Registration Dossier

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
0.44 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
Overall assessment factor (AF):
10
Modified dose descriptor starting point:
NOAEC
Value:
4.41 mg/m³
Explanation for the modification of the dose descriptor starting point:
Please refer to "Discussion"
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:
1.79 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
Overall assessment factor (AF):
40
Modified dose descriptor starting point:
NOAEL
Value:
71 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:
Please refer to "Discussion"
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
410 µg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Dose descriptor:
other: NESIL = 4100 µg/cm²
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
410 µg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Dose descriptor starting point:
other: NESIL = 4100 µg/cm²

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:
no hazard identified

Additional information - workers

Point of departure

Toxicity data on animals repeatedly treated with 2-(4-tertbutyl)propionaldehyde are available and are used for the derivation of respective DNELs.

The key study for repeated dose toxicity is a rat 90 day repeated dose gavage study according to OECD TG 408 and GLP (Givaudan 1986A-B, Givaudan 1987). On the basis of the effects observed, a no adverse effect level has been set at 25 mg/kg bw/d based on adverse effects on liver and testes. Since adversity such as neurotoxicological effects was not evident, a no effect level has been set at 5 mg/kg bw/d based on 2-(4-tertbutyl)propionaldehyde induced reversible decreases in plasma cholinesterase activity.

Various repeated dose toxicity studies demonstrated adverse effects of 2-(4-tertbutyl)propionaldehyde on the male reproductive system in rats (NOAEL = 25 mg/kg bw/d), whereas no evidence for testicular toxicity or general toxicity was observed in the mouse and guinea pig. Considering non-rodent species, the dog has been shown to be susceptible towards testicular toxicity as well, however at higher dose levels than the rat (NOAEL = 44.6 mg/kg bw/d). In contrast, short-term oral exposure to rabbits did not indicate a potential of 2-(4-tertbutyl)propionaldehyde to induce testicular toxicity or general toxicity. Furthermore in rhesus monkeys, no indication of testicular toxicity or symptoms of incompatibility was observed at doses causing testicular toxicity in the rats. Therefore, the rat appears to be the most susceptible species and exposure to 2-(4-tertbutyl)propionaldehyde above a clearly defined threshold dose seems sufficient to cause testicular toxicity.

In the key study for developmental toxicity, i.e. a study in Wistar rats acc. to OECD TG 414 and GLP, oral administration of 2-(4-tertbutyl)propionaldehyde via gavage induced general systemic and liver toxicity for high dose ( 40.7 (nominal dose: 45) mg/kg bw/d) and less pronounced for mid dose (12.7 (nominal dose: 15) mg/kg bw/d) dams (BASF SE 2004). Furthermore, serum and erythrocyte cholinesterase activities (but not brain CHE activities) were decreased in these dose groups. Increased numbers of fetuses with common skeletal variations, fetal growth retardations, increased early resorptions and the subsequent decrease in number of fetuses are considered manifestations of the non–specific maternal stress. Based on these findings, the NOAEL is set at 4.1 mg/kg bw/day (nominal dose: 5 mg/kg bw/d) for maternal and prenatal developmental toxicity.

 

In an one-generation range finding study in rats, general systemic toxicity, indications for liver toxicity and impaired male fertility was observed after oral administration of 2-(4-tertbutyl)propionaldehyde in capsules via feed (BASF 2006C). The NOAEL for fertility was set at 800 ppm (approx. 29 mg/kg bw/d lysmeral) based on the testicular toxicity and infertility observed. A LOEL for parental toxicity (females) of 400 ppm (10-14.5 mg/kg bw/d) and a NOAEL for parental toxicity (males) of 400 ppm (14.5 mg/kg bw/d) was set, based on clinicochemical findings such as decreases in serum and erythrocyte cholinesterase activities (but not brain CHE activities). According to the final decision from CoRAP (SEV1_201-289-8) dated 21 February 2014, the joint registrants are requested to perform a follow up reproductive toxicity study with 2-(4-tertbutyl)propionaldehyde, i.e. an EOGRTS according to OECD 443.

In order to ensure a sound dose selection for the required EOGRTS with the currently available testing material in an alternative formulation (change in capsule material), an one-generation range finding study in rats was performed (BASF 2017B) and resulted in general systemic toxicity (decreases in body weights and food consumption), hematological changes and liver toxicity starting at a dose of 750 ppm (7-12 mg/kg bw/d). Impaired male fertility was observed at the highest dose tested (2300 ppm; 25.1-27.5 mg/kg bw/d). Pup survival was affected at PND 0 - 4 and pup weights were decreased at starting at a dose of 750 ppm (7-12 mg/kg bw/d). No relevant lysmeral related adverse effects were observed at the lowest dose tested, i.e. 230 ppm (2 - 4 mg/kg bw/d).

 

In the main EOGRTS in rats (BASF SE 2017), impaired liver function and general systemic adverse effects on food consumption, body weights and clinical pathological parameters were identified as general, systemic toxicity in the two parental generations and adolescent animals at a nominal dose of 10 mg/kg bw/d (750 ppm; representing an overall mean dose of 15.1 mg/kg bw/d). In parallel, reduced pup body weights in the F1 and F2 offspring were observed at the same dose level. Inhibitory effects at this dose level on the peripheral AChE activity in pups and adolescent rats did not result in corresponding effects in neurobehavioral or neuropathological examinations. The respective NOAELs for general systemic and developmental toxicity has been set at a nominal dose of 3 mg/kg bw/d (230 ppm; representing an overall mean dose of 4.5 mg/kg bw/d). 

