CTEH is now Onterris

CTEH was purchased by Montrose Environmental Group in 2020, and as of April 2026, has rebranded as Onterris. While the name has changed, the organization’s team, expertise and service remain the same.

Yes. CTEH is now Onterris. The company continues to provide toxicology consulting, environmental health services, and emergency response support under the new name.

CTEH stood for the Center for Toxicology and Environmental Health. The organization now operates as Onterris.

No. The same team, leadership, and scientific expertise remain in place. Embedded within the greater company, your trusted experts now bring their knowledge and ER-mindset to the full organization! Clients continue to receive the same high-quality services, now delivered under the Onterris name.

Onterris provides rapid and scalable environmental and public health response during incidents involving chemical releases, industrial accidents, and environmental contamination. This includes air monitoring, exposure assessment, toxicology analysis, and real-time data interpretation to support decision-making.

Onterris draws upon state-of-the-science resources to develop action levels in air sampling and analysis plans. Where government agencies supply action levels, we consider those levels in the analysis. For example, the EPA establishes Acute Exposure Guideline Levels (AEGLs) that may be used to protect communities in the event of emergency chemical releases. Similarly, OSHA and the American Conference of Governmental Industrial Hygienists (ACGIH) establish values to protect workers over their working lifetime. Those values may be used as the basis for action levels across work areas.

Updating Federal exposure standards requires extremely long cycles. For example, OSHA Permissible Exposure Limits (PELs) require Congress to pass legislation to update values. As such, Onterris supplements Federal levels with state and third-party agency action levels in development of our plans. Our toxicologists also frequently review exposure studies published in scientific, peer-reviewed journals and resources like ACGIH and the American Industrial Hygiene Association (AIHA) to inform our sampling strategies. Accordingly, our action levels in Onterris-developed sampling and analysis plans are often significantly more conservative than published standards for some chemicals based on some of these trusted sources of information. On site, a response to an action level exceedance may vary from simply moving upwind or crosswind from a source to requiring enhanced respiratory protection to calling a work stoppage for hazard assessment.

Occupational exposure limits and community air exposure limits have differing assumptions of exposure duration, and frequency action levels. As such, action levels across work and community areas cannot be compared against each other. For example, an occupational limit may be based on a daily exposure for eight hours per day for 40 hours per week across a working lifetime. A community level might be based on a short-term exposure like less than an hour just once in a lifetime, or consider continuous exposure at a very low level across a lifetime for other chemicals. In the case of community action levels, sufficiently protective values must be balanced against the inherent risk associated with actions such as evacuation. At the same time, action levels implemented across work areas must account for the potential for daily exposures over a working lifetime.

For many chemicals, there is a difference between the limit of detection for an analytical instrument and the odor threshold, at which some individuals may be able to detect the scent of a chemical. There are often orders of magnitude differences for concentrations at which a chemical odor can be perceived versus when it becomes detectable or may cause health effects.

Odor sensitivities are highly subjective, and odor thresholds vary significantly between individuals based on a variety of factors, including a person’s physical ability (sensitivity) and their observational biases. Factors like genetics, health, whether the person is a smoker, and length of time experiencing an odor all affect the perceived strength of a particular odor. While this is very subjective, sampling and monitoring technologies are objective options for detecting the presence or absence of a chemical of concern. These technologies are carefully assessed to ensure they meet the accuracy, precision, specificity, sensitivity, linearity, and reliability requirement to ensure consistent performance. While some individuals may experience psychosomatic effects from the presence of a strong odor (e.g., headache, nausea, etc.), there is a difference between that temporary, transient experience and the significant health impacts against which exposure guidelines and standards are protective.

CTEH has supported response efforts for major environmental incidents across North America, including climate and weather-related incidents like hurricanes, wildfires and floods as well as large-scale industrial, transportation and chemical environmental emergencies. Our experts have provided consulting at every stage of the environmental lifecycle, from planning and training to field safety and environmental assessment to remediation and helping communities build back better.

Onterris provides clear, science-based communication, real-time monitoring data, and health risk assessments to help communities understand environmental conditions and make informed decisions.

