Reaction Mass of (4R)-4-isopropenyl-1-methylcyclohexene and (4R)-4-(2-methoxypropan-2-yl)-1-methylcyclohexene

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics, other

Remarks:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006 (REACH)

Type of information:

other: Desk-based assessment

Adequacy of study:

key study

Study period:

Not applicable

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Objective of study:

toxicokinetics

Principles of method if other than guideline:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006 (REACH)

GLP compliance:

no

Details on species / strain selection:

No animals were used in this desk-based assessment.

Details on test animals or test system and environmental conditions:

Not applicable

Details on exposure:

No animals were used in this desk-based assessment.

Duration and frequency of treatment / exposure:

No animals were used in this desk-based assessment.

No. of animals per sex per dose / concentration:

No animals were used in this desk-based assessment.

Positive control reference chemical:

No animals were used in this desk-based assessment.

Details on study design:

Not applicable

Details on dosing and sampling:

Not applicable

Statistics:

Not applicable

Preliminary studies:

Not applicable

Details on absorption:

The molecular weight of both constituents is low i.e. < 200 g/mol, it’s n-octanol/water partition coefficient is 4.6 for constituent I and 3.2 for constituent II, its water solubility is 1.71mg/L for constituent I and 101 mg/L for constituent II and vapour pressure of 58.6 Pa for constituent I and 14.3 Pa for constituent II are suggestive of favourable absorption via all routes. Although these properties make uptake from the dermal route possible, the surface tension (assumed >60 mN/m) could restrict transfer between the stratum corneum and the epidermis and therefore overall uptake via this route is limited. This is demonstrated by the lack of significant systemic and local toxicity from in vivo sensitisation study on the test item. Absorption from the gastro-intestinal tract and the respiratory tract epithelium: Oral absorption of the test item is mainly via passive diffusion to into portal circulation with delivery into the liver i.e. first pass metabolism and relative high pulmonary uptake. For example, d-Limonene is demonstrated to be well absorbed via the lungs in humans (i.e. u 70%) and the gastro-intestinal tract has been reported at up to 80% in humans as well as experimental animals.

Details on distribution in tissues:

The substance has physico-chemical properties that mean the test item can easily pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water into the liver. This will limit distribution of the parent compound systemically and limited half-life of the parent compound in blood plasma. A wide distribution of the substance via inhalation is expected as it can easily be taken up into circulatory system. For example, d-limonene and its metabolites has been shown to be detectable in kidney, liver, lung, serum and many other tissues, with higher concentrations detected in adipose tissue and mammary gland than in less fatty tissue.

Details on excretion:

The n-Octanol/water partition coefficient (log Pow of 3.2 – 4.6) and supporting bioaccumulation data (BCF <2,000) suggest accumulation of this substance in fatty tissues after absorption from gastro-intestinal tract is not significant, the substance could enter circulation via lymphatic system. Based on the molecular structure and solubility, excretion into urine as conjugated metabolites is assumed to be a preferred route of elimination. A small percentage of the parent compound may also be excreted via urine and faces. Elimination is assumed to be rapid, therefore no potential for bioaccumulation is to be expected, as demonstrated by the half-life of d-limonene in human i.e. about 12- 24 hours. The observed clinical changed in kidney would confirms urine as the most probably route of excretion. About 25-30% of an oral dose of d-limonene in humans eliminated in urine as d-limonene-8,9-diol and its glucuronide and about 7-11% eliminated as perillic acid and its metabolites.

Metabolites identified:

not measured

Details on metabolites:

