2-ethylhexanoic acid, zirconium salt

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Additional information

Read-across approach

Selected endpoints for the human health hazard assessment are addressed by read-across, using a combination of data on the metal cation and the organic acid anion. This way forward is acceptable, since metal carboxylates are shown to dissociate to the organic anion and the metal cation upon dissolution in aqueous media. No indications of complexation or masking of the metal ion through the organic acid were apparent during the water solubility and dissociation tests (please refer to the water solubility and dissociation in sections 4.8 and 4.21 of IUCLID). Once the individual transformation products of the metal carboxylate become bioavailable (i.e. in the acidic environment in the gastric passage or after phagocytosis by pulmonary macrophages), the “overall” toxicity of the dissociated metal carboxylate can be described by a combination of the toxicity of these transformation products, i.e. the metal cation and carboxylate anion according to an additivity approach.

 

2-ethylhexanoic, zirconium salt is the zirconium metal salt of 2-ethylhexanoic acid, which readily dissociates to the corresponding zirconium cation and 2-ethylhexanoate anions. The zirconium cation and the 2-ethylhexanoate anion are considered to represent the overall toxicity of 2-ethylhexanoic, zirconium salt in a manner proportionate to the free acid and the metal (represented by one of its readily soluble salts). 

 

A detailed justification for the read-across approach is added as a separate document in section 13 of IUCLID.

 

Toxicity for reproduction– effects on fertility

No toxicity data on adverse effects on sexual function and fertility with 2-ethylhexanoic acid, zirconium salt is available, thus the reproductive toxicity will be addressed with existing data on the dissociation products as detailed in the table below. Further details on the reproductive toxicity of the individual constituents are given below.

 

Table: Summary of toxicity data on adverse effects on sexual function and fertility of 2-ethylhexanoic acid, zirconium salt and the individual constituents.

	Zirconium	2-ethylhexanoic acid (CAS# 149-57-5)	2-ethylhexanoic acid, zirconium salt (CAS# 22464-99-9)
Repeated dose toxicity data	Not adverse effects on reproductive organs observed (weight of evidence, animal data)	See section on repeated dose toxicity	See section on repeated dose toxicity
Two-generation reproductive toxicity study	Not reprotoxic (weight of evidence, animal data) Not classified	NOAEL(rat; F1) = 100 mg/kg bw/day* NOAEL(rat; P) = 300mg/kg bw/day   Not classified	No data   Not classified

* Identified as most sensitive endpoint in the registration dossier for 2-ethylhexanoic acid, i.e. has been used for the DNEL derivation of this substance.

 

Zirconium

The systemic toxic effects of zirconium acetate after repeated oral dosing, as well as any toxic effects on reproduction and development, were investigated in Sprague Dawley rats up to early lactation (day 4 post partum) by Rossiello (2013). The study was performed according to OECD guideline 422 and under GLP principles. Three groups of 10 males and 10 females each received the test item, by oral gavage, at 100, 300 and 1000 mg anhydrous zirconium acetate/kg bw/day. A similar constituted control group received the vehicle alone during the treatment period. The overall dosing period was 32 days for males, which included 2 weeks before pairing and continuously thereafter up to the day before necropsy, and up to 50 days for females, including 2 weeks before pairing and thereafter during pairing, gestation and lactation periods until day 3 post partum.

The parental animals were followed for daily clinical signs, weekly body weight, food consumption, neurotoxicity assessment, oestrous cycle, mating performance, clinical pathology evaluation including haematology and clinical chemistry, and offspring delivery. A detailed macroscopic examination, determination of organ weights, and histopathological examination, including the spermatogenic cycle, were performed. Pups were also checked for sex, body weight, clinical signs and macroscopic observations.

No mortality occurred in the study. No treatment related findings were observed either during the in vivo phase or at post mortem examination of parent animals. Microscopically, a treatment related finding was seen in males receiving 300 and 1000 mg zirconium acetate/kg bw/day consisting of minimal focal vacuolation of squamous epithelium (limiting ridge) of the non-glandular region of the stomach. This change may be attributed to a local irritant effect of the compound administered by oral gavage and since humans do not have a forestomach or structural analogue to the forestomach, this finding is not considered of toxicological relevance. In addition, no abnormalities were found during the evaluation of the spermatogenic cycle. No treatment related effects were observed in the number of oestrous cycle, pre-coital intervals, copulatory and fertility indices between treated and control groups. No significant differences were observed in the number of implantations, corpora lutea, total litter size, pre-implantation loss, pre-birth loss and gestation length between control and treated groups.

