EPA Releases Key TSCA Risk Assessment Default Values

Sometimes the biggest regulatory news is not a flashy ban, a billion-dollar penalty, or a dramatic courtroom showdown. Sometimes it is a spreadsheet with consequences. That is essentially what happened when the U.S. Environmental Protection Agency released key default values used in new chemical risk assessments under the Toxic Substances Control Act, or TSCA. If that sounds like inside baseball for regulatory professionals, well, yes. But it is also a practical development with real consequences for chemical manufacturers, importers, labs, consultants, and anyone trying to move a new substance through EPA’s section 5 review process without triggering a paperwork migraine.

The short version is this: EPA has now made public a set of common assumptions it uses when submitters do not provide enough chemical-specific or process-specific information. These defaults help EPA estimate environmental releases and worker exposure during the life cycle of a new chemical. In plain English, when a company leaves blanks, offers vague descriptions, or submits data that do not hold up, EPA fills in the gaps with its own numbers. And those numbers matter.

For years, companies knew EPA used default assumptions in TSCA new chemical reviews. What changed is that the agency has now put several of the most important ones into a single, easy-to-find guide in the New Chemicals Division Reference Library. That move is part transparency, part efficiency, and part warning label. EPA is effectively saying, “Here is what we do when you make us guess.” Regulators love clarity, and so do businesses. Surprises are fun at birthday parties, not in premanufacture notices.

What EPA actually released

EPA’s November 2025 release focuses on common engineering defaults used in new chemical assessments under TSCA section 5. These are not random numbers pulled from a bureaucratic hat. The agency says the values come primarily from ChemSTEER, EPA generic scenario documents, and OECD emission scenario documents. The guide covers two big buckets: environmental release estimates and worker inhalation or dermal exposure estimates.

That distinction is important. A TSCA new chemical review is not just about whether a substance might be hazardous in theory. EPA also looks at how much of it could be released, where it could go, and who could be exposed. In practice, that means EPA needs workable assumptions about container residues, equipment cleaning losses, dust releases, transfer inefficiencies, ventilation, and skin contact. If a submitter does not supply solid, substantiated information, EPA uses screening-level defaults that tend to be protective and conservative.

The agency also made clear that the guide is an evolving document, not a binding rulebook carved into stone tablets. EPA keeps discretion to adjust assumptions when it thinks a particular chemical or scenario justifies a different approach. That flexibility is useful for the agency, though companies may reasonably prefer a little less “it depends” and a little more predictability.

Why this matters under TSCA section 5

Under TSCA section 5, EPA must review new chemical substances before they are manufactured, imported, processed, or used in commerce. That review includes a determination about whether the substance may present an unreasonable risk to health or the environment. The statutory review clock is fast by federal standards, and the data package is often less than perfect. That is why engineering defaults have such outsized importance.

Think of the defaults as the agency’s regulatory autopilot. If EPA does not know whether a new chemical arrives in drums or totes, whether a process is gravity-drained or pumped, whether a hood is a true overhead capture hood or just a brave fan doing its best, the agency still has to assess exposure and release. The default values provide a structured way to do that.

This is also happening against the backdrop of EPA’s broader effort to tighten and modernize the new chemicals program. In June 2024, EPA launched the New Chemicals Division Reference Library to make guidance, templates, manuals, and compliance materials easier to find. In December 2024, EPA finalized amendments to the regulations governing new chemicals review. In April 2025, the agency rolled out new implementation resources so companies could better match the required data elements in current submission systems. The default-values guide fits neatly into that broader push for more complete notices, fewer do-overs, and less guesswork on both sides.

There is also a workload reality here. EPA has been handling roughly 500 TSCA section 5 notices and related applications per year, and the agency is reviewing them on a 90-day statutory timeline. When the volume is high and the details are fuzzy, defaults stop being background noise and become the backbone of the review.

The numbers that companies should pay attention to

The newly released guide is full of details, but several defaults jump off the page because they can meaningfully change an exposure or release calculation.

1. Container residues for liquids

If EPA does not know the container type for a liquid new chemical substance, it typically assumes a 55-gallon drum. For drums emptied by pumping, the default residue is 3 percent. If the submission shows the drums are emptied by pouring, the default drops to 0.6 percent. For bulk containers such as totes, tank trucks, or rail cars, the default is 0.2 percent. Small containers under 20 gallons also default to 0.6 percent.

