Nanowaste is so small you can’t see it — there are no towering landfills or trash barges full of it — but it’s a huge concern among some experts.

What is nanowaste? It comes from nanotechnology. And what’s that? It’s the use of microscopic, engineered particles in everything from personal hygiene products to electronics to drug delivery systems.

The particles come from elements, such as metals (silver, titanium and others), carbon and calcium, and are engineered at nano scale. How small is “nano”? Nanoparticles are 1 to 100 nanometers. A nanometer is one billionth of a meter. They’re smaller than the thickness of a strand of DNA and much, much smaller than the diameter of a human hair, so small you’d need a special electron microscope to see them.

Nanoparticles exist in nature — in volcanic ash, viruses, sand and even ocean spray for instance — but the ones found in products are engineered by humans, and used to make those products work better. You probably have some of these engineered nanomaterials (ENMs) in your house. They are found in some:

  • Silver and ceramic hair-care devices, such as dryers, straighteners and curling irons
  • Shaving creams
  • Deodorants
  • Shampoos
  • Sunscreens
  • Makeup
  • Lithium ion batteries
  • Water-repellent clothing.

The Nanotechnology Consumer Products Inventory has a crowd-sourced list of items that use or are alleged to use ENMs.

Related: What to Do When Your Electronic Treasures Become Trash

ENMs are big business: The global nanotechnology industry is forecast to balloon to $75.8 billion by 2020, according to the World Economic Forum (WEF).

What’s the worry?

Nanowaste and the environment

Nanoparticles aren’t just mini versions of conventional (“bulk”) particles. They’re so tiny they behave differently. This makes them useful in many applications. But once the product is thrown out and enters a landfill, wastewater plant or recycling center, no one quite knows what will happen. And that has experts, including those at the Organisation for Economic Co-operation and Development (OECD), an international governmental forum of 34 member-states, concerned.

Nanoparticles are highly reactive — they interact with other particles, creating chemical reactions we can’t always foresee. Experts worry those reactions could turn nanowaste released into the environment into nanopollutants.

“Disposing of such chemically reactive materials without prior deactivation can lead to serious consequences for the environment and human health,” writes Bart Kolodziejczyk, a materials engineer, on the WEF website.

For example, silver nanoparticles aggressively fight bacteria. But if they’re released into the environment, could they kill beneficial bacteria in soil, asks Kolodziejczyk?

ENMs also release their own toxins, according to the OECD.

Related: How to Be a Zero Waste Consumer

Nanowaste and human health

Nanowaste could also, in theory, be bad for human health.

For example, if ENM products end up in an incinerator, the emissions could pose problems. According to a study by Duke University, the incinerator emissions of ENMs contain six times the level of polycyclic aromatic hydrocarbons (PAHs) as the emissions of their conventional particle counterparts. These PAHs “can induce cancer, can cause mutations in genetic material, and can interfere with the proper functioning of hormones,” the authors say.

The OECD report underscores the concern: “Although ENMs are very diverse and not all of them are potentially toxic, recent research shows that some nanomaterials may show cancer-causing properties in lungs [and] bypass important protective biological mechanisms such as the blood-brain barrier.”

Scientists are still trying to confirm the effects of nanomaterial toxins on human health, says the OECD. Whether the toxins are capable of seeping through biological barriers like skin and membranes, and how they’d interact with our biological processes if they did, is not entirely clear.

What’s being done?

Waste treatment facilities are working to prevent environmental contamination by capturing and diverting ENMs before they become pollutants. But according to a report from the OECD, initial testing suggests state-of-the-art processes are capable of retaining most, but not all, of engineered nanomaterials.

Even if we can capture all nanoparticles before they enter the environment, we need to figure out how to handle them in a safe and responsible way, says the OECD.

The good news, according to WEF, is that “international and national organizations are starting to take note,” and a growing number of groups are working to develop and apply better guidelines to ENM research.

Related: Plastic in the Ocean May Outweigh Fish by 2050

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Ann Babe writes about travel and culture, social problems and solutions and emerging technologies. She has contributed to BBC, VICE, Roads & Kingdoms, Techonomy, Travel + Leisure, Conde Nast Traveler and more.