PFBS, PFNA, and the EPA: Inside the Struggle to Regulate Toxicity in "Forever Chemicals"

1. Introduction: The Persistent Legacy of the Carbon-Fluorine Bond

In the vast lexicon of modern industrial chemistry, few innovations have proven as double-edged as the per- and polyfluoroalkyl substances, known colloquially and ominously as "forever chemicals." These compounds, defined by the distinctively robust carbon-fluorine bond, represent a triumph of mid-century engineering. They repel oil, grease, and water with an efficiency that revolutionized consumer products, from the non-stick pans in suburban kitchens to the stain-resistant carpets in corporate offices and the firefighting foams used on military bases. Yet, the very chemical stability that made them commercially indispensable has rendered them environmentally immortal. They do not degrade. Instead, they accumulate—in soil, in groundwater, in the tissues of wildlife, and, inevitably, in the blood of nearly every human being on the planet.¹

For decades, the regulatory narrative of these substances was dominated by two long-chain giants: perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These eight-carbon chains (C8) were the industry standards, the workhorses of the fluorochemical world. However, as the twenty-first century dawned, the toxicological bill for their widespread use came due. Epidemiological studies and internal industry documents revealed a litany of adverse health effects, ranging from immune system suppression and liver damage to developmental defects and cancer.⁴ Under immense public and regulatory pressure, major manufacturers like 3M and DuPont initiated a voluntary phase-out of these long-chain compounds, pivoting their production lines toward "short-chain" alternatives. The logic was seductive in its simplicity: fewer carbons meant a shorter half-life in the human body, which, theoretically, implied a wider margin of safety.⁴

Enter Perfluorobutane Sulfonic Acid (PFBS). With a four-carbon backbone, PFBS was heralded as the benign successor to the toxic legacy of PFOS. It cleared from the human body in days or weeks rather than years. It was less bioaccumulative. It was the "sustainable" solution. But as the years passed and the scientific scrutiny deepened, the assumption of safety began to crumble. Emerging data suggested that while PFBS might leave the body faster, it was far from harmless while it remained, targeting the thyroid, the kidneys, and the delicate hormonal choreography of fetal development.¹

This report explores the tumultuous regulatory journey of PFBS and its nine-carbon cousin, Perfluorononanoic Acid (PFNA). It is a story not just of chemistry and toxicology, but of the fragile interface between science and policy. It is a narrative that culminated in January 2021, when the Environmental Protection Agency (EPA), under the direction of political appointees, attempted to rewrite the scientific conclusions of a PFBS toxicity assessment to weaken safety standards. It is a narrative that appears to be repeating itself in 2025, with reports of the agency withholding a critical assessment of PFNA despite its completion months prior.⁹

By dissecting the mechanisms of toxicity, the mathematics of risk assessment, and the bureaucratic machinery of suppression, we reveal a systemic vulnerability in how the United States regulates toxic substances. We examine how "uncertainty factors"—the safety buffers meant to protect public health from scientific unknowns—were weaponized to serve industrial interests. We analyze the specific biological impacts of these chemicals, from the disruption of thyroid hormones in newborn mice to the reduction of birth weight in human infants. And we ask the fundamental question: when the science is completed, who decides if the public is allowed to see it?

2. The Mechanics of Federal Risk Assessment

To understand the gravity of the PFBS and PFNA controversies, one must first possess a nuanced understanding of the EPA’s Integrated Risk Information System (IRIS). This program, often described as the "gold standard" of federal toxicology, does not write regulations. Instead, it produces the scientific foundation upon which regulations are built. IRIS assessments identify hazards and quantify dose-response relationships, creating the critical numbers that program offices—such as the Office of Water or the Office of Land and Emergency Management—use to set enforceable limits.¹¹

2.1 The Reference Dose (RfD): Defining "Safe"

The centerpiece of a non-cancer toxicity assessment is the Oral Reference Dose (RfD). This value represents an estimate of the amount of a chemical that a person can ingest daily over a lifetime without a demonstrable risk of deleterious health effects. The derivation of the RfD is a rigorous, multi-stage process that blends empirical data with statistical caution.

