2-ethylhexanoic acid, molybdenum 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

Reason / purpose for cross-reference:

reference to same study

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, molybdenum salt as received, was tested. Therefore, no further preparation of the test item at ECTX was needed.

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:

997 mg/L Molybdenum 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, molybdenum 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 trial was 1.50 for the 0.2 g/L and 2 g/L loadings, 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 1.50 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 1.50 and 1.52 for the vessels at the 2 g/L loadings.

The Negative Control vessel showed no concentrations of molybdenum above the limit of quantification (i.e. accredited reporting limit) of 0.5 μg/L Mo.

The following observations could be made in the Positive Control item vessel containing a soluble form of molybdenum:
- 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 molybdenum concentration in the Positive Control item was 101 % and met the criterion (recovery: 100 % +/- 10 %) as indicated in the SOP.
The following observations could be made in the test vessels with a loading of 0.2 g/L 2-ethylhexanoic acid, molybdenum salt:
- Sticky undissolved test item could be observed spread over the bottom of the Erlenmeyer flasks at the end of the experiment. The glass cover slips sometimes covered a part of the test material. It is not clear if and how this could have affected the results.
- An average dissolved molybdenum concentration in solution of 1.27 +/- 0.22 mg/L Mo (corresponding to a dissolved molybdenum concentration per g test item of 5.73   0.46 mg/g Mo) was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5) with a between-vessel variation of 17 % which met the quality criteria at the 2 hours endpoint.
Based on the molybdenum content of the test item (i.e. 15.77 % Mo) and the average dissolved molybdenum concentration, a molybdenum release of 3.6 % 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, molybdenum salt:
- Sticky undissolved test item could be observed spread over the bottom of the Erlenmeyer flasks at the end of the experiment. The glass cover slips sometimes covered a part of the test material. It is not clear if and how this could have affected the results.
- An average dissolved molybdenum concentration in solution of 2.68 +/- 0.19 mg/L Mo (corresponding to a dissolved molybdenum concentration per g test item of 1.32 +/- 0.08 mg/g Mo) was measured after 2 hours of exposure to the simulated gastric fluid (pH 1.5) with a between-vessel variation of 7 % which met the quality criteria at the 2 hours endpoint.
Based on the molybdenum content of the test item (i.e. 15.77 % Mo) and the average dissolved molybdenum concentration, a molybdenum release of 0.84 % could be calculated at the 2 hours endpoint.

Conclusions:

During this study on 2-ethylhexanoic acid, molybdenum salt at a loading of 0.2 g/L in simulated gastric fluid (pH 1.5), it was shown that for molybdenum an average dissolved concentration in solution of 1.27 mg/L Mo (CVbetween-vessel = 17 %; N = 3) was found after 2 hours of extraction. This amount corresponds to a dissolved molybdenum concentration per g test item of 5.73 mg/g Mo or a molybdenum release of 3.6 % of the content.

During this study on 2-ethylhexanoic acid, molybdenum salt at a loading of 2 g/L in simulated gastric fluid (pH 1.5), it was shown that for molybdenum an average dissolved concentration in solution of 2.68 mg/L Mo (CVbetween-vessel = 7 %; N = 3) was found after 2 hours of extraction. This amount corresponds to a dissolved molybdenum concentration per g test item of 1.32 mg/g Mo or a molybdenum release of 0.84 % of the content.

The results are reliable since the test conditions stayed constant during the experiment. The recovery of Positive Control met the criteria of acceptance.

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 molybdenum ions from 2-ethylhexanoic acid, molybdenum 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”. 

This 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) in which the gastric medium will be prepared starting from a 0.1 M HCl solution. 

The extent of dissolution of 2-ethylhexanoic acid, molybdenum salt in the liquid form (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 molybdenum (Mo) concentrations obtained after 2 hours of extraction. 

The study was performed at ECTX. Analysis of the concentrations of dissolved molybdenum has been performed at WLN Business B.V. (The Netherlands), 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 trial was 1.50 for the 0.2 g/L and 2 g/L loadings, 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 1.50 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 1.50 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 no concentrations of molybdenum above the limit of quantification (i.e. accredited reporting limit) of 0.5 μg/L Mo. 

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

• 1.27 ± 0.22 mg/L Mo (CVbetween-vessel = 17 %; N = 3), corresponding to a dissolved molybdenum concentration per g test item of 5.73 ± 0.46 mg/g Mo, 

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

Based on the molybdenum content (i.e. 15.77 % Mo) in the test item and the average dissolved molybdenum concentrations in the test solutions, a release of: 

• 3.6 % 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, molybdenum salt, the following average dissolved molybdenum concentration in solution of: 

• 2.68 ± 0.19 mg/L Mo (CVbetween-vessel = 7 %; N = 3), corresponding to a dissolved molybdenum concentration per g test item of 1.32 ± 0.08 mg/g Mo, 

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

Based on the molybdenum content (i.e. 15.77 % Mo) in the test item and the average dissolved molybdenum concentrations in the test solutions, a release of: 

• 0.84 % of the content could be calculated at the 2 hours endpoint. 

Description of key information

The dissolution of molybdenum from 2-ethylhexanoic acid, molybdenum salt after 2h in simulated gastric acid (pH 1.5) at 0.2 and 2 g/L loading is 3.6 and 0.84%, respectively, corresponding to 1.27 and 2.68 mg Mo/L.