Common Tradeoffs in Choosing a Carpet: Many Shades of Recycled

Sarah Gilberg - April 27, 2011

Our carpet category is ever-evolving as we continue to engage manufacturers in submitting and reviewing data on their products.  On the surface, many of the carpet styles you'll find in Pharos may look similar in their environmental and health impacts, but some key differences can be found in their components.

For carpet backings in particular, manufacturers use a range of materials to increase their recycled content, including coal fly ash, glass cullet, polyvinyl butyral, and vinyl.  Of particular concern is the use of coal fly ash as a replacement for traditional limestone filler.

Over the past decade, LEED recycled material credits and government agencies have encouraged the incorporation of coal fly ash into carpet backings and other building materials.  Coal-fired power plant owners and fly ash marketing corporations (namely Boral Materials) capitalized upon these endorsements by moving wastes into the built environment. A Boral website states that "Coal combustion products are endorsed by the U.S. EPA and the US Green Building Council for use in construction materials."

As coal-fired power plant air pollution control (APC) technology improves, more of these heavy metals are "scrubbed" from gas releases and concentrated in coal fly ash and other coal combustion wastes.  The health effects of this material on the workers who process it -- and on the indoor environment -- are largely untested.  Therefore, in Pharos, carpet backings containing generic coal fly ash will tend to score better in the Renewable/Recycled Materials category, but worse in their User Toxics and Manufacturer Toxics scores.

The toxicological composition of fly ash is changing due to the introduction of powdered activated carbon to capture of mercury from flue gas.  Boral itself says in one presentation, "Deteriorating fly ash quality represents both a major challenge and a huge opportunity."[1]

"Changes in Air Pollution Control technologies will result in a greater amount of residue generated for each unit of electricity produced and an overall increase in the total content of mercury and other hazardous air pollutants in fly ash, FGD residues, and other APC residues," EPA researchers reported in a recent journal article.[2]

The EPA studied 34 fly ash samples and 20 samples of Flue Gas Desulfurization gypsum.[3]  Their test results indicated that some fly ash samples exceeded Toxicity Characteristic values for arsenic, barium, chromium, and selenium. Fly ash test results also exceeded Maximum Concentration Levels or Drinking Water Equivalent Levels[4] for nine metals: antimony, arsenic, barium, boron, cadmium, chromium, molybdenum, selenium, and thallium.

Coming soon, we'll take a closer look at some high recycled content carpet backings for which manufacturers have opted to use materials other than coal fly ash. These companies are participating in Pharos and are fully disclosing their carpet ingredients. For more information on carpets and carpet components, explore the Pharos Building Product Library, and see our carpet category description for more detailed analysis from our research team.


[1] "USA Analyst Site Visit 2008," Boral, available at:

[2] S. Thorneloe, D. Kosson, F. Sanchez, A. Garrabrants, and G. Helms,  "Evaluating the Fate of Metals in Air Pollution Control Residues from Coal-Fired Power Plants," Environ. Sci. Technol. 2010, 44, 7351-7356.

[3] This article focuses on carpet backings and the toxicological profile of fly ash that may be used in them, so the FGD gypsum results are not recited here. However, FGD gypsum is used in other indoor building materials -- particularly wallboard and ceiling tiles.  The results of the EPA sampling of FGD gypsum reinforces concerns about the composition of wallboard and ceiling tiles that are comprised of up to 95% FGD gypsum: the EPA study found that many samples exceeded TC values for selenium and MCL or DWEL for eight metals: antimony, arsenic, barium, cadmium, chromium, molybdenum, selenium, and thallium.

[4] Toxicity Concentration levels are used in crafting hazardous waste determinations.  DWEL is used for noncarcinogenic toxicity end points.

Sarah Gilberg is a Developer for the Healthy Building Network.