The process begins with the identification of a "Point of Departure" (POD). In the past, this was often the "No Observed Adverse Effect Level" (NOAEL)—the highest dose in an animal study at which no harmful effects were seen—or the "Lowest Observed Adverse Effect Level" (LOAEL). Modern toxicology, however, increasingly relies on the Benchmark Dose (BMD) approach. This method models the entire curve of dose-response data to estimate the dose that corresponds to a specific, low level of response (e.g., a 10% decrease in hormone levels). The lower confidence limit of this dose, known as the BMDL, serves as the POD.¹³

However, humans are not rats, and the general population includes vulnerable groups like infants and the elderly. To account for these differences, the POD is divided by a series of "Uncertainty Factors" (UFs). These factors are the mathematical embodiment of the precautionary principle.

2.2 The Arithmetic of Uncertainty

Uncertainty factors are typically applied in multiples of 10 (representing a full order of magnitude) or 3 (representing a half-order of magnitude, the square root of 10). The final composite uncertainty factor is the product of several specific factors:

• Interspecies Uncertainty (UFa): This factor accounts for the differences between the test animal and humans. It assumes that humans might be more sensitive to the chemical than the rodent models used in the lab. A standard default is 10, often reduced to 3 if toxicokinetic data allows for more precise scaling.¹¹

• Intraspecies Uncertainty (UFh): This accounts for variation within the human population. It protects those who are genetically susceptible, immunocompromised, or in critical developmental stages (like fetuses or infants) from being harmed by a dose that might be safe for a healthy adult. The standard value is 10.¹¹

• Database Uncertainty (UFd): This factor is critical to the PFBS controversy. It is applied when the overall body of scientific literature for a chemical is incomplete. If, for example, a chemical lacks a two-generation reproductive toxicity study or a developmental neurotoxicity study, risk assessors apply a UFd of 10 or 3 to account for the possibility that these missing studies might reveal effects at lower doses than currently known.¹¹

The equation for the Reference Dose is thus:

RfD = Point of Departure / (UFa × UFh × UFd...)

The mathematics here are powerful. A decision to change a database uncertainty factor from 10 to 1 increases the final "safe" dose by tenfold. In the context of environmental cleanup, this means a polluter might be required to clean groundwater to 10 parts per billion rather than 1 part per billion—a difference that can amount to millions or billions of dollars in remediation costs. It is in the selection of these factors, particularly the database uncertainty factor, that the friction between science and politics generates the most heat.¹

3. PFBS: The "Safe" Alternative?

Perfluorobutane Sulfonic Acid (PFBS) is the four-carbon homolog of PFOS. Structurally, it consists of a four-carbon fluorinated tail attached to a sulfonate functional group. This shorter chain length imparts distinct physicochemical properties compared to its eight-carbon predecessor. PFBS is more water-soluble, less lipophilic, and has a lower potential for bioaccumulation in protein-rich tissues.

3.1 Environmental Fate and Transport

The high water solubility of PFBS makes it an exceptionally mobile contaminant. Once released into the environment—whether from industrial wastewater, firefighting foam runoff, or the degradation of precursor chemicals—it moves rapidly through the soil column. Unlike longer-chain PFAS, which tend to adsorb to soil particles and organic matter, PFBS travels with the water front. This allows it to penetrate aquifers and contaminate groundwater plumes far faster and more extensively than PFOA or PFOS.²

This mobility presents a unique challenge for water treatment. Standard filtration technologies, such as granular activated carbon (GAC), rely on adsorption to remove contaminants. Because PFBS is less "sticky" (hydrophobic) than long-chain PFAS, it breaks through GAC filters much more quickly, requiring more frequent and costly carbon change-outs to maintain effective treatment. Thus, while PFBS may be less bioaccumulative in the body, it is harder to remove from the water supply, creating a different but equally persistent exposure vector for human populations.¹⁷

3.2 The Toxicological Profile

The marketing of PFBS as a safer alternative relied heavily on its rapid elimination half-life in humans, estimated to be on the order of weeks, compared to the years-long half-lives of PFOA and PFOS. However, toxicology is not merely a function of retention time; it is a function of potency and mechanism. The 2021 EPA assessment, and the underlying literature, identified several critical organs of toxicity for PFBS: the thyroid, the kidney, and the developing fetus.