State and federal agencies, including EPA, do not have the capabilities in-house to conduct air monitoring and sampling at the scale required for most incidents, so they hire contractors to help conduct air monitoring and sampling, just as the responsible party does. Onterris works side-by-side with EPA and their contractors to compare data collected in communities. The EPA has consistently approved our data processes and its interpretations regarding human health, having vetted our methods and procedures through numerous events, confirming our adherence to scientifically proven practices and methods.

We apply rigorous quality assurance and quality control (QA/QC) procedures, including calibration protocols, validated analytical methods, and expert review, to deliver accurate and reliable environmental data.

CTEH, now Onterris, provides independent, science-based assessments to support environmental due diligence, regulatory compliance, and risk management. This includes evaluating environmental data, identifying potential liabilities, and supporting informed decision-making.

Q: What was CTEH’s role in the East Palestine, Ohio rail incident?

A: CTEH’s role was to provide scientific expertise in industrial hygiene and environmental science, and to collect and report environmental data as approved and overseen by third parties, including U.S. state and federal regulators. CTEH was retained by Norfolk Southern to conduct outdoor air monitoring and sampling in work and community areas, indoor air monitoring in residents’ homes, and surface water sampling. Although retained by Norfolk Southern, CTEH primarily worked under the direction of the incident’s Unified Command, a joint incident management structure comprised of the U.S. Environmental Protection Agency (U.S. EPA), Ohio EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern.

Q: What are Incident and Unified Command and what were their respective roles in the East Palestine, Ohio rail incident?

A: The Incident Command Structure (ICS) is the standardized framework for managing emergency responses under the National Incident Management System (NIMS) and, for hazardous-substance releases, the National Contingency Plan (NCP). Under ICS, an Incident Commander is responsible for managing the response and directing incident operations.

Unified Command is formed when multiple agencies or jurisdictions share responsibility for an incident. Under Unified Command, the participating agency representatives jointly set response objectives, develop and approve plans, and make decisions while maintaining their respective authorities and responsibilities. Responsible parties may also participate in Unified Command to coordinate response activities.

Following the East Palestine rail incident that occurred on February 3, 2023, the East Palestine Fire Department initially established Incident Command, with the fire chief assuming the role of Incident Commander. Representatives from the U.S. EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern coordinated with Incident Command throughout the initial response. Incident Command directed firefighting operations and coordinated emergency response activities, including public safety measures and evacuations.

On February 21, 2023, the U.S. EPA issued a Unilateral Administrative Order under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), requiring Norfolk Southern to conduct cleanup activities under U.S. EPA oversight. A formal Unified Command was subsequently established, with U.S. EPA’s Region 5 assuming the lead Incident Commander role and directing the removal action.

Unified Command included representatives from the U.S. EPA, Ohio EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern as the responsible party. The Pennsylvania Department of Environmental Protection (Pennsylvania DEP), the Pennsylvania Department of Health and U.S. Health and Human Services Agency for Toxic Substances and Disease Registry (ATSDR) were also cooperating with and providing assistance to Unified Command. The organizational structure for Unified Command as of March 16, 2023 for this incident can be found here.

Unified Command coordinated environmental response and cleanup activities for the incident, including air monitoring, environmental sampling, and remediation. Work plans and subsequent revisions were reviewed by participating agencies within Unified Command and approved by U.S. EPA under its CERCLA authority. In June 2024, Unified Command transitioned to the Multi-Agency Coordination Group (MACG), which continued to direct recovery work.

Q: How was the air monitoring plan for East Palestine developed?

A: CTEH developed monitoring and sampling plans, which were reviewed and approved by state and federal regulators, and CTEH collected and reported data under those plans.

More specifically, CTEH’s Air Sampling and Analysis Plan was first prepared on February 3, 2023, and was shared with and reviewed by the U.S. EPA, Ohio EPA, and Pennsylvania DEP. When the Unified Command was established on February 21, 2023, CTEH further developed the Air Sampling and Analysis Plan with Unified Command oversight. The Unified Command, led by the U.S. EPA, then formally approved the Air Sampling and Analysis Plan in April 2023.

