Litsea cubeba, ext.

Endpoint summary

Description of key information

Litsea cubeba is expected to be readily absorbed, orally and via inhalation but somewhat less via the dermal route, based on study information on constituents and physico-chemical parameters. As adverse effects were observed in the repeated dose studies, route-to-route extrapolation will be performed to estimate the dermal DNELs.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

90

Absorption rate - dermal (%):

50

Absorption rate - inhalation (%):

100

Additional information

Toxicokinetic evaluation of Litsea Cubeba oil based on existing data

 

REACH indicates that an “assessment of the toxicokinetic behaviour of the substance to the extent that can be derived from the relevant available information” should be performed at Annex VIII level.

 

General information

Litsea Cubeba oil is a substance of Unknown or Variable composition, Complex reaction products or Biological material (UVCB substances), or more specifically a NCS (Natural Complex Substance). As such, Litsea Cubeba oil is an essential oil obtained from the fruits of Litsea cubeba, Lauraceae, obtained by steam distillation and optionally refined by distillation, and consists of the following identified constituents:

 

Name - Constituent	CAS Number - Constituent	Concentration Range in NCS (% w/w)
Geranial	141-27-5	24.84 – 43
Neral	106-26-3	20.24 – 35
L-Limonene	5989-54-8	2.3 - 18
β-Myrcene	123-35-3	0.74 - 1.8
Isogeranial	72203-98-6 / 55722-59-3	0.46 – 2.5
α-Pinene	7785-26-4	0.46 - 2
1,8-Cineole	470-82-6	0.31 - 1.7
Sabinene	3387-41-5	0.20 - 2
Nerol	106-25-2	0.18 - 1.2
(+)-Citronellal	2385-77-5	< 0.01 - 7
Methyl Heptenone	110-93-0	< 0.01 - 5
(-)-linalol	126-91-0	< 0.01 - 3.3
β-Caryophyllene	87-44-5	< 0.01 - 3
Geraniol	106-24-1	< 0.01 - 2.9
Verbenol	473-67-6	< 0.01 – 2.2
Isoneral	72203-97-5	< 0.01 - 2
β-(+)-Citronellol	1117-61-9	< 0.01 - 1.5

 

The main constituents are (E)-3,7-dimethylocta-2,6-dienal (Geranial ; CAS 141-27-5), (Z)-3,7-dimethylocta-2,6-dienal (Neral; CAS 106-26-3) and (S)-p-mentha-1,8-diene (L-Limonene; CAS 5989-54-8), which add up to a percentage range of approximately 47- 96%, andcan therefore be considered representative of the substance.

 

ADME data

Absorption, distribution, metabolism and excretion data on Litsea Cubeba oil itself are not available and therefore the toxicokinetic assessment is based on the available toxicology data for Litsea Cubeba oil, as well as data for the main constituents.

 

Information from physico chemical and toxicity studies:

An overview of the relevant physicochemical parameters for Litsea Cubeba oil is provided below.

 

Parameter	Litsea Cubeba oil
Physical state	Liquid
Structure	UVCB / NCB
Particle size	Not relevant
Log Kow	2.06 - 6.3 (16.90% of the known constituents has a log Kow >= 4)
Water solubility (mg/l)	0.5 - 4364 mg/L at 25°C.
Boiling point (°C)	83°C at 1013 hPa.
Vapour pressure	60.69 Pa at 25°C (The vapour pressure of the constituents range from 1.06 to 981 Pa.)

 

Absorption

Oral:As the molecular weight range of this UVCB is below 500, the molecules in this UVCB are likely to be absorbed via the oral/GI tract. Uptake through aqueous pores or carriage of such molecules across membranes with the bulk passage of water in the GI tract can be expected. Furthermore uptake by passive diffusion is likely based on the moderate log Kow values (between -1 and 4) of the constituents within the substance. The oral absorption of the more highly lipophilic constituents of this UVCB (log Kow > 4) may be more dependent on micellar solubilisation.

Based on the previous, the substance can be absorbed in the human body via the oral route. This is supported by the findings in an oral acute toxicity study, in which mortality was observed after 5000 mg/kg bw of Litsea Cubeba oil. Furthermore, in the oral repeated dose study, systemic effects were observed in rats and mice. These findings confirm that systemic absorption of the substance via the gastrointestinal tract takes place.

In addition to the above, some information regarding oral absorption is available for Citral. Citral consists of geranial and neral, which are two of the main constituents of Litsea cubeba oil. Geranial and neral can make up up to 78% of the UVCB. In the disseminated Citral dossier a 90% bioavailability has been set for the oral route, on the basis of available toxicokinetic data which shows rapid and high oral absorption (Diliberto JJ, Usha G, Birnbaum LS, 1988). Therefore, for the derivation of the systemic dermal -DNEL, an oral absorption rate of 90% is assumed.

