An assessment of the dietary bioavailability of TiO2 and inorganically carbon-based nanomaterials in rainbow trout, using the ex vivo gut sac technique and a in chemico digestibility assay

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Abstract

Abstract. Craig McHardyAn assessment of the dietary bioavailability of TiO2 and inorganically carbon-based nanomaterials in rainbow trout, using the ex vivo gut sac technique and a in chemico digestibility assay.Carbon based engineered nanomaterials (ENMs) are an emerging contaminant within modern society, as such their environmental risk assessment is of high importance. Testing for their persistence, toxicity and bioaccumulation potential is important for regulatory bodies to fully understand the hazard posed. To date, data on the bioaccumulation potential of these ENMs is lacking, especially within fish. A tiered approach to bioaccumulation testing has been posed in which precursory tests such as the in chemico digestibility assay and ex vivo gut sac method can be used to inform on a given materials bioaccumulation potential, with the aim of identifying materials with higher bioaccumulation potentials and highlighting them as materials urgently requiring full scale in vivo testing. These methods have shown promising potential to predict in vivo data within metallic and metal oxide ENMs but have yet to be used to test carbon-based ENMs. Therefore, the first aim of this thesis was to conduct the in chemico digestibility assay and generate bioacessablilty data for an established metallic ENM in terms of preexisting bioacessability data, such as TiO2 and compare it to its bulk counterpart in differing concentrations. TiO2 was more digestible in the simulated intestinal compartment, but with no difference between bulk and nano. When expressed as a percentage released from the dose spiked within diets, only the simulated stomach compartment showed statistically significant bioaccessibility of TiO2, with around 3% of the dose within the diets released. The next aim was to assess the utility of both methods for 3 carbon-based ENMs and identify if any should be highlighted as potentially hazardous in terms of their bioaccumulation potential. Graphene oxide gold nanohybrids (Au-GO) were compared to a soluble salt AuCl. The in chemico digestibility assay indicated Au-GO had dose dependant bioacessablilty, with a 10 mg kg-1 diet releasing 27% of the dose in simulated stomach conditions, significantly higher than the observed bioacessablilty of AuCl (15%). Once bioaccessibility data was generated the ex vivo gut sac method was conducted to demonstrate the potential bioavailability of Au-GO and AuCl across 5 regions of the gut (oesophagus, stomach, anterior intestine, mid intestine and hind intestine). The order of accumulation was AuCl > Au-GO; in the hind intestine muscularis, there was 1764.5 ± 634.7 and 230.5 ± 44.7 ng g-1 respectively. Indicating while the in chemico assay suggested Au-GO was more readily released and available to the gut than AuCl, AuCl was more readily taken up and across the mucosa into the muscularis within the ex vivo method. A europium coated polystyrene nanoplastic (Eu NP) was also assessed. In chemico digestibility assay data indicated an extremely low bioacessablilty of > 1% in both separately assessed simulated conditions of the stomach and intestine. Ex vivo gut sac data identified the hind intestine as the anatomical region responsible for the majority of Eu-NP uptake with 411.8 ng g-1 found within the hind mucosa and 22.3 ng g-1 within the muscularis. Finally, an alumina doped carbon nanotube (Al-CNT) was assessed and compared to AlCl3. In chemico data indicated Al-CNTs had dose dependant bioacessablilty, with 10 mg kg-1 diets releasing 19.80 ± 3.21 % within intestinal simulated conditions however Al-CNTs had significantly lower bioacessablilty than AlCl3. Ex vivo gut sac data demonstrated Al-CNTs have a propensity to accumulate with the mucosa and muscularis. The order of accumulation was AlCl3 > Al-CNT; in the hind intestine muscularis, there was 2291.8 ± 1100.3 and 5.6 ± 1.0 ug g-1 respectively. This thesis aimed to utilise a new tiered approach to bioaccumulation testing currently seeing use in metallic ENMs such as TiO2 and demonstrate its potential further use in assessing carbon-based ENMs. This thesis and the data therein were able to illustrate both the potential bioacessability and bioavailability of 3 distinct carbon based ENMs which based off currently accepted understandings, seemed to follow each materials prior perceived bioaccmulative risks. However, to validate the potential utility of the in chemico and ex vivo gut sac methods, future work aims to conduct full scale in vivo testing for all materials present in this thesis to better understand the potential predictive capabilities.

Document Type

Thesis

Publication Date

2025

Embargo Period

2025-12-31

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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This item is under embargo until 31 December 2025

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