Q: What was included in the air monitoring plan for East Palestine and what data was generated?

A: The Air Sampling and Analysis Plan outlined the strategy and methods for air monitoring and sampling in work and community areas, using a combination of real-time air monitoring instruments such as photoionization detectors (PIDs), chemical-specific colorimetric detector tubes, and analytical air samples sent to accredited laboratories for analysis.

Air monitoring and sampling results were available to the U.S. EPA through direct access to project databases, written data summaries (daily from February to April 2023, twice a week from April to June 2023, and weekly from June 2023 to September 2025), and in summary reports in Unified Command meetings.

Q: Who determined what chemicals would be monitored for following the derailment and fire?

A: In a derailment, monitoring and sampling priority is typically given to chemicals confirmed or suspected to be released, which are then prioritized according to potential risk to human health. The ultimate decision of what to monitor and sample for and at what levels was determined by Incident/Unified Command, not CTEH, and set forth in the Air Sampling and Analysis Plan described above. Unified Command was a joint incident management structure comprised of the U.S. EPA, Ohio EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern.

The strategy for air monitoring may also be influenced by the technology that exists to measure an individual chemical.

Q: Was any of the air monitoring in East Palestine conducted by more than one party?

A: Yes, including monitoring and sampling conducted by U.S. EPA, Texas A&M University, Carnegie Mellon University and other contractors.

More specifically, in addition to the CTEH air monitoring and sampling, other groups independently performed air monitoring and sampling, including the U.S. EPA’s Superfund Technical Assessment and Response Team (START), the U.S. EPA’s Trace Atmospheric Gas Analyzer (TAGA) mobile unit, and a mobile unit operated by the Texas A&M University Superfund Research Center and Carnegie Mellon University. During the week of April 10, 2023, the U.S. EPA operated its TAGA mobile unit on joint routes with CTEH’s Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) mobile unit to compare the two systems directly. The U.S. EPA’s April 17, 2023, update states: “EPA approved the use of the PTR-MS mobile lab after conducting joint TAGA/PTR-MS runs the week of April 10. Monitoring data collected by the contracted mobile lab was consistent with monitoring data collected by EPA’s TAGA lab, assuring confidence in its use.” Separately, the Texas A&M University Superfund Research Center and Carnegie Mellon University performed air monitoring using its mobile unit on February 20 and 21, 2023. The U.S. EPA’s June 2024 review of these independent studies states that this work corroborated EPA’s findings.

Q: Who determined the action levels for the home assessments and why were the levels changed during the monitoring?

A: For this incident, both the U.S. EPA and the ATSDR were consulted to determine the screening levels for chemicals, including butyl acrylate, during home assessments. ATSDR proposed a screening level of 3,300 ppb for butyl acrylate, which is approximately 1/3 of the EPA Acute Exposure Guideline Level-1 (AEGL-1) for butyl acrylate (8,300 ppb). The AEGL-1 is a guideline that describes the airborne concentration of a substance that may cause transient, reversible, and non-disabling discomfort, irritation, or other non-sensory effects in the general population. This screening level was adopted into the Air Monitoring and Residential Re-Entry Plan, which was developed alongside the U.S. EPA, Ohio EPA, Pennsylvania DEP, the Ohio and Pennsylvania Departments of Health, the Columbiana County Health District, and Norfolk Southern, and approved by the U.S. EPA.

Subsequently, ATSDR proposed applying an additional safety factor of 10 to the screening level to account for sensitive subpopulations, thereby lowering the proposed screening level to 330 ppb. This updated screening level was again adopted into the Air Monitoring and Residential Re-Entry Plan.

ATSDR later proposed further lowering the screening level for butyl acrylate during home assessments to 50 ppb, which was more than 150 times lower than its original proposed screening level. The proposed screening level of 50 ppb is a level at which humans can perceive a clearly defined objectionable odor and is not a health-based guideline. This level is also lower than the detection limits for butyl acrylate using handheld real-time air monitoring instruments. The proposed screening level of 50 ppb was considered by Incident Command but was not incorporated into the Air Monitoring and Residential Re-Entry Plan. Instead, odor detection continued to be used as an indicator of the presence of butyl acrylate at concentrations far below health-based guidelines (the odor threshold of butyl acrylate is as low as 0.29 ppb, compared to the AEGL-1 of 8,300 ppb), and actions were taken if butyl acrylate odors were observed, in accordance with the Air Monitoring and Residential Re-Entry Plan.