 

As a point of departure for the inhalative and dermal long term systemic DNEL, the NOEL of 5 mg/kg bw/d derived from the key study for repeated dose toxicity has been chosen. The NOEL used for the derivation of the systemic DNELs is generally considered sufficient covering the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde, i.e. impairment of male reproduction(spermatotoxicity and testicular toxicity). These effects have a NOAEL of 25 mg/ kg bw/d and are well above the chosen NOEL of 5 mg/kg bw/d. Further, this point of departure is supported by the NOAELs for pregnant animals observed in the developmental toxicity study as well as for the parental and offspring generations in the EOGRTS. The difference of the NO(A)ELs available in a range between 3 and 5 mg/kg bw/d is mainly driven by different dose selections, and the effects observed appear to be consistent between the different studies, dependent on their study design. There is strong concordance between the results of the 90-day study and the EOGRTS. Furthermore, there is no indication from the latter study that immature animals are more sensitive to the effects of 2-(4-tertbutyl) propionaldehyde than are adult animals. Overall, the NOEL of 5 mg/kg bw/d, derived from the 90 day repeated dose toxicity study in rats, is considered sufficiently conservative and represents a robust point of departure for the long term systemic DNELs.

 

 

Route to route extrapolation: oral – dermal:

There is clear evidence from kinetic and dermal toxicity studies in rats as well as from a dermal penetration study in human volunteers that systemic bioavailability of 2-(4-tertbutyl)propionaldehyde after dermal administration is considerably lower compared to that after oral administration. In rats, dermal administration of 2 -(4 -tertbutyl)propionaldehyde revealed lower Cmax plasma values compared to oral administration. Since rat skin is more permeable to dermally applied substances than human skin, and taking into account the results of a dermal penetration study in human volunteers, very limited percutaneous absorption and systemic bioavailability of 2-(4-tertbutyl)propionaldehyde is expected in humans. As a worst case assumption, a dermal absorption of max. 7% is assumed based on in vitro dermal penetration data, given that a value of 2% was derived in an in vivo study with human subjects (BASF SE 2016; Huntingdon Research Centre Ltd 1994).  Given its physicochemical properties, i.e. the low molecular weight (204 g/mol), moderate partition coefficient (log Pow around 4) and a readily water solubility (33 mg/l), lysmeral is likely to be taken up by passive diffusion and to have high bioavailability via the oral route. Therefore, an oral absorption of 100 % was assumed for 2-(4-tertbutyl) propionaldehyde being administered by gavage in the chosen key study.

Route to route extrapolation: oral – inhalation:

Due to the lack on route specific information, a default factor of 2 has been applied leading to the assumption, that half of the applied dose is absorbed via the oral route compared to the inhalative route according to current guidance document (R8, ECHA 2008).

For the worker, the following DNELs were derived:

Long-term systemic inhalative DNEL

The NOEL of the subchronic oral study was set at 5 mg/kg bw/d 2-(4-tertbutyl)propionaldehyde for males and females. For derivation of the long-term systemic inhalative DNEL, the oral NOEL was converted into a corrected inhalative NOAEC of 4.41 mg/m3 according to the procedure, recommended in the current guidance document (R8, ECHA 2008).

NOAEC corrected inhalative = 5*(1/0.38)*(50/100)*(6.7/10) = 4.41 mg/m3

 

Based on the profound toxicity databasis for 2-(4-tertbutyl)propionaldehyde, certain default assessment factors (acc. to ECHA GD R8) have been modified into substance specific assessment factors (AF), considering the intrinsic hazard properties of the registered substance. The following assessment factors (AF) were applied:

-         Interspecies differences/Allometric scaling = 1

Reasoning: Allometric scaling is not applicable according to R8 ECHA 2008.

 

-         Interspecies differences/Remaining differences = 1

Reasoning: On the basis of the multiple comparative studies using different rodent and non-rodent animal species (toxicodynamic) and additional toxicokinetic differences in relation to humans (formation of metabolites, i.e. TBBA), the rat has been identified as most susceptible species concerning the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde (impairment of male reproduction; spermatotoxicity and testicular toxicity). Furthermore, the lowest effect levels for other systemic effects, i.e. liver , were found in rats as well. Since the point of departure is based on a study with rats, identified as most susceptible species for 2-(4-tertbutyl)propionaldehyde induced toxicity, no additional safety factor to account for a putative higher sensitivity of humans besides aspects already covered by allometric scaling, is considered mandatory.

In general, although ‘residual’ interspecies variability may remain following allometric scaling, this is largely accounted for in the assessment factors proposed for intraspecies variability, i.e. reflecting the interdependency of inter- and intraspecies assessment factors (see also Calabrese et al., 1993, Regul. Toxicol. Pharmacol. 17: 44-51). Furthermore, within the ERASM project, it was found, that species are on average equally sensitive to equipotent doses, if doses are related to energy turnover. An animal to human interspecies extrapolation distribution with a geometric mean identical to the allometric scaling factor (e.g. 4 rat/human, 7 mouse/human) was identified, without an additional factor of 2.5 for putative toxicodynamic differences. Therefore, a factor of 2.5 for ‘remaining‘ interspecies differences may be questionable as a standard procedure (see also Escher et al., 2013, Toxicology Letters 218; 159– 165). 

