Selecting the Wrong Drywall Could Introduce Mercury into the Environment

HBN | July 2020 | Newsletter

In Summary:
Make a big impact without paying more or sacrificing performance by ensuring your specification provides an incentive for drywall with:

  1. The lowest amount of pre-consumer recycled content you can find; prefer natural gypsum over synthetic gypsum.
  2. A preference for post-consumer recycled content.

To promote a more circular, sustainable process, encourage your contractor to separate drywall scrap for recycling. Watch this short video on recycling drywall.

This is Why:
While one drywall board may look very much like another, some are made with naturally occurring gypsum, while others are made from coal-fired power plant waste and can introduce mercury into the environment during manufacturing. 

All drywall, also known as gypsum board or wallboard, is comprised of a mineral core of gypsum with a small percentage of additives and a facing material. In boards intended for interior use the facing is most commonly paper. 

The Healthy Building Network’s guidance on healthier drywall focuses on the core of the boards: the gypsum itself. 

The nature of drywall gypsum varies widely between companies, regions of the country, and individual plants where the boards are made. This is because gypsum is sourced through several avenues:

  • Natural gypsum is mined or quarried from the earth and ground into a powder. 
  • Synthetic gypsum is created from environmental control systems installed in the smokestacks of coal-fired power plants. These systems capture particles from coal burning as they travel through the smokestack or flue. This becomes synthetic or flue-gas desulfurization (FGD) gypsum, which is considered pre-consumer recycled content.  
  • Drywall cut-offs and other scrap from new construction are sometimes collected and recycled into new gypsum boards. This scrap can be made from mined, synthetic, or a mixture of both types of gypsum. A small amount of drywall collected from demolition sites may also be used. This is known as post-consumer recycled content.

In areas of North America with gypsum deposits in the ground, boards tend to be made entirely of, or in large part with, mined gypsum. However, in areas of the country where there are many coal-fired power plants, drywall manufacturers have increasingly shifted from natural, mined to synthetic gypsum.1

While it may seem counterintuitive to caution against recycled content in a high volume building material, it is important to keep in mind that not all material that is considered “recycled content” is created equal. Some recycled materials can contain legacy hazardous content from their prior use, and some, like FGD are industrial waste materials from other processes.

FGD materials begin as coal, and coal contains small amounts of mercury that can be emitted into the air when coal is burned. To address this problem the U.S. EPA established Mercury and Air Toxics Standards (MATS) for coal-fired power plants in 2011.2 To meet emission standards, coal power plant engineers are required to install pollution control devices that scrub emissions and capture pollutants, including mercury. Once the FGD residue is taken from the coal plant to the drywall manufacturing plant, it is mixed with water and other ingredients to make up the core of a drywall board and heated in an oven to drive off the water and bake the ingredients into a homogenous board. During this heating process, some of the mercury pollution that was captured in the flue of the power plant is released from the smokestacks of drywall factories.3 Mercury is a potent developmental and neurotoxic metal that persists in the environment, accumulates in the food chain and human bodies, and is highly toxic. 

Both FGD and natural gypsum contain and can release mercury during manufacturing.4 The amount released varies widely depending on a number of factors.5 Nevertheless, the highest levels of mercury emissions, by far, are reported for facilities producing drywall with high percentages of FGD gypsum.6 Between 2009 and 2018, drywall manufacturing plants in the USA released over three tons of mercury into the air, and the amount of mercury emitted from all of these facilities combined continues to climb every year as more and more FGD is used (see the graphs below comparing mercury emissions from drywall production and the amount of FGD used in drywall over time).7 Because mercury is persistent in the environment and bioaccumulative (it magnifies in the food chain), it doesn’t disappear, but instead becomes a global pollutant impacting people and the environment all over the world.

Natural gypsum is not without its environmental impacts. In addition to the lower levels of mercury emissions mentioned above, it is extracted through open-top surface mines powered by drills and explosives. Studies focused on greenhouse gas emissions, water use, and energy use conclude that drywall generated with natural gypsum has higher environmental impacts than FGD gypsum.8 This, however, does not include consideration of the impacts associated with burning coal to generate FGD gypsum and the studies do not indicate that they considered mercury emissions. 

