November 28, 2018

Keeping Up with Priorities

Paul C. DeLeo, Ph.D.

It was recent big news when Sears finished circling the drain and filed for chapter 11 bankruptcy protection after 132 years in business. It has been hailed as the Amazon of its era. Though Sears was once ahead of its day, it did not adapt with the times. A common challenge in the chemical regulatory space is keeping up with the times as science advances rapidly and new technologies emerge every day. One area of current contention is how governments select chemicals from among the thousands currently on the market for priority assessment and expedited risk management action. A trend over the past two decades has been to use criteria that focus on particular human health hazards, especially carcinogenicity, mutagenicity, or reproductive toxicity; or a more risk-based approach that combines human or ecological toxicity criteria with exposure surrogates of persistence in the environment and potential for bioaccumulation up the food chain—the so-called persistent, bioaccumulative, and toxic chemicals, or PBTs. The US Congress liked the PBT approach so much that it included a provision to address specifically PBT chemicals in to what is now section 6(h) of the amended Toxic Substances Control Act (TSCA).

A Short History of Assessment Criteria

Chemical assessment criteria go back to the 1970s and are chronicled in an excellent article by Matthies et al. (2016; DOI: 10.1039/c6em00311g). An early example of assessment criteria can be found in the Great Lakes Water Quality Agreement of 1978 between Canada and the United States. It shifted the focus from conventional pollutants, such as phosphorus and bacteria, to toxic and hazardous polluting substances. It called out persistent toxic substances because they may remain in the environment for very long periods, can accumulate in living organisms, and can have serious impacts on the health of wildlife and humans. A later annex on persistent toxic substances defined them as “any toxic substance with a half-life in water of greater than eight weeks,” which was among the first metrics associated with a criterion.

The US Environmental Protection Agency (EPA) applied the assessment criteria approach to new chemicals under section 5 of TSCA by developing a category of PBT chemical substances in 1999 (64 Fed. Reg. 60,194). Thresholds for persistence and bioaccumulation were established that could lead to potential action under TSCA section 5(e).

In the late 1990s and early 2000s, the approach to chemical assessment criteria crystallized in a variety of national, regional, and international activities largely around those of persistence, bioaccumulation potential, and toxicity. There has been some consistency in the metrics associated with those criteria. For persistence, the concept of the half-life transformation is uniform. Bioaccumulation typically relies on the bioconcentration factor (BCF) or the octanol/water partition coefficient (expressed as log Kow) used alone, or to predict the BCF. The toxicity criterion may emphasize human or ecological health and any one of a number of end points.

Among other chemical assessment criteria, the Stockholm Convention on Persistent Organic Pollutants (POPs) identifies potential for long-range transport among its criteria for identifying POPs, and the German government recently put forward a proposal to consider a mobility criterion among a persistent, mobile, and toxic (PMT) or a very persistent and very mobile (vPvM) assessment of substances registered in Europe under regulations for Registration, Evaluation, Authorization and Restriction of Chemicals (REACH).

The Work Plan Approach and TSCA Section 6(h) PBTs

In Europe, REACH requires a PBT and very persistent and very bioaccumulative (vPvB) assessment for all chemical substances. Under the 2016 amendments to TSCA, section 6(h) requires expedited action for chemicals that are persistent, bioaccumulative, and toxic. Section 6(h) appears, however, to be a “one-off” provision targeting the 90 chemicals in the TSCA Work Plan for Chemical Assessments:  2014 Update (https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/tsca-work-plan-chemical-assessments-2014-update)—once EPA meets its obligations under the section for those 90 chemicals, it does not appear to have a mandate to continue to take expedited action.

The most likely mechanism for potential application of assessment criteria to existing chemicals under TSCA will be through section 6(b)(1) Prioritization for Risk Evaluation. The question is What lessons can be learned from section 6(h) PBTs?

The Work Plan was an exercise identifying priority chemicals for review and assessment. Beyond PBT criteria, it also considered criteria of potential concern to children’s health, neurotoxic effects, probable or known carcinogens, use in children’s products, and detection in biomonitoring programs. The result of the section 6(h) mandate was the identification of five Work Plan chemicals for expedited action:

  • Decabromodiphenyl ethers (DecaBDE), a flame retardant;
  • Hexachlorobutadiene (HCBD), a solvent in the manufacture of rubber compounds;
  • Pentachlorothiophenol (PCTP), a cross-linking agent to make rubber more pliable;
  • Phenol, isopropylated, phosphate (3:1; PIP), a flame retardant; and
  • 2,4,6-Tris(tert-butyl) phenol (2,4,6-TTBP), a chemical intermediate and antioxidant in petroleum products.

In June 2018, EPA released an environmental and human health hazards summary of the five chemicals. It noted that all five chemicals scored high in the Work Plan for hazard and catalogued available hazard information. Perhaps more interesting was EPA’s exposure and use assessment also released in June. Among the noteworthy observations are:

  • Production volumes for DecaBDE have declined over 99 percent from 2010 to 2015.
  • HCBD has not been intentionally manufactured in decades and is primarily generated as a by‐product of the manufacture of chlorinated solvents.
  • The market volume of 2,4,6-TTBP is almost entirely consumed in its primary use as an intermediate (94 percent) and as an antioxidant in fuel (6 percent).
  • PCTP has not been reported as being manufactured and/or imported into the US in recent years and there is very limited use (e.g., in the manufacture of golf ball cores).

Emissions Omission

For three of the five section 6(h) PBT chemicals (HCBD, 2,4,6-TTBP, and PCTP), the information released by EPA does not support a compelling case that they should have been the subject of expedited action by the agency. The key missing element that would enhance an evaluation of priorities for existing chemicals is characterization of emission by examining use volume, use patterns, and related information. Unfortunately, there is little indication that emission information will be incorporated into TSCA implementation. EPA released its current thinking regarding prioritization of the TSCA Active Inventory in late September 2018 (A Working Approach for Identifying Potential Candidate Chemicals for Prioritization; 83 Fed. Reg. 50,366; https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/identifying-existing-chemicals-prioritization-under-tsca) and there is little emphasis on use volume or use patterns as criteria for prioritization and selection of chemicals for assessment and potential regulatory action. That may be because there are few good options for EPA to obtain information needed. Chemical Data Reporting (CDR) under TSCA is one opportunity, but the activity is infrequent (quadrennial) and use information reported is generally not sufficiently specific or accurate since it largely is not provided by actual users of the chemicals. The consideration of whether a chemical is primarily used as an intermediate is a welcome feature of EPA’s proposed prioritization approach but there are likely to be questions about the relevance of chemicals selected for assessment.

The same week that Sears declared bankruptcy Amazon announced its new chemicals management policy. One cannot help but wonder if EPA might not cede regulatory “market share” to Amazon and other retailers if TSCA implementation is not perceived as being relevant because EPA did not adapt with the times.

Paul C. DeLeo, Ph.D.

Published: November 28, 2018

Paul C. DeLeo, Ph.D., is a Principal with Integral Consulting Inc. Dr. DeLeo is a scientific professional whose focus over the past two decades has included applied research and regulatory and public outreach related to the human and environmental safety of food ingredients, pesticides, pharmaceutical and personal care products, and cleaning products.