The Trouble with Latex: Why Common Paints Can Be Harmful, and What You Can Do About It

Al Hodgson is research director and a partner at Berkeley Analytical Associates, LLC, an indoor air quality and product testing laboratory in Richmond, California. He also holds a research position in the Indoor Environment Department at Lawrence Berkeley National Laboratory. Hodgson, whose research focuses on airborne gaseous contaminants in homes, schools and offices, has been active in environmental science and chemistry for 30 years.

Latex paints are the most common coating used indoors. What concerns do they raise?
Conventional water-based latex paints contain both organic and inorganic ingredients—pigments, binder, additives, and water. We should be most concerned about the volatile ingredients that can contaminate indoor air during and after application. The volatile organic compounds (VOCs) in these paints are mostly additives consisting of solvents and a coalescing aid that facilitates film formation. Many paints are formulated with ethylene glycol, a listed toxicant, as the solvent, although alternatives are used in some paints. The coalescing aid probably causes the paint odor. These VOCs can result in acute and chronic indoor exposures. Biocides, which are used to prevent bacterial growth in the can, are rarely listed as ingredients and don’t show up in the VOC content of a paint, but they are important toxicants. Ammonia and acetaldehyde are frequently used for this function, but formaldehyde is used in some paints. All of these are very volatile compounds.

When these paints are applied in a home, what chemical exposures do occupants experience?
In addition to the high VOC exposures that occur during the painting and initial drying periods, occupants are chronically exposed to these chemicals over extended periods. The most typical surface for application of latex paints is gypsum wallboard. Laboratory experiments conducted by myself and others have shown that a large portion of the VOC components quickly absorb into the wallboard, then are slowly released over many months. This is evidenced by lingering paint odors in the early period and confirmed by air samples taken from occupied buildings long after painting occurred.

An exception is the acetaldehyde biocide, which—in simulated room experiments, at least—dissipated rapidly, though it did result in high short-term exposure for the painter. Ammonia, too, is probably mostly released during painting.

Are there alternatives to traditional latex paints?
Absolutely, and this is generally good news for consumers. The levels of VOCs in latex paints have decreased in recent years. I just looked on the South Coast Air Quality Management District’s website and saw a number of these interior paints with VOC contents around 50 grams per liter (gm/L) or less. Many major paint manufacturers now offer zero-VOC or near-zero VOC paints in a range of finishes.

Laboratory chamber studies have confirmed near-zero claims for the solvents and coalescing aid. These paints are available in all colors, are applied like regular paints, and are expected to perform like regular paints, but they may carry a price premium. We’ve exclusively used one brand of zero-VOC paint in our laboratory and I have no complaints. Another big advantage is the greatly reduced odor associated with these paints.

What about alternative coatings and finishes used in homes?
Many “natural” finishes are available. I don’t have much research or personal experience with them; however, I would caution consumers to find out what’s in these products before using them—"natural" doesn’t necessarily mean low impact. For example, the components of linseed oil react rapidly with ozone in air to produce aldehydes and carboxylic acids, which may include toxicants and may produce an odor nuisance. Citrus oil or orange oil is limonene, which also reacts rapidly with ozone to produce formaldehyde and oxygenated limonene species that have been shown to be potent irritants. Milk-based paints, if spoiled by bacterial growth, will contain butyric acid, which has a very foul odor that might be impossible to live with. This suggests that these paints must contain biocides and possibly other additives to be usable. My suggestion is not necessarily to avoid these products, but to do your research and work with experienced professionals if you choose this route.

Are there programs that can help consumers make informed choices?
Product and indoor air quality certification programs are generally in their infancy in the United States. An organization called Green Seal maintains the Green Seal Paints (GS-11) certification program.  For an interior paint to be certified it must have a VOC content of 50 gm/L or less if it’s a flat paint and 150 gm/L if it’s a nonflat. In addition, there is a list of chemicals that are not to be used, including formaldehyde. The current list of certified paints is rather short, so Green Seal Paints apparently has not attracted a lot of interest from manufacturers.

There is a general indoor air quality certification program called GreenGuard that includes some paints. This program uses a test conducted in an environmental chamber to evaluate a product’s VOC emissions. Here, the emphasis is not on individual toxicants but on total VOC emissions, which in my opinion is a somewhat arbitrary and dated approach.

What are some good sources of information on the toxicity of chemicals emitted by paints and other products used in the home?
I’m an environmental scientist, so I mostly rely on databases that compile and summarize a lot of the toxicological literature on the chemicals we encounter in our studies. One of my favorite resources is TOXNET, a free online toxicology data network maintained by the U.S. National Library of Medicine. The network includes the Hazardous Substances Data Bank and the Integrated Risk Information System (IRIS). One interesting component is the Household Products Database. For example, you can search ethylene glycol and the home maintenance category and find a long list of named paint products containing this compound. Environmental Defense also maintains a large database of toxicology information that is very informative.

Another good resource is the California Office of Environmental Health Hazard Assessment, which has a program to scientifically assess the health risks posed by hazardous substances. They actively manage the state’s lists of toxic substances and develop acute and chronic reference exposure levels (RELs) for a number of chemicals. RELs are considered safe for the general population, including sensitive individuals, for a one-hour exposure (acute RELs) or for long-term (ten years or more) exposures (chronic RELs). All of the technical assessments are available on their website.

What can consumers do to reduce chemical exposures from painting?
There are a number of common-sense techniques, but often they’re ignored for a variety of reasons. Product labels recommend that consumers use adequate ventilation. What’s adequate? In my opinion, you should maximize ventilation. This means opening windows and exterior doors and using an auxiliary fan placed in at least one window with the fan blowing outward at maximum speed. Continue to ventilate after you have finished painting for as long as possible. Turn off central heating or air conditioning fans to reduce mixing VOC emissions throughout the house. If you can move the item being painted, take the work outside or at least do it in a wide-open garage. Protect other family members, particularly the young and those who are chemically sensitive, by applying the finish when they are away, preferably for a day or two. Air in a house mixes very rapidly, so simple spatial separation of occupants, even with forced ventilation of the work area, may not provide much protection. And paint the new baby’s nursery well before the baby arrives. You can find other suggestions on the U.S. EPA website.

Once the paint’s on the wall, there’s not much that can be done except to ensure the house is adequately ventilated. When applying conventional latex paint in a simulated room, we attempted to reduce the long-term VOC emissions by applying substantial ventilation for three days after application and by heating the room with excess ventilation for three days. Neither of these somewhat extreme techniques had a quantitative mitigating effect on the longer-term VOC emissions compared to the base case of normal house ventilation.

What can people do to support the availability of better information?
Manufacturers respond to marketplace demand, so when consumers purchase products that have demonstrably lower VOC emissions or chemical toxicity, it supports the development of such products. It also supports more disclosure of the chemical contents of products. Also, if enough consumers start asking their suppliers for environmental test data on products they buy, that could have an impact up the chain, and manufacturers might start paying more attention to the issue.

Do you have any parting thoughts you want to share?
Yes: I’m a big proponent of VOC source reduction in the construction, renovation, and redecorating of homes. We spend a large fraction of our time in our homes, and house ventilation rates, particularly in new construction, tend to be very low, perhaps too low. These factors can lead to substantial chemical exposures. The best way to reduce that is to not introduce the chemical sources in the first place or to physically isolate them. It’s true that some sources can’t easily be avoided, but fortunately there are low-impact products to choose from and techniques that can be used to essentially encapsulate VOC sources (a potential topic for another day!).