With our waste, pollutants such as mercury and PFAS end up in the oceans. Biologists have found that they end up in the bodies of marine animals and seabirds in sometimes dangerous quantities through food and other routes. There, the pollutants disrupt cellular energy production in the mitochondria – the tiny power plants that generate energy for everyday activities from flight to reproduction. The mitochondria then work extremely ineffectively. This could have consequences for the fitness and survival of seabirds.
Numerous pollutants enter the environment through waste from human settlements and industrial wastewater. They also end up in the world’s oceans via rain, wind and rivers. These include, among others, per- and polyfluorinated alkyl compounds (PFAS), which are used in many everyday products. These substances are considered eternal chemicals because they cannot be broken down in nature and instead accumulate. They are highly toxic to living beings even in low concentrations.
Mercury also ends up in the oceans with industrial waste, where bacteria often convert it into the highly dangerous methylmercury. This also accumulates in the tissue of marine animals and disrupts their metabolism, as previous studies have already shown. PFAS and methylmercury can, among other things, impair energy production in the cells’ power plants, the mitochondria. However, it was previously unclear to what extent these studies captured the real conditions for wild animals and the current pollutant concentrations in ecosystems.
Pollution levels of cuttlefish shearwaters investigated
Biologists led by Guadalupe Lopez-Nava from the Max Planck Institute for Biological Intelligence in Seewiesen have now investigated this question. As a model, they chose cuttlefish shearwaters (Calonectris diomedea), which breed on Linosa, a small and remote volcanic island in the Mediterranean between Sicily and Tunisia. These seabirds are at the top of the marine food chain and also have a lifespan of up to 25 years. During this time they can accumulate plenty of pollutants from the sea in their bodies. These birds provide important information about the health of the oceans as a whole. During two breeding seasons, the researchers took blood samples from a total of 52 adult cuttlefish shearwaters. They determined the mitochondrial function in the red blood cells and the mercury content in the blood in all birds, and also the PFAS content in 20 birds.
The analyzes showed: Both mercury and PFAS changed the function of the mitochondria. In birds with higher blood mercury levels, mitochondrial membranes were more elastic and porous. This allowed some protons to migrate unhindered through the membrane, which hindered the buildup of an electrical charge and inhibited the production of the central energy building block adenosine triphosphate (ATP). Some of the electrical potential was lost – similar to water flowing past the turbines of a hydroelectric power plant, as the team explains.
In birds with high PFAS concentrations in their blood, the researchers found the opposite effect: the mitochondrial membranes were stiffer and more impermeable than usual. Theoretically, ATP production in the cells actually worked better. At the same time, however, a safety mechanism that would normally ward off harmful oxygen radicals was undermined. As a result, these molecules accumulated in the mitochondria, making them more susceptible to cell stress and ultimately disrupting energy production.
Lack of energy and cell damage caused by PFAS and mercury
The mitochondria of seabirds are disrupted by both mercury and PFAS, which in both cases can lead to oxidative cell damage and a lack of energy, albeit through different mechanisms of action. “We found that mercury and certain PFAS disrupt energy production in the cells of wild shearwaters and reduce the energy efficiency of the cells,” says Lopez-Nava. “The cells can compensate for this by increasing energy production, but this comes at a high cost – even small changes in cell efficiency can impair fitness without being noticed.”
But where exactly do the pollutants come from and how do they get into the bodies of birds? To find out, the researchers also carried out isotope analyzes and determined what the animals ate. It was shown that older birds and males have higher mercury levels. In females, some of the mercury is apparently excreted through the eggs. Overall, the results revealed that mercury accumulates in seabirds’ bodies over the course of their lives and comes predominantly from the fish and crustaceans they eat, according to the team. However, there was no connection between PFAS and the age, gender or diet of the birds. These pollutants therefore enter the animal bodies in a different way than mercury and do not come from food.
More protection needed for breeding seabirds
The team hopes that knowledge of these different exposure routes could help reduce pollution in marine ecosystems and better protect seabird populations, especially during the breeding season. “The breeding season is particularly demanding for adult birds: they alternate between long self-sufficiency trips and short foraging expeditions and at the same time care for their chicks. During this time, energy costs could be particularly high due to pollution,” explains co-author Lucie Michel from the University of Giessen.
Follow-up studies should now clarify to what extent pollutants such as mercury and PFAS affect the fitness of seabirds via inefficient mitochondria and what consequences this has for their survival and breeding success. It will also be discussed how such pollutants interact with overfishing and global warming. “Long-term monitoring of seabirds is essential for this – which also has an impact on understanding human health, as we are exposed to similar pressures,” says Michel.
Source: Max Planck Institute for Biological Intelligence; Specialist article: Environment & Health, doi: 10.1021/envhealth.5c00297