Biotransformation of nanomaterials while transferring in the food chain

To attract attentions and add to the misleading of readers, some online news mixe some true stories with their fake ones. That has happened lately to my research outcomes. Here is what I have discovered.

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I did my PhD at the Department of Environmental Geoscience, University of Vienna, Austria, where I focused on developing methods for extraction, characterization, and quantification of nanomaterials (NMs) in complex matrices of consumer products and environmental samples. Nanomaterials are considered as emerging contaminants with many challenges yet to be tackled to assess their risk. I gained the skills of measuring nanomaterials in consumer products and gained the skills of finding out how to use different techniques to develop a suited-for-purpose workflow for tracing and characterizing NMs in complex matrices. After my PhD, I developed an interdisciplinary idea of understanding the biological fate of NMs by merging my expertise in ecotoxicology and my skills in NM characterization. I am thankful to the European Commission that supported my idea through the Marie Skłodowska-Curie IF (Horizon 2020) funding scheme and offered me a great opportunity to test the idea.

Some NMs that are persistent in the environment raise concerns as they may, for instance, enter food webs and transfer through different trophic levels in food chains. Understanding the trophic transfer of NMs and their biological fate (bioaccumulation, biodistribution, biotransformation, and clearance) are challenging tasks. Because NM physicochemical properties such as type, size, shape, and composition may influence their trophic transfer and biological fate. Moreover, NMs agglomerate and/or transform in the environment and organisms over time, confounding measurement. However, the best possible way to support the development of nanotechnology is to understand the fate and adverse effects of NM to design them safe for the environment and humans.

To date, there are many methodological challenges in determining the uptake, transformation, and, finally, localization of NMs in organisms’ bodies. Existing ecotoxicity guidelines have been developed primarily for ecotoxicity testing of chemicals, where the total mass of internalized potential toxicants is measured after the chemical digestion of the samples. Application of these guidelines yields information about the total mass of the element of interest in the tissue, but no conclusions can be drawn on the physicochemical properties of the internalized NM  1 such as size, shape, and number, or whether the NM is still particulate. Reporting internalized dose as mass, as is commonly done, does not properly express the environmental risks of NMs, as it gives no insight into the form in which the particle exists2.

I developed international collaborations and with the help of my collaborators, we developed a sensitive workflow to trace and characterize NMs in organisms’ bodies. By having this set of methods and techniques at hand, now it was possible for me to analyse NMs in organisms’ bodies. With the help of my colleague and friend, Dr. Latifeh Chupani, we exposed algae to gold (Au)-NM of different sizes and shapes (Figure 1).

Transmission electron microscope images show the size and shape of the used particles. 

We used the exposed algae to feed daphnids and the exposed daphnids to feed zebrafish (Figure 2). It was extremely hard work because we had to count and take care of around 20000 daphnids and many fish every single day for few months. In this study, unlike previous studies, we use particle number and mass as dose metrics to provide a comprehensive understanding of the trophic transfer of Au-NMs by monitoring the number and size distribution of the NMs in organisms. This allowed us to determine how the initial shape and size of the Au-NMs influence their dissolution and agglomeration in each organism and how the organisms influence the NM size and shape following interaction/internalization, and how these processes influence the bioavailability of the NMs to the next trophic levels.

 

Our results show that Au-NMs have the potential to transfer to higher trophic levels, but no biomagnification took place. Although algae were exposed to similar numbers of each Au-NM size and shape (spherical 10 nm, spherical 60 nm, spherical 100 nm, rod-shaped 10 × 45 nm and rod-shaped 50 × 100 nm), a higher accumulation of the smaller Au-NMs (spherical 10 nm and rod-shaped 10 × 45 nm) was observed on the algae. The association of NMs to algae, as an important gateway for NMs entering aquatic food webs, strongly depended on NM shape and size. Only a small fraction of the NMs accumulate in daphnids, indicating that Au-NMs are notbioavailable in high concentrations to the higher trophic levels in the aquatic food chain. Daphnids modulate the size distribution of the Au-NMs, through the dissolution of the larger Au-NMs and dissolution-re-precipitation and agglomeration of the smaller Au-NMs, leading all the NMs to have similar sizes (ranging from ~25 nm to 40 nm mass-based size) in daphnids. Only a small fraction of the Au-NMs transferred from daphnids to fish. No further transformation and agglomeration of the Au-NMs occurred in fish, but biodistribution was observed in fish, with the brain and liver as the target organs. Although we documented the accumulation of Au-NMs in the brain of zebrafish, we still do not know if the NMs pass the brain barrier. In future research, I will use the developed analytical workflow to focus on assessing and quantifying other types of NMs and other food chains. I will investigate if NMs can pass the brain barrier as particles and if they undergo biotransformation in the brain.

 Publication link:

https://rdcu.be/cfDta

  1. Thomas, T., Bahadori, T., Savage, N. & Thomas, K. Moving toward exposure and risk evaluation of nanomaterials: Challenges and future directions. Wiley Interdiscip. Rev. Nanomedicine Nanobiotechnology (2009). doi:10.1002/wnan.34
  2. Abdolahpur Monikh, F. et al. Environmental Aspects of Nanotechnology A Dose Metrics Perspective on the Association of Gold Nanomaterials with Algal Cells. Environ. Sci. Technol. Lett. 6, 732–738 (2019).

Fazel A. Monikh

Postdoc, University of Eastern Finland

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