Nickel bis(2-ethylhexanoate)

Endpoint summary

Description of key information

- Acute oral toxicity:
In a GLP conform OECD 423 study, the acute oral LD50 value of the test item nickel bis(2-ethylhexanoate) was found to be 300 < LD50 ≤ 2000 mg/kg bw in female Han:WIST rats. Concerning Nickel moiety, the two key studies selected were conducted on Nickel sulfate in compliance with OECD guidelines. Both studies found similar LD50 values just above or below 300 mg/kg bw. One supporting study was conducted on human exposure, exhibiting Nickel (NiCl2 and NiSO4) poisoning and containing detailed monitoring of workers accidentally exposed to toxic levels of Nickel. 
Concerning 2-ethylhexanoic acid, the study selected was conform OECD guideline n°401 and an LD50 of 2043 mg/kg bw was found for female rats.
- Acute dermal toxicity:
For Nickel moiety, data on dermal toxicity of NiSO4 was selected: up to 100 mg/kg bw, no clinical signs of poisoning or mortality were found. 
Concerning 2-ethylhexanoic acid, data on dermal toxicity are limited and results of two publications are added to this dossier. These indicate that 2-ethylhexanoic acid is readily absorbed by the skin and the LD50 appeared to be between 3.6 and 4.5 g/kg bw. 
The few studies available do not allow determination of an exact effect level for acute dermal toxicity of Nickel bis(2-ethylhexanoate) (see discussion). However its LD50 for dermal exposure will probably be between 625 mg/kg (based on the data for Nickel) and 5000 mg/kg bw (based on the data for 2-ethylhexanoic acid). The key value is therefore expressed as a discriminating dose based on the NOEL for acute dermal exposure to Nickel of 100 mg/kg bw, extrapolated to Nickel bis(2-ethylhexanoate).      
- Acute inhalation toxicity:
This substance is a waxy solid which is not capable in creating an inhalable atmosphere, thus testing is technically not feasible. 	

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

07 July 2022 - 26 July 2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 423 (Acute Oral toxicity - Acute Toxic Class Method)

GLP compliance:

yes (incl. QA statement)

Test type:

acute toxic class method

Limit test:

no

Species:

rat

Strain:

Wistar

Remarks:

Han:WIST rats

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Toxi-Coop Zrt., H-1122 Budapest, Magyar Jakobinusok tere 4B
- Hygienic level at supplier: SPF
- Hygienic level during the study: Standard housing conditions
- Number of animals: 9 animals, 3 animals/group
- Sex: Female, nulliparous and non-pregnant animals
- Age of animals at dosing: Young adult rats, approx. 8 weeks old
- Body weight range at dosing: 170 - 184 g. The maximum difference of individual animal weights from the mean of the treatment group did not exceed 20%.
- Acclimatisation period: At least 15 days
- Animal health: Only healthy animals were used for the test. The health status was certified by the Veterinarian.
- Housing: Group caging (3 animals/cage)
- Cage type: T3H polycarbonate
- Bedding and nesting: “SAFE 3/4-S-FASERN” certified wooden chips and “Sizzle pet” nest material were available to animals during the study.
- Enrichment: Animals were housed by group to allow social interaction and with deep wood sawdust bedding to allow digging and other normal rodent activities.
- Animals received standard laboratory rat diet, ad libitum, and tap water from the municipal supply, as for human consumption from drinking bottles designed for rodents, ad libitum.
- The night before treatment, the animals were fasted. Food, but not water, was withheld overnight. Animals were weighed before dosing. Food was replaced 3 hours after the treatment.

ENVIRONMENTAL CONDITIONS
- Lighting period: 12 hours daily, from 6.00 a.m. to 6.00 p.m.
- Temperature: 19 – 24 °C (target: 22 ± 3 °C)
- Relative humidity: 34 – 70 % (target: 30 – 70 %)
- Ventilation: 15-20 air exchanges/hour

IN-LIFE DATES: From 07 July 2022 to 26 July 2022

Route of administration:

oral: gavage

Vehicle:

corn oil

Remarks:

Batch number: MKCM9808 Manufacturer: Sigma-Aldrich Expiry date: 30 April 2026 Storage: Room temperature

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 200 or 30 mg/mL
- Amount of vehicle (if gavage): 10 mL/kg bw
- Justification for choice of vehicle: The test item did not dissolve in distilled water, in 1% methyl cellulose solution and in PEG 400 (even if heated up to approximately 60º C), and dissolved partially in corn oil.
Because the best results were achieved in corn oil, a harsher mechanical treatment was chosen: the sonication (with a 1.3mm disruption horn) of the test item with corn oil resulted in a gavage-applicable clear solution of green color.

