2-ethylhexanoic acid, zirconium salt

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics in vitro / ex vivo

Remarks:

Bioelution in simulated gastric medium

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10 December 2021 to 12 February 2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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

Qualifier:

no guideline available

Principles of method if other than guideline:

Bioelution in simulated gastric medium according to Eurometaux (2019): The Standard Operating Procedure for Bioelution Testing of Metals, Inorganic Metal Compounds, and Complex Metal-Containing Materials: Simulated Gastric Fluid (Eurometaux Brussels, November 02, 2019).

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

The test item, 2-ethylhexanoic acid, zirconium salt, is a liquid and was tested as received. Therefore, there is no need for further preparation of the test item.

Vehicle:

other: simulated gastric fluid (0.032 N HCl)

Duration and frequency of treatment / exposure:

1 hour agitation and 1 hour to allow the sample to settle

Positive control reference chemical:

1000 mg/L Zirconium standard

Bioaccessibility (or Bioavailability) testing results:

Bioelution refers to the in vitro extraction methods used to measure the degree to which a substance is dissolved in simulated biological fluids. The resulting value is the “bioaccessibility”, and is defined as the “fraction of a substance that is soluble under physiological conditions and therefore potentially available for absorption into systemic circulation”. Simulated biological fluids (e.g. gastric fluid, interstitial fluid, lysosomal fluid,…), represents relevant exposure routes. In this study, the oral route was investigated. Therefore, simulated gastric fluid, as provided in the SOP, was used to measure the release/dissolution of the elements of interest from 2-ethylhexanoic acid, zirconium salt.

The temperature of the sampled test solutions including the Negative and Positive Control vessel at the 2-hours sampling point was between 36.8 °C and 37.0 °C and corresponded to the required test conditions of 37 °C ± 1 °C.

The measured pH of the test medium at the start of the test was 1.50, i.e. within the specifications of pH 1.5 ± 0.1. The pH measured in the additional test item vessel at the beginning of the test was 1.50 for both loadings, 0.2 g/L and 2 g/L, respectively, i.e. within the specifications of pH 1.5 ± 0.1. At the 2 hours endpoint of the test, the pH in the Negative Control vessel was 1.51 and 1.51 in the Positive Control. The pH in the test item vessels was between 1.50 and 1.51 for the vessels at the 0.2 g/L loadings and between 1.51 and 1.52 for the vessels at the 2 g/L loadings.

The Negative Control vessel showed small concentrations of zirconium above the reporting limit of 0.05 μg/L Zr.

The following observations could be made in the Positive Control item vessel containing a soluble form of zirconium:
- The Positive Control item solution remained clear at the tested concentration level. No precipitation could be observed on the filter and in the Erlenmeyer flask at the end of the experiment.
- The recovery of the dissolved zirconium concentrations in the positive control item was 89 % and did not meet the criterion (recovery: 100 % ±10 %) as indicated in the SOP. The lower recovery has no impact on the acceptability of the test item results.

The following observations could be made in the test vessels with a loading of 0.2 g/L 2-ethylhexanoic acid, zirconium salt:
- Precipitation or undissolved test material could be observed in the Erlenmeyer flasks at the end of the test.
- An average dissolved zirconium concentration in solution of 0.523 ± 0.048 mg/L Zr (corresponding to a dissolved zirconium concentration per g test item of 2.60   0.23 mg/g Zr) was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5) with a between-vessel variation of 9 % which met the quality criterion at the 2 hours endpoint.
Based on the zirconium content of the test item (i.e. 24.0 % Zr) and the average dissolved zirconium concentration, a zirconium release of 1.1 % could be calculated at the 2 hours endpoint.

The following observations could be made in the test vessels with a loading of 2 g/L 2-ethylhexanoic acid, zirconium salt:
- Precipitation or undissolved test material could be observed in the Erlenmeyer flasks at the end of the test.
- An average dissolved zirconium concentration in solution of 0.120 ± 0.032 mg/L Zr (corresponding to a dissolved zirconium concentration per g test item of 0.060 ± 0.016 mg/g Zr) was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5) with a between-vessel variation of 26 % which exceeded the quality criterion (≤20 % for measurements in 10x LOQ) at the 2 hours endpoint.
Based on the zirconium content of the test item (i.e. 24.0 % Zr) and the average dissolved zirconium concentration, a zirconium release of 0.025 % could be calculated at the 2 hours endpoint.

