World-first analysis of seabirds who’ve eaten plastic reveals slow, insidious health impacts
- Written by The Conversation
We all know microplastics are bad for the environment and our health, but do we really know how bad?
Our new study, published this week in the journal Science Advances, compared changes in 745 proteins found in seabirds with and without plastics in their stomachs.
We focused on young sable shearwaters (seabirds, Ardenna carneipes). They were less than 90 days old and appeared healthy. Despite their young age, the birds with plastic in their stomachs had signs or symptoms of neurodegenerative disease, as well as kidney and liver disease.
We also found evidence of significant damage to the lining of the stomach, likely from microplastics that became embedded in the tissue. It meant proteins that should only be found in the stomach were detected circulating in the blood.
While our findings don’t directly relate to human health, this work paints a distinct picture of the insidious and slow impacts plastic can have on a bird’s health – even if it doesn’t kill them.
Harmful but not deadly?
Some studies have found health impacts of plastics (such as increased exposure to heavy metals), while others have not. Why is that?
An initial study looking at plastic exposure might start out by just looking at what’s known as a single response. This could be the condition of the animal’s body, for example.
While important, such studies don’t account for the diversity of conditions an animal could realistically experience. If you’ve recently been unwell, you might respond to a health test differently than if you were fully healthy. Birds will, too.
Recently, a handful of more in-depth studies have documented a range of plastic impacts on birds; these were harmful, but not severe enough to cause death. For example, birds that consumed plastic had higher cholesterol, were smaller and had shorter wings, and had plasticosis, an inflammatory condition that leads to scar tissue formation.
But consider a loved one with an invisible, chronic health condition. To a stranger they might appear healthy, but their quality of life is actually impacted by their condition. The same is true for birds and other wildlife.
Thankfully, we have more fine-grained tools at our disposal.
Studying proteins
Proteomics is the study of protein composition and regulation, and the role these play in the body. While commonly used in the medical field and other disciplines, omic technologies (including proteomics) are rarely used in wildlife studies.
Certain key proteins are well-known markers of disease. For example, we found low levels of a protein called albumin in the blood of birds with plastic. Having less albumin is a sign of poor liver function.
Birds with plastic also had less of a protein called brain-derived neurotrophic factor. This protein plays a crucial role in the growth and survival of neurons (nerve cells), including those involved in the development of the birds’ ability to recognise each others’ song.
Our results suggest while not all birds die from plastics exposure, they may have health issues and suffer from reduced cognitive functions, including those needed for courtship (such as song). This may make it more difficult for them to successfully find mates and produce chicks.
Many of the health impacts from plastic exposure have been documented beyond the point of exposure – that is, the stomach. While our findings revealed notable damage to the stomach lining, changes have now been reported in liver, kidneys, spleen and brain of these chicks.
This suggests ingested plastic can have wide-ranging, potentially whole body consequences, and we’ve barely scratched the surface.
We must listen closely
It’s important to remember that all the worrying health impacts we found via protein analysis were documented in very young birds that were seemingly healthy.
So what does this mean for other wild species that haven’t yet benefited from proteomics analysis or other in-depth studies? Could these findings change our understanding of how microplastic exposure affects human health? This is a task for future research, but it’s not an easy one.
The reality is, we may never have comparable data for most of the world’s wild species. For our lab alone, it’s taken a decade of laying the groundwork to understand the complexity of this problem in a single bird species, one that’s relatively accessible and easy to work with.
For humans, we may never be able to put a number on the impact of plastics because of the huge array of personal, environmental and social determinants of health.
So, there’s a lot we can learn from these birds. As a society, it’s in our best interest to listen to the story they’re trying to tell us.
Acknowledgements: The authors would like to acknowledge research collaborator Alexander Bond from the Natural History Museum, UK.
