Nano: a party-cle in your paints?

By Noelle Wyman Roth

Throughout NaNovember, we’ve heard about how nano-titanium dioxide (TiO2) and nano-scale zero-valent iron (nZVI) might be useful for remediation, but how else are these compounds used? And do we need to be worried about any risks to human health?

Nano-scale zero-valent iron is an easy one: its primary use is for remediation. Thus, the primary pathway by which you could be exposed to nZVI is through contact with water or soil that has been remediated with nZVI. For most people, exposure to nZVI is unlikely—though we don’t yet know whether nZVI poses risks to human or ecological health.

Titanium dioxide is a different story. In addition to being useful for remediation, titanium dioxide­­ is the most widely used white pigment in the world. Titanium dioxide­­ is used to whiten paints and plastics, and it’s a common additive to food and cosmetics. Hundreds of consumer products we use contain titanium dioxide, however it’s unclear how many of those products contain nano-scale titanium dioxide.

Here are three ways titanium dioxide could enter your body:

  1. Skin absorption. In addition to cosmetics, nano-scale titanium dioxide is present in sunscreens because it functions very well as a broad-spectrum UV radiation blocker. In other words, titanium dioxide is really good at helping prevent sunburns and lessen the risks for skin cancer.
  2. Inhalation. The primary way people may be exposed to titanium dioxide is through occupational dust inhalation. In the US, we manufactured roughly 1.5 million metric tons of TiO2 in 2010 alone. These workers breathe in titanium dioxide nanoparticles everyday.
  3. Ingestion. The large presence of nanomaterials in our food is of increasing concern in recent years. In the case of titanium dioxide, the compound is found in many processed white foods (like frosting, candy, and coffee creamer) and personal care products (gum and toothpaste). This study concluded that we’re all exposed to nano-titanium dioxide, and children’s exposures are likely even higher because they consume more sweets.

As it turns out, we are frequently exposed to titanium dioxide. Which brings us to the second part of our question: should we be concerned? Are titanium dioxide nanoparticles toxic?

The short answer: we don’t know yet. We do know titanium dioxide­ isn’t acutely toxic, but we don’t yet have sufficient evidence to understand the impacts of chronic exposure in the human body or the environment.

First, sunscreen. Results of research so far have been mixed about whether titanium dioxide can or cannot penetrate the first layers of skin. However, no studies have found that titanium dioxide­ can reach internal organs through skin absorption. In addition, the American Cancer Society stresses that the risk of skin cancer is greater than the health risks posed by titanium dioxide. So lather up, because the titanium dioxide in your sunscreen is very likely safe.

We do have sufficient evidence indicating that inhaling titanium dioxide nanoparticles can harm the health of workers who are consistently exposed to TiO2 dust. Both the International Agency for Research on Cancer, part of the World Health Organization, and the US National Institute for Occupational Safety have categorized titanium dioxide­­ as a “possible carcinogen” to humans. This finding was due in part to studies that demonstrate a correlation between chronic exposure to titanium dioxidein rats and lung cancer when inhaled. The problem appears to be not the toxicity of titanium dioxideitself but due to tiny particles reaching delicate areas of the lungs.

As for titanium dioxide as a food additive, the long-term effects of ingestion are generally unknown. Several studies investigated a potential correlation between inflammatory bowel disease (such as Crohn’s) and titanium dioxide, but these studies didn’t find much evidence to suggest that titanium dioxide in your gut is harmful. Numerous other studies have suggested other impacts on human health, including potential links with genetic damage or neural disorders, and a study that demonstrated a link between exposure to titanium dioxide and pregnancy complication in mice. A review of existing toxicology information on nano-titanium dioxide found intravenous, high doses may result in lesions of the liver, kidneys, spleen, and brain; the same study emphasized that more research is needed on health effects.

We also don’t know how these billions of titanium dioxide nanoparticles will affect the environment once they leave our bodies and are flushed down the drain—or left in the environment after remediation of a contaminated site. Research indicates that nano-titanium dioxide can damage microbes at the base of marine ecosystems, which may negatively impact water chemistry to the detriment of the entire ecosystem. We don’t yet know the long-term impact of titanium dioxide in our wastewater or soil on microorganisms and, in turn, critters all the way up the food chain.

These nanoparticles are already used widely, and there’s a lot we don’t yet know about they may affect our health or environment. The Duke SRC is contributing to this understanding through Project 4’s research on whether titanium dioxide nanoparticles and nano-scale zero-valent iron may be contaminants on their own and how their use can help or hinder natural bioremediation.