DOSAGE PREPARATION: The test item was freshly formulated in the vehicle at the appropriate concentration (200 or 30 mg/mL), in the Pharmacy of NEXTREAT Laboratories on the day of administration. The formulations were stirred with magnetic stirrer up to finishing the treatment.

CLASS METHOD (if applicable)
- Rationale for the selection of the starting dose: As starting dose level for acute toxicity study, a dose of 2000 mg/kg body weight (bw) was selected based on the information published by ECHA.
- Initially three animals were treated at the starting dose of 2000 mg/kg bw (Group 1). All three animals died on Day 0, thus the second group (Group 2) was treated at the lower dose level (300 mg/kg bw). As no mortality observed after approximately 24 hours, three further animals were treated at the same dose level (Group 3). As no mortality was observed in this confirmatory dose group, no further animals were treated according to the study design of OECD 423.

Doses:

2000 mg/kg bw or 300 mg/kg bw

No. of animals per sex per dose:

3 female animals per group

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Clinical observations: Following the end of the dosage, the animals were observed individually once during the first 30 minutes, at 1, 2, 3, 4 and 6 hours after the treatment and once daily for 14 consecutive days thereafter. Individual observations were performed on the skin and fur, eyes and mucous membranes and also respiratory, circulatory, autonomic and central nervous system, somatomotor activity and behaviour pattern. Particular attention was directed to observation of tremors, convulsions, salivation, diarrhoea, lethargy, sleep and coma. The time of death was recorded as precisely as possible.
- Body weight: The body weight of the animals was recorded on Days 0 (prior to dosing), 7 and 14 (prior to necropsy), with a precision of 1 g. Terminal body weight of animals found dead was also recorded.
- Necropsy: Animals were subjected to a necropsy and a macroscopic examination. After examination of the external appearance, the cranial, thoracic and abdominal cavities were opened and the appearance of the tissues and organs were observed. All gross macroscopic changes were recorded for each animal.

Statistics:

The method used was not intended to allow the calculation of a precise LD50 value.

Key result

Sex:

female

Dose descriptor:

LD50

Effect level:

> 300 - <= 2 000 mg/kg bw

Based on:

test mat.

Sex:

female

Dose descriptor:

LD50 cut-off

Effect level:

500 mg/kg bw

Based on:

test mat.

Mortality:

At the dose level of 2000 mg/kg bw, 3/3 animals died on Day 0.
No mortality was observed at the dose level of 300 mg/kg bw.

Clinical signs:

other: other:

Body weight:

lower than 10% body weight loss

Gross pathology:

In the 2000 mg/kg bw groups, three animals were found dead on Day 0. In these animals diffuse red discoloration of the glandular mucosa of the stomach was observed. Green mucoid material in the stomach and non-collapsed lungs were also noted in all animals.

In the 300 mg/kg bw group, no macroscopic changes were observed.

Interpretation of results:

Category 4 based on GHS criteria

Remarks:

The test substance is classified Category 4 according to Regulation (EC) No 1272/2008 (CLP)

Conclusions:

Under the conditions of this study, the acute oral LD50 value of the test item Nickel-2-ethylhexanoate was found to be between 300 and 2000 mg/kg bw in female Han:WIST rats.
The LD50 cut-off value is 500 mg/kg bw.

The study result triggers the following classification/labelling:
- Regulation (EC) No 1272/2008 (CLP): Category 4
- GHS (rev. 9) 2021: Category 4

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

> 300 - <= 2 000 mg/kg bw

Quality of whole database:

GLP conform standard test

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

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.

 

Nickel bis(2-ethylhexanoate) is the nickel salt of 2-ethylhexanoic acid, which readily dissociates to the corresponding divalent nickel cation and monovalent 2-ethylhexanoate anions. The nickel cation and the 2-ethylhexanoate anion are considered to represent the overall toxicity of nickel bis(2-ethylhexanoate) 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.