3.2.1 Thyroid Disruption

The most sensitive endpoint—the effect that occurs at the lowest dose—identified in the EPA’s assessment was the disruption of thyroid hormones. The thyroid gland plays an indispensable role in regulating metabolism, growth, and, crucially, neurodevelopment. During pregnancy and early infancy, the developing brain relies heavily on maternal and endogenous thyroid hormones (thyroxine, T4, and triiodothyronine, T3) to guide neuronal migration and differentiation.⁶

Studies, particularly the pivotal work by Feng et al. (2017) and the National Toxicology Program (NTP) in 2019, demonstrated that PFBS exposure in mice leads to profound hypothyroxinemia—a reduction in circulating T4 levels. In the Feng study, newborn mice exposed to PFBS showed significant, dose-dependent decreases in serum total T4. This effect was observed even in the absence of a compensatory increase in Thyroid Stimulating Hormone (TSH), a complexity that suggests PFBS may disrupt the thyroid system through mechanisms other than direct inhibition of the thyroid gland, such as by displacing T4 from binding proteins or enhancing its clearance by the liver.¹⁵

The implications of this T4 reduction are severe. Even transient hypothyroxinemia during critical windows of development can lead to permanent deficits in cognitive function, motor skills, and auditory processing. By selecting this effect as the "critical effect" for the Reference Dose, the EPA acknowledged that protecting the thyroid function of the developing organism is paramount.⁶

3.2.2 Renal Toxicity and Hyperplasia

Beyond the thyroid, PFBS is a potent renal toxicant. The kidneys are the primary route of excretion for PFBS, and the chemical appears to concentrate in renal tissue. Animal studies have consistently shown that PFBS exposure leads to increased kidney weights and histopathological lesions. specifically, papillary epithelial tubular/ductal hyperplasia—an abnormal proliferation of cells in the lining of the kidney tubules.¹⁵

This hyperplasia is a concerning precursor to more severe kidney pathology. It suggests that the kidney cells are under stress and reacting to the toxic insult of PFBS. While PFBS has not been definitively classified as a carcinogen due to a lack of long-term cancer bioassays, the induction of hyperplasia is a "red flag" in toxicological risk assessment, indicating a potential for neoplastic transformation over a lifetime of exposure.⁷

3.2.3 Developmental and Reproductive Effects

The toxicological dossier on PFBS also includes evidence of reproductive harm. In animal models, PFBS exposure has been linked to delays in sexual maturation, such as delayed vaginal opening in female offspring. It has also been associated with changes in ovarian and uterine weights, suggesting an interference with the estrogenic signaling pathways or the hypothalamic-pituitary-gonadal axis.²¹

These findings challenge the narrative that short-chain PFAS are benign. While they may not accumulate to the same degree as PFOS, they act on the same fundamental biological systems—the endocrine system, the filtration organs, and the developmental programming of the fetus.

4. The January 2021 Crisis: A Case Study in Interference

The scientific assessment of PFBS began years before 2021, moving through the slow, deliberative channels of the EPA’s Office of Research and Development (ORD). By late 2020, the career scientists at ORD had produced a draft assessment that adhered to the agency’s rigorous guidelines. This draft identified the thyroid effects in newborn mice as the critical endpoint and proposed a single, scientifically defensible chronic Reference Dose.⁹

However, as the assessment moved toward final publication in the twilight of the Trump administration, it encountered a blockade. Political appointees in the Office of Chemical Safety and Pollution Prevention (OCSPP) and the Administrator’s office intervened in the scientific process. This was not a standard peer review; it was, as later described by the Inspector General, a "last-minute review" directed by a political appointee that resulted in "significant changes to the near-final, peer-reviewed work product".²²

4.1 The Battle Over the Uncertainty Factor

The focal point of this interference was the Database Uncertainty Factor (UFd). The career scientists in ORD had determined that the toxicological database for PFBS was incomplete. Specifically, there were no adequate studies on developmental neurotoxicity or immunotoxicity—two endpoints known to be sensitive targets for other PFAS like PFOS. Given these data gaps, the standard risk assessment practice is to apply a UFd of 10, or at a minimum 3, to account for the unknown risks.⁸

The political appointees, however, pushed for a UFd of 1. They argued that the database was sufficient and that the additional safety buffer was unnecessary. This was not merely a technical disagreement; it was a decision with profound economic consequences. Reducing the uncertainty factor from 10 to 1 would increase the "safe" level of PFBS in drinking water by a factor of ten, significantly lowering the cleanup burden for industries and the Department of Defense.¹¹

4.2 The "Unprecedented" Range

Unable to force the career scientists to fully capitulate to a single weakened number, the political appointees imposed a "compromise" that broke with decades of EPA precedent. Instead of publishing a single Reference Dose, the assessment released on January 19, 2021—just four days before the inauguration of President Biden—presented a range of values.