Q: How was the indoor air screening conducted for residents in East Palestine, and what chemicals were included in the screening?

A: Indoor air monitoring was conducted concurrently and independently by the U.S. EPA and CTEH pursuant to the Air Monitoring and Residential Re-Entry Plan, which was developed alongside the U.S. EPA, Ohio EPA, Pennsylvania DEP, the Ohio and Pennsylvania Departments of Health, and the Columbiana County Health District, and approved by the U.S. EPA. CTEH collected data and reported it as specified in the plan.

More specifically, when the evacuation order was lifted by state and local officials on February 8, 2023, indoor air monitoring was offered to every household within the evacuation area pursuant to the Air Monitoring and Residential Re-Entry Plan. Each indoor air monitoring team consisted of one or two CTEH specialists, an EPA representative, a local law enforcement officer, and a state representative (when available), with a household member present. Each team met the household member at a predetermined location (either at their home or at another location such that the resident could be escorted home by the team).

Once at the residence, the CTEH specialists and EPA representatives concurrently and independently performed air monitoring in every living space (including outdoor areas, each floor of the home, and the basement) for the presence of total volatile organic compounds (VOCs) using PID instruments. If VOCs were detected, follow-up monitoring for vinyl chloride was performed using chemical-specific colorimetric detector tubes. Vinyl chloride was not detected in any home that was tested. CTEH notes that VOCs are commonly detected in homes due to a variety of sources, such as common household products (aerosol sprays, disinfectants, and candles), among other causes unrelated to the incident.

EPA representatives also performed air monitoring for hydrogen chloride in every living space, and CTEH specialists documented any odors observed during the assessment. Air monitoring results collected by CTEH were recorded on a paper form given to the resident, logged in electronic data management software, and were available to the U.S. EPA through direct access to project databases.

More information about VOCs can be found here: USEPA Indoor Air Quality Information.

Q: What equipment was used for indoor air screening?

A: The strategy and methods, including equipment, used for indoor air screening are outlined in detail in the Air Monitoring and Residential Re-Entry Plan, which was developed alongside the U.S. EPA, Ohio EPA, Pennsylvania DEP, the Ohio and Pennsylvania Departments of Health, the Columbiana County Health District, and Norfolk Southern, and approved by the U.S. EPA.

More specifically, both CTEH specialists and EPA representatives used MultiRAE instruments with PIDs manufactured by RAE systems (Honeywell) to measure total VOCs. The PIDs used to measure total VOCs can detect more than 200 different substances, including those involved in the derailment (such as vinyl chloride and butyl acrylate), and many others not involved in the derailment (such as common household chemicals), at thresholds below the screening levels in effect and outlined in the Air Monitoring and Residential Re-Entry Plan. Because the PID cannot identify the specific VOC present in the air, if total VOCs were detected, CTEH specialists performed follow-up monitoring for vinyl chloride using Gastec pumps with chemical-specific colorimetric detector tubes for vinyl chloride, which change color when vinyl chloride is present in the air. In addition, EPA representatives used Honeywell SPM Flex instruments to measure hydrogen chloride.

A multi-organizational task force consisting of CTEH and the U.S. EPA (including the EPA’s START and Office of Research and Development), along with third-party reviewers, assessed the accuracy and precision of the types of PIDs used by CTEH and EPA for indoor and outdoor air monitoring in East Palestine. The full report can be found here.

Q: How many homes did CTEH perform indoor air screening for? How many were found to have high or potentially unhealthy levels of vinyl chloride?

