Trometamol

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

117.5 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

15

Modified dose descriptor starting point:

NOAEC

AF for dose response relationship:

1

AF for differences in duration of exposure:

3

AF for interspecies differences (allometric scaling):

1

AF for other interspecies differences:

1

AF for intraspecies differences:

5

AF for the quality of the whole database:

1

AF for remaining uncertainties:

1

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

166.7 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

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

No DNELs have been derived for the short-term dermal and inhalation exposure of 2-amino-2-(hydroxymethyl)-1,3-propanediol(trometamol) for workers, as it is assumed that the assessment of hazard is sufficiently covered by deriving the respective DNELs for long-term exposure.

No quantitative dose-response data are available for local short-term effects on skin and respiratory tract of trometamol

.

The long-term DNELs for trometamol were calculated based on the systemic NOAEL of ≥1000 mg/kg bw/day, derived from the reproductive/developmental toxicity screening study by Ellis-Hutchings et al. (2012). The study by Darby and Anderson (1966) also indicated minimal toxicity in rats and dogs, but only limited details were reported in the publication. Briefly, rats or dogs were administered trometamol (250 – 4000 mg/kg bw/day) per oral route for 30 days. The highest dose level tested in rats or dogs caused moderate diarrhoea orvomiting and loose stools, respectively. These effects are treatment-related, but not considered to be serious adverse effects.As no animals died andno gross pathological findings were noted in both species, the NOAELs were determined to be 4000 mg/kg bw/day. Thus, the results of Darby and Anderson (1966) confirmed the NOAEL derived in the study of Ellis-Hutchings et al. (2012).

 

A reproduction/developmental toxicity screening test was conducted in rats according to OECD 421 (Ellis-Hutchings et al., 2012). TRIS AMINO was administered by gavage to parental rats at dose levels of 100, 300 and 1000 mg/kg bw/day. Female rats were dosed once daily for approximately two weeks prior to breeding, through breeding (up to two weeks), gestation (three weeks), and lactation (four days) up to termination. Male rats were dosed for two weeks prior to breeding and continuing through breeding (two weeks) until necropsy (test day 30). Therefore, the duration of treatment was approximately 54 days for the females and 29 days for the males.

All animals survived to the scheduled termination of the study. Treatment-related parental toxicity was limited to point of contact irritation in the stomach of animals given 300 and 1000 mg/kg bw/day. This was interpreted to be a localized irritation effect on the stomach due to repeated oral gavage of the test substance (~ pH 9). No treatment-related systemic effects were observed in any animal at any dose level tested. As no effects were observed up to and including the highest dose level, the NOAEL is ≥ 1000 mg/kg bw/day.

The study performed by Ellis-Hutchings et al. (2012) was chosen as the starting point for deriving the dermal DNEL as there is no dermal repeated dose study. To convert the oral NOAEL [mg/kg bw/day] into a dermal NOAEL [mg/kg bw/day], the differences in absorption between routes as well as differences in dermal absorption between rats and humans have to be accounted for (Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose [concentration]-response for human health, European Chemicals Agency, Version 2, December 2010).

A quantitative study of percutaneous absorption in-vitro was carried out on human abdominal skin placed in a FRANZ diffusion cell (Noel-Hudson, 1993). After 24 h, the percutaneous absorption of trometamol through human skin was very low regardless of the concentration of the trometamol solution (10% and 0.1% trometamol solutions were tested). Less than 1% of the applied dose was found. For both solutions, the maximum value of flux was reached after 4 h and remained essentially constant during the rest of the experiment (totally 24 h). However, the value of flux was about 150 times higher for the 10% solution (6.922 ± 6.179 µg/cm²/h) than for the 0.1% solution (0.039 ± 0.052 µg/cm²/h). After washing, the retention of trometamol in the epidermis and dermis was also less than 1% of the applied dose. Therefore, trometamol did not retain in the horny layer but was almost totally eliminated by washing the skin. The washing waters contained more than 90% of the applied dose.

