Microplastics invade global waterways, triggering biodiversity and health crisis

Microplastic pollution has now reached crisis levels across aquatic ecosystems, with serious implications for biodiversity, food security, and human health. A new review paper titled, “Microplastics in Aquatic Ecosystems: A Global Review of Distribution, Ecotoxicological Impacts, and Human Health Risks”, published in Water, synthesizes findings from 119 peer-reviewed studies spanning freshwater, marine, wetland, and polar regions to offer the most comprehensive picture yet of the environmental and toxicological footprint of microplastics.

The review provides a timely synthesis of scientific knowledge, revealing that MPs are more widespread, persistent, and harmful than previously understood.

How are microplastics entering and spreading through aquatic systems?

Microplastics (MPs), defined as synthetic polymer particles smaller than 5 mm, originate from two primary sources: primary MPs, which are manufactured for use in cosmetics, pharmaceuticals, and industrial applications; and secondary MPs, which form when larger plastic debris fragments through exposure to sunlight, weathering, and microbial activity. These particles enter aquatic ecosystems through multiple pathways, including urban runoff, untreated sewage, industrial effluents, atmospheric deposition, stormwater drainage, maritime activity, and agricultural runoff.

Once released into the environment, the fate and movement of MPs are shaped by factors such as particle size, shape, density, and local hydrological conditions. Low-density polymers like polyethylene and polypropylene often remain suspended in surface waters, while heavier materials such as PVC and PET settle in sediments. Wetlands, estuaries, and low-velocity river systems are particularly vulnerable to MP accumulation due to their complex hydrology and sediment retention capacity.

Microplastics are now documented in every corner of the planet’s aquatic systems. From rivers like the Ganges, Volga, and Thames to remote polar seas, MPs have been found in freshwater lakes, estuarine mud, surface waters, and deep-sea sediments. In polar regions, MPs are present in snow, sea ice, and the digestive tracts of Arctic wildlife, indicating global dispersal through atmospheric and oceanic currents. The study highlights that the extent and profile of microplastic pollution vary significantly between regions, with developing countries facing disproportionately high contamination due to inadequate waste management infrastructure.

What are the ecological and toxicological consequences?

Microplastics pose serious ecological threats across trophic levels. Small organisms such as zooplankton and benthic invertebrates ingest MPs either directly or via contaminated food sources. These particles accumulate in their digestive tracts, disrupting feeding behavior, impairing reproductive functions, and causing cellular and tissue-level damage. In fish, MPs have been shown to penetrate epithelial barriers and accumulate in organs like the liver and brain, leading to oxidative stress, neurobehavioral changes, and endocrine disruption.

The review presents evidence of widespread trophic transfer of MPs from lower to higher organisms. Contaminated prey, such as copepods and mussels, introduce MPs into the diets of fish, seabirds, and marine mammals. These top-level consumers exhibit gastrointestinal blockages, immune suppression, and gut microbiota disruption. Laboratory and field studies in the Arctic, Bay of Bengal, and Mediterranean have confirmed MP ingestion in economically significant fish species, raising alarms over food safety and fisheries sustainability.

One of the most troubling aspects of microplastic contamination is its "Trojan Horse" effect. Due to their hydrophobic surfaces and large surface-area-to-volume ratio, MPs readily adsorb toxic environmental pollutants such as heavy metals, endocrine-disrupting chemicals, and persistent organic pollutants. These compounds desorb inside organisms upon ingestion, compounding toxicity. Chronic exposure, even at low concentrations, has been linked to hormonal imbalances, inflammation, compromised reproduction, and developmental abnormalities. Emerging research suggests these impacts can cascade through food webs, leading to ecosystem instability, biodiversity loss, and the collapse of key ecological functions.

How do microplastics affect human health and what policy gaps remain?

Human exposure to microplastics is no longer speculative. MPs have been detected in seafood, bottled and tap water, salt, beer, and even household air. More alarmingly, biomonitoring has found microplastics in human tissues including blood, lungs, placenta, and breast milk, confirming systemic internalization. Inhalation and ingestion are the primary routes of exposure, with urban populations and vulnerable communities in low- and middle-income countries at greatest risk.

Laboratory research on human cell lines has revealed that MPs can impair mitochondrial function, generate reactive oxygen species, and cause DNA damage. These effects are exacerbated when particles are laden with toxic additives or absorbed chemicals like BPA and phthalates. Although the full range of long-term and intergenerational health impacts is still under investigation, early evidence suggests risks of carcinogenicity, endocrine disruption, and immune dysfunction.

Despite this mounting evidence, regulatory frameworks remain fragmented and inadequate. Many nations have enacted bans on specific products like microbeads or single-use plastics, but comprehensive legislation targeting microplastic contamination in aquatic systems is rare. Global efforts, such as the 2022 United Nations resolution on plastic pollution, remain vague in scope and lack enforcement mechanisms. Meanwhile, the absence of standardized methods for sampling, classification, and toxicity testing impedes data comparability and hinders risk assessments.

The study calls for urgent interdisciplinary collaboration and investment in long-term ecosystem-scale research. It emphasizes the need for unified protocols for MP detection, inclusion of aquatic contamination indicators in global sustainability frameworks, and the adoption of circular economy models. Equitable solutions must also address environmental justice concerns, ensuring that mitigation strategies benefit populations most affected by MP pollution.