Fine particles, formaldehyde and other air contaminants are created when common cleaning agents are exposed to indoor ozone.

When used indoors in the presence of ozone, many household cleaners and air fresheners emit toxic pollutants at levels that may lead to health risks according to a new study by researchers at the University of California, Berkeley, and Lawrence Berkeley National Laboratory. This study was commissioned by the California Air Resources Board and was lead by Dr. William Nazaroff. The very comprehensive 330-page report is available at (http://www.arb.ca.gov/research/abstracts/01-336.htm).

The researchers examined various consumer cleaning products to determine if they contained either ethylene-based glycol ethers or terpenes. When the researchers tested the terpene-containing products in the presence of ozone, they found that reactions produced sub-micron sized particles with properties like those found in smog and haze; significant quantities of hydroxyl radicals (OH) and nitrate radicals (NO3); other oxidation products and formaldehyde, a respiratory irritant that is classified as a Group 1 carcinogen.

After analyzing the chemistry of the consumer cleaning products, the researchers ran a series of 18 experiments to determine the levels of exposure people might be subjected to when using the products in a confined space. The products were used in various ways according to package instructions: some at full strength and others at various dilutions as recommended on their labels. In some tests, used cleaning supplies such as paper towels and sponges were left in the room. In others, the supplies were promptly removed.

The tests produced various results - some reassuring and some raising concerns.

The good news is that when people use the products under ordinary circumstances, their exposure to ethylene-based glycol ethers, formaldehyde and fine particles will normally not reach guideline values: that is, levels set by regulatory agencies as the maximum exposure believed to be safe. However, the authors pointed out, because formaldehyde is also released from other sources such as plywood and pressed wood products that are found in most buildings, any increase in formaldehyde emissions is undesirable.

The study also presented several realistic scenarios to show the potential for exposure to dangerous levels of toxic pollutants. These scenarios included cleaning a shower stall in a small bathroom, cleaning when outdoor ozone levels are high (indoor ozone levels usually run between 20 and 70% of outdoor levels) and multi-house cleaning by a professional home cleaner.

Of particular interest is the scenario of using an air freshener and ozone in a child's bedroom. This could occur when people use both an air freshener and ozone-generating devices (like an ozone generator or an ionizer that generates ozone as a by-product) simultaneously in a room. This could lead to exposures to formaldehyde that are 25 percent higher than California's guideline value. Because other sources of formaldehyde could also be present in the room, exposure to formaldehyde would probably be even higher.

And air fresheners are not the only potential source of terpenes in a child's bedroom. For example, tests we have conducted with lemon-scented baby wipes and ozone from an ionizer showed substantial increases in sub-micron sized particles. This Cal-Berkeley study found that a major source of formaldehyde formation was the reaction between ozone, hydroxyl radicals and d-limonene (the active terpene in lemon-scented products). It is highly likely that another result of the ozone/lemon-scented baby wipes reaction would be significant levels of formaldehyde.

The study also sheds some light on the issue of what is a "safe" level of ozone in an indoor environment. Makers of ionizers, electrostatic precipitators, photocatalytic oxidizers and ozone generators continue to make claims that a "safe" level is below 50 ppb. This is the level required by the FDA for medical devices. However, this does not ensure safety in indoor environments. The truth is we simply do not have the research data to establish a safety level. Based on their experiments, this study found that "it is prudent to avoid the use of products with ozone reactive constituents in situations where indoor ozone concentrations are moderate to high (>20 ppb)"

The take-home message from these studies, according to Nazaroff, is that everyone - but especially cleaning professionals - should be cautious about overuse of products with high levels of ethylene-based glycol ethers and terpenes. Rooms should be ventilated during and after cleaning, some products should be used diluted as opposed to full-strength and cleaning supplies should be promptly removed from occupied spaces once cleaning is done. "Also, people should avoid the use of ozone generators or ionizing air cleaners, especially in the same space where terpene-containing cleaning products or air fresheners are being used," said Nazaroff.

This is an excellent study. It is well designed, well researched and well written. It provides a first-rate review of past research in this field and then breaks new ground. The Bibliography is extensive and a good starting place for anyone interested in this subject. Most importantly, it confirms, once again, that chemical reactions in indoor air are complex and the unintended outcomes are potentially dangerous to human health. It also emphasizes the dangers of using ozone and other reactive oxygen species (ROS) like OH and NO3 to "clean the air" in indoor environments.