This range included values derived using a UFd of 10 (the scientific choice) and values derived using a UFd of 1 (the political choice). The document presented these distinct values as equally valid options for risk managers to choose from.¹

The Inspector General’s report later condemned this approach as "unprecedented." By offering a range, the EPA effectively abdicated its responsibility to define a safe level. It gave regulated entities—the very companies polluting the water—the discretion to "select a less stringent value within this range, which may have been less costly but also less protective of human health".¹¹

The presentation of a range created immediate regulatory chaos. State agencies, which rely on the EPA for definitive toxicological benchmarks, were left without a clear standard. If a state regulator chose the lower end of the range to protect public health, they faced potential legal challenges from industry arguing that the EPA had also endorsed the higher, less protective number.

4.3 The Breakdown of Scientific Integrity

The fallout within the agency was swift. Career scientists recognized the publication of the compromised assessment as a violation of the EPA’s Scientific Integrity Policy. Dr. Jennifer Orme-Zavaleta, the agency’s Acting Science Advisor and a career toxicologist, took the extraordinary step of publicly disavowing the document. In an email and subsequent press statement, she declared that the PFBS assessment contained conclusions "purporting to reflect science when in fact they are the product of biased political interference".²⁴

This statement was significant. It framed the interference not as a policy disagreement, but as an infringement of authorship and a corruption of the scientific record. It highlighted a structural weakness in the agency: while career scientists do the work, political appointees control the printing press.

4.4 The Correction: April 2021

In February 2021, the Biden administration removed the compromised PFBS assessment from the EPA website. Following a review, the agency re-released the final assessment in April 2021. This corrected version discarded the "range" and established single, robust Reference Doses:

• Chronic RfD: 0.0003 mg/kg-day.

• Subchronic RfD: 0.001 mg/kg-day.

These values were derived using the appropriate uncertainty factors, including a database uncertainty factor of 10, acknowledging the missing developmental and immune data. The restoration of the single value signaled a return to standard scientific practice, but the episode left a scar on the agency’s credibility and highlighted the fragility of its independence.²¹

5. 2025: The Pattern Repeats with PFNA

If the PFBS scandal was a singular event, it might be dismissed as an aberration of a specific political moment. However, recent reporting suggests that the suppression of PFAS science has become a recurring motif. In October 2025, ProPublica broke the story that the EPA was once again withholding a completed toxicity report, this time for Perfluorononanoic Acid (PFNA).¹⁰

5.1 The Missing Report

According to internal agency documents and whistleblower accounts, the toxicity assessment for PFNA was "completed and ready to post" in mid-April 2025. It had passed through the requisite scientific peer reviews and internal clearances. Yet, six months later, it had not been released. EPA officials offered vague assurances that the report would be published "when finalized," despite career scientists confirming that, scientifically, it was done.⁹

This delay mirrors the PFBS timeline, where a finished scientific product was held in limbo to serve political or economic ends. The delay is particularly consequential because PFNA is currently unregulated in many jurisdictions, despite being found in the drinking water of an estimated 26 million Americans.²⁷

5.2 PFNA: A More Dangerous Beast?

The urgency of the PFNA report lies in its findings. PFNA is a nine-carbon (C9) perfluorinated carboxylic acid. It is chemically similar to PFOA but with an extra carbon, which makes it even more lipophilic and bioaccumulative. While PFBS lingers in the body for a month, PFNA can remain for years.

