:
1
Justification:
No indications for remaining uncertainties.
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
6.75 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
DNEL derivation method:
other: ECHA REACH Guidance and the ECETOC approach.
Overall assessment factor (AF):
40
Dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Modified dose descriptor starting point:
NOAEL
Value:
270 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:

No route to route extrapolation applied.

AF for dose response relationship:
1
Justification:
The NOAEL of the 90 d study (oral, rat) is set at the highest dose group, as there only very slight effects had been seen, which were reversible. Accordingly a special dose response effect could not be detected.
AF for differences in duration of exposure:
2
Justification:
Standard factor for extrapolation from sub-chronic to chronic according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".
AF for interspecies differences (allometric scaling):
4
Justification:
Standard factor for allometric scaling between rat and human according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health" and "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010).
AF for other interspecies differences:
1
Justification:
In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010) and “Derivation of Assessment Factors for Human Health Risk Assessment”Technical Report No. 86 (ECETOC 2003), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6-DTBP it has not been considered necessary to apply this factor.
AF for intraspecies differences:
5
Justification:
Intraspecies factor for general public according to "Guidance on Assessment Factors to Derive a DNEL” Technical Report No. 110 (ECETOC 2010)
AF for the quality of the whole database:
1
Justification:
The NOAEL on which the DNEL derivation is based was derived in a subchronic study conducted in full compliance with the OECD Principles of Good Laboratory Practice and OECD Guidelines for the Testing of Chemicals, No. 408, adopted 21 September 1998.
AF for remaining uncertainties:
1
Justification:
No indications for remaining uncertainties.
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:
no hazard identified

Additional information - General Population

Derivation of DNELS for the general population.

For 2,6 DTBP a general population DNEL for the inhalation route of exposure is required to enable the assessment of risk to consumers by the this route whilst an oral DNEL is also required to enable the assessment of risk to man exposed via the environment.

ASSESSMENT FACTORS

Study duration: The standard factor for extrapolation from sub-chronic to chronic was used according to "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health".

Oral absorption: Absorption of a chemical from the GI tract depends on its physical properties, including lipid solubility and the dissociation rate. 2,6 DTBP has water solubility of 4.11 mg/L and Log Kow of 4.5 indicating the substance is lipophilic and can diffuse across the lipid domain of cellular membranes. Generally, Log Kow values between 0 and 4 are optimal for absorption. 2,6 DTBP also has a molecular weight of 206.33 indicating that it is small enough to diffuse across the lipid domain of the membrane. Generally, molecular weights < 500 are optimal for absorption. Facilitated transportation across the cell membrane is not likely to occurviaformation of a complex with carrier proteins because 2,6 DTBP is not expected to bind to a protein (OECD Toolbox v.1.1). Therefore, absorption in the GI tract is expected to occur predominantly via simple diffusion. The mean predicted fractional absorption of 2,6 DTBP in the human is 0.89 (Simcyp v.10.0). Additionally, Tebufelone, a member of the chemical class of DTBP antirheumatic agents, has been shown to have complete absorption and bioavailability following oral (bolus) administration of the drug (Sietsema W.K. et al. 1993). Therefore, significant first pass effects are not expected for 2,6 DTBP either.

According to the "Guidance on information requirements and chemical safety assessment Chapter R.8: Characterisation of dose [concentration]-response for human health", section 8.4.2 an oral absorption of 89 % was assumed and an inhalation absorption of 100% ("Note that if data on the starting route (oral) are available these should be used, but for the end route (inhalation), the worst case inhalation absorption should still be assumed (i.e. 100%)").

Interspecies Assessment factors: In addition to the allometric scaling factor of 4 a further interspecies assessment factor of 2.5 (remaining difference) is proposed in REACH Guidance R8, section R8.4.3.3, Table R.8-6, however no scientific basis for this is reported. In ECETOC Technical Report No 86 and Technical Reprt 110 (ECETOC 2003 & 2010), a conclusion was reached that in the absence of a substance specific mode of action, allometric scaling based on metabolic rate is considered to provide an appropriate default assessment factor. As a specific mode of action has not been identified for 2,6 -DTBP it has not been considered necessary to apply this factor.

Intraspecies assessment factors: A factor for workers of 5 and for the general population of 10 has been suggested by the REACH Guidance R8, section 8.4.3.1, however, based on several analyses of large data sets and in accordance with many workplace OEL setting practices an intraspecies factor for workers of 3 is considered appropriate for the worker population (ECETOC, 2003 & 2010). Additionally following a review of human data which included both sexes and a variety of disease states and ages, the use of the 95th percentile is considered sufficiently conservative to account for intraspecies variability in the general population and thus a default assessment factor of 5 is recommended (ECETOC, 2003 & 2010).

