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Subscribe to this list via RSS Blog posts tagged in modeling

Posted by on in Centers of Excellence

Posted on behalf of Angie Perez

As of August 15, 2017, 29 states and Washington, D.C. have passed laws that legalize medical marijuana, and recreational marijuana is legal in eight states and Washington, D.C. These policy changes present new challenges for state regulators with respect to potentially increased impaired driving associated with marijuana use. A major hurdle in enforcing driving impairment laws is the lack of a standardized, non-invasive test that can determine a driver’s level of intoxication and impairment. Several calls for research have been put forth by various states (e.g., California and Colorado), as well as federal agencies (including the National Institute on Drug Abuse and the National Highway Traffic Safety Administration) in order to assist in determining impairment levels from marijuana use. Two companies, Hound Labs and Cannabix Technologies, are racing to develop and market instruments for detecting THC in breath (breathalyzer). While both companies have demonstrated that their devices are capable of detecting THC in breath, many challenges still exist in terms of correlating the concentration measured in breath with a driver’s impairment level.

A recent article by Lovestead and Bruno (2017) presented a three-pronged research approach for developing the “best” breathalyzer. According to the authors, these three prongs include: 1) providing fundamental data and models for the developing a breathalyzer; 2) studying the material properties in order to identify the best materials to “catch” and “release” THC; and 3) researching the chemical signature of breath that corresponds with intoxication (Lovestead and Bruno 2017). The authors found that THC and CB vapor pressures were two orders of magnitude lower than n-eicosane, a similar molecular weight compound with low vapor pressure, indicating that using surrogate data in models would have led to erroneous results. Ultimately, this finding illustrates the importance of having accurate fundamental data for developing and validating models. In light of this paper’s findings, then, although marijuana breathalyzers are near completion, ultimately identifying and establishing an impairment level will still require much work.

Cardno ChemRisk is evaluating methods based on existing published studies to model and correlate marijuana biomarker concentrations in blood with known metrics for behavioral and physiomotor impairment. Such pharmacodynamics-pharmacokinetic modeling and a better understanding of thresholds for physiomotor impairment will provide state regulators and law enforcement the necessary tools for adequately establishing and enforcing threshold impairment laws. If you would like to learn more about either these research areas, or our expertise in drug and alcohol pharmacokinetics and forensic toxicology, please contact Dr. Angie Perez or Dr. Ernest Fung.

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Posted by on in Centers of Excellence
This posting is the final installment 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 3: Five Reasons Why Computer Modeling is an Essential Tool for Manufacturers, Importers and Distributors of Composite Wood Products

This posting is last of a three-part series on formaldehyde emissions from hardwood plywood (HWPW), medium-density fiberboard (MDF) and particleboard (PB), collectively called composite wood products. Starting in the summer of 2017, manufacturers, distributors and importers of composite wood products will be subject to the new Emission Standards for Composite Wood Products posted as a pre-publication final rule on July 27, 2016 as Title VI of the Toxic Substance and Control Act (TSCA). The emission standards will mandate that wood products within the scope of the rule comply with emission test requirements conducted under prescribed conditions. The emission standard is consistent with and modeled after a similar existing regulation previously promulgated by California Air Resources Board (CARB) as an Airborne Toxic Control Measure (ATCM).

There are five important reasons why companies in the composite wood product supply chain should consider exposure modeling as part of their regulatory compliance and due diligence strategy. 

#1: Understand the contribution of emissions from your product to overall air quality

Computational models can help manufacturers, distributors and retailers assess the specific contribution of their product to indoor air quality in the environment for which the product is intended, which is likely less than what would be predicted by the controlled emissions tests that will be required by U.S. EPA. Under real-world conditions, formaldehyde emissions from consumer products are affected by aging of the material, interactions between materials, and attenuation of airborne concentration through loss of formaldehyde to adsorptive surfaces. Exposure models are an invaluable tool that can be used to understand how the introduction of a new product into a residence or workplace will affect air quality.

#2: Evaluate the effect of environmental factors on your product   

Environmental factors such as temperature, humidity, and fresh air turnover can alter how emissions from composite wood products affect indoor air quality. Exposure modeling can be very useful for understanding how a specific product may respond to changes in the environment.  For example, modeling can be used to predict the impact of a range of plausible and worst case scenario conditions. This knowledge can be very useful for responding to customer complaints, or in the preparation of product quality assessments.

#3: Assess emissions over the lifetime of a product

The controlled emissions tests used to comply with voluntary or regulatory standards do not consider the decrease in formaldehyde emissions that occur as the product ages with time. Exposure models provide useful information on the contribution of a product to indoor air formaldehyde concentrations over the lifetime of the product, not just when it is newly installed. This information can be very useful for understanding the length of time a product is likely to affect indoor air concentrations, or in the assessment of lifetime exposure.

#4: Interpret air concentration measurements that may have been collected by others    

Indoor air measurements can be commissioned by building owners or consumers to support a complaint or product defect claim. Alternatively, products may be removed by the owner and submitted for analysis in a laboratory. Room measurements or product samples collected by building owners are difficult to interpret because formaldehyde is used as a resin or preservative in a wide variety of consumer products, occurs naturally in wood, and is a component of ambient outdoor air. A single air sample collected in a room captures all sources formaldehyde, and is not specific to a product of concern.

