Are small plastic particles a big problem for zebrafish?

By: Sachi Villanueva, Brandon University

Have you gone a day without using plastic? Without leaving your home, you can probably find plastic in every room – shampoo bottles in the shower, plastic-packaged fruits in the fridge, and even shirts in the closet! Plastic has become a big part of our daily lives.

Plastic is fantastic, but also problematic. Since plastic does not degrade easily and is produced in large amounts, it builds up in the environment. About 40% of plastics produced are single-use items such as water bottles – disposable items that we only use for a few minutes but last in the environment for hundreds of years! Over time, sunlight, wind, and waves break down plastic into smaller pieces – those smaller than 5 millimetres are microplastics. Due to their tiny size, they are harder to clean up, can be eaten by animals, and even travel up the food chain.

For my master’s thesis, I will be studying the effects of microplastics on the health of a freshwater fish native to Southern Asia called zebrafish (Danio rerio). Zebrafish are the “lab rat” of the fish world, and used to study everything from animal development and behaviour to human diseases like cancer.

In our lab, I exposed zebrafish to microplastics by adding low but environmentally realistic amounts of plastic particles into their tanks. To see if there is something fishy with microplastics, I want to to answer these questions on their effects to the function and behaviour of zebrafish:

Will the microplastics enter and collect in the body? I think the plastic particles will get in the body, and stay in the gills and intestine as the fish unintentionally uptake and consume microplastic-contaminated water.

Will the prescence of microplastics affect the development of fish? Microplastics in the intestine may fill up the fish and lessen the amount of food they can eat, providing less nutrition for growth and reproduction.

Will the microplastics cause damage to the cells of different organs? Free radicals are molecules containing oxygen that are part of necessary reactions in our body to maintain good health. However, exposure to plastic particles can increase free radicals beyond what antioxidants can balance. This imbalance is called oxidative stress, which can cause cell damage and lead to diseases.

Will the microplastics cause fish to behave differently? Plastic particles can affect behaviour by causing damages in the central nervous system which is vulnerable to oxidative stress. Changes in behaviour can be seen through abnormal swimming and increased anxiety. I think microplastic-exposed fish will swim with fast and unpredictable patterns right before or after being stationary, and seek less risky environments to hide from predators such as the bottom and darker parts of the tank.

Are these changes permanent? Once fish are returned to clean water, I think the microplastics will disappear from the gills and intestines over time. This may enable the fish to eat properly, improve their overall health, and return to normal behaviour.

I hope the answers to those questions will help us understand different ways plastic particles can affect the health of animals. Compared to other studies, my research uses lower concentrations of microplastics that are more environmentally relevant. This will assess the range of threats that plastic particles pose to animals. I will also examine health from many aspects and test if the health effects are reversible. Despite their size, small plastic particles can have a big impact on the environment, travelling up food chains and eventually ending up on our plates.

Edited by B.G. Borowiec and A.E. McDonald. Header photo adapted by B.G. Borowiec. Stock photos from Unsplash and Wikimedia Commons.