Essential oil of Boswellia carterii (Burseraceae) obtained from gum by distillation

Endpoint summary

Description of key information

There were no studies available in which the toxicokinetic properties of the registered substance were investigated.

The registered substance is a liquid at 20°C, with the 10 major constituents, representing more than 80% of the substance, having a molecular weight between 134 and 204 g/mol. These constituents have limited water solubility (between 0.0844 - 14.3 mg/L), consequently, these constituents are lipophilic with log Kow>4.

The available evidence suggests that the substance is bioavailable via the oral and dermal routes. The substance is expected to be metabolised and mainly excreted in urine with low potential for bioaccumulation.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

100

Absorption rate - inhalation (%):

100

Additional information

In accordance with the section 8.1.1 of Annex VIII of Regulation (EC) No 1907/2006 (REACH), the toxicokinetic profile of the substance (i.e. absorption, distribution, metabolism and elimination) was derived from the relevant available information collated in the dossier. The physical chemical characteristics of the substance, the results obtained from acute, repeated-dose, and reproductive toxicity studies on the substance were used to predict its toxicokinetic behaviour.

 

Physico-chemical properties:

The substance is a UVCB substance with 10 known constituents accounting for more than 80% of the substance. They have a relatively low molecular weight between 134 and 204 g/mol. The substance is a limited water-soluble liquid (<14 mg/L). Consequently, it is mainly lipophilic based on the octanol/water partition coefficient (Log Kow >4 at 25°C except for 2 constituents with log Kow around 6.3 but accounting for less than 5% of the substance). The substance has moderate volatility according to the vapour pressure of the constituents (between 2.91 and 651 Pa at 25 °C).

 

Absorption:

Oral/GI absorption

The physical chemical characteristics described above suggest that the substance could slightly be absorbed in the gastro-intestinal tract by passive diffusion. However, some evidence of oral absorption were evidenced in acute oral toxicity study with lethargy observed after single dose administration at 5000 mg/kg bw of the read-across substance Pepper black oil although no mortality was recorded.

The observation of such systemic effects indicates the oral bioavailability of the registered substance and/or its metabolites.

In light of these data, and the lack of specific information on oral absorption, the substance was assumed to be 100% bioavailable by oral route for the purposes of human health risk assessment.

 

Dermal absorption

Regarding dermal absorption, systemic absorption by the dermal route is expected to be limited but to occur based on the Log Kow of most of the main constituents (slightly > 4) and the low molecular weight (< 500 g/mol) although no systemic clinical signs were observed in the acute dermal toxicity study up to 2000 mg/kg bw.

In light of these data, the substance was conservatively assumed to be 100% bioavailable by dermal route for the purposes of human health risk assessment.

 

Respiratory absorption

The potential for inhalation toxicity was not evaluated in vivo.

The vapour pressure of the substance (Vp = 2.91-651 Pa at 25°C with most constituents > 100 Pa) indicates a moderate volatility and inhalability and therefore exposure by inhalation may occur. Thus, at ambient temperature, respiratory absorption is expected under normal use and handling of the substance. Also, when used as a vapour or in aerosol, the substance is expected to be directly absorbed across the respiratory tract epithelium by passive diffusion.

In light of these data, and the lack of specific information on respiratory absorption, the substance was conservatively assumed to be 100% bioavailable by inhalation for the purposes of human health risk assessment.

 

Distribution:

There is no experimental evidence to indicate distribution but the physico-chemical data suggests that wide distribution could occur. The log Kow value > 4 at 25°C suggests that the substance could accumulate in fatty tissues. However, distribution and bioaccumulation are highly dependent on the rate of biotransformation and elimination. Some of the main constituents like limonene are expected to be extensively metabolised. This may explain why no evidence of cumulative effects was observed from the repeated dose oral toxicity study.

  

Metabolism:

The two major constituents of the registered substance, alpha-pinene and limonene, are known to be extensively and rapidly metabolised and excreted principally via urine.

 

Excretion:

Biotransformation is expected and elimination of metabolites would most likely occur in urine, although elimination of conjugates in bile is possible. As the parent substance is relatively volatile, elimination via the lungs, in expired air could also be possible.

The registered substance has constituents with log Kow>4 at 25 °C and slightly above the criterion of 4.5 for bioaccumulation. However, these constituents are expected to be extensively metabolised therefore, the registered substance is considered to have low bioaccumulation potential.