PhD defence on microplastics and their potential risk to marine plankton

Small plastic particles – microplastics – have been found in every corner of the ocean. Microplastics overlap in size with plankton, which increases the risk of microplastics being ingested by zooplankton and transferred into the marine food chains. Hence, it is crucial to understand the interactions between plankton and microplastics to evaluate the environmental risks posed by plastic pollution.

In his PhD project, Gunaalan Kuddithamby from DTU Aqua has investigated the abundance, distribution, and composition of small microplastics (down to 10 µm) in Danish waters. Furthermore, he has assessed the potential impact of microplastics from conventional plastics on plankton communities. 

His results show that the concentration of microplastics in the studied area (Kattegat-Skagerrak, Denmark) was lower than in other regions and approximately six orders of magnitude lower than microplastics levels known to cause adverse effects on marine planktonic organisms. 

Furthermore, Gunaalan Kuddithamby’s research shows that the number of microplastics found in field-collected zooplankton and fecal pellets are low. He suggests that this can be due to the selective feeding behavior of zooplankton and the high abundance of natural prey compared to plastic particles in the water (500 to 100,000 times more natural prey than microplastic particles).

In a controlled experiment, Gunaalan Kuddithamby showed that weathered conventional microplastics at environmentally relevant concentrations did not impact plankton communities after five weeks of exposure. 

Based on these findings, Gunaalan Kuddithamby concludes that the risk of negative impacts of conventional microplastics on the pelagic food web is expected to be minor. However, he also points out the need for further investigations on the abundance and effects of microplastics derived from other types of plastic, such as tire rubbers and bioplastics, especially those with high levels of harmful additives.

About the defence

Gunaalan Kuddithamby will defend his PhD thesis “Microplastics in marine waters and their potential risk to marine plankton” on Wednesday 10 January 2024 at 13:00. The defence takes place at DTU Lyngby Campus and can also be followed online (please see the box below).

Examiners

• Professor Marja Koski, DTU Aqua (chair)
• Professor Penelope Kate Lindeque, Plymouth Marine Laboratory, UK
• Professor Maiju Pirita Lehtiniemi, Finnish Environment Instiute (Syke)

Chair at defence

• Senior Researcher Sigrún H. Jónasdóttir, DTU Aqua

Supervisors

• Principal supervisor: Professor Torkel Gissel Nielsen, DTU Aqua
• Co-supervisor: Senior Researcher Rodrigo Almeda, University of Las Palmas de Gran Canaria, ULPGC, and DTU Aqua
• Co-supervisor: Professor Jes Vollertsen, Aalborg University

Learn more

A copy of the thesis is available for reading at DTU Aqua. Please contact PhD Coordinator Susan Zumbach Johannesen, szjo@aqua.dtu.dk