Filter feeders transform microplastics into a bigger threat 

A study led by Tel Aviv University has revealed alarming insights into how microplastic particles are transformed within marine ecosystems, posing new challenges to the health of the ocean’s food web. 

The research highlights how filter-feeding marine organisms alter the behavior and composition of microplastics, creating unforeseen risks for marine environments.

Investigating microplastic pollution

While previous research has documented the dangers of marine animals ingesting microplastics, this study goes a step further, exploring how these particles change after passing through the digestive systems of filter feeders. 

Conducted by PhD student Eden Harel, Professor Noa Shenkar, and Professor Ines Zucker from Tel Aviv University, the study focused on ascidians – marine animals that efficiently filter tiny particles from water. 

The findings reveal how the interaction between filter feeders and microplastics contributes to the spread and transformation of these particles.

“We aimed to examine whether and how plastic changes after passing through the digestive system of a marine organism and how this process affects the presence of plastic and its availability to other organisms,” Shenkar explained.

How filter feeders transform microplastics

Using a controlled laboratory experiment, the researchers simulated seawater environments containing ascidians and introduced two types of microplastic particles.

These particles included polystyrene (PS), a common conventional plastic, and polylactic acid (PLA), a biodegradable bioplastic marketed as environmentally friendly. The team monitored the filtration, digestion, and excretion processes over 48 hours.

The results showed stark differences between the two types of plastic. Ascidians removed 90% of polystyrene particles from the water within two hours, but these particles were reintroduced to the water after 48 hours following digestion.

Polylactic acid particles, on the other hand, decreased significantly in concentration and remained at low levels. Larger PLA particles appeared to break down during digestion – likely returning to the water as smaller, undetectable nanoparticles.

These findings reveal that while some microplastics persist in their original form, others may fragment into smaller particles, potentially amplifying their environmental impact.

Plastic disguised as organic matter

To understand the changes microplastics undergo during digestion, the team used Raman spectroscopy to analyze particles excreted by the ascidians. 

The analysis revealed a surprising transformation: the plastic particles were no longer identifiable as plastics. Instead, they appeared to be organic matter due to a fecal coating acquired in the digestive system.

“Our findings revealed that microplastic particles are excreted from the ascidian’s digestive system coated with a fecal layer, and it is likely that the marine environment also identifies these particles as this organic material,” Harel said.

This transformation increases the likelihood of these particles being ingested by other marine animals that feed on feces, further embedding microplastics into the food web. 

The fecal coating also facilitates bacterial colonization and the adhesion of pollutants like heavy metals and residual organic compounds, such as antibiotics, making these particles even more hazardous.

According to Zucker, plastic particles undergo many transformations in the environment, from weathering to digestive processes, turning them into carriers of pollutants and diseases within the food web.

Impacts of microplastics on feces

In addition to examining how filter feeders transform microplastics, the study explored how these particles affect the physical properties of feces – a vital nutrient source for many marine organisms. Feces containing microplastics displayed significant changes in behavior.

Rapid sinking

Unlike normal feces, which sink slowly and provide sustenance to organisms along their descent, feces containing microplastics sank rapidly to the seafloor. This deprives marine organisms in the water column of a crucial food source.

Localized accumulation

The faster sinking caused feces and microplastics to accumulate on the seafloor near the filter feeders, instead of dispersing evenly. This buildup can lead to increased carbon and nitrogen levels, fostering algal blooms that disrupt marine ecosystems.

“This accumulation can increase carbon and nitrogen levels on the seafloor and trigger algal blooms, representing another critical impact of microplastics on the balance of the marine food web,” Harel explained.

Complexity of microplastic pollution 

The study highlights the complexity of microplastic pollution, showing that the problem goes far beyond the particles themselves. Their transformation through biological processes and environmental exposure creates unexpected and far-reaching consequences.

“The most alarming conclusion is that the microplastic problem is far more complex than initially thought,” said the researchers. 

“Plastic pollution in the marine environment has many unexpected dimensions, and its complexities continue to grow. Sometimes, neither we nor the environment can even recognize it as plastic.”

The findings emphasize the urgent need for better technologies and strategies to mitigate the spread and impact of microplastics.

Addressing the microplastics crisis

As microplastic pollution continues to infiltrate marine ecosystems in unpredictable ways, this study reveals just how urgent the issue has become. With microplastics transforming into carriers of pollutants, altering the balance of marine food webs, and contributing to environmental degradation, addressing this crisis is essential.

“As time goes on, plastic continues to harm more and more marine ecosystems,” the researchers concluded. “It is our duty to develop new technologies to mitigate this dangerous phenomenon.”

This research provides a crucial step toward understanding the hidden dimensions of microplastic pollution and calls for global action to protect marine life and the delicate ecosystems that sustain it.

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