PhD Defence: Shubham Varshney

Thesis title​​​:

From nanoplastics to chemical pollutants: Exploring mixture toxicity in zebrafish

Trial lecture topic:

The global significance of urban stormwater runoff and municipal wastewater impacts on aquatic ecosystems

Evaluation Committee:

• Associate Professor Markus Brinkmann, University of Saskatchewan, Canada
• Researcher Elisabeth Støhle Rødland, Norwegian Institute for Water Research (NIVA)
• Professor Mark J. Costello, Nord University

Supervisory Committee:

• Main supervisor: Professor Pål A. Olsvik, Nord University
• Co-supervisor: Professor Kiron Viswanath, Nord University
• Co-supervisor: Researcher Tanja Kögel, Institute of Marine Research
• Co-supervisor: Head of Research Robin Ørnsrud, Institute of Marine Research

Thesis summary​:

Emerging pollutants include contaminants that have recently been identified or have gained increased attention due to their potential environmental impacts. Nanoplastics (NPs) and tyre wear chemicals are examples of such emerging pollutants. Research on emerging contaminants is vital as it provides scientific data on their possible source, uptake and toxicity, which is very important to be able to develop mitigation strategies.

This PhD thesis focuses on the toxicity of NPs, tyre wear chemicals (6PPD and 6PPD-quinone) and p,p’-DDE, a major metabolite of DDT found in the environment. The results indicate that exposure to 6PPD and 6PPD-quinone (6PPDq) can significantly affect the development, behaviour, and respiration of zebrafish larvae. We also found enhanced toxicity at the behavioural and molecular levels in zebrafish co-exposed to NPs+p,p’-DDE and NPs+6PPDq. The transcriptomic results indicate mitochondrial dysfunction in adult zebrafish exposed to 6PPDq.

This thesis brings significant new knowledge on the ecotoxicity of NPs and tyre wear chemicals through a comprehensive multi-endpoint approach. Additionally, it highlights the importance of understanding the effects of complex mixtures of contaminants.