The oral DNELlong-term (general population) is required in order to assess the risk to man via the environment and the deriviation of this DNEL is shown below:

Using 270 mg/kg/d NOAEL from the 90 day oral toxicity study in rats. No modification of the starting point is required.

For interspecies differences, apply factor for allometric scaling (4 for rat)

                               = 270 mg/kg bw/d /4
                               = 67.5

For intraspecies differences, apply factor of 5

                               = 67.5 mg/kg bw/d /5
                               = 13.5 mg/kg bw/d

Conversion from sub-chronic to chronic DNEL, apply a factor of 2

                              = 13.5 mg/kg bw/d / 2
                              = 6.75

Oral DNELlong-term(general population) = 6.75 mg/kg bw/d

General population DNELs for inhalation exposure are based on consumers being exposed to 2,6-DTBP for 24h exposure per day. Following the guidance in REACH Guidance R8, section R.8.4.2, Table R.8-2, the sRVratfor 24 hour exposure is calculated to be 1.15 m3/kg bw.

Corrected inhalatory N(L)OAEC

           =oral NOAEL * 1/sRVrat* ABSoral-rat/ABSinh-rat* ABSinh-rat/ABSinh-human

           =oral NOAEL * 1/1.15 m3/kg/d* ABSoral-rat/ABSinh-human 

ABS: absorption; sRV: standard respiratory volume;

Using 270 mg/kg/d NOAEL, a factor of 89 %/100 % is used for oral to inhalation extrapolation based on the assumption of 89% oral absorption

           = 270 * 1/1.15 m3/kg/d * 89 % / 100%

           = 208.96 mg/m3

Intraspecies Assessment factors; a factor of 5 is used

           = 208.96 mg/m3/ 5

           = 41.8 mg/m3

Conversion from sub-chronic to chronic DNEL

           = 41.8 mg/m3/ 2

           = 20.9 mg/m3

Inhalation DNELlong-term(general population) = 20.9 mg/m3 (24h exposure/d)

1)     Batke M, et al. Poster presentation at the Eurotox conference, Dresden, 2009

2)     ECETOC, 2003, Technical Report No. 86, "Derivation of Assessment Factors for Human Health Risk Assessment."

3) ECETOC, 2010, Technical Report No. 110 "Guidance on Assessment Factors to Derive a DNEL”

4) Sietsema WK, J Pharm Sci. 1993 Jun;82(6):610 -2. Absorption, bioavailability, and pharmacokinetics of tebufelone in the rat.

Conversion of oral NOAEL to dermal DNEL, General public.

REACH ECHA guidance Chapter R. 8: Characterisation of dose [concentration]-response for human health, Appendix R8-2, route to route extrapolation and allometric scaling, Part 2, Modification of starting point, Example B. 5.

Correct oral NOAEL rat (in mg/kg bw/d) into dermal NOAEL rat (in mg/kg bw/d) by correcting for differences in absorption between routes (if the case) as well as for differences in dermal absorption between rats and humans (if the case):

Corrected dermal NOAEL = oral NOAEL * ABSoral-rat/ABSdermal-rat* ABSdermal-rat/ ABSderm-human

           = oral NOAEL * ABSoral-rat/ ABSderm-human

(note - on the assumption that, in general, dermal absorption will not be higher than oral absorption, no default factor (i.e. factor 1) should be introduced when performing oral-to-dermal extrapolation (chapter R8.4.2).

For interspecies differences, apply factor for allometric scaling (4 for rat).

           = 270/4 mg/kg bw/d

           = 67.5 mg/kg bw/d

For intraspecies differences apply factor of 5.

= 67.5 mg/kg bw/d / 5

           = 13.5 mg/kg bw/d

Conversion from sub-chronic to chronic DNEL

           = 13.5 mg/kg bw/d / 2

           = 6.75 mg/kg bw/d

Dermal DNELlong-term(general population) = 6.75 mg/kg bw/d

1)     Batke M, et al. Poster presentation at the Eurotox conference, Dresden, 2009

2)     ECETOC, 2003, Technical Report No. 86, "Derivation of Assessment Factors for Human Health Risk Assessment."

3) ECETOC, 2010, Technical Report No. 110 "Guidance on Assessment Factors to Derive a DNEL”

4) Sietsma WK, J Pharm Sci. 1993 Jun;82(6):610-2. Absorption, bioavailability, and pharmacokinetics of tebufelone in the rat.