Penguins are threatened by mercury contamination

In 1962, environmentalist Rachel Carson galvanized public concern with her book Silent Spring, which warned of the reproductive dangers posed by DDT – particularly to birds like the bald eagle. Now, six decades later, scientists are sounding the alarm again, and this time the focus is on mercury contamination.

Once more, birds are the primary concern – specifically, penguins living on the icy fringes of Antarctica.

“With mercury, there’s an analogy to DDT,” said John Reinfelder, professor of environmental sciences at Rutgers University and co-author of a new study. 

“In the 1960s, we were discovering DDT in remote places where it wasn’t being used. It’s a similar story today with mercury. There are no human sources near the Southern Ocean, but because of long-distance transport through the atmosphere, it has the potential to accumulate in penguins.”

Global reach of mercury contamination

Mercury is a potent neurotoxin that builds up in the food chain, especially in aquatic ecosystems. Fish-eating animals – including penguins – are at high risk. Chronic exposure can impair reproduction and damage the nervous system. In high enough doses, mercury contamination is lethal.

To understand how far mercury has traveled – and how much has made it into remote food chains – Reinfelder and Rutgers postdoctoral researcher Philip Sontag analyzed feathers from three penguin species collected on Anvers Island in the West Antarctic Peninsula. 

The feathers, taken during the 2010–2011 breeding season, were gathered by William Fraser of the Polar Oceans Research Group. Due to agricultural safety regulations, the samples remained in storage for over a decade before they could be analyzed.

Mercury contamination in penguins

The team measured not only mercury concentrations, but the isotopic signatures of carbon-13 and nitrogen-15 in the feathers.

These isotopes offer important clues: carbon-13 reveals where a penguin has been feeding, while nitrogen-15 indicates its position in the food chain. Together, these data points help pinpoint both the source and degree of mercury exposure.

Adelie and gentoo penguins showed relatively low mercury levels – among the lowest recorded in Southern Ocean penguins. Chinstrap penguins, however, stood out with significantly higher levels.

Learning more about penguin ecology

Sontag believes their feeding behavior explains the difference in mercury contamination among penguin species.

Unlike the other two species, chinstraps tend to migrate to lower latitudes during the winter, where mercury levels are higher.

“These data give us a way to learn not only about mercury accumulation, but about penguin ecology more broadly,” Reinfelder said.

The finding is also notable because it’s the first study to identify carbon-13 – not nitrogen-15 – as the stronger predictor of mercury levels in penguins across the Southern Ocean.

Mercury contamination lingers

Although mercury emissions from coal-fired power plants have decreased thanks to global efforts like the Minamata Convention on Mercury – signed by 140 countries in 2013 – mercury is still being released into the environment, especially through small-scale gold mining. 

In many developing regions, miners use elemental mercury to extract gold from ore. This releases over 1,000 tons of the toxin each year into air, water, and soil.

A recent MIT study found that atmospheric mercury levels dropped by 10% from 2005 to 2020, a promising trend largely attributed to the decline of coal-burning power stations. But mercury already in the environment can linger, circulating through the ocean’s vast currents and entering food webs in even the most isolated regions of the planet.

“Just like DDT in the 1960s, the scientific community today is focused on monitoring mercury,” Reinfelder said. “Are we going to see a decrease in levels in the fish that people and animals eat? That’s the hope.”

Penguins as pollution sentinels

For researchers, penguins are more than charismatic wildlife – they are living indicators of global pollution including that of mercury contamination. Their feathers provide a snapshot of the environments they’ve traveled through and the toxins they’ve absorbed.

Sontag and Reinfelder’s findings add a new layer to our understanding of how pollutants like mercury travel through ecosystems. By linking penguin foraging behaviors with their mercury burden, the study offers both a warning and a call to action.

“Before this study, we didn’t know that penguins migrating farther north had higher exposures to mercury,” Reinfelder noted.

In a world still grappling with the consequences of industrial pollution, these birds are once again showing us what’s at stake.

The study is published in the journal Science of the Total Environment.

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