Isotope Fact Sheet Warrants a Close Look

July 10, 2013
EPA issues guidance to help aid and enforce compliance

The U.S. Environmental Protection Agency (EPA) recently released a fact sheet (www.epa.gov/oppt/newchems/pubs/isotopes.pdf ) on reporting chemical substances that contain different isotopes of the same elements listed on the Toxic Substances Control Act (TSCA) Inventory. The document has enforcement consequences so stakeholders should review it carefully. This column explains its significance.
Elemental isotopes and chemical compounds that contain elements of differing isotopes find commercial use in medical and other technical applications, some of which are not subject to TSCA jurisdiction. Elemental isotopes have the same number of protons and are the "same" element, but differ in molecular weight and possibly other properties because of a differing number of neutrons. The EPA says the goal of the fact sheet is to help entities comply with Premanufacture Notice (PMN) requirements for chemical substances that "contain deliberate isotopic modification to an element in the substance."

Little guidance exists on TSCA reporting of isotopes. In 2008, EPA outlined its approach to determining whether a nanoscale substance is a "new" chemical for TSCA Inventory purposes. EPA clarified then that it considers chemical substances with any differences in certain structural and compositional features to have different molecular identities, including, among others, "hav[ing] different isotopes of the same elements."

The EPA addressed in a 1997 enforcement proceeding whether a substance containing a distribution of isotopes in one or more of its atoms that's different from the distribution of naturally-occurring isotopes for those atoms requires TSCA notification. In a case regarding Concord Trading Corporation, Judge Greene rejected the EPA's motion for a summary decision on the issue of liability for TSCA Section 5 violations for importing depleted zinc oxide (DZO). Concord Trading contended that DZO was listed on the Inventory because zinc oxide was listed, arguing that because these chemicals have the same molecular structure and the only distinction between DZO and zinc oxide occurs at the sub-atomic level, EPA's assertion of liability must fail. Judge Greene concluded the EPA hadn't demonstrated DZO wasn't listed on the Inventory and that "greater certainty than is afforded by the current record must accompany legal conclusions of this type."

Several differences between the 2008 carbon nanotube (CNT) document and the fact sheet are interesting in that both seek to clarify "TSCA Inventory" status issues.  First, the fact sheet isn't published in the Federal Register, a distribution vehicle that arguably provides greater notice to stakeholders. Second, the fact sheet makes no mention of the enforcement consequences for failure to address any TSCA notification issues that may arise based on the EPA's new guidance. However, the fact sheet does offer a year in which to address what might (or might not) be compliance issues. In the CNT guidance, stakeholders had three months to address their TSCA notification obligations. At least one interpretation of this difference is that the EPA has diminished concerns with the consequences of any lack of clarity on the TSCA Inventory status of isotopes.

The EPA states in the fact sheet that chemical substances "have different molecular identities for the purposes of TSCA when they contain different isotopes of the same element or the isotopic composition of a constituent element has been intentionally changed from the naturally-occurring isotopic composition." If a specific isotope of a chemical substance isn't currently listed on the TSCA Inventory, it's subject to TSCA's new chemical reporting requirements. Similarly, if a chemical compound contains a constituent element that differs in its isotopic state from the Inventory-listed substance, it's subject to the new reporting requirements.

Manufacturers and importers of elemental isotopes or chemical compounds that contain isotopes other than those specified as part of the compound's TSCA Inventory listing should review this guidance carefully. While the EPA's fact sheet makes no reference to enforcement consequences, the agency could, and likely will, use its enforcement authority to address failures to notify the EPA of isotopes deemed "new" under TSCA Section 5.

LYNN BERGESON is Chemical Processing's Regulatory Editor. You can e-mail her at [email protected]Lynn is managing director of Bergeson & Campbell, P.C., a Washington, D.C.-based law firm that concentrates on conventional, biobased, and nanoscale chemical industry issues. She served as chair of the American Bar Association Section of Environment, Energy, and Resources (2005-2006).

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