 

Dermal:In an acute dermal toxicity study, mortality and clinical signs were observed in rabbits exposed to 2500 mg/kg bw group (1/4 rabbits died), as well as the 5000 mg/kg bw (2/4 rabbits died). Though these findings suggest high dermal absorption, in this study the skin was abraded, thereby promoting its dermal absorption. In the two available OECD TG 404 in vivo skin irritation studies where exposure was done to intact skin, no systemic effects were reported. Even though Litsea cubeba is not a corrosive, the skin irritating properties observed in the in vivo skin irritation test suggest that this UVCB may damage the skin and thereby increase its penetrating potential. As sensitisation is also observed for this substance in an OECD TG 429 study, some uptake must occur. Based on the physico chemical properties of the substance, its molecular weight would not exclude dermal uptake, and its water solubility and logP value would predict low to moderate absorption of at least a part of its constituents (ECHA guidance, 7.12, Table R.7.12-3).

Furthermore, some information regarding dermal absorption is available for geranial and neral, two of the main constituents of Litsea cubeba oil tested in the form of Citral. Even though a large part of Citral is expected to be lost due to evaporation, studies indicate that the remainder has the potential to be absorbed dermally. In an in vivo dermal application study by Diliberto et al. (1988) about 50% of dermally applied Citral was lost due to evaporation and absorption by the application device during dermal administration. However, after 72 hr recoveries were ca. 10% on the treated skin site, ca. 10% in the remaining tissues, ca. 20 or 30% in the excreta (5 or 50 mg/kg-dose groups). Furthermore, Scolnik et al (1994) reported percutaneous absorption into the systemic circulation within 2.5 min after topical application of Citral. Dermal permeability has also been shown in anin vitrostudy by Hayes et al. (2003) in which Citral was absorbed in all layers or freshly excised human skin.

 

Taken together, the available information on Litsea cubeba oil and its constituents indicate that low to moderate dermal absorption of at least a part of its constituents is to be expected, though the high volatility of the constituents may limit its absorption. Therefore, for the derivation of the systemic dermal DNEL, a dermal penetration rate of 50% is assumed.

 

Inhalation:Uptake via the lungs, for the highly lipophilic constituents (log Kow >4), with a low water solubility may be mainly via micellar solubilisation. The constituents with a more moderate log Kow values (between -1 and 4) would favour absorption directly across the respiratory tract epithelium by passive diffusion. These physico-chemical properties would also facilitate absorption directly across the respiratory tract epithelium following aspiration.

 

Distribution

Distribution of Litsea Cubeba oil and its major constituent is expected based on the relatively low molecular weights. Also distribution (of constituents) throughout the body would be possible due to the wide range of water solubilities, while the higher Log Kow range also suggests possible distribution into cells. Signs of toxicity and target organs suggest that the substance is at least distributed to the kidney and bone marrow.

 

Metabolism

No information on metabolism can be derived from the physicochemical data that is available for Litsea Cubeba oil. For the main constituents of the UVCB L-Limonene, Neral and Geranial, oxidation of the aldehyde group into alcohols is expected, as well as the formation of dicarboxylic acid metabolites and glucuronide conjugates.

 

Elimination

Based on the renal effects observed in the repeated dose toxicity study, excretion is expected to take place though the kidney. This is supported by the relatively low molecular weights. Excretion via bile is not likely, as in the rat it has been found that substances with molecular weights below 300 do not tend to be excreted into the bile (Renwick, 1994). Some excretion via breast milk, saliva and sweat is cannot be excluded, as some constituents of the UVCP can be regarded as lipophilic (Log Kow > 4).

 

Accumulation

There is the potential for the more highly lipophilic constituents of this UVCB (log P >4) to accumulate in individuals that are frequently exposed (e.g. daily at work) to these substances. Once exposure stops, the concentration within the body will decline at a rate determined by the half-life of the substance (Rozman and Klaassen, 1996).

 

Conclusion

Oral uptake is expected based on information from the available studies and favourable physico chemical parameters. For dermal absorption low to moderate dermal absorption of at least a part of its constituents is to be expected based on information from available studies, and physicochemical parameters . Relatively wide distribution and excretion through urine is expected based on water solubility ranges and low molecular weights. The absorption values to be used for hazard assessment are therefore taken as 100% for the inhalation route, 90% for the oral route and 50% for the dermal route.

 

References:

 

Diliberto JJ, Usha G, Birnbaum LS (1988) Disposition of Citral in male Fischer rats. Drug Metab. Dispos. 16, 721-727

 Hayes AJ, Markovic B (2003) Toxicity of Australian essential oil Backhousia citriodora (lemon myrtle). Part 2: Absorption and histopathology following application to human skin. Food Chem Toxicol 41: 1409-1416

 Renwick AG (1994) Toxicokinetics - pharmacokinetics in toxicology. In Hayes, A.W. (ed.) Principles and Methods of Toxicology. Raven Press, New York, USA, pp.103.

 Rozman KK and Klaassen CD (1996) Absorption, Distribution, and Excretion of Toxicants. In: Klaassen CD (Ed.) Cassarett and Doull's Toxicology: The Basic Science of Poisons. McGraw-Hill, New York, USA.

 Scolnik M, Konichezky M, Tykochinsky G, Servadio C, Abramovici A (1994) Immediate vasoactive effect of Citral on the adolescent rat ventral prostrate. Prostrate 25: 1-9