Metabolism is mainly through the liver via phase I and II enzymes as demonstrated by centrilobular hepatocyte hypertrophy in the liver in both sexes. For constituent I (d-limonene); oxygenation of parent compound resulting in acidic and alcohol metabolites such as perillic acid, dihydroperillic acid, and limonene-1-,2-diol. These will be conjugated by phase II enzymes forming glucuronides conjugates. In circulatory system, d-limonene is known to induce unique nephropathy syndrome in rats after subacute or chronic exposure which is associated with α2u globulin accumulation in hyaline droplets, a condition not relevant to human. This is supported by the clinical observations slight increase in the incidence and severity of cortical tubular basophilia and changes in renal functions such as acidic urine with high urea and uniary chlorine, triglyceride, total creatinine and total potassium. For constituent II, metabolism mainly involve reduction of the ketone by carbonyl reductases to generate a secondary cyclic alcohol which may either be converted back to parent compound or conjugated with glucuronic acid and excreted in the bile and urine. Another route to consider is the microbial metabolism where the cyclic ketones undergoing oxidation forming a cyclic lactone which is further metabolized via ester hydrolysis forming hydroxyl carboxylate derivatives which would undergo phase II metabolism and eliminated via urine.

Conclusions:

The substance has physico-chemical properties with favourable ADME. Exposure from oral and inhalation routes are most favourable and therefore the substance is expected to be widely distributed especially via inhalation exposure. Based on the log Pow of 3.2 – 4.6 and BCF <2,000, bioaccumulation is not significant and elimination is rapid as demonstrated by half-life of 12-24 hours. The lack of systemic and local toxicity observed following in vivo sensitisation study shows that systemic bioavailability of this substance may be limited via dermal exposure. The clinical signs observed following oral sub-acute exposure support oral absorption of the test item and clinical signs reported in liver and kidney are demonstrative of distribution, biotransformation and elimination of the test item. Furthermore, full reversibility of clinical signs observed during recovery period following the repeated exposure of the test item in rats demonstrate no bioaccumulation and rapid elimination of the test item. It can be concluded that the toxicokinetic of the test item does not pose significant toxicological concern based on available data.

Executive summary:

A desk-based assessment of the toxicokinetics of the substance Reaction Mass of (4R)-4-isopropenyl-1-methylcyclohexene and (4R)-4-(2-methoxypropan-2-yl)-1-methylcyclohexene (test item), in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006 (REACH).  The substance has physico-chemical properties with favourable ADME. Exposure from oral and inhalation routes are most favourable and therefore the substance is expected to be widely distributed especially via inhalation exposure.  Based on the log Pow of 3.2 – 4.6 and BCF <2,000, bioaccumulation is not significant and elimination is rapid as demonstrated by half-life of 12-24 hours.  The lack of systemic and local toxicity observed following in vivo sensitisation study shows that systemic bioavailability of this substance may be limited via dermal exposure.  The clinical signs observed following oral sub-acute exposure support oral absorption of the test item and clinical signs reported in liver and kidney are demonstrative of distribution, biotransformation and elimination of the test item. Furthermore, full reversibility of clinical signs observed during recovery period following the repeated exposure of the test item in rats demonstrate no bioaccumulation and rapid elimination of the test item.  It can be concluded that the toxicokinetic of the test item does not pose significant toxicological concern based on available data.

Description of key information

Toxicokinetics Assessment: no bioaccumulation potential; desk-based assessment in accordance with Annex VIII, Section 8.8.1 of REACH; Anon. (2017)

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

A desk-based assessment of the toxicokinetics of the substance Reaction Mass of (4R)-4-isopropenyl-1-methylcyclohexene and (4R)-4-(2-methoxypropan-2-yl)-1-methylcyclohexene (test item), in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006 (REACH).  The substance has physico-chemical properties with favourable ADME. Exposure from oral and inhalation routes are most favourable and therefore the substance is expected to be widely distributed especially via inhalation exposure.  Based on the log Pow of 3.2 – 4.6 and BCF <2,000, bioaccumulation is not significant and elimination is rapid as demonstrated by half-life of 12-24 hours.  The lack of systemic and local toxicity observed following in vivo sensitisation study shows that systemic bioavailability of this substance may be limited via dermal exposure.  The clinical signs observed following oral sub-acute exposure support oral absorption of the test item and clinical signs reported in liver and kidney are demonstrative of distribution, biotransformation and elimination of the test item. Furthermore, full reversibility of clinical signs observed during recovery period following the repeated exposure of the test item in rats demonstrate no bioaccumulation and rapid elimination of the test item.  It can be concluded that the toxicokinetic of the test item does not pose significant toxicological concern based on available data.