I don’t eat fish guts, so do I really eat microplastics?

Our study suggests yes, but not many.

We all use plastic at least once a day. It’s everywhere. It’s in the laptop I’m using to write this blog, it’s in the clothes I’m wearing as I sit at my desk, and it’s in the packaging protecting the food I bought from the grocery store. It’s easy to see how much we rely on plastic. But what we don’t see is that this widespread dependence on plastics has led to widespread contamination of microplastics – tiny pieces of plastic (< 5mm in size) that float in the air around us and lurk in the food we eat and water we drink.

Recently, researchers in the Rochman Lab and collaborators at the Ontario Ministry of the Environment, Conservation and Parks sampled seven species of sportfish from Lake Simcoe – situated in Ontario, Canada. With these fish, we were trying to understand how much microplastic they were eating and whether these particles were also present in the fillets that we eat. To do this, we looked for microplastics in the stomach, fillet and liver of each fish. Our study revealed that microplastics were present in the stomachs of nearly all of the fish sampled, and this did not come as a surprise, given a recent study where we demonstrated relatively high concentrations of microplastics in several species of fish from Lake Ontario and Lake Superior.

However, we also found microplastics were widespread in the fillets and livers of all seven species. This means that plastics are not just being excreted after being ingested (i.e., via poop), but they’re also travelling to other parts of the body – including the parts we eat. 

Lead author, Hayley McIlwraith, looking at the microplastics found in the tissues of fish from Lake Simcoe in Ontario, Canada.

Previous research has suggested that microplastics can transfer from a gut to a fillet, but here we show widespread occurrence in wild fish. Around 74% of fillets and 63% of livers had at least one microplastic present, while 99% of fish had at least one particle present in any of the three studied tissues.

Now before raising the alarm bells and cutting fish out of your diet, keep in mind the levels we found were low relative to other sources of microplastics we may be exposed to. In our study, we calculated the yearly intake of microplastics based on a diet of eating half a pound of fish twice per week. For most of the fish species in our study, average consumption would be less than 1000 microplastics a year.

A graph showing the annual intake of microplastics by humans based on a diet of 0.5 lbs of fish twice per week. This is based on data from our study.

In comparison, another study estimated that 35,000 – 62,000 microplastics are inhaled annually by the average adult. These other exposure routes include drinking water, beer, salt and even honey. All of this raises questions about the many routes of exposure, and how microplastic contamination relates to risk for humans.

Average number of microplastics humans are exposed to from multiple sources.

But that’s not all, we found something else that was really interesting. For seafood, we are used to being advised about how much to eat in our diets due to contamination from organic chemicals – such as mercury or PCBs. We are generally told to eat fewer top predators or long-lived fish, because these fish tend to have higher levels of these toxins. In this study, our data suggests the opposite may be true for microplastics. We found that while larger fish contained a higher number of microplastics overall, it was the smallest fish that contained more microplastics per gram of tissue. So, if you cut a piece of fillet of the exact same size from the largest fish and from the smallest fish, the fillet from the small fish would have more pieces of plastic inside it. These results highlight the uniqueness of microplastics as a contaminant – i.e., they are physical particles rather than dissolved organic chemicals, and thus may behave differently than chemical contaminants. These unique properties are important, especially when considering their risks and effects in the environment.

The uniqueness of our results opens up new avenues of research relevant to the fate and risks of microplastics in food webs. Don’t worry, members from our lab are already on it! A current project is looking at fish fillets from Lake Ontario, where we already know fish have lots of microplastics in their guts – some up to 900 particles!

Of course, knowing that these small plastics are getting inside our bodies is scary. And we don’t yet know what that means for us. Luckily, there are many researchers already looking into the effects on humans. But just like fish excrete most plastics, we likely do too.

Overall, this study raises many more questions than it answers and until then, we need to reduce our plastic waste, reuse as much as possible and recycle when we can. Each of these actions will reduce plastic emissions to the environment and reduce plastic exposure for us.

Written by Hayley McIlwraith, Research Assistant in the Rochman Lab and Chelsea Rochman, Assistant Professor at the University of Toronto, co-founder of the University of Toronto Trash Team and Scientific Advisor to the Ocean Conservancy.

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