Chemical cocktails: understanding the combined effects of nanoparticles and pharmaceutical on microbial species and populations.

Given that pharmaceuticals and nanomaterials (NMs) used in consumer products such as sunscreens and cosmetics have the same discharge pathways (i.e. down the sink), there is a strong potential for combined effects. This is amplified by the intrinsic tendency of both NMs and pharmaceuticals to interact with their surrounding medium, and the tendency of NMs to bind a “corona” of biomolecules from their surroundings. Thus, there may be a likelihood of interaction between them leading to mixture toxicity and/or enhanced uptake of pharmaceuticals via active transport alongside NMs in the so-called Trojan horse effect.

For this reason, it becomes crucial to understand how this co-existence can affect the transport and fate of both NMs and pharmaceuticals and the toxicity of both categories of contaminants toward indicator organisms. Freshwater microbial communities, such as biofilms, play a vital role as indicator species, as changes in the diversity, structure and function can arise in response to pollution, climate stress or other factors, which can be utilised to monitor ecosystem health. Building on a long track record of assessing interactions of NMs with microbial communities or chemical mixtures, this project will further enhance our knowledge of mixture toxicity by exploring the co-exposure of NMs and pharmaceuticals.

Starting from the concept of the acquired ecological biomolecule corona, the coating of biomolecules acquired by engineered nanomaterials when exposed to a biological medium, the pharmaceutical-containing eco-corona composition is a new and fascinating area of research.

The results from the project will have important policy and regulatory implications, such as for REACH and the Water Framework Directive.

Task 1a focuses on investigating fundamental interactions of surface-functionalised nanomaterials with environmentally relevant media such as different artificial (e.g. OECD, artificial freshwater as well as different natural freshwaters (natural organic matter content, pH, ionic strength and salinity). Physico-chemical characterisation (size distribution, surface charge, surface speciation) of NMs will be carried out with different techniques.

Task 1b will investigate interactions between NMs and extrapolymeric substances (EPS) exuded by microbes. Biomolecules secreted by model single bacterial and algal species will be characterised, as will NM stability therein. Eco-corona formation and its dynamic behaviour will also be analysed.

Task 1c will analyse interactions, i.e. adsorption kinetics, thermodynamic stability and stoichiometry, ligand exchange, between pharmaceuticals and NMs which have been altered by either biomolecules from the abiotic environment such as humic substances or biomolecules exuded by microbes (EPS).

Task 2a will deal with the effects of stress on the formation and composition of extracellular polymer substances (EPS) with the NMs. Selected single microbial species such as green algae and bacteria will used as model systems.

Task 2b will investigate the effects of this changed ‘stressed’ EPS on toxicity of the NMs as well as the mixtures with the pharma-containing eco-coronas. Ecotoxicity tests with the model organisms selected in Task 2a will be performed to study the relative dose-response parameters.

Task 2c will combine data from Tasks 2a and 2b to extrapolate results from model species to more complex and ecologically relevant microbial communities. Validation experiments will be carried out to infer how NMs with different eco-coronas affect the co-transport, bioavailability and toxicity of pharmaceuticals for a representative algal species.