Mercury is a toxic heavy metal that contaminates the environment. Plants absorb mercury from their surroundings and transfer it to higher levels of the food web through dietary intake.
– Top predators, such as larger fish and humans, can accumulate significant concentrations of mercury, which can cause long-term damage to neurological, gastrointestinal, and renal systems, writes Natalia Kozak to inn.no.
Natalia Kozak has been affiliated with the PhD programme in Applied Ecology and Biotechnology at Evenstad.
She explains that the mechanisms behind mercury accumulation in animals are not fully understood. However, with ongoing climate and global changes, understanding these processes is becoming increasingly urgent.
In her dissertation, Kozak examined molecular, biological, and environmental factors – such as amino acids, interactions within fish communities, climate change, and land use management – that can explain mercury pathways in subarctic freshwater fish and food webs.
The title of her dissertation is 'Mercury accumulation in fish and lake food webs – from molecules to ecosystems'.
Main findings in the doctoral work:
- A study of 19 lakes demonstrated that mercury is clearly transferred to fish at higher trophic levels (a trophic level is a step in the transfer of energy through an ecosystem).
- Larger and older fish contained more mercury.
- Of 16 amino acids studied, only proline and cysteine showed significant changes with mercury levels in fish: mercury increased with higher proline levels but decreased with higher cysteine levels.
- Fast-growing fish contained less mercury than slow-growing fish.
- Lakes with high fish density transferred less mercury to top predators than lakes with low fish density.
- Warmer climates and higher productivity increased mercury uptake from the environment into algae.
- Lakes with low mercury levels in fish had favourable environmental conditions that supported faster fish growth.