Registration Dossier

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
basic toxicokinetics, other
Remarks:
Assessment of toxicokinetic behaviour
Type of information:
other: In accordance with REACH Annex VIII (8.8) an assessment of toxicokinetic behavior has been conducted to the extent that can be derived from the relevant available information.
Adequacy of study:
key study
Study period:
Not applicable
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Relevant studies were reviewed by a qualified toxicologist with a view to fulfilling the requirements of Annex VIII (8.8).
Objective of study:
absorption
distribution
excretion
metabolism
toxicokinetics
Qualifier:
no guideline required
Principles of method if other than guideline:
Summaries of studies and literature were reviewed by a qualified toxicologist with a view to fulfilling the requirements of Annex VIII, point 8.8 of REACH. The assessment of the likely toxicokinetic behaviour of the substance was provided to the extent that can be derived from the relevant available information at the time of the assessment. The assessment is based on the Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA)
GLP compliance:
no

Absorption:

Oral absorption:

Although the low molecular weight of (Z)-3-hexenyl salicylate will favour absorption from the gastrointestinal tract, the low water solubility will limit how readily this compound dissolves in the gastrointestinal fluid. (Z)-3-hexenyl salicylate is highly lipophilic, however, and therefore micellular solubilisation will aid absorption.  

No data is available on the hydrolysis of (Z)-3-hexenyl salicylate at different pH values, however it is anticipated that the ester bond will be vulnerable to hydrolysis in the gastrointestinal tract, to form 3-hexen-1-ol (hex-3-en-1-ol, leaf alcohol) and salicylic acid, which will be readily absorbed from the gastrointestinal tract.

Acute oral and repeat dose toxicity studies have been conducted which provide evidence of systemic toxicity, and therefore of oral absorption. 

In an acute oral toxicity study (OECD 401) conducted with cyclohexyl salicylate, there were signs of systemic toxicity (including death) following administration (Potokar, 1984a).

Evidence of oral absorption was also seen in a repeat oral dose study (OECD 422) conducted with (z)-3-hexenyl salicylate. Decreased bilirubin levels, increased triglyceride levels and changes in albumin/globulin ratios were observed in males and females. Effects on liver and thymus weights were seen in males at the top dose level. Macroscopic and histological findings were seen in the kidney, stomach, liver and testes. Effects on reproduction and breeding were seen which increased with dose level (Damme, 2013).   

A repeat dose, reproductive toxicity study conducted with cyclohexyl salicylate, rats showed signs of systemic toxicity, including reduced weight gain, effects on liver weights and dystocia(Schmidt, 1995).

Other studies are available with (Z)-3-hexenyl salicylate (acute oral toxicity study (Moreno, 1975)) and cyclohexyl salicylate (28 day oral (Potokar, 1984b), 90 day oral(Pittermann, 1995), and developmental toxicity study (Pittermann, 1996)), but in the absence of systemic signs of toxicity nothing can be inferred about oral absorption from these studies.

For risk assessment purposes, because of the immiscibility of the material in water (log Pow >4) absorption via the oral route is unlikely, although in the absence of other information, for the purposes of human DNEL setting, 50% bioavailability is assumed.

Dermal absorption:

(Z)-3-hexenyl salicylate is a lipophilic, sparingly water soluble liquid. The lipophilicity of the substance means that it will be taken up into the stratum corneum, but the penetration into the epidermis will be limited by the low water solubility and therefore the dermal absorption will be low to moderate.

Some acute dermal toxicity studies report irritation to the skin (Kästner, 1984) (Moreno, 1975) from which some penetration might be inferred, however in other studies available (Sanders, 1999) (Middeke & Küster, 2001) (Kligman, 1975) (Ullmann, 1999) (Küster & Goluchowski, 1999), no such reactions were seen or reported and nothing can be concluded.

Estimation of mammalian dermal absorption is made in accordance with principles adopted within the EFSA guidance on estimating dermal absorption of pesticide active substances (EFSA, 2012)and the PPR Panel opinion on the science behind the dermal absorption guidance document(EFSA, 2011). On this basis, a dermal absorption of 25% in humans is considered appropriate for (Z)-3-hexenyl salicylate, and this default value will be used for risk assessment purposes.

Inhalation absorption:

(Z)-3-Hexenyl salicylate has a low vapour pressure (0.15 Pa at 25°C) and therefore inhalation of vapour is not anticipated. Use of this substance will not result in aerosols, particles or droplets of an inhalable size, therefore exposure via the inhalation route is unlikely to occur.

In the absence of any experimental data on toxicity following inhalation exposure, and considering that exposure via inhalation is unlikely, the same extent of oral absorption (100%) will be used for inhalation for risk assessment purposes.

Distribution:

Any (Z)-3-hexenyl salicylatethat is absorbed will be distributed via the blood to the liver and other organs and tissues. Due to its low water solubility and high log Pow, there is potential for accumulation in fatty tissues. The changes in liver and thymus weights and findings in the kidney, stomach, liver and testes in the OECD 422 study in rat, along with changes to clinical chemistry parameters, provide evidence that the substance is widely distributed (Damme, 2013). 