That may sound like small potatoes, but in risk assessment math, percentages like these can move the needle quickly. EPA’s own example shows that a 50,000-kilogram-per-year liquid imported in drums could generate a default daily release estimate of 6.2 kilograms per site-day. If the same substance is known to arrive in totes, the refined estimate falls to 4.2 kilograms per site-day. Same chemical, same annual volume, different container detail, different result.

2. Equipment cleaning losses

For a process involving a single vessel, EPA uses a 1 percent residue default if equipment is drained by pumping. If the submission shows the equipment is gravity-drained, that can drop to 0.2 percent. Where multiple pieces of equipment need cleaning, EPA uses a 2 percent default. Once again, the message is simple: detailed process information is not a luxury add-on. It can materially affect the release estimate.

3. Solid material transfers

For dust or airborne particulate releases during solid handling operations, EPA uses a 0.5 percent released default. The guide also includes assumptions for capture and control efficiencies. Unknown capture technology or generic local exhaust ventilation gets a 32.1 percent capture efficiency default, while an overhead capture hood or laboratory fume hood gets 95 percent. Unknown control technology gets 26 percent control efficiency, while a baghouse or HEPA filter gets 99 percent.

This is a big deal because not all ventilation descriptions are created equal. Telling EPA that a process has “LEV” may not buy the same refinement as documenting an overhead hood plus HEPA filtration with supporting details. In other words, “trust us, there’s ventilation” is not the same as “here is the system design, capture point, and control device.”

4. Worker inhalation and dermal exposure defaults

For handling solids, EPA uses a default inhalation exposure of 0.161 mg/kg body weight when less than 54 kilograms per site-day are handled in low-volume activities such as scooping, weighing, or pouring. For higher-volume solid handling, EPA uses 15 mg/m³ total particulates and 5 mg/m³ respirable particulates. Those values align with OSHA particulate benchmarks that EPA assumes workplaces are generally expected to meet.

For dermal contact with solids, EPA uses 3,100 mg per event as a high-end default adjusted for the weight fraction of the new chemical substance. For liquids, inhalation exposure is calculated using ventilation assumptions, including 500 to 3,000 cubic feet per minute indoors and 237,600 cfm outdoors based on average wind speed. Dermal exposure to liquids uses 2.1 mg/cm²-event, with 1,070 cm² for two hands as the default surface area and 535 cm² for one hand. EPA also notes that, by default, it assumes one contact event per day.

That last point matters because many submissions still treat skin contact like an afterthought. EPA plainly does not.

Why the release is more important than it looks

At first glance, the guide may seem like a technical housekeeping update. It is more than that. It changes the practical relationship between submitters and the agency in at least three ways.

It reduces hidden assumptions

Before this release, many companies knew defaults existed but did not always know which assumptions EPA was likely to plug in during review. Now the fog is thinner. That alone is valuable. A submitter can prepare a notice knowing that if container type, draining method, or ventilation details are missing, EPA has a defined starting point.

It raises the bar for PMN preparation

EPA has been signaling for years that incomplete notices slow review, create rework, and increase the odds that the agency will rely on conservative assumptions. The new guide sharpens that message. If your process description is vague, EPA’s number becomes the number that matters.

It creates a more practical roadmap for refinement

Perhaps the most useful feature of the guide is that it hints at exactly where targeted, high-quality data can refine a risk assessment. Container size. Transfer method. Capture technology. Control device. Throughput. Drainage. Surface contact assumptions. These are not abstract scientific mysteries. They are operational facts that many companies already know, or should know, about their own facilities and supply chains.

That said, not everyone is ready to throw confetti. Practitioner commentary has welcomed the transparency but also noted a lingering concern: EPA has not fully spelled out how much evidence is enough for the agency to depart from a default. In other words, publishing the default values is helpful, but the real-world question remains whether EPA will consistently accept credible alternative data when companies submit it.

What chemical companies, labs, and consultants should do next

The smartest response to EPA’s release is not panic. It is preparation.

• Audit your current submission habits. Review recent PMNs, exemption applications, and supporting materials. See where your team tends to rely on generic process descriptions.
• Map your engineering details early. Container type, unloading method, residue handling, cleaning method, capture and control technologies, and worker contact scenarios should be documented before the filing crunch begins.
• Substantiate, do not merely state. EPA’s guide repeatedly points toward the value of documented, representative information. A good attachment beats a confident adjective every time.
• Coordinate regulatory and plant personnel. The legal team may know TSCA, but the engineers know whether the vessel is gravity-drained, the EHS team knows the hood design, and operations knows how often workers actually touch the material.
• Use the guide as a pre-submission stress test. Ask where EPA would default if your filing landed on a reviewer’s desk today. If the answer is uncomfortable, fix it before submission.

