Part II: Formaldehyde Exposure Modeling Science Series
This posting is the second of a three-part series on formaldehyde emissions from hardwood plywood (HWPW), medium-density fiberboard (MDF), and particleboard (PB), collectively called composite wood products. This series focuses on the benefits of applying computer modeling tools to the interpretation of formaldehyde emission data, and subsequent risk management decisions.
Part 2: Five Facts about Formaldehyde and Composite Wood Products
Formaldehyde is a component of one of the types of glue used to manufacture composite wood products. Formaldehyde emissions have recently been in the spotlight because U.S. EPA posted a pre-publication version of the Emission Standards for Composite Wood Products final rule on July 27, 2016, as Title VI of the Toxic Substance and Control Act (TSCA). The U.S. EPA has associated sufficiently high airborne concentrations of formaldehyde with eye, nose, and throat irritation, and possibly some types of cancer with sufficient exposure. These Standards will have a broad impact on manufacturers, distributors, importers, and sellers because a wide range of building structures and furniture contain composite wood products.
#1: Wood products made with "no-added formaldehyde" glues still emit naturally occurring formaldehyde
Formaldehyde is a simple, single carbon volatile chemical that comes from many sources including fossil fuel combustion, animal and plant metabolism, as well as consumer product use or off-gassing. Notably, measurable formaldehyde emissions occur from wood-based products manufactured with "formaldehyde-free" glues because formaldehyde is a natural component of wood. For example, a recent emission study of particleboard glued with a no-added formaldehyde resin and a traditional urea-formaldehyde resin estimated standardized emission test chamber air concentrations of 0.023 and 0.063 parts per million (ppm) after 7 days of conditioning, respectively. Thus, even if the use of formaldehyde-based glues was eliminated, indoor air concentrations where wood-based construction materials are used will likely exceed outdoor concentrations.
#2: Indoor formaldehyde concentrations are unlikely to decrease appreciably after the U.S. EPA emission standard is implemented
The U.S. EPA emission standard is likely to reinforce the current best manufacturing practice rather than cause a dramatic shift in exposures to formaldehyde. This observation reflects three decades of significant innovation and improvements in resin technology, the natural occurrence of formaldehyde in wood, and the adoption of the California formaldehyde emission standard by many manufactures prior to the finalization of the EPA standard. In 2012, U.S. EPA drafted a report titled "Formaldehyde from Composite Wood Products: Exposure Assessment" that described the results of various modeling scenarios developed in preparation for the emission standard. The results indicated that reductions in indoor formaldehyde concentrations as a result of the emission standard will decrease by a modest amount for most exposure scenarios. For example, the model indicated that initial formaldehyde concentration would decrease by about 9% in a new single-family detached home, 13% in a manufactured home, and 26% in a camper trailer for emissions assumptions similar to the final standard.
#3: The whole is less than the sum of parts
A common misconception is that wood-based sources of formaldehyde to indoor air are additive. The CDC recently published a simplified modeling analysis to assist in the interpretation of laminate flooring emission test results. The CDC model assumes that the addition of a laminate floor source to an indoor space would add to the existing levels by the full amount measured in a test chamber under controlled conditions. Under real-world conditions, formaldehyde sources and room surfaces exhibit a complex set of interactions that reduce the likely impact of a single product on indoor air quality. One important process is the capture and retention of formaldehyde by porous materials such as drywall and furnishings that can reduce peak airborne concentrations. Another important mechanism that limits formaldehyde emissions is the decrease in emissions that occurs when airborne molecules of formaldehyde in a room "push back" on a potential source, sometimes called a "back-pressure" effect. The U.S. EPA exposure assessment report qualitatively discussed the effect of porous materials, and the model quantitatively addressed "backpressure."
#4: Emissions from consumer products diminish over time
Another common misconception is that formaldehyde emissions from wood products remain elevated for a long period of time. This misunderstanding is due in part to voluntary and regulatory emissions testing, which has emphasized the emission potential of newly manufactured products. Under real-world conditions, emissions from composite wood products gradually decay over time as the product ages. For example, the U.S. EPA exposure model performed during the development of the emission standard assumed that formaldehyde concentrations would decrease to "near-zero" concentrations in 10 years or less. Not surprisingly, lower formaldehyde levels are typically found in older as compared to newly constructed residential structures.
#5: Temperature, humidity, and fresh air turnover impact air concentration
Increases in ambient environmental factors including temperature and humidity increase formaldehyde emissions. A recent emission study evaluating particleboard resin emissions in an "extreme" environment of 85 F and 75% relative humidity as compared to a typical environment of 77 F and 50% relative humidity found that emissions could be up to 2 to 3-fold higher in the extreme environment. Emissions diminished with time as expected in both environments, and the effects the extreme environment had on emission rates were reversible when typical conditions were restored. The impact of increases in emissions rates with elevated temperature and humidity can be mitigated by steps taken to increase fresh air turnovers, such as opening windows or introducing fresh air through mechanical heating and cooling systems. The U.S. EPA considered temperature, humidity, and fresh air turnover during the development of the emission standard.
The above factors represent important considerations when prospectively and retrospectively estimating formaldehyde exposure from composite wood products subject to the new U.S. EPA emission standard. The final installment of this series will explain the benefits of exposure modeling to manufacturers, distributors, importers, and sellers of composite wood products.
How Cardno ChemRisk Can Assist with Questions about Formaldehyde
As a state-of-the-art scientific consulting firm, Cardno ChemRisk is well respected for its leadership in human health risk assessment – including computational modeling and statistical services. Cardno ChemRisk has extensive experience using computational modeling to understand past and future exposures in both occupational and environmental settings, especially in situations where collecting measurements is either impossible or impractical. In addition, Cardno ChemRisk applies a variety of statistical methods to understand the important relationships hidden within an environmental or occupational data set. If you are interested in discussing our recommendations for consumer product formaldehyde exposure modeling in more detail, please contact the Ken Unice, Science Advisor, and Computational Science Service Area Lead at Cardno ChemRisk.