EPA’s scientific peer reviewers don’t mince words in blasting its 1,4-dioxane and HBCD risk evaluations

Richard Denison, Ph.D., is a Lead Senior Scientist.

Late Friday is getting to be a popular time for the toxics office at the Environmental Protection Agency (EPA) to publicly release the peer review reports of its Scientific Advisory Committee on Chemicals (SACC).

As EPA did for the Committee’s peer review report on the agency’s first draft risk evaluation under the Toxic Substances Control Act (TSCA), EPA quietly posted sometime quite late last Friday the SACC’s reports on the next two chemicals:  the likely carcinogenic solvent 1,4-dioxane and the developmentally toxic flame retardant hexabromocyclododecane (HBCD).

Even a quick read of the Executive Summaries of those reports amply illustrates why EPA sought to bury them.  I’ll focus here on 1,4-dioxane.

The SACC did note that the content and organization of this draft risk evaluation was “much improved” over the first one for Pigment Violet 29.  So much for the good news; things went downhill from there for EPA. 

Systematic review:  The SACC blasted EPA’s jerry-rigged TSCA systematic review (SR) approach, which EDF and others have roundly criticized for its major departures from best practice in SR and EPA’s failure to submit its approach to the National Academy of Sciences (NAS) for peer review, which it promised to do nearly a year ago.

Here’s what the SACC had to say (p. 17):

Committee members did not find the systematic review to be a transparent and objective method for gathering the relevant scientific information, scoring its quality, and integrating the information.  Committee members noted consistent problems with both the design and implementation of the systematic review.  The Committee found it difficult to determine whether the relevant information was properly evaluated and considered in the Evaluation because key references that were relied on in the risk evaluation were not in the systematic review bibliography and/or the Data Quality evaluation.  Committee members consistently found mistakes and inconsistencies in the systematic review and disagreed with some of the data quality ratings.

Exclusions of uses and exposures:  The SACC also castigated EPA for its highly controversial decisions to exclude from its risk evaluations both known uses of, and known releases of and exposures to, 1,4-dioxane.  After concluding that EPA’s “environmental fate, exposure, and effects assessment was inadequate,” the SACC elaborated (p. 18, emphases added):

The dearth of measured data to inform a robust risk assessment of 1,4-Dioxane is an artifact of any approach to eliminate uses that may influence determination of environmental concentrations, frequency of occurrence, or spatial distribution.  Much more information is required to inform a robust risk assessment.  Some Committee members stated that omission of consumers and the general United States (U.S.) population is inappropriate, unless risk assessments have been completed at this point in time.  Exposure scenarios that include consumers are important given the known presence of 1,4-Dioxane in plastics, other commercially available products, surface water, drinking water, groundwater, and in sediments.  The Committee also had concerns that the omission of these multiple routes of exposure puts workers who inhale or ingest 1,4-Dioxane outside the workplace at even greater risk.

The SACC roundly rejected EPA’s unsupported assertion that other statutes adequately address consumer, general population and environmental risks (p. 18, emphases added):

The Committee discussed that if each program office of the EPA says others are assessing the risks and thus not including them in their assessment, the U.S. public will be left with no overall assessment of risks.  If risks have been assessed by other program offices of EPA then the Agency should present them as part of the underlying data to support this TSCA Evaluation—if not, the Agency must gather the data for an assessment or include an assessment based on the assumption of near-worst-case exposures.  General human population and biota exposure must be assessed for inhalation, ingestion, and dermal routes.

The SACC went on to say:

The Committee concurred with the public comments of Dr. Fenner-Crisp that the current process does not follow EPA guidance for risk assessment. The Committee agreed with the National Tribal Toxics Council and the Environmental Defense Fund in the call for the Agency to consider all exposure routes for the broader populations.

The SACC concluded (pp. 18-19, emphases added):

Unfortunately, many of the inadequacies of the draft Evaluation have their genesis in a faulty problem formulation. There are several areas where the problem formulation strayed from basic risk assessment principles by omitting well known exposure routes such as water consumption by all occupationally and non-occupationally-exposed humans as well as similar exposures to other biological receptors. …

The decision by the EPA to defer concerns of consumer exposure, or exposure of the general public, through ambient water or air because “other environmental statutes administered by EPA adequately assess and effectively manage these exposures” was not deemed acceptable by many of the Committee members.

Reliance on voluntary information:  The SACC also was highly critical of EPA’s heavy reliance on information submitted voluntarily by industry.   After noting that even for considered exposure sources and routes, the data used by EPA are “inadequate,” the SACC noted (pp. 18-19, emphases added):

Some Committee members noted that TSCA does not call for use of voluntary data, rather the law “requires that EPA operate in a manner that is consistent with the best available science and make decisions based on the weight of the scientific evidence.” Note this statute does not say best available data, but best available science.

EPA’s characterization of occupational inhalation exposure which lead to the Agency finding that 1,4-Dioxane, as used in manufacturing (import), processing (repackaging), and distribution in other considered downstream uses, does not present an unreasonable risk of injury to health is not adequately supported in this draft Evaluation.  The information used to evaluate worker exposure was generally lacking in its ability to present a coherent picture of this critical element of risk.  Reliance on meager air monitoring data that were presented without context failed to provide the needed confidence that exposures were being reasonably evaluated.

Cancer mode of action (MOA):  The SACC also addressed EPA’s introduction of an hypothesized alternative MOA for 1,4-dioxane’s carcinogenicity that would assume a “safe” threshold for the chemical, which EPA ultimately proposed to reject.  The SACC affirmed the need to retain a no-threshold approach, stating (p. 20) that “the Committee concluded that there was not sufficient evidence for [the hypothesized alternative MOA], or indeed, any other MOA. The Committee, in general, agreed that a default linear extrapolation for cancer risk was appropriate.”

Assumed acceptable level of cancer risk:  The SACC raised serious concerns with EPA’s allowance for a 1-in-10,000 level of excess cancer risk, noting that it was used “without adequate explanation and justification” (p. 23).  The SACC noted EPA’s only reference was to the National Institute for Occupational Safety and Health (NIOSH) – which operates within the confines of the Occupational Safety and Health Act, not TSCA.

Assumed use of PPE:  The SACC heavily criticized EPA’s assumption that personal protective equipment (PPE) would always be used and would be universally effective.  A section of the report addressing this is titled “The Assumed Use of PPE (i.e., Respirators) is Not Appropriate” (p. 53), and a critique of EPA’s assumptions regarding dermal exposures begins by stating:  “Glove use should not always be assumed to be protective” (p. 55).


Finally, the SACC raised the broad concern that conducting these early risk evaluations correctly is critical to ensuring sound assessments going forward, and explicitly rejected EPA’s constant refrain that it doesn’t have enough time to do a good job (pp. 18-19, emphasis in original):

The Committee considered that procedures refined in these first TSCA assessments will be important to improving future assessments, and as such they must protect the environment and human health.  Recognizing that haste is incompatible with robust, protective, and reliable risk assessments, the Committee recommended that a comprehensive risk assessment, including all routes to non-occupational routes of exposure include currently available data or in the absence of data near-worst-case estimates of release and exposure scenarios along with safety factors.


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