Scientists issue urgent warning over potential health threat lurking in global waterways: 'Trojan Horse effect'

Microplastics have already been a growing concern — now a new publication shows how the pollution could be escalating to crisis levels worldwide. 

What's happening?

Also known as MPs, the plastic particles of less than 5 millimeters in diameter are now widely understood as a major form of pollution with the potential to harm habitats, wildlife, and human health. But the growing body of knowledge around MPs has been, as an international group of co-authors noted in their new systematic review, "fragmented" and "limited to specific regions or ecological compartments."

The review, recently published in the journal Water, sought to synthesize results from over 100 papers looking at MPs in aquatic ecosystems. The co-authors' goal was to help consolidate relevant findings and sharpen understanding of this issue as pressing and widespread.

Among the details amassed in the study for consideration are common "dispersion patterns" of MPs in global waters. As Devdiscourse notes in a summary of the review, primary MPs (manufactured to be small for the purpose of inclusion in consumer products such as pharmaceuticals and cosmetics) and secondary MPs (the result of larger plastics breaking down over time) can pollute water systems by multiple routes, including industrial outflow, agricultural runoff, stormwater drainage, and more.

With so many entry points for these tiny, hard-to-remove particles of material that will never really decompose but only degrade into smaller and smaller pieces, it's no surprise that MP contamination is so ubiquitous. In turn, it demands a comprehensive, coordinated response, the co-authors say.

Why is the study important?

Fractured understanding of MP infiltration of waterways, soil, the air, and food supplies makes it nearly impossible to address the crisis effectively. As the co-authors of this study make clear, potential threats to human health — via ingestion, inhalation, and possibly prenatal exposure — are still incompletely understood.

But human exposure itself has been confirmed. In addition to fragile habitats — where, as Devdiscourse notes, plastic contaminants can be transferred up the food chain from fish to seabirds to marine mammals — MPs have been found in human blood, breast milk, the placenta, and lungs. 

While scientists are still investigating the ostensible impacts of MPs on humans in particular, the review identifies one particularly insidious threat. The "Trojan Horse effect," Devdiscourse explains, means that there is not only the potential for the plastic itself to toxify an environment or body but also to carry on its surface "environmental pollutants such as heavy metals, endocrine-disrupting chemicals, and persistent organic pollutants." 

Definitive results are pending, but MPs are already being studied for possible links to health concerns such as poor liver function, reproductive issues, and cognitive decline. While further research is needed, emerging evidence may already warrant action, especially considering that already vulnerable low- and middle-income countries face disproportionate exposure risks.

What can be done about the microplastic problem?

The co-authors of the systematic review call for "a unified global effort" to address the ubiquity of MP contamination. In particular, they express the need for "establishing standardized monitoring mechanisms, investing in multidisciplinary research, and implementing ecosystem-specific mitigation strategies." 

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With policymaking a likely underpinning of many of these activities, it's worth noting emerging policies aimed at reducing plastic pollution. In Nepal, for example, a sweeping ban on common, flimsy plastic items will go into effect later this year. A similar ban is being discussed in Hong Kong. And municipalities across countries like the United States have begun to phase out single-use plastics and plastic bags.

While these moves are important, there is still a ton of work to be done, particularly on the level of culture change to normalize more sustainable behaviors. In addition to organizing support for pro-environment policies at local, national, and global levels, individuals can take smaller steps to limit MP contamination and personal exposure. 

Switching to plastic-free alternatives for everyday items, for instance, taking reusable bags to the grocery store, and bringing your own reusable to-go containers when eating at restaurants can all add up — especially if you share these ideas with friends and family.

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