Environmental Sustainability Spotlight

Microplastics and Zebrafish

Submitted by the IZFS Environmental Sustainability Committee

Long before making their way to that fateful pet shop in Oregon, zebrafish swam around in the Ganges River basin in South Asia for tens of thousands of years. The slow, temperate waters and predictable weather cycles allowed zebrafish, among hundreds of other fish species, to thrive across the subcontinent [1]. Today, however, it is difficult to look at the Ganges River and imagine anything thriving in its polluted waters. Even if the animals manage to evade the tangled mess of plastic and food waste, the tiny fragments leaching out of them are inescapable.

As plastic products are discarded and exposed to the environment, they slowly release tiny particles called microplastics. This simply refers to any plastic particle smaller than 5 mm but can include a wide range of materials with different properties [2]. They can exist in different shapes and sizes depending on the initial material and environmental conditions, from fragments of plastic bags and bottles to microbeads from beauty products to microfibres from clothes. Factors such as heat, pH, water currents, and wind determine the type of fragments that are released [3]. The one thing they have in common though, is that they are found everywhere: from icy mountain peaks to arid deserts to the depths of the Mariana trench [4, 5]. Living organisms around the world are exposed to them and will often ingest many of these particles on a regular basis. What makes these ubiquitous particles dangerous is that they are not biodegradable. The speed at which we have polluted the world with plastic has meant that evolution has not been allowed the time to adapt.

Fish are not the only species exposed to microplastics. Researchers have looked at the impact of microplastic exposure on various aquatic and terrestrial organisms [6-8]. But we all know how powerful of a model zebrafish can be for an in-depth understanding of various aspects of biology. They benefit from a rare combination of being a prolific model organism and one which is commonly exposed to microplastics in nature. As a result, researchers are beginning to use zebrafish to better understand the biological implications of microplastic pollution [9].

Zebrafish are amenable to high resolution live imaging, allowing researchers to visualize microplastics within the organism. Fluorescently labelled microplastics have been used to study their biodistribution within the body and interactions with different tissues. In embryos and larvae, large particles remain on the chorion and may interfere with hatching, while smaller particles can pass through the pores of the chorion [10, 11]. They then tend to accumulate in the yolk sac and may circulate through the gastrointestinal tract of the developing larva. In adult fish, microplastics can be absorbed through the mouth, gills or skin and circulate through the bloodstream [11, 12]. They have been found in a range of organs including the heart, intestines, muscles, brain, and liver, causing inflammation wherever they accumulate. In particular, researchers have found that exposure of polystyrene microplastics induces oxidative stress in the liver and impaired metabolism of lipids and amino acids, which can cause inflammation of the liver and lipid accumulation [13]. Multiple groups have reported an acute immune response to the foreign particles and severe inflammation that can damage tissues of adult zebrafish [14, 15]. More research will be needed to establish whether the body can clear these tiny poisons and how long-lasting their effects may be.

Decades of research have led to an advanced understanding of the developmental biology of zebrafish, which serves as a strong foundation to study how vertebrate development is affected upon exposure to microplastics. Researchers have found that zebrafish larvae exposed to polyethylene microplastics (the most commonly used type of plastic) developed a range of morphological deformities including larger optic vesicles, enlarged swim bladders and yolk sacs, and abnormal angles between myosepta [10]. Exposure to microplastics also impaired the hatching of larvae, possibly due to physical interference with the chorion, and a lower rate of survival [16]. The few that survive develop morphological defects when older, such as curved spines and pericardial edemas [10]. Similar developmental defects and hatching abnormalities have also been reported for Medaka larvae [17]. These indicate a possible loss of reproductive success for fish species in the wild exposed to water-borne microplastics.

