Eugenol

Endpoint summary

Description of key information

Weight-of-evidence NOAEL = 300 mg/kg bw/d (Chronic study, rats, Rel.2)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

300 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

The available information as a whole meets the tonnage driven data requirement of REACH. Moreover, reliability and consistency are observed across the different studies.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The repeated dose toxicity of Eugenol was investigated across several key studies performed to assess Eugenol potential for carcinogenicity and for toxicity to reproduction (read-across approach using Isoeugenol), in rats and/or mice exposed by oral route.

In a 90-day repeated day toxicity study in rats (used as range-finding for carcinogenicity), a 10% reduced final body weight together with a 12% reduced body weight gain were observed only in male rats administered 12,500 ppm Eugenol (equivalent to 1250 mg/kg bw/d) compared to control males. The authors also reported that no chemically-related gross or histopathological effects were observed among the rats investigated.

In a similar study conducted in mice (used also as range-finding for carcinogenicity), no statistically significant, test article-related effects on mortality, body weight, body weight gain, gross pathology, and histopathology were noted following dietary administration of Eugenol up to 6,000 ppm daily (900 mg/kg bw/d) for 90 days.

In a carcinogenicity study conducted in rats exposed to Eugenol by diet for 104 weeks, up to 15% reduced body weight from weeks 51 to 102 of treatment together with a decreased body weight gain of 10% during the entire study were observed in the highest dose female group (625 mg/kg bw/d). This effect was considered as a slight adverse systemic effect in the absence of any other effect. No change of body weight or body weight gain that could be considered as adverse was observed in males up to 300 mg/kg bw/d. Furthermore, under the experimental conditions described in the study, the NTP panel concluded that there was no evidence of carcinogenicity for Eugenol in male or female rats.

In a similar carcinogenicity study, dietary administration of Eugenol to mice did not result in any statistically significant test article-related changes in mean food consumption and survival. However, transient decreased mean body weight (week 101 and 104) slightly higher to 10% (limit to consider as adverse effect) was observed in high-dose female together with a decreased body weight gain of 21% during the entire study. Furthermore, under the experimental conditions, the weight of evidence indicates that Eugenol is not a carcinogen in mice (See Iuclid §7.7).

In a two-generation study, the supporting substance, Isoeugenol, was administered to rats daily via oral gavage at dose levels of 0, 70, 230 or 700 mg/kg bw/d. Body weight, food consumption, clinical signs, organ weight, gross and microscopic pathology information allowed to assess the repeated dose toxicity potential of Isoeugenol, and by analogy to Eugenol across the generations. Based on an expert judgement a LOAEL for parental toxicity was determined at 70 mg/kg bw/d, based on decreased body weight gains at all dose-levels, although probably linked to the bolus effect due to the type of administration (gavage) considered as worst-case and less realistic than by diet.

In an embryo-foetal development study, the supporting substance Isoeugenol was administered to female rats via oral gavage at dose levels of 0, 250, 500 and 1000 mg/kg bw/d. The LOAEL was reported to be the low dose level of 250 mg/kg bw/d based on a statistically and dose-dependent reduced gestation body weight gain. Other effects in maternal animals included several types of clinical effects at higher doses and lower maternal relative food intake at the highest dose (1000 mg/kg bw/d).

Therefore, the overall no-observed adverse observed effect (NOAEL) and the lowest-observed adverse observed effect (LOAEL) for repeated dose toxicity study determined in the different key studies are summarised in the table 7.5.

Table 7.5: Overall NOAEL and LOAEL for repeated dose toxicity identified across key studies

Study types	Substance tested	Species	Routes of exposure	NOAEL (mg/kg bw/d)	LOAEL (mg/kg bw/d)	Basis
90-day	Eugenol	Rat	Diet	Male: 600 Female: 1250 (highest dose)	Male: 1250 (highest dose)	Reduced final body weight of 10% and body weight gain of 12% in male rats tested at 1250 mg/kg bw/d compared to controls
90-day	Eugenol	Mouse	Diet	Male and female : ≥ 900	-	Highest dose level, no effect
Carcinogenicity	Eugenol	Rat	Diet	Female: 300* Male : ≥ 300 (highest dose)	Females: 625 (highest dose)	Reduced body weight up to 15% in high dose female group from weeks 51 to 102 of treatment and decreased body weight gain of 10% within the 104 weeks
Carcinogenicity	Eugenol	Mouse	Diet	Females: 450 Males: 900 (highest dose)	Females: 900 (highest dose)	Reduced body weight gain, considered as adverse effect (>10%) at the highest dose and observed only during the two last weeks of treatment (week 101 and week 104). Transient body weight gain decrease up to 21% within the104 weeks at the highest dose.
Two generation study	Isoeugenol	Rat	Gavage	Male and female : 70 (lowest dose)	Male and female : 230(mid-dose)	Decreased body weight gains at all dose-levels, although probably linked to the bolus effect due to gavage
Embryo-fœtal developmental study	Isoeugenol	Rat	Gavage	Not identified	Female : 250 (lowest dose)	Dose-dependent reduced gestation body weight gain

*Relevant NOAEL determined from expert judgement according to the following criteria.

In a weight of evidence approach, i.e. taking into account the whole database (see Table 7.5), the following criteria were considered to determine the most relevant NOAEL for repeated dose toxicity of Eugenol:

- the substance tested: studies on Eugenol preferred to Isoeugenol, which showed higher irritating potential than Eugenol inducing local effects in animals,

- the duration of the study: long-term studies preferred to short-term studies to detect delayed systemic effect,

- the route of exposure: diet preferred to gavage which induced bolus effects reflecting less realistic conditions

- the effects observed: obvious relevant systemic effects observed with dose-related changes preferred to transient effects inducing equivocal results.

According to these criteria, results from the carcinogenicity study conducted in rats allowed to identify the most relevant NOAEL at 300 mg/kg bw/d for repeated dose toxicity of Eugenol. This value was used to extrapolate the different DNELs for worker and general population.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Weight of evidence approach taking into account the whole database: repeated dose toxicity, reproductive toxicity and carcinogenicity.

Justification for classification or non-classification

No specific target organ toxicity was observed following repeated exposure to Eugenol. As a result, the substance does not meet the criteria for classification as STOT-RE according to Regulation (EC) No 1272/2008, Annex I section 3.9.