No effects were noted on reproduction and development at any dose. On the basis of the results obtained in this study, the NOAEL for reproduction/developmental toxicity was considered to be ≥ 1000 mg/kg bw/day (expressed as anhydrous zirconium acetate, equivalent to ≥530 mg Zr/kg bw/day), i.e., the highest dose tested.

Zirconium dioxide shows a limited toxicological activity as highlighted by the acute toxicity studies via oral (LD50 in rats > 5000 mg/kg) and inhalation route (LC50 in rats > 4.3 mg/L, maximal technically achievable mean concentration), as well as by the repeated dose toxicity studies via inhalation by Spiegl et al. (1956) (30 days NOAEC > 100.8 mg/m3 air and 60 days NOAEC > 15.4 mg/m3 air in cat, dog, guinea pig, rabbit, rat). Furthermore, the toxicokinetic assessment concluded of a low systemic absorption of zirconium dioxide. Absorption factors of 10% were proposed for oral, inhalation and dermal absorption, and it was argued that these factors were probably overestimated.

Additionally the study by Spiegl et al. (1956) showed no impact on the reproductive organs (at least testes) after inhalation of zirconium dioxide. After exposure of 28 animals (2 dogs, 6 rabbits, 20 rats) to 100.8 mg ZrO2 /m3 during 30 days and 123 animals (4 cats, 8 dogs, 20 guinea pigs, 6 rabbits and 72 rats) to 15.4 mg ZrO2/m3 during 60 days, no abnormal findings were noted for the reproductive organs during the histology realized on the 14 animals (2 dogs, 6 rabbits, 6 rats) exposed to 100.8 mg/m3 and the 46 animals (4 cats, 4 dogs, 18 guinea pigs, 10 rabbits and 10 rats) exposed to 15.4 mg/m3.

In a study on another poorly soluble zirconium substance, hydrated zirconium carbonate (HZC) containing 20.9% equivalent ZrO2 in which rats were exposed to diet containing equivalent dose of ZrO2 at level up to 7080 mg/kg bw/d for 17 weeks, no effects were observed on the genital organs Harrisson et al. (1951).

It is interesting to mention that in the study by Spiegl et al. (1956), exposure to zirconium tetrachloride dissolved into water, so in the form of zirconium dichloride oxide was as well realized. 124 animals (4 cats, 8 dogs , 20 guinea pigs, 20 rabbits and 72 rats) were exposed during 60 days to ZrCl4 at an equivalent dose of 6 mg Zr/m3. In this study, histology was realized on 60 animals (4 cats, 4 dogs, 17 guinea pigs, 10 rabbits and 25 rats) testicular atrophy on 2 cats was observed.

An additional study on zirconium dichloride oxide (ZOC) was done by oral route by Delongeas et al. (1983). This study showed that a weak fraction of Zr was absorbed after oral exposure for 16 days of rats to ZOC (3000 and 5300 mg/kg). However a small portion of this absorbed fraction could reach the ovaries and induce hypervascularization.

 

2-Ethylhexanoic acid

2-Ethylhexanoic acid was administered via drinking water to an unspecified number of male and female rats at 0, 100, 300, or 600 mg/kg bw/day. There were no deaths. The relative epididymal weights in high-dose males were significantly increased, but no histological changes were noted. A slight, but not statistically significant increase in the number of abnormal sperm was noted in the highest two dose groups; however, the incidence per animal was not provided. Treated groups required more time to successfully complete mating, and the mean litter size in high-dose pregnant females was significantly reduced. The mean pup weights in the high-dose group were significantly lower on postnatal day 7 and 14. Mean fetal weight per litter and mean placental weights were significantly reduced in the mid- and high-dose groups. Clubfoot was the only skeletal malformation; changes in skeletal variations were also noted (wavy ribs, reduced cranial ossification, and twisted hind legs). Corrected maternal body weights at termination and weight gains of high-dose females were significantly reduced. Physical development of the eyes, teeth and hair appeared to be slightly later in the pups from the high-dose groups; the significance of this finding is unclear since no data were presented on the length of gestation in treated and control dams. The high-dose of 600 mg/kg bw/day significantly reduced overall water consumption and body weights in female animals. The NOAEL for reproductive effects in parental animals was 300 mg/kg bw/day; this effect occurred in the presence of maternal toxicity. The NOAEL for F1 offspring was 100 mg/kg bw/day. Based on these results, 2-ethylhexanoic acid is not likely to cause effects on fertility but is likely to be a developmental toxicant. The developmental toxicity of 2-ethylhexanoic acid is at least partially related to disruption of Zn metabolism and distribution in the mother, and that higher zinc levels in the mothers leads to lower developmental toxicity in offspring.