Overall, the use of an AF of 1 instead of 2.5 for remaining differences for interspecies differences besides allometric scaling can be justified for 2-(4-tertbutyl)propionaldehyde.

 

-         Intraspecies differences= 5

Reasoning: Default assessment factor according to R8 ECHA 2008.

 

-         Exposure duration = 2

Reasoning: Extrapolation from subchronic to chronic toxicity according to the default assessment of R8 ECHA 2008.

 

-         Dose response = 1

Reasoning: No issues related to reliability of the dose-response according toR8 ECHA 2008.

 

-         Quality of whole database = 1

Reasoning: No issues related to completeness and consistency of the available data according toR8 ECHA 2008. 

 

AF = 1 x 1 x 5 x 2 x 1 x 1 = 10. Consequently, the inhalative long-term systemic DNEL was set at 0.44 mg/m3 for the worker.

 

  

Long-term systemic dermal DNEL

For derivation of the long-term systemic dermal DNEL, the oral NOEL was converted into a corrected dermal NOAEL of 71 mg/kg bw/d according to the procedure, recommended in the current guidance document (R8, ECHA 2008).

 

NOAEL corrected dermal = 5*(100/7) = 71 mg/kg bw/d

 

Based on the profound toxicity databasis for 2-(4-tertbutyl)propionaldehyde, certain default assessment factors (acc. to ECHA GD R8) have been modified into substance specific assessment factors (AF), considering the intrinsic hazard properties of the registered substance. The following assessment factors (AF) were applied:

-         Interspecies differences/Allometric scaling = 4

Reasoning: Allometric scaling is applied according to R8 ECHA 2008.

 

-         Interspecies differences/Remaining differences = 1

Reasoning: On the basis of the multiple comparative studies using different rodent and non-rodent animal species (toxicodynamic) and additional toxicokinetic differences in relation to humans (formation of metabolites, i.e. TBBA), the rat has been identified as most susceptible species concerning the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde (impairment of male reproduction; spermatotoxicity and testicular toxicity). Furthermore, the lowest effect levels for other systemic effects, i.e. liver , were found in rats as well. Since the point of departure is based on a study with rats, identified as most susceptible species for 2-(4-tertbutyl)propionaldehyde induced toxicity, no additional safety factor to account for a putative higher sensitivity of humans besides aspects already covered by allometric scaling, is considered mandatory.

In general, although ‘residual’ interspecies variability may remain following allometric scaling, this is largely accounted for in the assessment factors proposed for intraspecies variability, i.e. reflecting the interdependency of inter- and intraspecies assessment factors (see also Calabrese et al., 1993, Regul. Toxicol. Pharmacol. 17: 44-51). Furthermore, within the ERASM project, it was found, that species are on average equally sensitive to equipotent doses, if doses are related to energy turnover. An animal to human interspecies extrapolation distribution with a geometric mean identical to the allometric scaling factor (e.g. 4 rat/human, 7 mouse/human) was identified, without an additional factor of 2.5 for putative toxicodynamic differences. Therefore, a factor of 2.5 for ‘remaining‘ interspecies differences may be questionable as a standard procedure (see also Escher et al., 2013, Toxicology Letters 218; 159– 165). 

Overall, the use of an AF of 1 instead of 2.5 for remaining differences for interspecies differences besides allometric scaling can be justified for 2-(4-tertbutyl)propionaldehyde.

 

-         Intraspecies differences= 5

Reasoning: Default assessment factor according to R8 ECHA 2008.

 

-         Exposure duration = 2

Reasoning: Extrapolation from subchronic to chronic toxicity according to the default assessment of R8 ECHA 2008.

 

-         Dose response = 1

Reasoning: No issues related to reliability of the dose-response according toR8 ECHA 2008.

 

-         Quality of whole database = 1

Reasoning: No issues related to completeness and consistency of the available data according to R8 ECHA 2008. 

 

 

AF = 4 x 1 x 5 x 2 x 1 x 1 = 40. Consequently, the dermal long-term systemic DNEL derived was 1.79 mg/kg bw/d for the worker.

 

Further endpoint systemic dermal/inhalative DNELs: 

Derivation of endpoint specific DNELs addressing reproductive, developmental toxicity and maternal toxicity during pregnancy would result in higher DNELs as derived above. In the key developmental toxicity study, animals have been dosed throughout the whole relevant gestation period and time extrapolation does not need to be considered. Furthermore, no time extrapolation is mandatory for the NOAELs of the EOGRTS, since dosing occurred through the whole reproductive cycle (i.e. treatment of parental animals and a respective F1 generation to deliver a F2 generation). For the derivation of the systemic DNELs, based on the endpoint and NOEL for repeated dose toxicity, an AF of 2 has been applied for time extrapolation from subchronic to chronic exposure and would therefore also cover developmental and reproductive toxicity, where no such AF would be mandatory. It further needs to be pointed out, that the endpoint specific DNEL addressing developmental and maternal toxicity would have a low relevance for occupational settings, since exposure of pregnant workers to 2-(4-tertbutyl) propionaldehyde at high concentrations can be excluded due to common industrial practice.

