Microplastics and Anthropogenic Fibres in Apex Sharks: Lessons from Australian Waters
When we think about plastic pollution in the ocean, we often picture floating plastic bottles, discarded fishing nets, or dirty coastlines. But have you ever considered that anthropogenic particles can also be found inside some of the ocean's top predators?
Our study, published in Chemosphere, revealed that apex sharks off the coast of Southeast Queensland (SEQ) are carrying microplastics and other human-made (anthropogenic) fibres not just in their digestive tracts (spiral intestines), but also within their muscle tissues.
This study was the first investigation of its kind into microplastic and anthropogenic fibre contamination in both intestine and muscle samples of large apex shark species in Australian coastal waters.
We analysed samples from four iconic, high-trophic-level apex shark species:
Bull sharks (Carcharhinus leucas)
Scalloped hammerheads (Sphyrna lewini)
Tiger sharks (Galeocerdo cuvier)
White sharks (Carcharodon carcharias)
Because these predators sit near the top of the marine food web (with trophic levels ranging from 4.1 to 4.5), they act can be considered barometers of ecosystem health. The results paint a concerning picture of how far-reaching environmental pollution has become:
Intestinal contamination: Microplastics and anthropogenic fibres were detected in 82% of the analyzed intestine samples. Across all species, the mean abundance was to 3.1 ± 2.6 particles per individual, or 0.03 ± 0.02 particles per gram of intestinal tissue
Presence in muscle tissue: Most strikingly, 60% of shark muscle samples also contained these
foreignparticles, proving that contamination goes beyond the digestive tract.Particle characteristics: Under the microscope, particle sizes ranged significantly: the fibres ranged from 190 to 4860 µm in length, while the fragments ranged from 34 to 306 µm. Overall, 92% of the recovered particles were fibrous in shape, with the remaining 8% being fragments.
While many people associate microplastics with petroleum-based synthetic polymers, our study uncovered an unexpected result. Using FTIR (Fourier-transform infrared) spectroscopy, the composition of these materials was identified as follows (Figure 1):
70% of the fibres were cellulose-based (such as cotton, rayon, and viscose).
Polyethylene terephthalate (PET) was the most common synthetic polymer identified among the fibres. fibres made up the next most common group.
The rare plastic fragments recovered were identified as polyethylene and polypropylene.
Figure 1.: Chemical composition of fibres and fragments found in shark intestinal samples. Adapted from Lu et al. (2024)
The results raised a question: why are cellulose-based fibres dominating? While natural or regenerated plant-based fibres are generally considered "eco-friendly," they are massively abundant in everyday textiles like clothing and carpets, shedding heavily into wastewater during laundering and drying processes.
Recent studies have suggested that cellulose-based fabrics actually shed significantly more microfibres during washing than synthetic plastics. Some experimental studies have found that cellulose-based fabrics can release more microfibres during laundering than polyester under specific washing conditions Zambrano et al. (2019)
While they are natural or semi-synthetic, these fibres often carry “a cocktail” of chemical additives, dyes, and finishing agents added during production. Because non-plastic fibres degrade faster than synthetic equivalents, they risk releasing these chemical payloads directly into marine tissues. However, this study did not measure these chemicals or demonstrate their release within shark tissues.
Because these apex sharks feed on a diverse diet of fish, crustaceans, and marine mammals, the presence of these particles likely points to two main pathways:
Direct ingestion of environmental pollutants present in coastal waters.
Trophic transfer, through contaminated prey where the sharks absorb particles accumulated by their prey lower down the food chain.
We further emphasized the broader implications of the findings: "While microplastics have been widely reported in the marine environment and marine organisms at different trophic levels, our knowledge about the exposure and ingestion of microplastics by marine megafauna, such as whales and sharks, is still limited... The presence of microplastics in these four large apex shark species further highlights how widespread these small but potentially harmful plastic particles have now spread in our environment."
Beyond quantifying pollution levels, a major goal of our study was to tackle the methodological hurdles plaguing microplastic research. Because different research groups use varying sample preparation techniques, size classifications, and detection limits, comparing pollution data across global studies remains a massive challenge.
The presence of microplastics and cellulose-based fibres deep inside muscle tissues underscores an urgent need for proactive measures. Protecting marine ecosystems, especially vulnerable top predators, requires a deeper look into how anthropogenic pollution moves through the entire marine environment.
Read the full open-access study published in Chemosphere:
Lu, H.-C., Smith, J.L., Ziajahromi, S., & Leusch, F.D.L. (2024). Microplastics and other anthropogenic fibres in large apex shark species: Abundance, characteristics, and recommendations for future research. Chemosphere, 349, 140957. DOI: 10.1016/j.chemosphere.2023.140957
By Hsuan-Cheng Lu
Postdoctoral Research Fellow
Reef Catchments Science Partnership (RCSP)
The School of the Environment. The University of Queensland
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