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### TSCA Inventory Status of Nanosc ale Substances – General Approach January 23, 2008

Purpose

The approach outlined in this document describes how EPA currently determines whether a nanoscale substance is a “new” chemical only for the purposes of the Toxic Substances Control Act (TSCA) Inventory. The Agency may use different approaches under its other authorities (e.g., the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA)) in making regulatory status determin ations. In adopting this approach under TSCA, EPA is not establishi ng a precedent on how nanot echnology issues arising under other EPA programs, other Federal Government agencies, or other federal statutes will be
addressed.

Background

With the rapid advancement of nanot echnology and the introduction of nanoscale substances into U.S. commerce, it has b ecome important for the U.S. Environmental Protection Agency (EPA) to consider the exte nt to which these substances may be “new
chemical substances” under the Toxic Substan ces Control Act (TSCA), and thus subject to new chemical reporting under section 5( a) of TSCA. All substances, including nanoscale substances, that meet the TSCA defi nition of chemical substance are subject to
TSCA. 1

The TSCA Chemical Substance Inventory, established under section 8(b) of the Act, is comprised of substances that are consid ered to be “existing” in U. S. commerce. A substance not already included on the Inventory is considered to be a “new” chemical substance pursuant to TSCA section 3(9). Under section 5(a) of TSCA, a person must submit a Premanufacture Notice (PMN) to EPA at least 90 days before commencing manufacture or import, for a commercial purp ose, of a chemical substance not on the Inventory, unless the substance is exempt fr om reporting under section 5(h) of the Act.
The notification must include the information described in subparagraphs (A), (B), (C), (D), (F), and (G) of section 8(a)(2). After PMN review and upon receipt of a Notice of

1 Certain categories of chemical substances are not subject to TSCA. Examples include foods and food additives, pesticides, drugs, cosmetics, tobacco, nuclear material, or munitions.2 Commencement of Manufacture or Import (NOC), a chemical substance is added to the Inventory and becomes an “existing” chemical substance. Certain nanoscale substances that will be manufactured or imported fo r commercial purposes are expected to be new chemical substances and therefore subj ect to TSCA new chemical reporting requirements, as are any other new chemical substances.

EPA does not expect, however, that all nanoscale substances will qualify as new
chemicals under TSCA. EPA t hus intends to determine whet her nanoscale substances are new or existing chemical substances based on the case-by-case approach that the Agency has historically applied in determining the I nventory status of chemical substances.

Note that the principles in this paper are not rules or regulations, nor do they otherwise impose legally-binding requireme nts on EPA or the regulated community. Rather, this paper informs the public of the approach EPA has historically taken under TSCA in evaluating whether chemical substanc es are new, and further informs the public of EPA’s intention to follow this approach for nanomaterials that are chemical substances. Interested parties will be free to raise questions about the validity or applicability of these principles and EPA w ill consider whether the principles and their application are appropriate in that context at that time. Any decision regarding whether a chemical substance is a new chemical substance will be made based on the applicable statutory and regulator y requirements.

Determination of Whether A Chemical Substance is New or Existing

Section 3(2)(A) of TSCA defines the term “chemical substance” to mean “any organic or inorganic s ubstance of a particular molecular identity....” 2 Thus, in determining whether a chemical substance is a new chemical for purposes of TSCA Section 5, or instead is an existing chemical, EPA determines whether the chemical substance has the same molecular identity as a substance already on the Inventory. A chemical substance with a molecular identity that is not identical to any chemical substance on the TSCA Inventory is considered to be a new chemical substance (i.e. not

2 The text of section 3(2)(A) states that “the term ‘chemical substance’ means any organic or inorganic substance of a particular molecular identity, including

− (i) any combination of such substances occurring in whole or in part as a result of a chemical reacti on or occurring in nature, and (ii) any element or

uncombined radical.”3 on the Inventory); a chemical substance th at has the same molecular identity as a
substance listed on the Invent ory is considered to be an existing chemical substance.

Molecular Identity of a Chemical Substance

In general, a molecule is the smallest unit of matter that retains all of its chemical properties. Molecules that are made up of two or more atoms of like or different elements are held together by chemical bonds, with the princi pal types of chemical bonds being the ionic, cova lent, and metallic bonds.

EPA views molecular identity as being based on such structural and compositional features as the types and numbe r of atoms in the molecule, the types and number of chemical bonds, the connectivity of the atoms in the molecule, and the spatial arrangement of the atoms within the molecule . EPA considers chemical substances that differ in any of these structural and compos itional features to have different molecular identities. For example, EPA considers chemi cal substances to have different molecular identities for the purposes of TSCA when they:

• have different molecular formulas, i.e., th ey have the same types of atoms but a different number of atoms, e.g., ethane (C 2 H 6 ) and propane (C 3 H 8 ), or they have
the same number of atoms but different types of atoms, e.g., bromomethane (CH 3 Br) and chloromethane (CH 3 Cl), or they differ in both the types and numbers
of atoms

.

• have the same molecular formulas but ha ve different atom connectivities, i.e., they have the same types and number of atoms but are structural isomers (e.g., nbutane and isobutane) or positional isomers (e.g., 1-butanol and 2-butanol).

• have the same molecular formulas and atom connectivities but have different spatial arrangements of atoms, e.g., they have the same types, number, and connectivity of atoms but are isomeric (e.g., ( Z )-2-butene and ( E )-2-butene).

• have the same types of atoms but have di fferent crystal lattices, i.e., they have different spatial arrangements of the atom s comprising the crystals, e.g., anatase (atoms arrayed tetragonally) and brookite (atoms arrayed orthorhombically) forms
of titanium dioxide.

