Mercury and PFAS Disrupt Mitochondria in Seabirds

Even on isolated islands encircled by open sea, ocean pollution reaches far beyond the coast. Chemicals invisible to the eye, transported through the atmosphere and ocean currents, can enter food webs and subtly disrupt animals’ most fundamental processes – within their cells.

A new study finds that mercury and PFAS, frequently referred to as “forever chemicals”, interfere with mitochondria, the microscopic structures that generate cellular energy.

By making cells less efficient, these contaminants could influence the survival, reproduction and long-term health of seabirds already facing the rigours of life at sea.

To investigate these concealed impacts, researchers at the Max Planck Institute for Biological Intelligence studied Scopoli’s shearwaters nesting on Linosa, a small volcanic island in the Sicilian Channel.

With its remote location and absence of major industry, the island provides a natural laboratory for examining how worldwide pollution can reach even marine settings that appear untouched.

Pollution travels across oceans

Coal combustion, mining, waste disposal and other industrial processes release mercury into the oceans. Bacteria then transform mercury into methylmercury, an especially toxic form.

Methylmercury builds up in animals, with concentrations rising higher up food webs. As long-lived predators, seabirds can consequently accumulate substantial loads.

PFAS are man-made chemicals found in non-stick pans, stain-repellent textiles and numerous industrial goods. Since these substances seldom degrade in the environment, researchers commonly describe PFAS as forever chemicals.

PFAS are carried across oceans by atmospheric transport and wastewater discharges. Laboratory research had already established that both contaminants can disrupt mitochondria.

Until recent developments in minimally invasive techniques, however, evidence from wild animals was scarce.

Energy production inside cells

Mitochondria function as cells’ energy-generating units. They produce energy through oxidative phosphorylation, a process that makes adenosine triphosphate, or ATP.

Respiration does not always result in ATP production. Energy can instead be lost through proton leak, which decreases efficiency but also helps shield cells from damaging oxygen molecules.

The scientists assessed mitochondrial respiration in red blood cells, which retain functioning mitochondria in birds. These blood measurements indicate whole-body metabolism and make it possible to conduct field research without injuring animals.

Mercury increases energy loss

Greater mercury concentrations led to more proton leak. By changing membrane proteins and lipid composition, mercury makes mitochondrial membranes more permeable. Energy therefore escapes without generating ATP, reducing efficiency.

Cells sought to offset this loss by increasing total respiration. Such compensation requires extra energy and could place metabolism under pressure during demanding times, including breeding and migration.

In other species, higher proton leak has often been associated with shorter longevity and weaker immune responses.

Forever chemicals block protection

PFAS produced a contrasting pattern. Overall PFAS levels appeared to have little effect, whereas particular compounds, including PFOS and PFOA, altered how cells regulate energy.

On the surface, this may appear beneficial. Less energy loss might seem to mean greater efficiency. Yet cells depend on a modest degree of energy loss as a safety mechanism against damage.

If this safety mechanism is diminished, pressure increases within mitochondria. This heightens the chance of harmful oxygen byproducts that can harm cells. Laboratory studies indicate that, although this condition can appear energy-efficient, it may damage cells over time.

Rather than enhancing performance, PFAS seem to disable a key protective mechanism within mitochondria.

Seabird diet shapes exposure

Stable isotope analysis connected contamination with diet. Nitrogen isotope readings indicated trophic position, and birds feeding at higher levels of the food web had more mercury. Carbon isotope readings indicated that feeding nearer the shore raised exposure.

No clear association emerged between PFAS and diet, age or sex. PFAS may follow different pollution routes from mercury, likely arriving via atmospheric transport or contaminated local water rather than food chains.

Mercury did show patterns related to age and sex. Older birds had higher concentrations because of accumulation over time.

Male birds had more mercury, as females can eliminate part of their mercury load through egg laying.

Pollution strains breeding energy

Breeding requires substantial energy investment. Adult birds alternate extended feeding journeys with intervals spent tending chicks.

Lower cellular efficiency at these times could restrict the energy available for flight, feeding and thermoregulation.

“Chemical pollution is one of the more complex threats to marine ecosystems at all levels, due to its inconspicuous nature and diverse impacts,” said study co-author Lucie Michel, a graduate student at Justus Liebig University Giessen.

“During the demanding breeding season, when adults alternate long self-provisioning and short foraging trips while caring for chicks, energy costs from pollutant exposure could be especially significant. Future work must examine impacts on survival, breeding success, and overall fitness.”

Pollution adds to ocean stress

Chemical pollution also combines with other pressures affecting today’s oceans. Shifts in food supply, increasing temperatures and plastic waste could worsen the cellular harm caused by chemical exposure, making lasting consequences more difficult to forecast and manage.

“It is also critical to understand these impacts in the context of other threats to wildlife such as including overfishing, plastic pollution, and global heating,” said Michel.

“Long term monitoring will be essential to answer these questions, with implications also for understanding their impacts on human health, since we face similar exposures.”

Small damage, big consequences

Minor losses of energy within cells could undermine populations before outward declines become apparent. Over time, reduced ATP availability may constrain growth, reproduction and immune defence.

Seabirds serve as indicators of ocean health, revealing threats that could eventually affect other wildlife and people.

By connecting diet, pollution exposure and mitochondrial function, the researchers offer a more detailed understanding of how unseen pollutants influence biological performance.

Ongoing monitoring will be vital to safeguard marine ecosystems and assess long-term health threats in a changing world.