Derivation of endpoint specific DNELs addressing the impairment of male reproduction would result in higher DNELs as derived above, since these effects have a NOAEL of 25 mg/ kg bw/d and are well above the chosen point of departure (NOEL of 5 mg/kg bw/d).

Overall, the multiplicatory principle of AF together with the choice of the NOEL as point of departure assures a sufficient degree of conservatism for the risk characterization performed.

 

 

Short term / long term dermal local DNEL

To assess the DNEL for local effects after short term or long term dermal exposure, data for skin sensitization were considered.

 

In a human sensitization studies, i.e. human repeated insult patch test (HRIPT), no sensitization reactions were observed after repeated application of 4125 µg/cm²2-(4-tertbutyl)propionaldehyde(IFF 1980) whereas skin sensitization reactions of a single subject has been reported after application of approx. 30000 µg/cm² (Cocchiara 2003). Quantitative animal data from several LLNA using different vehicles, i.e. ethanol (EtOH), diethylphtalate (DEP), EtOH/DEP (3:1), EtOH/DEP (1:3) support the data from human studies (Lalko 2004). The EC3 value reported ranged from 3 % to 14% (743 -3478 µg/cm²). Furthermore, an EC3 value of 18.7% (4675µg/cm²) was reported after application of 2 -(4 -tertbutyl)propionaldehydein acetone/olive oil (4:1); (Basketter 2001). In a weight of evidence on the data listed above, the no expected sensitization induction level (NESIL) for2-(4-tertbutyl)propionaldehydehas been set at 4100 µg/cm² by the expert panel of the Research Institute for Fragrance Materials (RIFM), being the basis for the recommended concentration limits for 2 -(4 -tertbutyl)propionaldehyde in final products, i.e. IFRA standard of the international fragrance association (Api et al. 2008). This value has been chosen as point of departure for the derivation of the DNEL for demal local short/long term effects.

 

Intraspecies differences:

It is recognized that a general DNEL must take into account that the threshold for skin sensitization varies between individuals. This may be due to differences in parameters such as genetic effects, sensitive subpopulations, inherent barrier function, age, gender, and ethnicity (Api et al., 2008). Whereas the latter three are recognized to have some effect on the sensitization threshold, it is generally recognized that genetic differences, the inherent barrier function and especially sensitive subpopulations play a major role (Api et al., 2008). The barrier function of the skin may be compromised which in turn may lead to a greater susceptibility of the individual. At the same time the barrier function is thought to be very similar from infancy to adulthood. The influence of the genetic setting is not well understood, however, may be plausible in the light of the immunological effect under consideration. The term sensitive subpopulations refers mostly to individuals who have previously been sensitized to other substances which may increase the susceptibility to further sensitizers (Api et al., 2006, Api et al., 2008). Overall , an assessment factor of 10 for intraspecies differences is applied to adequately address the combined influence of these effects.  

Therefore a DNEL for skin sensitization was set at 410 µg/cm2/day. The derived DNEL on the basis of skin sensitization is considered sufficient to ensure the absence of skin irritation after short or long term exposure.

  • Api AM, Basketter DA, Cadby PA, Cano M-F, Graham E, Gerberick F, Griem P, McNamee P, Ryan CA, Safford B (2006). Dermal Sensitization Quantitative Risk Assessment (QRA) for fragrance ingredients. Technical dossier.March 15, 2006 (revised May 2006).
  • Api AM, Basketter, DA, Cadby PA, Cano M-F, Ellis G, Gerberick GF, Griem P, McNamee PM, Ryan CA, Safford R (2008).Dermal sensitization quantitative risk assessment (QRA) for fragrance ingredients. Reg Toxicol Pharmacol 52: 3-23

 

Other DNELs

No DNELs were derived for local effects after short term or after long term inhalative exposure as the substance exhibits no hazardous potential in terms of these endpoints.

No DNELs were derived for systemic effects after short term dermal or inhalative exposure, since the respective long term DNELs are considered sufficient to ensure the absence of acute toxic effects.

 

 

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
0.11 mg/m³
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
Overall assessment factor (AF):
20
Modified dose descriptor starting point:
NOAEC
Value:
2.17 mg/m³
Explanation for the modification of the dose descriptor starting point:
Please refer to "Discussion"
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:
0.89 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
Overall assessment factor (AF):
80
Modified dose descriptor starting point:
NOAEL
Value:
71 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:
Please refer to "Discussion"
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
410 µg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Dose descriptor:
other: NESIL = 4100 µg/cm²
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
410 µg/cm²
Most sensitive endpoint:
sensitisation (skin)
DNEL related information
Overall assessment factor (AF):
10
Dose descriptor starting point:
other: NESIL = 4100 µg/cm²

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
0.062 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
Route of original study:
Oral
DNEL related information
Overall assessment factor (AF):
80
Modified dose descriptor starting point:
other: NOEL
Value:
5 mg/kg bw/day
Explanation for the modification of the dose descriptor starting point:
Please refer to "Discussion"
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

Point of departure

Toxicity data on animals repeatedly treated with2-(4-tertbutyl)propionaldehydeare available and are used for the derivation of respective DNELs.

The key study for repeated dose toxicity is a rat 90 day repeated dose gavage study according to OECD TG 408 and GLP (Givaudan 1986A-B, Givaudan 1987). On the basis of the effects observed, a no adverse effect level has been set at 25 mg/kg bw/d based on adverse effects on liver and testes. Since adversity such as neurotoxicological effects was not evident, a no effect level has been set at 5 mg/kg bw/d based on 2-(4-tertbutyl)propionaldehyde induced reversible decreases in plasma cholinesterase activity.