Situations like this are complex, where one must weigh the impacts of virgin materials against existing materials that bring with them significant human health impacts (such as industrial waste with heavy metal contamination). HBN’s guidance prioritizes hazard avoidance, and in this case, choosing a product that reduces the environmental release of mercury, a volatile, persistent, bioaccumulative and toxic compound, is a priority. Further, we encourage practices that reduce the use of virgin materials, such as using lightweight drywall and participating in drywall scrap recycling programs. 

When selecting drywall for your next project, Healthy Building Network recommends that you:

1. Choose drywall with the lowest amount of pre-consumer recycled content you can find.  

In other words, prefer natural gypsum and avoid FGD or synthetic gypsum.  

Do this by reviewing Technical Data Sheets, LEED sheets, recycled content certifications, or other product literature. These sources will often provide a breakdown of the pre-consumer and post-consumer recycled content used in boards made at each of the company’s facilities. Because FGD gypsum is classified as pre-consumer recycled content, look for products with lower levels of this type of recycled content to avoid products made with FGD gypsum.

Below is an excerpt from one manufacturer’s product literature that lists the recycled content composition of its boards. You can see that the boards made in plants marked by red arrows contain high amounts of pre-consumer recycled content (FGD). The boards made in plants marked with green arrows do not and are therefore made primarily with mined gypsum.

Source: Excerpted from Certainteed Gypsum Sustainable Materials Data Sheet, Jan 30, 2016. Available: http://www.certainteed.com/resources/CTG_ProRoc_Board-LEED.pdf. (Arrows added by Healthy Building Network, 2016.) Check current product literature for the most up to date information on recycled content for specific products.


2. Look for drywall with post-consumer recycled content when you can. 
 
Currently, most post-consumer recycled content in drywall refers to the paper used in the facings. This can account for approximately 3-8% of the product weight.9 Construction trim scrap is also increasingly used as post-consumer recycled content thanks to programs in the Pacific Northwest and Europe that include up to 20% post-consumer gypsum in new board manufacture. This product innovation is expanding through partnerships, such as the Building Product Ecosystems’ collaboration. Through the Closed Loop Wallboard Collaborative, manufacturers, drywall processors, and construction crews are working together to collect drywall scrap from worksites and reprocess it into new drywall. Be on the lookout for the  availability of such drywall and consider how your projects can separate wallboard waste to help in this collaborative, recycling effort. 

In summary, when it comes to wallboard there isn’t currently an ideal solution. This opens a real opportunity to innovate new types of wallboard with fewer environmental and human health impacts, and better recyclability and circularity. In the meantime, until we have better products, if you have FGD drywall facilities in your area, encourage environmental regulations that require pollution control and use our advice for selecting safer drywall. 

This blog was originally posted on September 9, 2016. It has been updated with additional data and citations, including data from the U.S. Geological Survey (USGS) and American Coal Ash Association (ACAA) and additional TRI data.
 

Footnotes

[1] Based on annual survey results between 2000 and 2018 from the American Coal Ash Association and on gypsum statistics released by USGS. See: ACAA. “Coal Combustion Products Production & Use Statistics.” Accessed June 25, 2020. https://www.acaa-usa.org/publications/productionusereports.aspx. and USGS. “Gypsum Statistics and Information.” Accessed June 11, 2020. https://www.usgs.gov/centers/nmic/gypsum-statistics-and-information. During that timeframe there has been a statistically significant increase in the use of FGD gypsum in drywall in the U.S. relative to the amount of drywall sold. See the chart above for further details on annual use of FGD gypsum in drywall.

[2] US EPA, OAR. “Cleaner Power Plants.” Overviews and Factsheets. US EPA, November 9, 2015. https://www.epa.gov/mats/cleaner-power-plants. Accessed July 1, 2020.

[3] Sanderson, Jessica. “Fate of Mercury in Synthetic Gypsum Used for Wallboard Production.” USG Corporation, December 31, 2007. https://doi.org/10.2172/943310. FGD waste from coal-fired power plants that is not used in products such as drywall ends up in landfills and surface impoundments. Without proper protections, this can also result in the release of heavy metals into the environment. See: “Frequent Questions about the 2015 Coal Ash Disposal Rule.” Other Policies and Guidance. United States Environmental Protection Agency. Accessed June 25, 2020. https://www.epa.gov/coalash/frequent-questions-about-2015-coal-ash-disposal-rule. Specifiers and purchasers should consider the range of options available and whether they want to support the coal power industry. Manufacturers using FGD gypsum should strive to understand and reduce their mercury releases to the environment, as well as gain better understanding of any potential impacts during use. This information should be transparently provided to customers to allow them to consider all the environmental impacts of their purchasing decisions.