For neat trometamol (i.e. a solid substance resulting in a basic solution), a QSAR based modelling published by Potts and Guy (1992), taking into account molecular weight and low Kow, estimated a dermalpermeability constant Kp of 7.54E-06 cm/h. Similar to the approach taken by Kroes et al. (2007), the maximum flux Imax (Imax = Kp [cm/h] x water solubility [mg/cm³]) was calculated, resulting in dermal absorption of 5.2 µg/cm²/h trometamol. Usually, this value is considered as indicator for a dermal absorption of 40% (Mostert and Goergens, 2011). However, given the fact that experimental data are available, the information on dermal absorption generated from experiments is more relevant for the risk assessment compared to QSAR based calculations. Taking into account that the washing waters contained more than 90% of the applied dose (Noel-Hudson, 1993), a dermal uptake of 10% has to be regarded as a worst case scenario.

 

The long-term worker DNEL for inhalation systemic effects is again based on the reproduction/developmental toxicity screening test performed according to OECD 421 (Ellis-Hutchings et al., 2012). This study was chosen as the starting point for deriving the DNEL as there is no inhalation repeated dose study. According to the “Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose [concentration]-response for human health” (European Chemicals Agency, Version 2, December 2010), the oral NOAEL should be converted into an inhalatory NAEC: the oral dose for the rat is converted to the corresponding air concentration using a standard breathing volume for the rat (0.38 m³/kg for 8 h exposure). Additionally, it should be taken into account that during 8 hours light activity at work the respiratory rate becomes higher (10 m³/person) than standard (6.7 m³/person). Considering these differences, the corrected starting point is a NAEC of 1763.2 mg/m³. The absorption via the inhalative route is considered to be in the same order as via the oral route.

 

In general, assessment factors (AF) recommended by ECHA (Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose[concentration]-response for human health. European Chemicals Agency, Version 2, December 2010) were used when applicable to derive the DNELs. Several AFs for which there is additional information were refined.

The difference in metabolic rate between humans and the test species has been taken into account, where relevant. The AF for remaining interspecies differences has been set at 1, as the toxicokinetic data indicates that trometamol will not be metabolised, when absorbed. An AF for exposure duration is applied to take into account the difference between experimental exposure duration and the exposure duration for the worker.

trometamol administered via the oral, inhalation or dermal exposure route will only be absorbed in small amounts based on the fact that predominantly the unionised form of trometamol can permeate the cell membrane and based on its physico-chemical properties. As trometamol acts as proton acceptor in-vivo, it is rapidly ionised e.g. by the acid content of the stomach and is therefore not absorbed. The limited amounts of trometamol that are systemically bioavailable are not bound to plasma proteins and exist in the ionised form. At physiological blood pH, trometamol supplements the buffering capacity of the blood bicarbonate system, accepting a proton. Bioavailable levels of trometamol are rapidly eliminated by the kidneys and found not metabolised in the urine. No relevant metabolism is expected, based on experimental data and QSAR modelling. The AF for remaining interspecies differences has been set at 1, as the toxicokinetic data indicates that trometamol will not be metabolised.

 

An AF for exposure duration is applied to take into account the difference between experimental exposure duration and the exposure duration for the worker. In the reproduction/developmental toxicity screening test (OECD 421) that is used to derive the long-term exposure DNELs, rats were exposed for at least 29 days (approximately 54 days for the females and 29 days for the males). Based on a recent publication (Batke et al., 2011), an AF of 3 has been chosen in this case, as it reflects the exposure duration accurately. The study of Batke et al. (2011) performed an assessment of the time extrapolation factors based on the comparison of NOELs from different duration studies. Batke et al. (2011) concluded that in the majority of cases a factor of 3 is sufficient to convert the subacute exposure duration to chronic exposure duration. As in the present case, the NOAEL corresponds to the highest dose tested with no evidence of treatment-related adverse effects, a factor of 3 can be used according to Batke et al. (2011).