Various repeated dose toxicity studies demonstrated adverse effects of 2-(4-tertbutyl)propionaldehyde on the male reproductive system in rats (NOAEL = 25 mg/kg bw/d), whereas no evidence for testicular toxicity or general toxicity was observed in the mouse and guinea pig. Considering non-rodent species, the dog has been shown to be susceptible towards testicular toxicity as well, however at higher dose levels than the rat (NOAEL = 44.6 mg/kg bw/d). In contrast, short-term oral exposure to rabbits did not indicate a potential of 2-(4-tertbutyl)propionaldehyde to induce testicular toxicity or general toxicity. Furthermore in rhesus monkeys, no indication of testicular toxicity or symptoms of incompatibility was observed at doses causing testicular toxicity in the rats. Therefore, the rat appears to be the most susceptible species and exposure to 2-(4-tertbutyl)propionaldehyde above a clearly defined threshold dose seems sufficient to cause testicular toxicity.

In the key study for developmental toxicity, i.e. a study in Wistar rats acc. to OECD TG 414 and GLP, oral administration of 2-(4-tertbutyl)propionaldehyde via gavage induced general systemic and liver toxicity for high dose ( 40.7 (nominal dose: 45 mg/kg bw/d) and less pronounced for mid dose (12.7 (nominal dose: 15) mg/kg bw/d) dams (BASF SE 2004). Furthermore, serum and erythrocyte cholinesterase activities (but not brain CHE activities) were decreased in these dose groups. Increased numbers of fetuses with common skeletal variations, fetal growth retardations, increased early resorptions and the subsequent decrease in number of fetuses are considered manifestations of the non–specific maternal stress. Based on these findings, the NOAEL is set at 4.1 mg/kg bw/day (nominal dose: 5 mg/kg bw/d) for maternal and prenatal developmental toxicity.

In an one-generation range finding study in rats, general systemic toxicity, indications for liver toxicity and impaired male fertility was observed after oral administration of 2-(4-tertbutyl)propionaldehyde in capsules via feed (BASF 2006C). The NOAEL for fertility was set at 800 ppm (approx. 29 mg/kg bw/d lysmeral) based on the testicular toxicity and infertility observed. A LOEL for parental toxicity (females) of 400 ppm (10-14.5 mg/kg bw/d) and a NOAEL for parental toxicity (males) of 400 ppm (14.5 mg/kg bw/d) was set, based on clinicochemical findings such as decreases in serum and erythrocyte cholinesterase activities (but not brain CHE activities). According to the final decision from CoRAP (SEV1_201-289-8) dated 21 February 2014, the joint registrants are requested to perform a follow up reproductive toxicity study with 2-(4-tertbutyl)propionaldehyde, i.e. an EOGRTS according to OECD 443.

In order to ensure a sound dose selection for the required EOGRTS with the currently available testing material in an alternative formulation (change in capsule material), an one-generation range finding study in rats was performed (BASF 2017B) and resulted in general systemic toxicity (decreases in body weights and food consumption), hematological changes and liver toxicity starting at a dose of 750 ppm (7-12 mg/kg bw/d). Impaired male fertility was observed at the highest dose tested (2300 ppm; 25.1-27.5 mg/kg bw/d). Pup survival was affected at PND 0 - 4 and pup weights were decreased at starting at a dose of 750 ppm (7-12 mg/kg bw/d). No relevant lysmeral related adverse effects were observed at the lowest dose tested, i.e. 230 ppm (2 - 4 mg/kg bw/d).

 

In the main EOGRTS in rats (BASF SE 2017), impaired liver function and general systemic adverse effects on food consumption, body weights and clinical pathological parameters were identified as general, systemic toxicity in the two parental generations and adolescent animals at a nominal dose of 10 mg/kg bw/d (750 ppm; representing an overall mean dose of 15.1 mg/kg bw/d). In parallel, reduced pup body weights in the F1 and F2 offspring were observed at the same dose level. Inhibitory effects at this dose level on the peripheral AChE activity in pups and adolescent rats did not result in corresponding effects in neurobehavioral or neuropathological examinations. The respective NOAELs for general systemic and developmental toxicity has been set at a nominal dose of 3 mg/kg bw/d (230 ppm; representing an overall mean dose of 4.5 mg/kg bw/d). 

 

As a point of departure for the inhalative and dermal long term systemic DNEL, the NOEL of 5 mg/kg bw/d derived from the key study for repeated dose toxicity has been chosen. The NOEL used for the derivation of the systemic DNELs is generally considered sufficient covering the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde, i.e. impairment of male reproduction(spermatotoxicity and testicular toxicity). These effects have a NOAEL of 25 mg/ kg bw/d and are well above the chosen NOEL of 5 mg/kg bw/d. Further, this point of departure is supported by the NOAELs for pregnant animals observed in the developmental toxicity study as well as for the parental and offspring generations in the EOGRTS. The difference of the NO(A)ELs available in a range between 3 and 5 mg/kg bw/d is mainly driven by different dose selections, and the effects observed appear to be consistent between the different studies, dependent on their study design. There is strong concordance between the results of the 90-day study and the EOGRTS. Furthermore, there is no indication from the latter study that immature animals are more sensitive to the effects of 2-(4-tertbutyl) propionaldehyde than are adult animals. Overall, the NOEL of 5 mg/kg bw/d, derived from the 90 day repeated dose toxicity study in rats, is considered sufficiently conservative and represents a robust point of departure for the long term systemic DNELs.

