By Dr Nadira Ahmad Rosllan & Assoc. Prof Dr Roslina Abdul Rahim Department of Basic Medical Science, Kuliyyah of Medicine, International Islamic University Malaysia

These conveniences have made modern life easier, but they have also created an invisible form of pollution: microplastics and nanoplastics.

Plastics do not completely decompose when discarded. Over time, sunlight, heat, friction and mechanical breakdown cause larger plastic items to fragment into smaller pieces.

Microplastics are generally defined as plastic particles smaller than 5 mm, while nanoplastics are even smaller particles that may be measured at the nanoscale. Because of their tiny size, these particles are often invisible to the naked eye, yet they are increasingly being detected in the air, water, soil and food chain.

Human exposure to microplastics may occur through several routes. The main suspected pathways are inhalation and ingestion. Tiny plastic particles can be released into the air from synthetic textiles, tyre wear, industrial activity, household dust and degrading plastic waste.

They may also enter the body through contaminated food and drinking water. Microplastics have been reported in seafood, table salt, bottled water, tap water, and other food sources, although the amounts and significance of exposure vary widely across studies.

The World Health Organisation has highlighted that humans may be exposed to micro- and nanoplastics through food, water and air, but also emphasises that many uncertainties remain regarding their long-term health effects.

FINDING PLASTICS INSIDE THE HUMAN BODY

One reason microplastics have attracted growing scientific attention is their ability to move beyond the environment and into biological systems.

Recent studies have reported microand nanoplastics in several human tissues and biological samples, including the

lungs, blood, placenta, liver, kidney and, more recently, postmortem human brain tissue. However, detection alone does not prove that these particles cause disease.

Researchers are still working to improve sampling methods, avoid contamination during analysis, and understand what levels of exposure may be biologically meaningful.

The brain is of particular concern because it is one of the body’ s most highly protected and energy-demanding organs. It depends on a constant supply of oxygen and nutrients and contains billions of neurons that communicate through precise electrical and chemical signals.

Even small disturbances in this delicate environment may affect memory, learning, movement, mood and behaviour.

Normally, the brain is protected by the blood – brain barrier, a specialised structure that helps regulate which substances can pass from the bloodstream into brain tissue.

Experimental studies suggest that very small particles, especially nanoplastics, may cross or interfere with this barrier under certain conditions. Some laboratory and animal studies have shown that micro- and nanoplastics may affect blood – brain barrier integrity, enter neural cells, and trigger biological responses linked to cellular stress.

However, scientists have not yet determined how much microplastic or nanoplastic enters the human brain during ordinary environmental exposure.

WHAT RESEARCH HAS FOUND SO FAR

Several possible mechanisms have been proposed to explain how micro- and nanoplastics could affect brain health.

In laboratory and animal studies, these particles have been associated with oxidative stress, inflammation, mitochondrial dysfunction, disruption of cell membranes, altered neurotransmitter activity and impaired neuronal communication.

Oxidative stress occurs when harmful reactive molecules overwhelm the body’ s normal protective systems, potentially damaging DNA, proteins and lipids. Inflammation, when persistent, may also disturb normal brain function.

Together, these processes could theoretically

affect neural networks involved in memory, learning and motor control.

At present, most evidence linking microplastics to brain effects comes from cell-based studies and animal models. These studies are important because they help scientists identify possible biological pathways.

However, findings from experimental models cannot be directly translated to humans without caution. The dose, type of plastic, particle size, exposure duration, and route of exposure used in laboratory studies may differ from those in everyday human exposure.

This distinction is important. Current evidence does not yet demonstrate that ordinary exposure to microplastics causes neurological disease in humans.

However, the possibility is concerning enough to justify further research. Scientists are particularly interested in whether long-term exposure may contribute to subtle effects on neurodevelopment, cognition, behaviour or neurodegenerative processes later in life.

More human studies are needed to determine exposure levels, vulnerable groups, dose – response relationships and safe thresholds.

GROWING PUBLIC HEALTH CONCERN

The issue of microplastics therefore sits at the intersection of environmental health and human health. Plastic pollution is no longer only an ecological concern affecting oceans, rivers and wildlife.

It is increasingly being studied as a possible public-health issue because the particles created from plastic waste may eventually return to us through the air we breathe, the water we drink and the food we eat.

Although it is almost impossible to avoid microplastics completely, several practical steps may help reduce unnecessary exposure while also reducing environmental pollution.

These include limiting single-use plastics, avoiding heating food in plastic containers, using glass or stainless-steel bottles when practical, improving indoor ventilation, reducing indoor dust, choosing personal care products without plastic microbeads, washing synthetic clothing