 

References

Potts, R. and Guy, R. (1992) Predicting skin permeability. Pharm. Res. 9(5): 663-669

Kroes, R. et al. (2007) Application of the threshold of toxicological concern (TTC) to the safety evaluation of cosmetic ingredients. Food Chem. Toxicol. 45, 2533–2562

Mostert, V. and Goergens, A. (2011) Dermal DNEL setting: using QSAR predictions for dermal absorption for a refined route-to-route extrapolation. Society of Toxicology, Annual Meeting, ISSN 1096-6080 (http://www.toxicology.org/AI/PUB/Toxicologist11.pdf), 120(2): 107

Batke et al., 2011, Evaluation of time extrapolation factors based on the database RepDose. Toxicol Lett, 205(2):122 -129

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

29 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

30

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

83.3 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

12

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

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:

8.3 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

120

Modified dose descriptor starting point:

NOAEL

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

No DNELs have been derived for the short-term dermal, inhalation and oral exposure of 2 -amino-2-(hydroxymethyl)-1,3-propanediol (trometamol) for the general population, as it is assumed that the assessment of hazard is sufficiently covered by deriving the respective DNELs for long-term exposure. No quantitative dose-response data are available for local short-term effects on skin and respiratory tract of trometamol.

 

The long-term DNELs for trometamol were calculated based on the systemic NOAEL of ≥1000 mg/kg bw/day, derived from the reproductive/developmental toxicity screening study byEllis-Hutchings et al. (2012). The study of Darby and Anderson (1966) also indicated minimal toxicity in rats and dogs, but only limited details were reported in the publication. Briefly, rats or dogs were administered trometamol (250 – 4000 mg/kg bw/day) per oral route for 30 days. The highest dose level tested in rats or dogs caused moderate diarrhoea orvomiting and loose stools, respectively. These effects are treatment-related, but not considered to be serious adverse effects. Since no animals died andno gross pathological findings were noted in both species, the NOAELs were determined to be 4000 mg/kg bw/day. Thus, the results of Darby and Anderson (1966) confirmed the NOAEL from the study performed by Ellis-Hutchings et al. (2012).

 

A reproduction/developmental toxicity screening test was conducted in rats according to OECD 421 (Ellis-Hutchings et al., 2012). TRIS AMINO was administered by gavage to parental rats at dose levels of 100, 300 and 1000 mg/kg bw/day. Female rats were dosed once daily for approximately two weeks prior to breeding, through breeding (up to two weeks), gestation (three weeks), and lactation (four days) up to termination. Male rats were dosed for two weeks prior to breeding and continuing through breeding (two weeks) until necropsy (test day 30). Therefore, the duration of treatment was approximately 54 days for the females and 29 days for the males.

All animals survived to the scheduled termination of the study. Treatment-related parental toxicity was limited to point of contact irritation in the stomach of animals given 300 and 1000 mg/kg bw/day. This was interpreted to be a localized irritation effect on the stomach due to repeated oral gavage of the test substance (~ pH 9). No treatment-related systemic effects were observed in any animal at any dose level tested. As no effects were observed up to and including the highest dose level, the NOAEL is ≥ 1000 mg/kg bw/day.

The study performed by Ellis-Hutchings et al. (2012) was chosen as the starting point for deriving the DNEL as there is no dermal repeated dose study. To convert the oral NOAEL [mg/kg bw/day] into a dermal NOAEL [mg/kg bw/day], the differences in absorption between routes as well as differences in dermal absorption between rats and humans have to be accounted for (Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose [concentration]-response for human health, European Chemicals Agency, Version 2, December 2010).

A quantitative study of percutaneous absorption in-vitro was carried out on human abdominal skin placed in a FRANZ diffusion cell (Noel-Hudson, 1993). After 24 h, the percutaneous absorption of trometamol through human skin was very low, regardless of the concentration of the trometamol solution (10% and 0.1% trometamol solutions were tested). Less than 1% of the applied dose was found.