 

Route to route extrapolation: oral – dermal:

There is clear evidence from kinetic and dermal toxicity studies in rats as well as from a dermal penetration study in human volunteers that systemic bioavailability of 2-(4-tertbutyl)propionaldehyde after dermal administration is considerably lower compared to that after oral administration. In rats, dermal administration of 2 -(4 -tertbutyl)propionaldehyde revealed lower Cmax plasma values compared to oral administration. Since rat skin is more permeable to dermally applied substances than human skin, and taking into account the results of a dermal penetration study in human volunteers, very limited percutaneous absorption and systemic bioavailability of 2-(4-tertbutyl)propionaldehyde is expected in humans. As a worst case assumption, a dermal absorption of max. 7% is assumed based on in vitro dermal penetration data, given that a value of 2% was derived in an in vivo study with human subjects (BASF SE 2016; Huntingdon Research Centre Ltd 1994).  Given its physicochemical properties, i.e. the low molecular weight (204 g/mol), moderate partition coefficient (log Pow around 4) and a readily water solubility (33 mg/l), lysmeral is likely to be taken up by passive diffusion and to have high bioavailability via the oral route. Therefore, an oral absorption of 100 % was assumed for 2-(4-tertbutyl) propionaldehyde being administered by gavage in the chosen key study.

Route to route extrapolation: oral – inhalative:

Due to the lack on route specific information, a default factor of 2 has been applied leading to the assumption, that half of the applied dose is absorbed via the oral route compared to the inhalative route according to current guidance document (R8, ECHA 2008).

For the general population, the following DNELs were derived:

 

Long-term systemic oral DNEL

The NOEL of the subchronic oral study was set at 5 mg/kg bw/d2-(4-tertbutyl)propionaldehydefor males and females.

 

Based on the profound toxicity databasis for 2-(4-tertbutyl)propionaldehyde, certain default assessment factors (acc. to ECHA GD R8) have been modified into substance specific assessment factors (AF), considering the intrinsic hazard properties of the registered substance. The following assessment factors (AF) were applied:

-         Interspecies differences/Allometric scaling = 4

Reasoning: Allometric scaling is applied according to R8 ECHA 2008.

 

-         Interspecies differences/Remaining differences = 1

Reasoning: On the basis of the multiple comparative studies using different rodent and non-rodent animal species (toxicodynamic) and additional toxicokinetic differences in relation to humans (formation of metabolites, i.e. TBBA), the rat has been identified as most susceptible species concerning the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde (impairment of male reproduction; spermatotoxicity and testicular toxicity). Furthermore, the lowest effect levels for other systemic effects, i.e. liver, were found in rats as well. Since the point of departure is based on a study with rats, identified as most susceptible species for 2-(4-tertbutyl)propionaldehyde induced toxicity, no additional safety factor to account for a putative higher sensitivity of humans besides aspects already covered by allometric scaling, is considered mandatory.

In general, although ‘residual’ interspecies variability may remain following allometric scaling, this is largely accounted for in the assessment factors proposed for intraspecies variability, i.e. reflecting the interdependency of inter- and intraspecies assessment factors (see also Calabrese et al., 1993, Regul. Toxicol. Pharmacol. 17: 44-51). Furthermore, within the ERASM project, it was found, that species are on average equally sensitive to equipotent doses, if doses are related to energy turnover. An animal to human interspecies extrapolation distribution with a geometric mean identical to the allometric scaling factor (e.g. 4 rat/human, 7 mouse/human) was identified, without an additional factor of 2.5 for putative toxicodynamic differences. Therefore, a factor of 2.5 for ‘remaining‘ interspecies differences may be questionable as a standard procedure (see also Escher et al., 2013, Toxicology Letters 218; 159– 165). 

Overall, the use of an AF of 1 instead of 2.5 for remaining differences for interspecies differences besides allometric scaling can be justified for 2-(4-tertbutyl)propionaldehyde.

 

-         Intraspecies differences= 10

Reasoning: Default assessment factor according to R8 ECHA 2008.

 

-         Exposure duration = 2

Reasoning: Extrapolation from subchronic to chronic toxicity according to the default assessment of R8 ECHA 2008.

 

-         Dose response = 1

Reasoning: No issues related to reliability of the dose-response according toR8 ECHA 2008.

 

-         Quality of whole database = 1

Reasoning: No issues related to completeness and consistency of the available data according to R8 ECHA 2008. 

 

 

AF = 4 x 1 x 10 x 2 x 1 x 1 = 80. Consequently, the oral long-term systemic DNEL derived was 0.0625 mg/kg bw/d for the general population.

 

 

Long-term systemic inhalative DNEL 

For derivation of the long-term systemic inhalative DNEL, the oral NOEL was converted into a corrected inhalative NOAEC of 2.17 mg/m3 according to the procedure, recommended in the current guidance document (R8, ECHA 2008).