A: Indoor air monitoring was offered to every household within the evacuation area, in accordance with the Air Monitoring and Residential Re-Entry Plan, which was developed alongside U.S. EPA, Ohio EPA, Pennsylvania DEP, the Ohio and Pennsylvania Departments of Health, the Columbiana County Health District, and Norfolk Southern. More than 630 homes and commercial spaces participated in voluntary indoor air screening. Vinyl chloride was not detected in any of the indoor air screenings.

Q: Did CTEH test for dioxins? If not, why not?

A: CTEH performed air monitoring and sampling in accordance with plans approved by the Unified Command (comprised of the U.S. EPA, Ohio EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern). Dioxins were not expected to be significant combustion products of the prescribed burn conducted on the railcars involved in the derailment. In addition, they are ubiquitous in the environment and can be created by many combustion sources. For those reasons, they were not part of the testing plan approved by Unified Command.

Q: Is CTEH continuing to perform indoor air screening for Norfolk Southern?

A: CTEH’s indoor air screening work concluded in April 2023. More information regarding the conclusion of indoor air screening can be found here: USEPA East Palestine Operational Updates (April 2023) and USEPA East Palestine Newsletter (May 2023).

Q: What was CTEH’s involvement in the air knifing in East Palestine?

A: The decision to perform air knifing was made by Unified Command, and air knifing was performed by a different contractor pursuant to a plan approved by Unified Command. CTEH was not involved in the decision to conduct air knifing, nor did it perform any air knifing. CTEH’s role was to conduct air monitoring and sampling during air knifing by another contractor and report the results to Unified Command pursuant to the approved health and safety plan approved by Unified Command. CTEH’s role did not include occupational medical care of the contractors performing air knifing.

Q: Who did CTEH submit the “Air Knifing Operations Assessment and Data Summary” to?

A: CTEH’s Air Knifing Operations Assessment and Data Summary was submitted to Unified Command, the joint incident management structure comprised of the U.S. EPA, Ohio EPA, Columbiana County Emergency Management Agency, the Village of East Palestine, and Norfolk Southern, in May 2023. The report was also shared with Unified Command partners, including ATSDR.

Q: What was CTEH’s role in the International Terminals Company (ITC) Deer Park, Texas incident?

A: CTEH was initially called to action by the City of Deer Park in response to a fire at the International Terminals Company (ITC) Deer Park facility. CTEH was then contracted by ITC to perform air monitoring and sampling, which grew to include water and soil sampling in later stages of the response efforts. CTEH toxicologists and consultants interacted continuously with the Unified Command providing air monitoring and operational updates for work done in the facility, assessments at neighboring facilities, and in the industrial and residential communities in the general vicinity of ITC.

While CTEH was not part of Unified Command (UC) in the ITC event, CTEH gave scientific input on the action levels approved and implemented by UC during the response. Based on CTEH’s experience, the 1 ppm action level for 1 minute for benzene across community areas was highly conservative. It was substantially below the USEPA AEGL levels used to protect communities from short-term exposure scenarios. The benefit of establishing such short-term action levels (1 minute) is the quick identification of zones that are actually involved in a chemical release, allowing UC to take early actions and inform responses such as shelters-in-place.

CTEH continued to provide consulting and monitoring services through the deconstruction of the tank farm and removal of all affected soils from the impact zone.

Q: What was CTEH’s role in the West Point, Kentucky rail incident?

A: In the West Point, Kentucky incident, CTEH conducted community and worker air monitoring and sampling. An unfortunate accident occurred that resulted in response workers being injured while conducting hot work, a procedure that uses a torch to cut metal in the process of separating damaged rail cars. A proper risk assessment was not conducted by those responsible for the hot work, and spilled chemicals were ignited. CTEH does not authorize or conduct hot work, and was not responsible for the accident.

Q: What was CTEH’s role in the BP Deepwater Horizon oil spill incident?

A: CTEH was hired as the prime air monitoring consultant for the Deepwater Horizon response, operating across the entire Gulf region. CTEH’s work for the response involved many disciplines including industrial hygiene, safety, and environmental science.

Following the Deepwater Horizon response, CTEH has since been retained to provide testimony relevant to CTEH’s involvement and the risk to workers, as evidenced by the data collected.