It is noteworthy that low emitting formaldehyde sources can capture formaldehyde from other sources, and subsequently reemit formaldehyde that was not present in the original product.  Both indoor air measurements and tests of used products are impacted by these other sources. Exposure modeling can be a useful tool for understanding how a specific product may have contributed to a measured indoor air concentration. Similarly, modeling can be used to understand whether a sample of a used product may have been impacted by environmental formaldehyde.

#5: Develop an action plan to address non-compliant products

The existing CARB and newly finalized U.S. EPA emissions standards have many steps in place to prevent non-compliant products from entering the chain of commerce. The possibility exists, however, that a non-compliant product will be sold to consumers and subject to a customer complaint or regulatory compliance action. In these cases, exposure modeling is a very valuable tool for assessing whether a non-compliant product will have a meaningful impact on air quality. Additionally, a model can be used to evaluate the duration of time the product would remain non-compliant before aging processes sufficiently reduce the airborne concentration. These factors may impact risk mitigation plans in the event a product is determined to be non-compliant in one of the various stages of the supply chain.  

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  This e-mail address is being protected from spambots. You need JavaScript enabled to view it , the Science Advisor and Computational Science Service Area Lead at Cardno ChemRisk.
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Posted by on in Health & Environmental Risk Assessment
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, measureable 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 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 adoption of the California formaldehyde emission standard by many manufactures prior to 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 to 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 "back pressure."

#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 rate 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 turnover, 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 This e-mail address is being protected from spambots. You need JavaScript enabled to view it , Science Advisor and Computational Science Service Area Lead at Cardno ChemRisk.
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Posted by on in Exposure Assessment and Dose Reconstruction
This posting is the first 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 will focus on the benefits of applying computer modeling tools to the interpretation of formaldehyde emission data, and subsequent risk management decisions. Part 1 of this series provides an overview of the new U.S. EPA formaldehyde emissions standards, and explains how computational exposure modeling was used in the agency cost-benefit analysis. The remaining parts of this series will explain the factors that affect formaldehyde emissions from composite wood products, and our recommendations for how computational modeling can be used to help stakeholders interpret emission testing results.

Part 1: U.S. EPA Formaldehyde Emission Standard Highlights the Importance of Exposure Modeling in Rule Implementation

The pre-publication version of U.S. EPA's Emission Standards for Composite Wood Products final rule was posted July 27, 2016 as Title VI of the Toxic Substance and Control Act (TSCA), with most provisions expected to become effective in the summer of 2017. U.S. EPA's rule focuses on reducing exposures to formaldehyde, and avoidance of adverse health effects. Although rarely a focus of most media reports, U.S. EPA frequently relies on complex modeling and cost-benefit analysis to support a conclusion that total quantified benefits outweigh costs. U.S. EPA's formaldehyde rulemaking relied on the use of modeled estimates of formaldehyde exposure to calculate hypothetical benefits quantified by willingness to pay to avoid eye irritation, and number of cases of nasopharyngeal cancer.

The U.S. EPA Emission Standards for Composite Wood Products applies to all types of HWPW, MDF, PB and finished products that are sold, supplied or manufactured in the United States. The requirements of the Standard are consistent and coordinated with the similar California Air Resources Board (CARB) Airborne Toxic Control Measure (ATCM). The key points of the rule include:

• Producers of composite wood products within the scope of the rule will be required to comply with specific emission standards;

• Products manufactured with ultra-low formaldehyde or no-added formaldehyde (NAF) resins will be exempt with proper recordkeeping practices; and

• Regulated products must comply with emission standards, as determined by a third-party certifier, in order for a product to be labeled as TSCA Title VI compliant.

While most provisions will become effective within one year of rule publication, laminated products fabricated with a wood or woody-grass veneer attached to MDF or PB will be subject to the same certification and testing requirements as hardwood plywood seven years after rule publication.

The exposure model used by the U.S. EPA is called the Formaldehyde Indoor Air Model – Pressed Wood Products (FIAM-pwp). The model has been peer reviewed, and is publically available. The model uses emissions test data similar to the data that will be required under the U.S. EPA emissions standard. It estimates the concentration of formaldehyde released from one or more composite wood products, and the subsequent human inhalation exposure. The model considers important determinants of exposure like indoor temperature, age of source materials, and the amount of time spent indoors. As is true with any model, there are some limitations in the modeling approach used by U.S. EPA. One important thing to know about formaldehyde is that porous materials such as drywall and furnishings can absorb and retain formaldehyde. U.S. EPA's model does not account for this phenomenon, so it is possible that in some environments, short-term peak formaldehyde exposure could be lower than predicted.

EPA used FIAM-pwp to evaluate scenarios of airborne formaldehyde concentrations in homes, daycares, schools, workplace, vehicles, and the outdoors for various types of structure types in different climatic zone. In total, U.S. EPA evaluated several thousand exposure scenarios during the preparation of the standard. In the final standard, U.S. EPA focused on a comparison of a standard consistent with the CARB ATCM to several alternative emission standards for laminate flooring. Taking into account the cost-benefit analysis, the agency elected to include laminate flooring in the definition of hardwood plywood, with exemptions for certain types of resins. The FIAM-pwp model, and other computational modeling techniques, can be used to prospectively and retrospectively estimate formaldehyde emissions from composite wood products subject to the new U.S. EPA emission standard. These topics, and more, will be discussed in more detail in future blogs in this series.

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.
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