 

NOAEC corrected inhalative = 5*(1/1.15)*(50/100) = 2.17 mg/m3

 

Based on the profound toxicity databasis for 2-(4-tertbutyl)propionaldehyde, certain default assessment factors (acc. to ECHA GD R8) have been modified into substance specific assessment factors (AF), considering the intrinsic hazard properties of the registered substance. The following assessment factors (AF) were applied:

-         Interspecies differences/Allometric scaling = 1

Reasoning: Allometric scaling is not applicable according to R8 ECHA 2008.

 

-         Interspecies differences/Remaining differences = 1

Reasoning: On the basis of the multiple comparative studies using different rodent and non-rodent animal species (toxicodynamic) and additional toxicokinetic differences in relation to humans (formation of metabolites, i.e. TBBA), the rat has been identified as most susceptible species concerning the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde (impairment of male reproduction; spermatotoxicity and testicular toxicity). Furthermore, the lowest effect levels for other systemic effects, i.e. liver, were found in rats as well. Since the point of departure is based on a study with rats, identified as most susceptible species for 2-(4-tertbutyl)propionaldehyde induced toxicity, no additional safety factor to account for a putative higher sensitivity of humans besides aspects already covered by allometric scaling, is considered mandatory.

In general, although ‘residual’ interspecies variability may remain following allometric scaling, this is largely accounted for in the assessment factors proposed for intraspecies variability, i.e. reflecting the interdependency of inter- and intraspecies assessment factors (see also Calabrese et al., 1993, Regul. Toxicol. Pharmacol. 17: 44-51). Furthermore, within the ERASM project, it was found, that species are on average equally sensitive to equipotent doses, if doses are related to energy turnover. An animal to human interspecies extrapolation distribution with a geometric mean identical to the allometric scaling factor (e.g. 4 rat/human, 7 mouse/human) was identified, without an additional factor of 2.5 for putative toxicodynamic differences. Therefore, a factor of 2.5 for ‘remaining‘ interspecies differences may be questionable as a standard procedure (see also Escher et al., 2013, Toxicology Letters 218; 159– 165). 

Overall, the use of an AF of 1 instead of 2.5 for remaining differences for interspecies differences besides allometric scaling can be justified for 2-(4-tertbutyl)propionaldehyde.

 

-         Intraspecies differences= 10

Reasoning: Default assessment factor according to R8 ECHA 2008.

 

-         Exposure duration = 2

Reasoning: Extrapolation from subchronic to chronic toxicity according to the default assessment of R8 ECHA 2008.

 

-         Dose response = 1

Reasoning: No issues related to reliability of the dose-response according toR8 ECHA 2008.

 

-         Quality of whole database = 1

Reasoning:No issues related to completeness and consistency of the available dataaccording toR8 ECHA 2008.  

 

 

AF = 1 x 1 x 10 x 2 x 1 x 1 = 20.Consequently, the inhalative long-term systemic DNEL was set at 0.11 mg/m3for the general population.

 

 

Long-term systemic dermal DNEL 

For derivation of the long-term systemic dermal DNEL, the oral NOEL was converted into a corrected dermal NOAEL of 71 mg/kg bw/d according to the procedure, recommended in the current guidance document (R8, ECHA 2008).

 

NOAEL corrected dermal = 5*(100/7) = 71 mg/kg bw/d

 

Based on the profound toxicity databasis for 2-(4-tertbutyl)propionaldehyde, certain default assessment factors (acc. to ECHA GD R8) have been modified into substance specific assessment factors (AF), considering the intrinsic hazard properties of the registered substance. The following assessment factors (AF) were applied:

-         Interspecies differences/Allometric scaling = 4

Reasoning: Allometric scaling is applied according to R8 ECHA 2008.

 

-         Interspecies differences/Remaining differences = 1

Reasoning: On the basis of the multiple comparative studies using different rodent and non-rodent animal species (toxicodynamic) and additional toxicokinetic differences in relation to humans (formation of metabolites, i.e. TBBA), the rat has been identified as most susceptible species concerning the leading toxicological effect of 2-(4-tertbutyl)propionaldehyde (impairment of male reproduction; spermatotoxicity and testicular toxicity). Furthermore, the lowest effect levels for other systemic effects, i.e. liver , were found in rats as well. Since the point of departure is based on a study with rats, identified as most susceptible species for 2-(4-tertbutyl)propionaldehyde induced toxicity, no additional safety factor to account for a putative higher sensitivity of humans besides aspects already covered by allometric scaling, is considered mandatory.

In general, although ‘residual’ interspecies variability may remain following allometric scaling, this is largely accounted for in the assessment factors proposed for intraspecies variability, i.e. reflecting the interdependency of inter- and intraspecies assessment factors (see also Calabrese et al., 1993, Regul. Toxicol. Pharmacol. 17: 44-51). Furthermore, within the ERASM project, it was found, that species are on average equally sensitive to equipotent doses, if doses are related to energy turnover. An animal to human interspecies extrapolation distribution with a geometric mean identical to the allometric scaling factor (e.g. 4 rat/human, 7 mouse/human) was identified, without an additional factor of 2.5 for putative toxicodynamic differences. Therefore, a factor of 2.5 for ‘remaining‘ interspecies differences may be questionable as a standard procedure (see also Escher et al., 2013, Toxicology Letters 218; 159– 165). 

Overall, the use of an AF of 1 instead of 2.5 for remaining differences for interspecies differences besides allometric scaling can be justified for 2-(4-tertbutyl)propionaldehyde.