For laboratories and pilot-scale operations, the guide is especially useful because it translates abstract compliance risk into physical details. A drum is not just a drum. A hood is not just a hood. A phrase like “closed system” is not magic dust sprinkled over an exposure scenario. EPA wants specifics.

The bigger policy takeaway

EPA’s release of key TSCA risk assessment default values is part of a broader shift toward a more structured, transparent, and documented new chemicals program. It reflects an agency that wants fewer mystery inputs, fewer incomplete filings, and a more standardized starting point for exposure and release modeling.

For industry, the change is both a convenience and a challenge. The convenience is obvious: there is less guesswork about how EPA may model a submission. The challenge is equally obvious: once the defaults are public, companies have less excuse for turning in filings that leave critical operational details floating around like unlabeled vapor in a poorly ventilated room.

That is why this release matters beyond the engineering tables themselves. It is a signal about how EPA wants the conversation to go. The agency is not saying, “Please send whatever you have and we will sort it out.” It is saying, “Here is our starting point. If you want a different answer, bring better facts.”

Real-world experiences: what this looks like when the defaults meet the plant floor

In real compliance work, the experience of dealing with TSCA default values is often less dramatic than a headline and more dramatic than a conference call agenda. It usually starts with a team believing it has described a process clearly enough, only to realize that EPA reads “clearly enough” very differently.

A common example is packaging. A submitter may think it has explained that a liquid chemical is moved in “containers” and then unloaded into a formulation system. That sounds fine until someone asks the obvious follow-up question: what kind of containers? Drums, totes, tank trucks, rail cars, and bottles do not leave the same residues. Once EPA’s guide is on the table, that missing detail is no longer a minor omission. It becomes a built-in release assumption. Suddenly, a regulatory team is calling supply chain, plant operations, and procurement to confirm whether the material arrives in 55-gallon drums or 550-gallon totes. The answer can reshape the release estimate, the exposure narrative, and sometimes the whole tone of the review.

Ventilation is another place where real-world experience gets interesting fast. Many facilities genuinely believe they have “good controls.” EPA, however, thinks in terms of capture efficiency, control efficiency, hood type, and supporting documentation. A site may have local exhaust ventilation, but that phrase alone does not necessarily tell EPA whether the system performs like a generic LEV setup or more like an overhead hood with high-efficiency filtration. The practical lesson is that engineering controls are not only physical equipment; they are also documentation exercises. If the paperwork is thin, the default may stay thick.

Worker exposure assumptions create similar tension. On the plant floor, employees may handle a substance briefly, use gloves consistently, and touch only one part of a process line. In a submission, if those details are not documented well, EPA may default to two-hand dermal exposure, one contact event per day, and high-end contact values. Nobody is being dramatic here. EPA is doing what regulators do when faced with uncertainty: it chooses a protective screening-level assumption. The frustration for companies is that the actual operation may be tighter, cleaner, and better controlled than the model suggests. The fix is rarely a clever argument. It is usually better records.

That is why experienced TSCA teams tend to treat default values as a planning tool, not just a regulatory obstacle. They ask early where EPA is most likely to substitute assumptions. They compare the guide against real operating conditions. They identify the handful of variables most likely to change the outcome. And then they gather evidence before the filing goes in, not after EPA has already built the assessment around generic defaults.

So yes, the release of TSCA default values is technical. But the experience of working with them is deeply practical. It affects how operations are described, how risks are framed, and how much credibility a submitter brings to the table. In that sense, the guide is not just a set of numbers. It is a reminder that in chemical regulation, details are not decoration. They are destiny wearing a hard hat.

Conclusion

EPA’s release of key TSCA risk assessment default values is one of those developments that rewards close attention. It does not rewrite TSCA section 5, but it does make the agency’s new chemical review process more visible and, in some respects, more predictable. The guide shows exactly how EPA may model environmental releases and worker exposure when submissions are incomplete or under-supported. That is good news for companies that want to prepare stronger notices and reduce avoidable rework.

At the same time, the release raises the stakes for process detail and supporting documentation. The published defaults are now a clear benchmark. If your filing does not answer the operational questions EPA cares about, the agency already has its own answers ready to go. For manufacturers, importers, labs, and consultants, the message is unmistakable: better facts lead to better assessments. And in the world of TSCA, better assessments are often the difference between a smoother review and a long walk through regulatory molasses.

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