Plastic pollution causing dementia-like signs in seabird chicks

Looking fit is no guarantee of health for some of the world’s most plastic polluted birds.

New research, published in the journal Science Advances, suggests that the illusion of health in sable shearwaters is only skin-deep. Samples taken on Lord Howe Island, which lies between Australia and New Zealand, showed that young birds which appeared healthy were suffering from severe damage to multiple organs.

Shearwaters which had only eaten less than a gram of plastic were already suffering serious consequences. These impacts extended to the brain, where declines in a crucial protein known as brain-derived neurotrophic factor (BDNF) were similar to levels associated with conditions like Alzheimer’s disease, Parkinson’s disease and dementia in other animals.

University of Tasmania PhD student Alix de Jersey, who led the research, said that this could have severe consequences for the shearwaters if they survive to adulthood.

“Seabird colonies are an overwhelming symphony of calls, screeches and chatter that can be so loud we can barely talk to one another while collecting data,” she says. “To live in this noisy environment, sable shearwaters need to be able to distinguish between fine scale acoustic cues to locate their partner.”

“Plastic, however, decreases levels of BDNF and interrupts the development of their song control system. This could have implications for their ability to create and maintain pair-bonds with other shearwaters.”

Dr Alex Bond, one of our bird experts who co-authored the paper, adds that the level of impact plastic has on the brain was “surprising”.

“These birds don’t appear to be ill from the outside, but samples of their blood contain a variety of indicators of cell damage and death,” explains Alex.

“We expected proteins normally found inside cells to have escaped into the blood, based on our previous research, but it was quite unexpected to find that proteins associated with brain damage were also present.”

Seabirds and the plastic pollution crisis

Every year, over 20% of all plastic waste enters the environment in an ‘uncontrolled’ way. This means it ends up littering the cities, countryside and oceans.

Scientists from the Adrift Lab have been focusing on the impacts on Lord Howe Island, where seabirds bring hundreds of thousands of plastic pieces back to its shores every year. Sable shearwaters feed this plastic to their chicks, where it clogs their digestive system so there’s less space left for food.

The team even named a specific disease, plasticosis, to describe the scarring that plastic causes inside the stomachs of these seabirds.

Beyond these more obvious impacts, plastic also sheds minute fragments that can travel even deeper into the body. These are known as microplastics if they’re less than five millimetres in size, or nanoplastics if they’re less than a micron.

These tiny plastics have been found in every environment, even inside our own bodies. Recent research suggests that our brains contain around a spoon’s worth of micro- and nanoplastics, but the health impacts of this are still not entirely understood.

In seabirds, the evidence is clearer. Nanoplastics have been linked with organ damage in sable shearwaters and are known to alter their blood chemistry. However, a lot of previous research only focused on certain impacts of plastic, limiting a broader understanding of its impact on animals as a whole.

“A lot of past work has focused on one individual stressor or response, which disguises a lot of stuff beneath the surface that we can’t see,” Alex explains. “Here, we screened 745 different proteins without any particular assumptions in mind.”

“Instead, we looked at how the expression of these proteins changed between the different groups, so that we could take a broader view of the impacts of plastic.”

The hidden impacts of plastic

To investigate the full range of plastic’s impacts on sable shearwaters, the Adrift Lab took blood samples from over 30 different young birds. The researchers specifically focused on healthy-looking animals with no signs or symptoms of disease to get an idea of the hidden effects plastic might be having.

The 90-day-old chicks were divided into low and high-impact groups depending on how much plastic they’d consumed. This was assessed by flushing their stomach and measuring how much plastic was found inside.

Their blood samples were then analysed, revealing that around a quarter of all protein expression was different between the two groups. As these birds were sampled from the same colony at the same time and with similar body conditions, this suggests the differences were being caused by the presence of plastic.

Pepsinogen, for example, is a precursor of the enzyme that breaks down dietary proteins in the stomach. It was found at much higher levels in the blood of birds that had eaten a lot of plastic, suggesting that damage to the stomach was causing it to leak into the body.

Where protein expression levels were lower in the plastic-impacted birds, the team thinks that damage to the organs means they can no longer produce and secrete complex proteins. In the kidneys, for instance, levels of the protein GPX3 were significantly lower, which suggests chronic kidney disease.

As GPX3 is also an important antioxidant, it will also have serious impacts for the shearwaters as they prepare to take flight for the first time. Flying is a very stressful activity, especially when these birds may have to migrate as much as 10,000 kilometres. Without antioxidants to mitigate the damage, these individuals may not be able to survive out over the ocean.

To help other scientists investigate these threatened seabirds, the team hope that a database of their protein signatures can be built up. Many of the proteins are shared between different species, so having a broader resource to draw on would allow them to make better judgements of how wildlife is affected by plastic.

“Seabirds are among the animals most affected by plastic ingestion, and studies of their protein signatures are increasingly revealing plastic’s association with inflammation, oxidative stress, fibrosis, and altered metabolism,” Alix adds.

“Establishing a comprehensive protein signature database for seabirds would improve how well we can identify these proteins and enable greater health assessments in the future.”