For both solutions, the maximum value of flux was reached after 4 h and remained essentially constant during the rest of the experiment (totally 24 h). However, the value of flux was about 150 times higher for the 10% solution (6.922 ± 6.179 µg/cm²/h) than for the 0.1% solution (0.039 ± 0.052 µg/cm²/h). After washing, the retention of trometamol in the epidermis and dermis was also less than 1% of the applied dose. Therefore, trometamol did not retain in the horny layer but was almost totally eliminated by washing the skin. The washing waters contained more than 90% of the applied dose.

For neat trometamol (i.e. a solid substance resulting in a basic solution), a QSAR based modelling published by Potts and Guy (1992), taking into account molecular weight and low Kow, estimated a dermal permeability constant Kp of 7.54E-06 cm/h. Similar to the approach taken by Kroes et al. (2007), the maximum flux Imax (Imax = Kp [cm/h] x water solubility [mg/cm³]) was calculated, resulting in dermal absorption of 5.2µg/cm²/h trometamol.Usually, this value is considered as indicator for a dermal absorption of 40% (Mostert and Goergens, 2011). However, given the fact that experimental data are available, the information on dermal absorption generated from experiments is more relevant for the risk assessment compared to QSAR based calculations. Taking into account that the washing waters contained more than 90% of the applied dose (Noel-Hudson, 1993), a dermal uptake of 10% has to be regarded as a worst case scenario.

 

The long-term worker DNEL for inhalation systemic effects is again based on the reproduction/developmental toxicity screening test performed according to OECD 421 (Ellis-Hutchings et al., 2012). This study was chosen as the starting point for deriving the DNEL as there is no inhalation repeated dose study. According to the “Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose [concentration]-response for human health” (European Chemicals Agency, Version 2, December 2010), the oral NOAEL should be converted into an inhalatory NAEC: the oral dose for the rat is converted to the corresponding air concentration using a standard breathing volume for the rat (1.15 m³/kg for 24 h exposure). Therefore, the corrected starting point is a NAEC of 869.6 mg/m³. The absorption via the inhalative route is considered to be in the same order as via the oral route.

 

In general, assessment factors (AF) recommended by ECHA (Guidance on information requirements and chemical safety assessment. Chapter R.8: Characterisation of dose[concentration]-response for human health. European Chemicals Agency, Version 2, December 2010) were used when applicable to derive the DNELs. Several AFs for which there is additional information were refined.

The difference in metabolic rate between humans and the test species has been taken into account, where relevant. The AF for remaining interspecies differences has been set at 1, as the toxicokinetic data indicates that trometamol will not be metabolised, when absorbed. An AF for exposure duration is applied to take into account the difference between experimental exposure duration and the exposure duration for the general population.

In the reproduction/developmental toxicity screening test (OECD 421) that is used to derive the long-term exposure DNELs, rats were exposed for at least 29 days (approximately 54 days for the females and 29 days for the males). Based on a recent publication (Batke et al., 2011), an AF of 3 has been chosen in this case, as it reflects the exposure duration accurately. The study of Batke et al. (2011) performed an assessment of the time extrapolation factors based on the comparison of NOELs from different duration studies. Batke et al. (2011) concluded that in the majority of cases a factor of 3 is sufficient to convert a subacute exposure duration to chronic exposure duration. As in the present case, the NOAEL corresponds to the highest dose tested with no evidence of treatment related adverse effects, a factor of 3 can be used according to Batke et al. (2011).

 

References

Potts, R. and Guy, R. (1992)Predicting skin permeability.Pharm. Res. 9(5): 663-669

Kroes, R. et al. (2007) Application of the threshold of toxicological concern (TTC) to the safety evaluation of cosmetic ingredients. Food Chem. Toxicol. 45, 2533–2562

Mostert, V. and Goergens, A. (2011) Dermal DNEL setting: using QSAR predictions for dermal absorption for a refined route-to-route extrapolation. Society of Toxicology, Annual Meeting, ISSN 1096-6080 (http://www.toxicology.org/AI/PUB/Toxicologist11.pdf), 120(2): 107

Batke et al., 2011, Evaluation of time extrapolation factors based on the database RepDose. Toxicol Lett, 205(2):122 -129