 

2-ethylhexanoic acid, zirconium salt

Since no toxicity data on adverse effects on sexual function and fertility is available for 2-ethylhexanoic acid, zirconium salt, information on the individual constituents zirconium and 2-ethylhexanoic acid will be used for the hazard assessment and, when applicable, for the risk characterisation of 2-ethylhexanoic acid, zirconium salt. For the purpose of hazard assessment of 2-ethylhexanoic acid, zirconium salt, the point of departure for the most sensitive endpoint of each constituent will be used for the DNEL derivation.

 

2-ethylhexanoic acid, zirconium salt is not expected to show adverse effects on sexual function and fertility, since the two constituents zirconium and 2-ethylhexanoic acid have not shown adverse effects on sexual function and fertility in relevant bioassays. Thus, 2-ethylhexanoic acid, zirconium salt is not to be classified according to regulation (EC) 1272/2008 as reproductive toxicant: fertility impairment. Further testing is not required. For further information on the toxicity of the individual constituents, please refer to the relevant sections in the IUCLID and CSR.

Short description of key information:
2-ethylhexanoic acid, zirconium salt is not expected to show adverse effects on sexual function and fertility.

Justification for selection of Effect on fertility via oral route:
Information from read-across substances:
animal data for zirconium: NOAEL(rat) ≥530 mg Zr/kg bw/day
animal data for 2-ethylhexanoic acid: NOAEL(rat, P) = 300mg/kg bw/day

Effects on developmental toxicity

Additional information

Read-across approach

Selected endpoints for the human health hazard assessment are addressed by read-across, using a combination of data on the metal cation and the organic acid anion. This way forward is acceptable, since metal carboxylates are shown to dissociate to the organic anion and the metal cation upon dissolution in aqueous media. No indications of complexation or masking of the metal ion through the organic acid were apparent during the water solubility and dissociation tests (please refer to the water solubility and dissociation in sections 4.8 and 4.21 of IUCLID). Once the individual transformation products of the metal carboxylate become bioavailable (i.e. in the acidic environment in the gastric passage or after phagocytosis by pulmonary macrophages), the “overall” toxicity of the dissociated metal carboxylate can be described by a combination of the toxicity of these transformation products, i.e. the metal cation and carboxylate anion according to an additivity approach.

 

2-ethylhexanoic, zirconium salt is the zirconium metal salt of 2-ethylhexanoic acid, which readily dissociates to the corresponding zirconium cation and 2-ethylhexanoate anions. The zirconium cation and the 2-ethylhexanoate anion are considered to represent the overall toxicity of 2-ethylhexanoic, zirconium salt in a manner proportionate to the free acid and the metal (represented by one of its readily soluble salts). 

 

A detailed justification for the read-across approach is added as a separate document in section 13 of IUCLID.

 

Toxicity for reproduction – developmental toxicity

No toxicity data on adverse effects on development of the offspring with 2-ethylhexanoic acid, zirconium salt are available, thus the reproductive toxicity will be addressed with existing data on the dissociation products as detailed in the table below. Further details on the genetic toxicity of the individual constituents are given below.

 

Table: Summary of toxicity data on adverse effects on development of the offspring of 2-ethylhexanoic acid, zirconium salt and the individual constituents.

	Zirconium	2-ethylhexanoic acid (CAS# 149-57-5)	2-ethylhexanoic acid, zirconium salt (CAS# 22464-99-9)
Screening test / Pre-natal developmental toxicity study	NOAEL(rat; mat.) ≥530 mg/kg bw/day   NOAEL(rat; dev) ≥530 mg/kg bw/day   Not classified	NOAEL(rat; mat.) = 250 mg/kg bw/day   NOAEL(rat; dev) = 100 mg/kg bw/day*   Category 2, H361d (CLP) Category 3, R63 (DSD)	No data   Self-classified Category 2, H361d (CLP) Category 3, R63 (DSD)
Two-generation reproductive toxicity study	No data	NOAEL(rat; F1) = 100 mg/kg bw/day* NOAEL(rat; P) = 300mg/kg bw/day   not classified	No data

* Identified as most sensitive endpoint in the registration dossier for 2-ethylhexanoic acid, i.e. has been used for the DNEL derivation of this substance.

