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Biotransformation of nanomaterials while transferring in the food chain

Nanotechnology enables us to manipulate materials and design particles at extremely small scales (nanomaterials: smaller than 100 nm in at least one dimension) to achieve specific and useful characteristics. For example, using nanotechnology it is possible to make materials effectively stronger, lighter, more durable, more reactive, better electrical conductors, etc. Thus, nanotechnology can revolutionize many technologies and industry sectors such as medicine, transportation, information technology, energy, food safety, to name a few. The increased application of nanomaterials has resulted in an enhanced release of these materials in the environment. Some nanomaterials that are persistent in the environment raise concerns as they may, for instance, enter organisms’ bodies, accumulate in their organs, and transfer through different trophic levels in food chains. If these small, active, durable, and strong materials enter the environment and humans’ bodies, it is necessary to understand how they interact with biological molecules and cells and where they will eventually end up. It is important to shed light on the behaviour of nanomaterials in organisms’ tissues and cells and to understand whether and to what extent they transfer from prey to predator and accumulate in predator tissues as well as how their unique physicochemical properties influence these processes. For example, it is important to know if they follow the same pathways as their non-nanomaterial chemical counterparts in organisms or their physicochemical properties drive them through totally new pathways. This information allows designing safe nanomaterials for the environment and humans and supports the development of nanotechnology. The specific and unique physicochemical properties of nanomaterials call for specialized risk assessment.

Figure describing the experimental design and method validation

The figure adopted from Nature Communication

What are the obstacles?

However, tracing, and characterizing nanomaterials in organisms’ tissues and cells to understand their biological fate (bioaccumulation, biodistribution, biotransformation, and clearance) and their possible trophic transfer in food webs are challenging tasks. First, they are so small that most of the available techniques cannot be used directly to measure nanomaterials, particularly when they are in organisms’ bodies. Second, nanomaterials agglomerate and/or transform in the environment and organisms over time, confounding measurement. Third, the existing ecotoxicity guidelines have been developed primarily for ecotoxicity testing of molecular chemicals, where the total mass concentration of accumulated toxicants is measured in organisms’ tissues. By using these ecotoxicology guidelines, no conclusions can be drawn on the physicochemical properties of the accumulated nanomaterials 1, such as their size, shape, and number or whether they are still particulate.

I developed international connections and with the help of my collaborators and the support of the EU Horizon 2020, we developed a sensitive workflow to trace and characterize nanomaterials in organisms’ bodies. By having this set of methods and techniques at hand, now it was possible for me to analyse and count the number of nanomaterials in organisms’ tissues and cells and to understand their behaviour in organisms and their trophic transfer through food chains.

Developing an analytical workflow

We used the exposed algae to feed daphnids and the exposed daphnids to feed zebrafish (Figure 2). 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 gold-Nanomaterials by monitoring the number and size distribution of the nanomaterials in organisms. This allowed us to determine how the initial shape and size of the gold-Nanomaterials influence their dissolution and agglomeration in each organism and how the organisms influence the nanomaterial size and shape following interaction/internalization, and how these processes influence the bioavailability of the nanomaterials to the next trophic levels.

Biotransformation and trophic transfer of Au-Nanomaterials

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

Are nanomaterials good or not?

Like many other human-made materials and chemicals, nanomaterials also come with advantages and disadvantages. Phasing out all new technologies that include nanomaterials, which hold great promises for new solutions to many of our old problems, is probably not a reasonable and economically feasible solution to prevent their potential adverse effects on the environment and humans. Adopting the safe by design strategy could be a potential solution to balance between the benefits and the possible ecological effects of nanomaterials. The aim of my research is to support designing safe nanomaterials by understanding the possible effects of these materials in the environment and in organisms. Scientific research on nanomaterials is of great interest to the public and other stakeholders and requires accurate and clear communication with the public. Transferring information from a laboratory to the general public is a sensitive and important issue, which is likely to take place through communication via the press, including press releases. Unfortunately, sometimes the main message of a study is lost due to the inappropriate or inaccurate derivation of information from the study.

Fazel A. Monikh

Fazel A. Monikh

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 e.g. consumer products and environmental samples. Nanomaterials are considered as emerging contaminants with many challenges yet to be tackled to assess their risk. I am interested in synthesizing safe nanomaterials and tracking and characterizing them (metal-based and carbon-based nanomaterials) in biological matrices to understand their biological fate (e.g., biodistribution, localization, bioaccumulation, and clearance). During my Postdoc, I could merge my skills in nano-analytical chemistry with environmental science and toxicology to use different techniques to develop a suited-for-purpose workflow for tracing and characterizing nanomaterials in organisms. I am thankful to the European Commission that supported my ideas through the Marie Skłodowska-Curie IF (Horizon 2020) funding scheme and offered me a great opportunity to test the idea.

 

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Astrid Portero
EUON LinkedIn discussion group here.
07/05/21 15:28