The unreleased 2025 assessment reportedly confirms that PFNA is a potent reproductive and developmental toxicant. The specific findings leaked to the press include:

• Decreased Birth Weight: The assessment concludes that PFNA interferes with human development, causing statistically significant reductions in birth weight. This finding is supported by a robust body of epidemiological evidence showing an inverse relationship between maternal serum PFNA levels and infant birth weight.¹⁰

• Male Reproductive Toxicity: Perhaps most alarmingly, the report identifies likely damage to the male reproductive system. Animal evidence indicates that PFNA exposure leads to reductions in testosterone levels, decreased sperm production, and atrophy of reproductive organs.²⁷

These findings—targeting the fundamental capability of the population to reproduce and develop normally—place PFNA in a high-hazard category. By acknowledging these effects in a formal IRIS assessment, the EPA would trigger statutory obligations to regulate PFNA more strictly under the Safe Drinking Water Act (SDWA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

5.3 The Strategic Logic of Delay

Why withhold the report? The answer likely lies in the regulatory cascade that follows a finalized toxicity value. Once the EPA publishes a Reference Dose for PFNA, it establishes a "safe" level. If this level is extremely low—in the parts per trillion or quadrillion range, as expected for a chemical this potent—it would force water utilities across the country to install expensive filtration systems. It would also increase the liability for chemical manufacturers and industrial users of PFNA, who could be sued for contaminating water supplies above the federal health benchmark.

By delaying the release of the science, the administration effectively pauses the regulatory clock. It allows the status quo—unfiltered water and unmitigated exposure—to continue, prioritizing short-term economic stability over long-term public health.²²

6. The Comparative Toxicology of the "Forever Chemicals"

To fully appreciate the EPA’s reluctance, one must contextualize PFBS and PFNA within the broader family of PFAS. While they share the defining C-F bond, their biological behaviors differ in ways that complicate the "one-size-fits-all" approach to regulation.

Feature	PFBS (C4 Sulfonate)	PFOS (C8 Sulfonate)	PFNA (C9 Carboxylate)
Structure	4 Carbons, Sulfonic Acid	8 Carbons, Sulfonic Acid	9 Carbons, Carboxylic Acid
Half-Life (Human)	~ 1 month (approx.)	3.4 – 5.4 years	2.5 – 4.3 years
Bioaccumulation	Low (Serum)	High (Liver, Serum)	Very High (Liver, Serum)
Critical Effect (EPA)	Thyroid hormone reduction (T4)	Immune suppression	Dev. (Birth Weight), Repro.
Target Organs	Thyroid, Kidney	Immune, Liver, Thyroid	Liver, Repro, Immune
EPA Chronic RfD	0.0003 mg/kg-day (2021)	0.000002 mg/kg-day (proposed)	Withheld (2025)

6.1 The "Short-Chain" Trade-off

The industry’s pivot to PFBS was predicated on the shorter half-life. And indeed, PFBS is excreted much faster than PFOS. However, the 2021 assessment revealed that "faster excretion" does not equal "no toxicity." The mechanism of thyroid disruption (T4 reduction) occurs even with short-term exposures. Furthermore, the kidney hyperplasia observed with PFBS suggests that the very act of rapidly excreting the chemical places toxic stress on the renal system.⁷

6.2 The Long-Chain Persistence of PFNA

PFNA represents the other end of the spectrum. Its nine-carbon chain makes it incredibly difficult for the body to eliminate. It binds tenaciously to serum albumin and liver proteins. The leaked 2025 findings regarding male reproductive toxicity suggest that PFNA may act as an endocrine disruptor in ways distinct from PFOA and PFOS, potentially interfering with androgen synthesis or signaling.²⁷

The comparison also highlights the "whack-a-mole" problem. Regulators spent decades chasing PFOA and PFOS. Just as those were brought under control, PFBS emerged as a thyroid threat. Now, PFNA is identified as a reproductive hazard. With thousands of PFAS in commerce, the chemical-by-chemical approach of the IRIS program—which takes years to complete a single assessment—cannot keep pace with the introduction of new compounds.

7. Systematic Vulnerabilities in Environmental Policy

The PFBS and PFNA sagas reveal that the EPA’s scientific integrity is not a static fortress but a constantly besieged outpost. The vulnerabilities are structural and procedural.