 

Zirconium

An OECD 422 test (scored for reliability K1) has been performed with zirconium acetate (Rossiello, 2013). The test results indicate that zirconium acetate is a substance of low toxicological potential, as the NOAEL for reproductive/developmental toxicity was considered to be higher than or equal to the highest dose tested: 1000 mg/kg bw/day expressed as anhydrous zirconium acetate, equivalent to 530 mg Zr/kg bw/day. Furthermore no effects were observed in any of the parameters evaluated for pups. In addition, and based on the assessment of all available data, low absorption of zirconium acetate is expected. Also low toxicity is expected based on the available acute and subacute experimental data with zirconium acetate. Therefore, no further testing seems to be required for this substance as no adverse effects or hazards need to be addressed. Due to the extremely low absorption and toxicity, it will be scientifically unjustified to perform a prenatal developmental toxicity study, since this study reasonably requires testing up to doses that cause maternal toxicity. Based on the evaluation and results mentioned above, it is considered acceptable to assume that effects on reproduction or development are not to be expected (if at all) at exposure levels well below the unbound values from the repeated dose toxicity studies.

 

2-Ethylhexanoic acid

2-Ethylhexanoic acid was administered via drinking water to an unspecified number of male and female rats at 0, 100, 300, or 600 mg/kg bw/day. There were no deaths. The relative epididymal weights in high-dose males were significantly increased, but no histological changes were noted. A slight, but not statistically significant increase in the number of abnormal sperm was noted in the highest two dose groups; however, the incidence per animal was not provided. Treated groups required more time to successfully complete mating, and the mean litter size in high-dose pregnant females was significantly reduced. The mean pup weights in the high-dose group were significantly lower on postnatal day 7 and 14. Mean fetal weight per litter and mean placental weights were significantly reduced in the mid- and high-dose groups. Clubfoot was the only skeletal malformation; changes in skeletal variations were also noted (wavy ribs, reduced cranial ossification, and twisted hind legs). Corrected maternal body weights at termination and weight gains of high-dose females were significantly reduced. Physical development of the eyes, teeth and hair appeared to be slightly later in the pups from the high-dose groups; the significance of this finding is unclear since no data were presented on the length of gestation in treated and control dams. The high-dose of 600 mg/kg bw/day significantly reduced overall water consumption and body weights in female animals. The NOAEL for reproductive effects in parental animals was 300 mg/kg bw/day; this effect occurred in the presence of maternal toxicity. The NOAEL for F1 offspring was 100 mg/kg bw/day. Based on these results, 2-ethylhexanoic acid is not likely to cause effects on fertility but is likely to be a developmental toxicant. The developmental toxicity of 2-ethylhexanoic acid is at least partially related to disruption of Zn metabolism and distribution in the mother, and that higher calcium levels in the mothers leads to lower developmental toxicity in offspring. Based on the above given information, 2-ethylhexanoic acid was classified as toxic for reproduction, developmental toxicity category 2 (H361d).

 

2-ethylhexanoic acid, zirconium salt

Since no reproductive toxicity study is available for 2-ethylhexanoic acid, zirconium salt, information on the individual constituents zirconium and 2-ethylhexanoic acid will be used for the hazard assessment and, when applicable, for the risk characterisation of 2-ethylhexanoic acid, zirconium salt. For the purpose of hazard assessment of 2-ethylhexanoic acid, zirconium salt, the point of departure for the most sensitive endpoint of each constituent will be used for the DNEL derivation. In case of 2-ethylhexanoic acid in2-ethylhexanoic acid, zirconium salt, the NOAEL of 100 mg/kg bw/day for the reproductive toxicity in the F1 offspring will be used.

Considering the read-across principles as detailed above for 2-ethylhexanoic acid, zirconium salt based on the toxicological assessment of the individual constituents, it is therefore proposed to also read-across the classification of toxic for reproduction, developmental toxicity category 2 (H361d) of 2-ethylhexanoic acid to 2-ethylhexanoic acid, zirconium salt.

Justification for selection of Effect on developmental toxicity: via oral route:
Information from read-across substances:
animal data for zirconium: NOAEL(rat) ≥530 mg/kg bw/day
animal data for 2-ethylhexanoic acid: NOAEL(rat, F1) = 100 mg/kg bw/day

Justification for classification or non-classification

2-ethylhexanoic acid, zirconium salt is not expected to show adverse effects on sexual function and fertility, since the two constituents zirconium and 2-ethylhexanoic acid have not shown adverse effects on sexual function and fertility in relevant bioassays. Thus, 2-ethylhexanoic acid, zirconium salt is not to be classified according to regulation (EC) 1272/2008 as reproductive toxicant: fertility impairment.

Considering the read-across principles as detailed above for 2-ethylhexanoic acid, zirconium salt based on the toxicological assessment of the individual constituents, it is therefore proposed to also read-across the classification of toxic for reproduction, developmental toxicity category 2 (H361d) of 2-ethylhexanoic acid to 2-ethylhexanoic acid, zirconium salt