Seabirds Reveal Global Mercury Pollution Hotspots

Mercury contamination does not remain where it is emitted. After entering the atmosphere-particularly through coal combustion-it can be carried by winds between continents, deposited by rainfall into the ocean, and gradually accumulate through marine food chains.

Until now, scientists have largely used ocean simulation models to predict where mercury settles and the concentrations it reaches.

A new international study took a more direct route by using seabirds as biological measuring instruments.

Rather than relying on computer predictions of mercury distribution, the researchers examined its presence in animals that feed over enormous areas of ocean.

The experts assessed mercury concentrations in blood samples from 11,215 seabirds representing 108 species around the world.

Their dataset combined 659 newly obtained samples with more than 10,500 records taken from published research spanning several decades.

Why use seabirds and blood samples?

Seabirds are well suited to this kind of environmental investigation. Many species forage far offshore, occupy high positions in marine food webs, and return to regular breeding colonies where researchers can collect samples.

The researchers selected blood from adult seabirds because it indicates what the birds have consumed over approximately the previous two months. This makes it more straightforward to connect mercury exposure to a particular location and period than when using tissues such as feathers.

Collecting blood also has comparatively little impact on the birds.

Methods used by the scientists

The study brought together two major sources of evidence.

Between 2017 and 2024, researchers gathered 659 blood samples from 10 seabird species at breeding colonies in Japan, Alaska and New Zealand. They then measured total mercury using atomic absorption techniques.

They also carried out an extensive systematic review of 106 scientific papers published from 1980 to 2025, with most appearing after 2010. This supplied data for 10,556 adult birds from 105 species.

Combined, these sources produced a worldwide dataset large enough to identify patterns in mercury exposure by diet, region and seabird type.

Which seabirds carried more mercury?

The clearest predictors made sense in light of the way mercury travels through ecosystems.

Mercury concentrations were greater in birds feeding higher up the food chain. Mercury biomagnifies: small organisms accumulate it, while larger predators build up still higher amounts.

Levels were also elevated in birds with greater body mass, a trait generally associated with longer lives and more cumulative exposure.

In addition, seabirds consuming prey from depths of 200 to 1,000 metres had greater mercury exposure. Mercury processes in this depth range can differ from those in surface waters.

The researchers further found that albatrosses and shearwaters often had particularly high exposure compared with many other seabirds, probably because of their feeding locations and foraging methods.

Global mercury pollution patterns and unexpected hotspots

When the team mapped regional mercury trends, distinct areas of relatively higher and lower ocean contamination emerged.

Mercury concentrations were higher in the North Atlantic, North Pacific and the South Pacific south of 40°S.

These regions have low productivity, as indicated by lower chlorophyll-a levels. Chlorophyll-a is a satellite measurement commonly used as a broad indicator of how biologically active the ocean surface is.

By contrast, mercury levels were substantially lower in the South Atlantic and the Southern Ocean.

This does not automatically mean that these southern waters are “clean”, but it does indicate that seabirds feeding there take in less mercury through the food web on average than birds feeding in certain other ocean basins.

The big twist

One of the most significant-and uncomfortable-results was that the seabird-derived mercury map corresponded only weakly with conventional marine biogeochemical simulation models.

This is important because models underpin many policy assumptions and scientific estimates. If they overlook important processes or place hotspots in the wrong areas, our global understanding of mercury risk could be less clear than previously assumed.

“The seabird model is based on empirical measurements from organisms and is therefore considered more reliable than values from marine simulation models,” said senior author Akiko Shoji, a scientist at Nagoya University.

“Seabirds live in diverse environments, from coastal and tropical zones to polar regions. Their varied feeding patterns make them effective indicators of global ocean health.”

Implications beyond seabirds

Mercury is particularly concerning because some of it is transformed in the ocean into highly toxic forms, including methylmercury, which accumulate within food webs.

Because seabirds are close to the top of these webs, mercury detected in their blood provides a warning sign not only for the birds themselves, but also for the broader ecosystem below them.

The authors present this seabird-based method as a possible means of assessing whether international policy is delivering real results.

Mercury emissions are controlled internationally through agreements such as the Minamata Convention, yet demonstrating improvement in the real world is difficult without effective ways to measure the ocean.

Using seabirds as “mobile sampling stations” could provide a practical approach to monitoring change over time, particularly in remote locations where ships and direct ocean sampling are costly and scarce.

In essence, the study argues that, rather than depending solely on model predictions, scientists can use animals already travelling the oceans as a biological monitoring network.

Its findings show that mercury exposure differs sharply according to region, diet and foraging behaviour, and that some places thought to be well understood may require closer examination.

Above all, the research is a reminder that the ocean is not simply chemistry recorded in a spreadsheet. It is a dynamic system, and the animals inhabiting it may offer the clearest evidence available of what is truly taking place.