 

Acute toxicity

An acute oral toxicity study is available for nickel bis(2-ethylhexanoate). Acute dermal and inhalation toxicity will be addressed with existing data on the dissociation products as detailed in the table below. Further details on the acute toxicity of the individual constituents within the framework of regulation (EC) 1907/2006 are given below.

 

Table: Summary of acute toxicity data of nickel bis(2 -ethylhexanoate) and the individual constituents.

	nickel ion	2-ethylhexanoic acid (CAS# 149-57-5)	nickel bis(2 -ethylhexanoate) (CAS# 4454-16-4)
Acute oral toxicity	LD50(rat)= 80.8 mg Ni/kg bw (361.9 mg NiSO4.6H2O/kg bw)	LD50(rat) = 2,043 mg/kg bw	LD50cut-off = 500 mg/kg bw (measured) LD50 = 345 mg/kg bw (read-across)
Acute inhalation toxicity	LC50 = 0.55 mg Ni/L air (2.48 mg NiSO4.6H2O/L)	LC0 = 0.11 mg/L air (nominal)	waived, since the substance is used and placed on the market in a non-inhalable form
Acute dermal toxicity	waived	LD50 > 2,000 mg/kg bw	LD50 >2,000 mg/kg bw (read-across)

 

Under the assumption that the constituents of nickel bis(2-ethylhexanoate) show their toxicological profile individually upon dissolution, the acute oral toxicity of nickel bis(2-ethylhexanoate) can be calculated using the equation given in regulation (EC) 1272/2008, Annex I, Section 3.1.3.6.1. The calculated oral LD50 for nickel bis(2-ethylhexanoate) based on read-across from its constituents is 345 mg/kg bw. In an experimental acute oral toxicity study with nickel bis(2-ethylhexanoate) according to the OECD 423 guideline, the LD50 cut-off is 500 mg/kg (3 mortalities at first step with 2,000 mg/kg bw and no mortalities at 300 mg/kg bw). Because the predicted LD50 based on data for the two transformation products is still below the measured acute oral LD50 cut-off value for nickel bis(2-ethylhexanoate), it can be concluded that read-across for the two transformation products together with the additivity approach to predict the (eco)toxicological effects of the target substance based on maximum concentration sof the two constituent ions is conservative and no synergistic effects are expected between the transformation products.

 

A study for acute toxicity via inhalation was not conducted with nickel bis(2-ethylhexanoate), since it is produced and placed on the market in a form in which no inhalation hazard is anticipated, thus acute toxic effects are not likely to occur during manufacture and handling of that substance.

 

Conduct of an acute dermal toxicity study is unjustified as the physicochemical properties of the nickel cation do not suggest a significant rate of absorption through the skin. Further the LD50 for the constituent 2-ethylhexanoic acid is above 2,000 mg/kg bw, hence does not require a classification for acute dermal toxicity. Based on the above given information nickel bis(2-ethylhexanoate) is not expected to show any acute toxic effects via dermal route (cf. Annex VIII section 8.5 Column 2 of regulation (EC) 1907/2006)

 

For further information on the toxicity of the individual constituents, please refer to the relevant sections in the IUCLID and CSR.

Justification for classification or non-classification

Acute oral toxicity:

The experimentally measured oral LD50 for nickel bis(2-ethylhexanoate) was found to be 300 < LD50 ≤ 2000 mg/kg bw in a GLP conform OECD 423 study. The study result triggers the classification as Acute oral toxicity Category 4 according to regulation (EC) 1272/2008. No classification is required for specific target organ toxicity, single exposure (STOT SE).

 

Acute dermal toxicity:

Conduct of an acute dermal toxicity study is unjustified as the physicochemical properties of the nickel cation do not suggest a significant rate of absorption through the skin. Further the LD50 for the constituent 2-ethylhexanoic acid is above 2000 mg/kg bw, hence does not require a classification for acute dermal toxicity. Based on the above given information nickel bis(2-ethylhexanoate) is not expected to show any acute toxic effects via dermal route (cf. Annex VIII section 8.5 Column 2 of regulation (EC) 1907/2006).

 

- Acute inhalation toxicity:

This substance is a waxy solid which is not capable in creating an inhalable atmosphere, thus testing is technically not feasible.