7.1 The "Pocket Veto" of Science

The primary mechanism of suppression is the administrative bottleneck. While career scientists conduct the research and draft the assessments, the final release requires sign-off from political leadership. This allows an administration to simply "pocket veto" a report by refusing to finalize it. This was the tactic used for PFNA in 2025. There is no statutory deadline that forces the EPA to release an IRIS assessment once it is scientifically complete, leaving the timeline vulnerable to political manipulation.²⁷

7.2 The Manipulation of Uncertainty

When suppression is not possible, manipulation becomes the tool of choice. The PFBS case demonstrated how easily the complex math of risk assessment can be exploited. By targeting the "Uncertainty Factors"—which are, by definition, matters of professional judgment—political appointees can alter the final safety standard by orders of magnitude without changing the underlying data. They can argue that a factor of 1 is "sufficient" while scientists argue for 10, framing it as a difference of opinion rather than a violation of science.¹¹

7.3 The Role of the Inspector General

The one bright spot in this narrative is the role of the Office of Inspector General (OIG). The OIG’s 2023 report on the PFBS interference provided a definitive, independent account of the wrongdoing. It validated the complaints of the career scientists and established a historical record of the breach. However, the OIG is reactive, not proactive. It can investigate a scandal after it happens, but it cannot force the release of a withheld report in real-time.²²

8. Conclusion: The Integrity of the Number

Toxicology is often viewed as a grim and dusty discipline, a cataloging of the ways in which chemicals break the body. But in the context of environmental regulation, toxicology is the bedrock of justice. The Reference Dose is not just a number; it is a line in the sand. Below that line, the water is safe to drink. Above that line, a community is being poisoned.

The controversy over the PFBS and PFNA reports is a struggle over who gets to draw that line. In 2021, political appointees attempted to erase the line and replace it with a blurry "range," effectively prioritizing the financial health of polluters over the thyroid health of newborns. In 2025, the agency appears to be refusing to draw the line at all for PFNA, keeping the public in the dark about the risks to reproductive health and fetal development.

These events underscore the necessity of a firewall between the scientific assessment of risk and the political management of risk. The EPA’s "Scientific Integrity Policy" is a noble document, but as the PFBS scandal proved, it is only as strong as the people willing to enforce it. When career scientists like Dr. Orme-Zavaleta stand up to political interference, the system holds. When they are silenced or ignored, the system fails.

As we look to the future, the challenge of the "forever chemicals" will only grow. With thousands of PFAS in the environment, the EPA must find a way to assess toxicity faster and more transparently. It must insulate its scientists from the pressures of the election cycle. And it must recognize that while uncertainty is an inherent part of science, it should never be used as a hiding place for political expediency. The health of the next generation—their thyroids, their kidneys, their development—depends on the integrity of the number.

Table 1: Evolution of PFBS Toxicity Values (2021)

Assessment Version	Date Released	Chronic RfD (mg/kg-day)	Subchronic RfD (mg/kg-day)	Key Controversy
Compromised Assessment	Jan 19, 2021	Range: 0.0003 – 0.001	Range: 0.001 – 0.003	Political appointees ordered a range of values; reduced Database Uncertainty Factor (UFd) from 10 to 1 for upper bound.
Final Assessment	Apr 8, 2021	Single Value: 0.0003	Single Value: 0.001	Restored single value based on scientific consensus; reinstated UFd of 10 to account for missing developmental/immune data.

Table 2: Key EPA Personnel and Roles in the PFBS Controversy

Name	Role (2021)	Action/Stance
Andrew Wheeler	EPA Administrator (Trump)	Implicated by OIG in directing the "last-minute review" and alteration of the PFBS assessment.
Dr. Jennifer Orme-Zavaleta	Acting Science Advisor (Career)	Publicly declared the Jan 2021 assessment "compromised by political interference"; initiated its removal.
OCSPP Appointees	Political Staff	Disagreed with career scientists on Uncertainty Factors; pushed for the "range" approach to weaken standards.
EPA OIG	Oversight Body	Issued 2023 report confirming the interference and violation of Scientific Integrity Policy.

Table 3: Summary of Findings in Withheld 2025 PFNA Report

Endpoint	Finding	Significance
Developmental	Reduced birth weight in infants	Confirms human relevance of animal data; critical for protecting prenatal populations.
Reproductive (Male)	Reduced testosterone, sperm count	Identifies PFNA as a potent endocrine disruptor affecting male fertility; expands toxicity profile beyond liver/immune.
Hepatic	Liver damage (PPAR-alpha)	Consistent with other PFAS, reinforcing the "additive toxicity" concern for mixtures.
Status	"Completed and ready to post" (Apr 2025)	Reportedly withheld by administration despite passing scientific review.

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