Conclusions:

During this study on 2-ethylhexanoic acid, zirconium salt at a loading of 0.2 g/L in simulated gastric fluid (pH 1.5), it was shown that for zirconium an average dissolved concentration in solution of 0.523 mg/L Zr (CVbetween-vessel = 9 %; N = 3) was found after 2 hours of extraction. This amount corresponds to a dissolved zirconium concentration per g test item of 2.60 mg/g Zr or a zirconium release of 1.1 % of the content.

During this study on 2-ethylhexanoic acid, zirconium salt at a loading of 2 g/L in simulated gastric fluid (pH 1.5), it was shown that for zirconium an average dissolved concentration in solution of 0.120 mg/L Zr (CVbetween-vessel = 26 %; N = 3) was found after 2 hours of extraction. This amount corresponds to a dissolved zirconium concentration per g test item of 0.60 mg/g Zr or a zirconium release of 0.025 % of the content.

The results are reliable since the test conditions stayed constant during the experiment.

Executive summary:

Bioelution refers to the in vitro extraction methods used to measure the degree to which a substance (e.g., metal or mineral ion) is dissolved in artificial biological fluids. Simulated biological fluids represent relevant exposure routes. The release/dissolution of zirconium ions from 2-ethylhexanoic acid, zirconium salt in the simulated gastric fluid was measured. 

The resulting value is the “bioaccessibility”, and is defined as the “fraction of a substance that is soluble under physiological conditions and therefore potentially available for absorption into systemic circulation”. 

The study was conducted according to The Standard Operating Procedure for Bioelution Testing of Metals, Inorganic Metal Compounds, and Complex Metal-Containing Materials: Simulated Gastric Fluid (Eurometaux, November 2, 2019). 

The extent of dissolution of 2-ethylhexanoic acid, zirconium salt (solution), as received, was tested in a simulated gastric fluid at 37 °C and pH 1.5 for 2 hours (0.2 g/L and 2 g/L loadings) at an agitation speed of 100 revolutions per minute (rpm) for 1 hour followed by 1 hour of settling (without shaking). The bioelution endpoint is based on the dissolved zirconium concentrations obtained after 2 hours of extraction. 

The study was performed at ECTX. Analysis of the concentrations of dissolved zirconium has been performed at the analytical laboratory of the Soil Service of Belgium (SSB), an ISO 17025 accredited laboratory, as delegated by ECTX. 

The measured pH of the test medium at the start of the test was 1.50, i.e. within the specifications of pH 1.5 ± 0.1. The pH measured in the additional test item vessel at the beginning of the test was 1.50 for both loadings, 0.2 g/L and 2 g/L, respectively, i.e. within the specifications of pH 1.5 ± 0.1. At the 2 hours endpoint of the test, the pH in the Negative Control vessel was 1.51 and 1.51 in the Positive Control. The pH in the test item vessels was between 1.50 and 1.51 for the vessels at the 0.2 g/L loadings and between 1.51 and 1.52 for the vessels at the 2 g/L loadings. 

The temperature of the sampled test solutions, including the Negative and Positive Control vessel was between 36.8 °C and 37.0 °C and corresponded to the required test conditions of 37 °C ± 1 °C. 

The Negative Control vessel showed small concentrations of zirconium above the reporting limit of 0.05 μg/L Zr. 

In the test item vessels with a loading of 0.2 g/L 2-ethylhexanoic acid, zirconium salt, the following average dissolved zirconium concentration in solution of: 

• 0.523 ± 0.048 mg/L Zr (CVbetween-vessel = 9 %; N = 3), corresponding to a dissolved zirconium concen-tration per g test item of 2.60 ± 0.23 mg/g Zr, 

was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5). 

Based on the zirconium content (i.e. 24.0 % Zr) in the test item and the average dissolved zirconium concentrations in the test solutions, a release of: 

• zirconium of 1.1 % of the content could be calculated at the 2 hours endpoint. 

 

In the test item vessels with a loading of 2 g/L 2-ethylhexanoic acid, zirconium salt, the following average dissolved zirconium concentration in solution of: 

• 0.120 ± 0.032 mg/L Zr (CVbetween-vessel = 26%; N = 3), corresponding to a dissolved zirconium con-centration per g test item of 0.060 ± 0.016 mg/g Zr, 

was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5). 

Based on the zirconium content (i.e. 24.0 % Zr) in the test item and the average dissolved zirconium concentrations in the test solutions, a release of: 

• zirconium of 0.025 % of the content could be calculated at the 2 hours endpoint. 

Description of key information

The dissolution of zirconium from 2-ethylhexanoic acid, zirconium salt after 2h in simulated gastric acid (pH 1.5) at 0.2 and 2 g/L loading is 1.1 and 0.025%, respectively, corresponding to 0.523 and 0.120 mg Zr/L.