Seabird Eggs Are Tainted With 'Everywhere Chemicals,' Study Finds

A mix of chemical additives used in some plastics has been discovered in the eggs of newly laid herring gull eggs, new research finds.

These phthalates are used in plastics to keep them flexible. But passed on from the mother birds to their babies, the chemicals are linked to oxidative stress which can damage cells.

Egg health is critical because mother birds pass on key nutrients to their offspring as they grow.

“Bird eggs need to provide all of the resources required for embryo development in a self-contained package, in order that the offspring can develop outside of the mother—this includes various nutrients but also antibodies and hormones,” co-author Jon Blount, professor of animal ecophysiology of the Centre for Ecology and Conservation at the University of Exeter's Penryn Campus in Cornwall, U.K., tells Treehugger.

Sometimes contaminants can make their way into bird eggs, Blount says. This is especially true for fat-soluble materials such as phthalates which mainly are deposited into the yolk.

“This is an accidental consequence of the transfer of lipids into eggs. We don’t yet know what impacts this may have on gull offspring, but in studies of other species, phthalates have been found to disrupt the production and regulation of hormones,” he says.

“Phthalates can also cause a type of stress known as ‘oxidative stress,’ which results in damage to important molecules such as DNA, proteins, and lipids.”

For the study, Blount and his colleagues collected 13 freshly laid herring gull eggs at three sites in Cornwall. They analyzed the biochemical composition of the eggs for levels of phthalates, as well as lipid damage and vitamin E—the primary antioxidant that mothers transfer to their offspring.

The researchers found that all the eggs contained phthalates, though the number and concentration of exact chemicals varied among the individual eggs.

“There was a positive correlation between yolk concentrations of one specific phthalate—dicyclohexyl phthalate (DCHP)—and levels of malondialdehyde, which is a marker of oxidative damage to lipids. We also found a negative correlation between yolk concentrations of the antioxidant vitamin E and malondialdehyde,” Blount says.

“These associations point to the possibility that DCHP may be associated with oxidative stress in mothers, and they transfer this cost to their eggs. However, I would stress that these are correlational data, and further work including experimental approaches will be necessary to establish whether phthalates may cause oxidative stress in gulls.”

The results were published in the journal Marine Pollution Bulletin.

The Impact of 'Everywhere Chemicals'

Researchers didn’t determine where exactly the birds got the phthalates but they are often referred to as “everywhere chemicals” because they are so common and are found everywhere on Earth.

In this instance, the scientists believe that the birds likely ingested them.

“They must be diet-derived, but we don’t know the route of exposure and it may well vary between individuals,” Blount says. “Gulls are opportunistic foragers—some may favour a natural diet and are exposed to phthalates by eating fish, crabs, shrimps and so on. Others may be exposed to phthalates by eating human food waste.”

A lot of research has focused on the impact of plastic when birds swallow it or get entangled in it. But this time, researchers were more concerned with the effects it might have in an entirely different manner. 

There’s evidence in other species that phthalates can cause endocrine disruption and oxidative stress, which can negatively affect growth and development. That’s what the researchers plan to investigate next.

“When birds are exposed to fat-soluble contaminants, these can get laid down in fatty tissues and they often find their way into eggs. While it is concerning that a diverse array of phthalates was found in this sample of gull eggs, it’s not all that surprising,” Blount says. “We’ve only really begun to scratch the surface of understanding the invisible impacts of plastic pollution.”

Researchers hope that people will learn from these findings. They hope that it will make an impact not just in the lab, but in the environment.

“I think that these kinds of data should make us sit up and think about the complex ways in which human behaviour can impact on wildlife,” Blount says.

“Plastic pollution is an issue of growing concern internationally, but much of the focus to date has been on visual impacts and mechanical threats such as entanglement and ingestion. We’ve really only just started to scratch the surface in understanding the invisible impacts from phthalates and other plastic additives.”