Metabolism:

In the in vitro chromosome aberration test in Chinese hamster V79 cells (Baduhn, 1995) and the mammalian cell gene mutation assay in Chinese hamster V79 cells(Poth, 1994),cyclohexyl salicylate was shown not to be mutagenic, either in the presence or absence of metabolic activation with S9-mix. On the basis of these studies, no conclusions can be drawn about the metabolism of cyclohexyl salicylate, or by analogy of (Z)-3-hexenyl salicylate.

The metabolism of (Z)-3-hexenyl salicylate is expected to proceed via hydrolysis of the ester bond in the gastrointestinal tract, blood and liver to form (Z)-3-hexen-1-ol (hex-3-en-1-ol, leaf alcohol) and salicylic acid. 

The metabolism of linear short chain aliphatic alcohols such as 3-hexen-1-ol is well documented (JECFA, 1999).  (Z)-3-hexen-1-ol will be oxidised to the aldehyde and then to the carboxylic acid, which will be completely metabolised to CO2and H2O in the fatty acid and tricarboxylic acid pathways. (Z)-3-hexen-1-ol will also be conjugated with glucuronic acid.

Salicylic acid is a metabolite of aspirin (acetyl salicylic acid) and therefore the metabolism of this moiety is also well documented (La Du, Mandel & Way, 1979). Metabolism proceeds via glycine conjugation to salicylurate (major metabolite in urine in man) and glucuronidation to salicyl acyl glucuronide and salicyl phenolic glucuronide. Hydroxylation is a minor route of metabolism, resulting in 2,5-dihydroxybenzoic acid (gentisic acid), 2,3-dihydroxybenzoic acid and 2,3,5-trihydroxy benzoic acid.

A postulated metabolic pathway for(Z)-3-hexenyl salicylate is shown in background material.

Elimination:

Although (Z)-3-hexenyl salicylate is of low molecular weight, the low water solubility will not favour direct urinary excretion, instead biotransformation to more polar metabolites will be required to promote excretion.  

Metabolites of(Z)-3-hexenyl salicylate are of low molecular weight and are polar in nature, and therefore will be eliminated primarily via the urine. Salicylic acid and its metabolites are known to be eliminated in urine (La Du, Mandel & Way, 1979). The carboxylic acid metabolite and glucuronide conjugate of (Z)-3-hexen-1-ol are also expected to be rapidly eliminated in urine.

Conclusions:
Based on the physical-chemical properties of (Z)-3-hexenyl salicylate, some absorption is expected by the oral and dermal routes.

Acute oral and repeat dose toxicity studies have been conducted with (Z)-3-hexenyl salicylate and the structurally similar analogue cyclohexyl salicylate which provide evidence of systemic toxicity, and therefore of oral absorption. The effects on organs in the repeat dose study with (Z)-3-hexenyl salicylate showed that the absorbed material is widely distributed. For risk assessment purposes, (Z)-3-hexenyl salicylate is considered to be partly absorbed (50%) following oral administration.

Although no clear evidence of dermal absorption was seen in the acute dermal toxicity, skin irritation or skin sensitisation studies, based on estimation of mammalian dermal absorption in accordance with principles adopted within the EFSA guidance on estimating dermal absorption of pesticide active substances (EFSA, 2012), a dermal absorption value of 25% will be used for risk assessment purposes.

Description of key information

A toxicokinetic profile for (Z)-3-hexenyl salicylate has been determined on the basis of the physical-chemical properties of (Z)-3-hexenyl salicylate, and on in vitro studies and acute and repeat dose toxicity studies with(Z)-3-hexenyl salicylate and the structurally similar analogue cyclohexyl salicylate.

Based on these data, (Z)-3-hexenyl salicylate is considered to be partially absorbed (50%) following oral administration. A dermal absorption value of 25% and an inhalation exposure value of 50% will be used for risk assessment purposes.

Key value for chemical safety assessment

Absorption rate - oral (%):
50
Absorption rate - dermal (%):
25
Absorption rate - inhalation (%):
50

Additional information

Based on the physical-chemical properties of (Z)-3-hexenyl salicylate, some absorption is expected by the oral and dermal routes. Acute oral and repeat dose toxicity studies have been conducted with (Z)-3-hexenyl salicylate and the structurally similar analogue cyclohexyl salicylate which provide evidence of systemic toxicity, and therefore of oral absorption. The effects on organs in the repeat dose study with (Z)-3-hexenyl salicylate showed that the absorbed material is widely distributed. For risk assessment purposes, (Z)-3-hexenyl salicylate is considered to be partly absorbed (50%) following oral administration. 

Although no clear evidence of dermal absorption was seen in the acute dermal toxicity, skin irritation or skin sensitisation studies, based on estimation of mammalian dermal absorption in accordance with principles adopted within the EFSA guidance on estimating dermal absorption of pesticide active substances (EFSA, 2012), a dermal absorption value of 25% will be used for risk assessment purposes.

Exposure to (Z)-3-hexenyl salicylate via the inhalation route is not expected, however in the absence of any experimental data on toxicity following inhalation exposure, the same extent of oral absorption (50%) will be used for risk assessment purposes.

(Z)-3-hexenyl salicylate is expected to undergo ester hydrolysis to form (Z)-3-hexen-1-ol and salicylic acid. The metabolism of these metabolites is well documented, and results in small, polar metabolites which are readily excreted via the urine.