During the Deepwater Horizon response, CTEH identified numerous situations where air quality was negatively impacted by the spill and communicated those instances to the Unified Command (that included EPA, U.S. Coast Guard, the states of Texas, Louisiana, Mississippi, Alabama, and Florida, and with oversight from OSHA, NIOSH, numerous other state and local agencies, and BP), resulting in actions to further protect those potentially impacted by those conditions. The data collected by CTEH, through methods approved by the Unified Command, was used to ensure the protection of human health. CTEH collected accurate data based on Unified Command-approved methods and reported those data daily for the benefit of all stakeholders.

Q: What was CTEH’s involvement in Knauf Plasterboard Tianjin defective Chinese drywall in Florida?

A: In the case of Chinese drywall in Florida, CTEH testing found that there were significant levels of chemicals attributed to the Chinese drywall inside the wall spaces where electrical components were found to be corroded and failing. CTEH results outside the wall spaces, in the breathable air in the homes, found that though there were detectable nuisance odors attributable to the drywall, the levels were not high enough to cause health effects in humans. CTEH’s interpretation of the data and resulting potential for human health effects in the air that people can breathe, as opposed to the air inside the walls, was accurate, based on the toxicology of the chemicals at issue, and not contradictory to studies conducted by other agencies.

Q: What was CTEH’s involvement in the coal fly ash spill at the Tennessee Valley Authority’s Kingston Fossil Plant?

A: In the emergency phase of the response, CTEH was responsible for the community air monitoring for fly ash dust conducted outside the facility. That data was confirmed as accurate and correct. Following the emergency phase, a number of other contractors were hired to conduct long-term air monitoring onsite, and CTEH’s involvement ended. CTEH was neither involved during the cleanup phase nor conducted any air monitoring or sampling related to worker health and safety at the site.

Q: What was CTEH’s involvement in the Murphy Oil incident following Hurricane Katrina?

A: Hurricane Katrina devastated the Chalmette, LA community. Floodwaters destroyed many homes and also carried with them crude oil from a Murphy Oil tank severely damaged by the flood that contaminated hundreds of homes in the Chalmette community. The area was completely evacuated, and the police and first responders did not allow any homeowners into the area for a considerable period of time. There were many hazards to people after Hurricane Katrina, including structural damage to homes, wildlife, and other physical hazards such as flood damage and mold, in addition to oil contamination inside and outside people’s homes that remained after the floodwaters receded. The homes in the impacted areas were destroyed and uninhabitable, and many homes had more than a foot of sediment inside brought in by flood waters. CTEH was hired to determine which homes were impacted by the oil, and a federal judge agreed with the CTEH/EPA/Louisiana Department of Environmental Quality (LDEQ) boundaries of Murphy Oil-impacted homes.

Q: What sampling methodology did CTEH use in the Murphy Oil incident following Hurricane Katrina?

A: Under the approved LDEQ / EPA sampling plan, and with the physical presence of EPA during sampling events, CTEH collected composite samples from several locations at each home. In accordance with the approved work plan, composite samples are considered more representative of conditions in an area than a single point sample. Such samples are classified as composites when multiple points within a small area, or grid, have a small amount of material collected into the same sample container. A method like this might be used, for example, to take sample material from several locations in a home’s yard to be representative of the full yard area rather than a pinpoint sample location within the yard. Some soil samples were baked by the sun into a hard brick-like state and had to be broken up prior to compositing and splitting samples with EPA. It is best practice when analyzing for volatile organic compounds in soil and water samples that air in the sample container is minimized since volatiles can evaporate from the soil or water into the headspace, which may cause the sample to be biased low if volatiles were present. Breaking up these brick-like bits of soil then tapping containers to better pack the containers, reducing available headspace, is the best practice for soil samples of this type.

The affected homes were identified by this sampling plan and then remediated. Confirmation samples were collected and sent to an approved laboratory for analysis. The results were below RECAP standards, and based on those findings, LDEQ/EPA issued a No Further Action (NFA) letter. The NFA letter indicated that following the cleanup of the impacted properties, there was no additional risk to residents because the data proved that the oil had been removed.