New Concern About Pesticides in Exterior Paints

Although exterior paints have moved beyond lead and the most toxic solvents, new coatings contain biocides that may pose a different set of concerns.

Biocides play an important role in a paint's durability by protecting it from mildew, but biocides cannot make up for poor application practices.Photo: Bob Cusumano, Coatings Consultants, Inc.

Most of us are familiar with the volatile solvents found in alkyd, or “oil-based” paints. These are typically hazardous airborne pollutants with large volumes of smog-causing VOCs. Coatings containing these solvents are regulated in many areas of the country, such as the South Coast Air Quality Management District (SCAQMD).

Biocides in coatings, however, have largely flown under the regulatory radar in the U.S. In the June issue of Environmental Building News, we take a look at the environmental tradeoffs of exterior coatings (member link).

Biocides: necessary or nefarious?

Biocides are used to protect latex paints from bacteria while in the can, acting as a preservative, and to protect a paint’s film from mildew and algae.

These biocides are necessary, but unfortunately paint breaks down, so over time they can wash off into the environment, where their impact is uncertain. There are many different types of biocides used in paint, including organic compounds such as IPBC (Iodopropynyl Butylcarbamate), OIT (octylisothiazolinone), terbutryn, diuron, isoproturon, and many others.

Some are persistent in the environment, are hazardous to organisms—particularly those at the base of the ecosystem—or may cause these organisms to develop biocide resistance.

Regulations ramping up

The U.S. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) requires biocides be registered as pesticides with the Environmental Protection Agency (EPA), but the biocides in paint are exempt from FIFRA regulation unless the manufacturer makes claims that they improve human health.

Europe is taking a closer look at biocide safety as it relates to people and the environment, however. Its Biocidal Product Directive, which has a specific product group dedicated to biocides found in paint, has effectively banned once-common biocides such as carbendazim from the market.

The industry has responded with less-persistent products and delivery systems that minimize the amount required.

Reining in the chemical Wild West

There could be good reason to keep a closer eye on biocides in paint. Recent research from the École Polytechnique Fédérale de Lausanne in Switzerland estimates that coatings on façades in Lausanne release about 30% of their biocides into the environment annually (potentially hundreds of pounds of biocides), most within the first couple of years.

The corresponding author, Sylvain Coutu, pointed out in an email to me that the amounts are very site-specific, and “we estimate that only 0.035% of biocides that leach from façades actually reach surface waters (rivers, lakes), the rest being absorbed in soils and/or degraded during transport.”

Though the amount that reaches the watershed is small, it does not take much to affect the environment, especially considering that biocides can be found in nearly every exterior paint. (Don’t look for biocides on the material safety data sheet; manufacturers don’t have to list ingredients unless they make up 1% or more of the product, or 0.1% for carcinogens.)

Tradeoffs

The main job of exterior coatings is to protect the building, and the best way to do that is with a durable paint job.

Most paint ingredients today are a vast improvement over the lead stabilizers and volatile solvents of the past, but they may still contain some unsavory ingredients, so making them last—by using biocides, for example—may be the best way to minimize their overall environmental footprint.

This month’s feature explores some of the issues that affect paint durability and even provides a couple of environmentally responsible coating options that don’t need any VOCs or biocides. You can also find these high-performance coating options as well as stains in GreenSpec.