If your workers are exposed to the sun regularly, titanium dioxide (TiO2) might seem like fantastic stuff. Unlike some of the other active ingredients used in sunscreens, titanium dioxide won't cause skin irritation and blocks both UVA and UVB rays, protecting workers from the full spectrum of harmful light. It also has safe and beneficial uses in many other commercial products, including paint, cosmetics, plastics, paper, and food.
However, when titanium dioxide particles are inhaled by the workers who make all of those products, the story can take a different turn.
In April, the National Institute for Occupational Safety and Health (NIOSH) issued a Current Information Bulletin on the hazards of airborne titanium dioxide. It turns out that the very substance that is so useful at preventing skin cancer may, in fact, cause another type of cancer—lung cancer. Read on to learn about the risks NIOSH identified and the agency's recommendations to protect workers.
The titanium dioxide produced for use in the manufacture of commercial products typically comes in particulate (powdered or finely divided solid) form. Particle sizes are described as "fine" (particles are small enough to be respirable and large enough to be collected on a respirable particle filter) and "ultrafine" (particles with a primary particle diameter of less than one-tenth of one micron, which are by definition "nanoparticles").
When it comes to potential health effects, this size distinction matters. Nanoparticles of titanium dioxide, like nanoparticles of many other substances, act with greater potency in the body than larger particles do. Nanoparticles are more likely than larger particles to cause persistent lung inflammation.
In 1988, NIOSH recommended that titanium dioxide be classified as a potential occupational carcinogen, and that exposures be kept as low as feasible. In 2006, the International Agency for Research on Cancer (IARC) classified titanium dioxide as "possibly carcinogenic to humans (Group 2B)." (California does not include titanium dioxide on its Proposition 65 carcinogens list.)
Based on its most recent review of existing research, NIOSH has determined that ultrafine titanium dioxide is a potential occupational carcinogen; the data do not currently support that classification for fine titanium dioxide.
A group of international research agencies that includes NIOSH has created a website where employers can find information on controlling exposure to nanomaterials in the workplace. You can visit it at http://www.goodnanoguide.org/.
Recommended Exposure Limits
The current federal OSHA permissible exposure limit for titanium dioxide is 15 mg/m3, based on the airborne mass fraction of total titanium dioxide dust. California regulates airborne exposure to titanium dioxide with other "particulates not otherwise regulated," limiting worker exposure to 10 mg/m3 of total particulates and 5 mg/m3 of respirable particulates. Neither federal OSHA nor Cal/OSHA distinguishes between fine and ultrafine particles.
NIOSH's new recommended exposure limits (RELs) are considerably lower than both federal and Cal/OSHA's limits and account for the different carcinogenic potential of different-sized particles. The new NIOSH RELs call for exposures not to exceed 2.4 mg/m3 for fine titanium dioxide and 0.3 mg/m3 for ultrafine (including engineered nanoscale) as time-weighted average (TWA) concentrations for up to 10 hours per day during a 40-hour workweek.
If your workers are potentially exposed to titanium dioxide particulates, you should identify the size (fine or ultrafine) and quantity of particles. To control excess exposures, first look at engineering controls, including reducing the amount of titanium dioxide in the workplace and controlling airborne dusts through good manufacturing practice and ventilation. Administrative controls—such as limiting the number of workers who are exposed through the creation of regulated areas—can also be used. If exposures cannot be controlled by these methods, use respirators to achieve the best possible control of worker exposures.