Owing to their small size, microplastics have a high surface area-to-volume ratio, allowing for the adsorption of chemicals and pollutants onto their surface. Researchers have found that various organic compounds commonly found in industrial waste easily attach to microplastic particles due to their hydrophobicity [18]. Their toxicity and potency to cause developmental defects in zebrafish larvae are higher when adsorbed on microplastics than when freely dissolved in water [19]. Additionally, some particles are small enough to interact with individual cells and biomolecules within the body. Adult zebrafish exposed to polystyrene and polyethylene microplastics through their diet exhibited altered transcriptional activity of many genes, often related to inflammation, cell adhesion, and DNA repair [15, 20]. Further research will be needed to understand the specific molecular and sub-cellular interactions, and the zebrafish model will undoubtedly be a key tool.

The most overt evidence of the impact of microplastics is in the way it alters the behaviour of fish. The swimming ability of zebrafish is impaired when exposed to 50 nm sized plastic particles [21]. This has been linked with the capacity of these particles to cross the blood-brain barrier and interfere with neurotransmitters such as acetylcholine, dopamine, melatonin and oxytocin [22]. Such neurological disruptions can impact the feeding and mating behaviour of various aquatic species and impact entire ecosystems. Moreover, this model of neurotoxicity is likely to be of concern for all species exposed to microplastics, including humans.

We are only beginning to understand the impact that our overconsumption of plastic is having on ecosystems around the world. Even as countries sluggishly reduce their plastic waste, the estimated 8.3 billion tons of plastic already present in the environment will continue to poison organisms for decades to come [23]. Zebrafish researchers are leading the way in revealing the impact of microplastics on aquatic life and vertebrates in general. The world needs to keep an eye on the findings from this field as we figure out the best way to conserve ecosystems and limit the adverse health effects of these microscopic toxins.

 

References:

  1. Engeszer, R. E., Patterson, L. B., Rao, A. A., & Parichy, D. M. (2007). Zebrafish in the wild: a review of natural history and new notes from the field. Zebrafish, 4(1), 21-40.
  2. Barnes, D. K., Galgani, F., Thompson, R. C., & Barlaz, M. (2009). Accumulation and fragmentation of plastic debris in global environments. Philosophical transactions of the royal society B: biological sciences364(1526), 1985-1998.
  3. Andrady, A. L. (2017). The plastic in microplastics: A review. Marine pollution bulletin, 119(1), 12-22.
  4. Napper, I.E., Davies, B.F., Clifford, H., Elvin, S., Koldewey, H.J., Mayewski, P.A., Miner, K.R., Potocki, M., Elmore, A.C., Gajurel, A.P. and Thompson, R.C. (2020). Reaching new heights in plastic pollution—preliminary findings of microplastics on Mount Everest. One Earth, 3(5), 621-630.
  5. Peng, X., Chen, M., Chen, S., Dasgupta, S., Xu, H., Ta, K., Du, M., Li, J., Guo, Z. and Bai, S. (2018). Microplastics contaminate the deepest part of the world’s ocean. Geochemical Perspectives Letters, 9(1), 1-5.
  6. De Sá, L. C., Oliveira, M., Ribeiro, F., Rocha, T. L., & Futter, M. N. (2018). Studies of the effects of microplastics on aquatic organisms: what do we know and where should we focus our efforts in the future? Science of the total environment, 645, 1029-1039.
  7. Ribeiro, F., O'Brien, J. W., Galloway, T., & Thomas, K. V. (2019). Accumulation and fate of nano-and micro-plastics and associated contaminants in organisms. TrAC Trends in analytical chemistry, 111, 139-147.
  8. Huerta Lwanga, E., Gertsen, H., Gooren, H., Peters, P., Salánki, T., Van Der Ploeg, M., Besseling, E., Koelmans, A.A. and Geissen, V. (2016). Microplastics in the terrestrial ecosystem: implications for Lumbricus terrestris (Oligochaeta, Lumbricidae). Environmental science & technology50(5), 2685-2691.
  9. Bhagat, J., Zang, L., Nishimura, N., & Shimada, Y. (2020). Zebrafish: An emerging model to study microplastic and nanoplastic toxicity. Science of The Total Environment728, 138707.
  10. Malafaia, G., de Souza, A. M., Pereira, A. C., Goncalves, S., da Costa Araujo, A. P., Ribeiro, R. X., & Rocha, T. L. (2020). Developmental toxicity in zebrafish exposed to polyethylene microplastics under static and semi-static aquatic systems. Science of The Total Environment700, 134867.
  11. Pitt, J.A., Kozal, J.S., Jayasundara, N., Massarsky, A., Trevisan, R., Geitner, N., Wiesner, M., Levin, E.D. and Di Giulio, R.T., 2018. Uptake, tissue distribution, and toxicity of polystyrene nanoparticles in developing zebrafish (Danio rerio). Aquatic Toxicology194, pp.185-194.
  12. Lu, Y., Zhang, Y., Deng, Y., Jiang, W., Zhao, Y., Geng, J., Ding, L. and Ren, H. (2016). Uptake and accumulation of polystyrene microplastics in zebrafish (Danio rerio) and toxic effects in liver. Environmental science & technology50(7), 4054-4060.
  13. Zhao, Y., Bao, Z., Wan, Z., Fu, Z., & Jin, Y. (2020). Polystyrene microplastic exposure disturbs hepatic glycolipid metabolism at the physiological, biochemical, and transcriptomic levels in adult zebrafish. Science of The Total Environment710, 136279.
  14. Gu, W., Liu, S., Chen, L., Liu, Y., Gu, C., Ren, H. Q., & Wu, B. (2020). Single-cell RNA sequencing reveals size-dependent effects of polystyrene microplastics on immune and secretory cell populations from Zebrafish intestines. Environmental science & technology54(6), 3417-3427.
  15. Limonta, G., Mancia, A., Benkhalqui, A., Bertolucci, C., Abelli, L., Fossi, M. C., & Panti, C. (2019). Microplastics induce transcriptional changes, immune response and behavioral alterations in adult zebrafish. Scientific reports9(1), 1-11.
  16. Cheng, H., Feng, Y., Duan, Z., Duan, X., Zhao, S., Wang, Y., Gong, Z. and Wang, L. (2021). Toxicities of microplastic fibers and granules on the development of zebrafish embryos and their combined effects with cadmium. Chemosphere269, 128677.
  17. Le Bihanic, F., Clérandeau, C., Cormier, B., Crebassa, J.C., Keiter, S.H., Beiras, R., Morin, B., Bégout, M.L., Cousin, X. and Cachot, J. (2020). Organic contaminants sorbed to microplastics affect marine medaka fish early life stages development. Marine pollution bulletin154, 111059.
  18. Wu, C., Zhang, K., Huang, X., & Liu, J. (2016). Sorption of pharmaceuticals and personal care products to polyethylene debris. Environmental Science and pollution research23(9), 8819-8826.
  19. Chen, Q., Yin, D., Jia, Y., Schiwy, S., Legradi, J., Yang, S., & Hollert, H. (2017). Enhanced uptake of BPA in the presence of nanoplastics can lead to neurotoxic effects in adult zebrafish. Science of the Total Environment609, 1312-1321.
  20. Qiao, R., Lu, K., Deng, Y., Ren, H., & Zhang, Y. (2019). Combined effects of polystyrene microplastics and natural organic matter on the accumulation and toxicity of copper in zebrafish. Science of the Total Environment682, 128-137.
  21. Chen, Q., Gundlach, M., Yang, S., Jiang, J., Velki, M., Yin, D., & Hollert, H. (2017). Quantitative investigation of the mechanisms of microplastics and nanoplastics toward zebrafish larvae locomotor activity. Science of the total environment584, 1022-1031.
  22. Sarasamma, S., Audira, G., Siregar, P., Malhotra, N., Lai, Y.H., Liang, S.T., Chen, J.R., Chen, K.H.C. and Hsiao, C.D. (2020). Nanoplastics cause neurobehavioral impairments, reproductive and oxidative damages, and biomarker responses in zebrafish: throwing up alarms of wide spread health risk of exposure. International journal of molecular sciences21(4), 1410.
  23. Geyer, R., Jambeck, J. R., & Law, K. L. (2017). Production, use, and fate of all plastics ever made. Science advances3(7), e1700782.

 

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