 

-         Intraspecies differences= 10

Reasoning: Default assessment factor according to R8 ECHA 2008.

 

-         Exposure duration = 2

Reasoning: Extrapolation from subchronic to chronic toxicity according to the default assessment of R8 ECHA 2008.

 

-         Dose response = 1

Reasoning: No issues related to reliability of the dose-response according toR8 ECHA 2008.

 

-         Quality of whole database = 1

Reasoning: No issues related to completeness and consistency of the available data according to R8 ECHA 2008. 

 

 

AF = 4 x 1 x 10 x 2 x 1 x 1 = 80. Consequently, the dermal long-term systemic DNEL derived was 0.89 mg/kg bw/d for the general population.

 

 

Further endpoint systemic oral/dermal/inhalative DNELs:

Derivation of endpoint specific DNELs addressing reproductive, developmental toxicity and maternal toxicity during pregnancy would result in higher DNELs as derived above. In the key developmental toxicity study, animals have been dosed throughout the whole relevant gestation period and time extrapolation does not need to be considered. Furthermore, no time extrapolation is mandatory for the NOAELs of the EOGRTS, since dosing occurred through the whole reproductive cycle (i.e. treatment of parental animals and a respective F1 generation to deliver a F2 generation). For the derivation of the systemic DNELs, based on the endpoint and NOEL for repeated dose toxicity, an AF of 2 has been applied for time extrapolation from subchronic to chronic exposure and would therefore also cover developmental and reproductive toxicity, where no such AF would be mandatory. Derivation of endpoint specific DNELs addressing the impairment of male reproduction would result in higher DNELs as derived above, since these effects have a NOAEL of 25 mg/ kg bw/d and are well above the chosen point of departure (NOEL of 5 mg/kg bw/d).

 Overall, the multiplicatory principle of AF together with the choice of the NOEL as point of departure assures a sufficient degree of conservatism for the risk characterization performed.

 

Short term / long term dermal local DNEL 

To assess the DNEL for local effects after short term or long term dermal exposure, data for skin sensitization were considered.

In a human sensitization studies, i.e. human repeated insult patch test (HRIPT), no sensitization reactions were observed after repeated application of 4125 µg/cm² lysmeral (IFF 1980) whereas skin sensitization reactions of a single subject has been reported after application of approx. 30000 µg/cm² (Cocchiara 2003). Quantitative animal data from several LLNA using different vehicles, i.e. ethanol (EtOH), diethylphtalate (DEP), EtOH/DEP (3:1), EtOH/DEP (1:3) support the data from human studies (Lalko 2004). The EC3 value reported ranged from 3 % to 14% (743 -3478 µg/cm²).Furthermore, an EC3 value of 18.7% (4675µg/cm²) was reported afterapplication of lysmeral in acetone/olive oil (4:1); (Basketter 2001).In a weight of evidence on the data listed above, the no expected sensitization induction level (NESIL) for lysmeral has been set at 4100 µg/cm² by the expert panel of the Research Institute for Fragrance Materials (RIFM), being the basis for the recommended concentration limits for lysmeral in final products, i.e. IFRA standard of the international fragrance association (Api et al. 2008). This value has been chosen as point of departure for the derivation of the DNEL for demal local short/long term effects.

 

Intraspecies differences:

It is recognized that a general DNEL must take into account that the threshold for skin sensitization varies between individuals. This may be due to differences in parameters such as genetic effects, sensitive subpopulations, inherent barrier function, age, gender, and ethnicity (Api et al., 2008). Whereas the latter three are recognized to have some effect on the sensitization threshold, it is generally recognized that genetic differences, the inherent barrier function and especially sensitive subpopulations play a major role (Api et al., 2008). The barrier function of the skin may be compromised which in turn may lead to a greater susceptibility of the individual. At the same time the barrier function is thought to be very similar from infancy to adulthood. The influence of the genetic setting is not well understood, however, may be plausible in the light of the immunological effect under consideration. The term sensitive subpopulations refers mostly to individuals who have previously been sensitized to other substances which may increase the susceptibility to further sensitizers (Api et al., 2006, Api et al., 2008). Overall , an assessment factor of 10 for intraspecies differences is applied to adequately address the combined influence of these effects.  

Therefore a DNEL for skin sensitization was set at 410 µg/cm2/day. The derived DNEL on the basis of skin sensitization is considered sufficient to ensure the absence of skin irritation after short or long term exposure.

  • Api AM, Basketter DA, Cadby PA, Cano M-F, Graham E, Gerberick F, Griem P, McNamee P, Ryan CA, Safford B (2006). Dermal Sensitization Quantitative Risk Assessment (QRA) for fragrance ingredients. Technical dossier.March 15, 2006 (revised May 2006).
  • Api AM, Basketter, DA, Cadby PA, Cano M-F, Ellis G, Gerberick GF, Griem P, McNamee PM, Ryan CA, Safford R (2008).Dermal sensitization quantitative risk assessment (QRA) for fragrance ingredients. Reg Toxicol Pharmacol 52: 3-23

Other DNELs 

No DNELs were derived for local effects after short term or after long term inhalative exposure as the substance exhibits no hazardous potential in terms of these endpoints.

No DNELs were derived for systemic effects after short term oral, dermal or inhalative exposure, since the respective long term DNELs are considered sufficient to ensure the absence of acute toxic effects.