[4] Test data on mercury content compiled by the EPA indicates that natural gypsum contained <0.004 (not detected) to 0.26 ppm mercury while FGD gypsum contained between 0.007 and 3.1 ppm mercury - the maximum concentration in FGD gypsum being over ten times the maximum in natural gypsum. Note that this is a limited data set. Additional testing would be needed to more fully understand the variations. See: “Coal Combustion Residual Beneficial Use Evaluation: Fly Ash Concrete and FGD Gypsum Wallboard.” United States Environmental Protection Agency: Office of Solid Waste and Emergency Response and Office of Resource Conservation and Recovery, February 2014. https://www.epa.gov/coalash/coal-combustion-residual-beneficial-use-evaluation-fly-ash-concrete-and-fgd-gypsum-wallboard.

[5] The amount of mercury released into the environment can vary based on a variety of factors related to the sourced FGD gypsum and the drywall manufacturing facility. For instance, one study looked at how several variables affected mercury concentrations in FGD gypsum used for wallboard. These included the type of coal used, whether or not the coal plant was equipped with a selective catalytic reduction system for nitrogen oxide emissions control, purge rates of chlorides and fine solid particles from wet FGD systems, and the addition of trimercapto-s-triazine, tri-sodium salt to precipitate dissolved mercury in wet FGD systems. See Sanderson, Jessica. “Fate of Mercury in Synthetic Gypsum Used for Wallboard Production.” USG Corporation, December 31, 2007. https://doi.org/10.2172/943310.

[6] Based on HBN’s comparison of manufacturer declarations of pre-consumer recycled content for specific facilities to U.S. EPA Toxics Release Inventory data for mercury and mercury compounds for those same facilities. “High percentages of FGD gypsum” refers to products containing ≥90% pre-consumer recycled content.Reported mercury emissions were not strongly correlated with relative production volume, meaning that the increase in mercury emissions over time cannot simply be attributed to more drywall being manufactured. There is a correlation in the increase in mercury emissions and the increased use of FGD gypsum. Production volumes were estimated based on data from 2013 reported in “Gypsum Wallboard in the USA,” September 9, 2013. https://www.globalgypsum.com/magazine/articles/679-gypsum-wallboard-in-the-usa.

[7] HBN analysis based on data reported in the U.S. EPA’s Toxics Release Inventory (TRI). Point source and fugitive air emissions of mercury and mercury compounds reported to the agency from any US drywall manufacturing locations in the years 2000 - 2018 were included in the analysis. The annual consumption of FGD gypsum used in wallboard increased from 3 million tons in 2000 to 12 million tons in 2018. Based on annual survey results from the American Coal Ash Association: ACAA. “Coal Combustion Products Production & Use Statistics.” Accessed June 25, 2020. https://www.acaa-usa.org/publications/productionusereports.aspx.

[8] Lee, Jin Cheol, Sabrina L. Bradshaw, Tuncer B. Edil, and Craig H. Benson. “Quantifying the Benefits of Using Flue Gas Desulfurization Gypsum in Sustainable Wallboard Production.” Coal Combustion and Gasification Products 4, no. 1 (January 1, 2012): 17–20. https://ccgp.scholasticahq.com/article/12384-quantifying-the-benefits-of-using-flue-gas-desulfurization-gypsum-in-sustainable-wallboard-production.; Peng, Zhen Guo, Li Li Ma, and Xian Zheng Gong. “Comparison of Life Cycle Environmental Impacts between Natural Gypsum Board and FGD Gypsum Board.” Key Engineering Materials. Trans Tech Publications Ltd, 2014. https://doi.org/10.4028/www.scientific.net/KEM.599.15.

[9] Based on research for HBN’s Common Product profiles for drywall and the sources referenced there: Drywall (FGD), Type X Drywall, and Mold and Moisture Resistant Drywall.