One of the reasons plastic has become so ubiquitous is that, generally, it’s very chemically stable, meaning it does not readily react with the substances around it. That's why this material is so often used for food packaging and water bottles. But now, a new study published in Nature has revealed that microplastics—those tiny pieces of debris that break off from larger plastic objects—can become chemically active when exposed to water, turning them into a potential hazard.

The scientists at Columbia University and UC Berkeley have discovered that the presence of water can make the surfaces of microplastics chemically active, triggering the spontaneous formation of chemicals capable of altering other molecules, like those essential for living organisms. This activity can occur even under normal environmental conditions, without the need for sunlight or other agents that cause plastic degradation. The greater available surface area of microplastics, as they fragment into smaller and smaller particles, is a key factor in this chemical reactivity.

The potentially dangerous chemical products, known as reactive oxygen species, stand out, particularly as they can snatch electrons from the proteins and fats that make up cell membranes, disrupting their structure and function. Among these, hydroxyl radicals are especially dangerous. These are textbook examples of the kinds of molecules that can damage animal and human tissue.

Our body has some defenses against this kind of damage, but if the reactive compounds greatly outnumber antioxidants, this line of defense can be overwhelmed. This can develop into a scenario called oxidative stress, leading to the damage of cells. Research into the effects of microplastics has long focused on other chemicals leaching from the particles or on their physical effects, often considering the plastic itself chemically inert. But these findings challenge the assumption that what is true of plastic on a grand scale is also true of the microscopic pieces it breaks down into.

When the researchers exposed red blood cells extracted from mice to different types of microplastics, the cells became deformed and ruptured—a phenomenon known as hemolysis. The effects were greater with plastics that were more reactive with water, indicating that this activity was the cause of cellular damage. This story originally appeared on WIRED en Español and has been translated from Spanish.