• are different allotropes of the same elemen t, e.g., graphite (carbon atoms arranged in hexagonal sheets with each atom bonded to three other atoms in the plane of a given sheet) and diamond (carbon atoms a rranged in a tetrahedral lattice with4 each atom bonded to four other atoms).

• have different isotopes of the same elements.

Molecules can themselves be arranged or aggregated into particles or other physical forms of various types, shapes, and sizes with concomitant physical properties. EPA does not consider these particles or ph ysical forms themselves to be different molecules with different molecular identities, but rather to be aggregates of molecules that have the same molecular identity, with no chemical bonding between the molecules. Consequently, EPA has not treated the mere a ggregation of molecules into particles or varying physical forms to result in different chemical substances with different molecular identities for the purposes of TSCA.

Fundamental to TSCA is the identificati on of chemical substances as precisely as practicable for listing on the TSCA Inventor y. Class 1 substances can be represented by a distinct chemical structure and specifi c molecular formula. Class 2 substances, including UVCB substances (substances of Unknown or Variable composition, Complex reaction products, and Biological materials), ar e an extremely broad category of chemical substances that cannot be represented by unique chemical structures or, in most cases, by unique molecular formulas. They can, howev er, be described using either partly indefinite names indicating va riable structures (e.g., heptene), or names that are descriptive of complex or poorly defined compos itions (e.g., tall-oil fatty acids), or that include sets of compositional characteris tics (e.g., C15-18 .alpha.-alkenes). UVCB substance names may also include a supplemental definition (e.g., pentene, hydroformylation products, with the supplementa l definition “A complex combination of products produced by the hydroformylation of pentene. It consists predominantly of C5 olefins and paraffins, C6 alcohols and alde hydes, and C18 acetals and boils in the range of approximately 45 degrees C to 290 degrees C...”). Class 2 substances that differ in such indefinite, variable, or complex struct ures, descriptive compositions, or sets of compositional characteristics, are considered di fferent chemical substances with different molecular identities for the purposes of TSCA.

Since EPA generally has not considered units of matter beyond molecules, such as physical aggregates, to be reportable to th e TSCA Inventory, EPA has not used particle size to distinguish for Inventory purposes two substances that are known to have the same molecular identity. Under principles of tr aditional chemistry these different forms of such substances would not be considered different chemicals. However, the form in5 which a chemical is manufactured, processed, used, or disposed of may play a role in evaluating the risk of a substa nce and considering whether to address it in some fashion
under TSCA.

TSCA Inventory Determination of Nanoscale Substances

As stated above, historically, EPA has not used particle size to distinguish substances that are known to have the same molecular identity for the purposes of the TSCA Inventory. In determining whether a nanoscale substance is a new or existing chemical, the Agency intends to continue to apply its current Invent ory approaches based on molecular identity, rather th an focus on physical attributes such as particle size.

New Chemicals

A chemical substance with a molecular identity that is not identical to any substance on the TSCA Inventory is consider ed to be a new chemical (i.e., not on the Inventory). A nanoscale substa nce might not have a non-na noscale counterpart with the same molecular identity (e.g ., nanotubes and carbon fullerenes), or a substance might be
found in both nanoscale and non-nanoscale form s, but if the substance has not been reported previously to EPA and placed on the Inventory in either form, it is considered a
new chemical.

A substance of this type would be subject to PMN reporting requirements regardless of whether it is manufactured or imported in the nanoscale form or the nonnanoscale form. When manufacture or im portation commences and the substance is added to the Inventory, the listing is considered to en compass both nanoscale and nonnanoscale forms of the substance. Consequently, subsequent forms of the substance manufactured or imported, whether nanoscal e or macroscale, which have the same molecular identity, would be consid ered existing chemical substances.

Systematic chemical nomenclature conve ntions may not exist for all nanoscale
substances identified as new chemicals. In these cases, EPA will likely need to apply new nomenclature conventions to fully, uniquely, unambiguously, and consistently identify and name these new chemical s ubstances for the purposes of the TSCA Inventory. As with existing nomencla ture conventions, EPA expects that new nomenclature conventions developed for Inventory listing of these novel substances will6 include data elements necessary to descri be and distinguish their unique molecular identities but will not describe different physical forms (e.g., particle sizes) of these new substances. In the interim, EPA intends to describe new chemical substances (including new substances that exist in nanoscale forms) to the best of its ability for listing these substances on the Inventory, recognizing th at names assigned to these substances and even their Inventory status may change on ce nomenclature conventions are developed. As necessary, EPA will provide interim guidance on molecular identity data elements that could be used by the notifier and the Agency to id entify and name these new chemical substances for listing on the Inventory.

Existing Chemicals

Under the approach outlined in this paper, a nanoscale substance that has the same molecular identity as a substance listed on th e Inventory (whether or not reported to the Agency as being manufactured or processed in nanoscale form) is considered an existing chemical, i.e., the nanoscale and non-nanoscale forms are considered the same chemical substance because they have the same molecular identity.

EPA’s rationale for considering this gr oup of nanoscale substan ces to be existing
chemicals is based on the TSCA definiti on of “chemical subs tance.” Although a
nanoscale substance that has th e same molecular identity as a non-nanoscale substance listed on the Inventory differs in particle size and may diffe r in certain phys ical and/or chemical properties resulting from the difference in particle size, EPA considers the two
forms to be the same chemical substance beca use they have the same molecular identity. The Inventory listing in this case is considered to repres ent both the nanoscale and nonnanoscale forms of the substance and, as su ch, does not distinguish between two forms having the same molecular identity that differ only in particle size and/or physical/chemical properties resulting from the difference in particle size.

Assistance to Manufacturers and Importers

In order for manufacturers or importers of nanoscale substances to determine whether their substances are new or existing ch emicals, and thus whether they are subject to PMN reporting requirements, EPA enc ourages companies to contact the New Chemicals Program to arrange a pre-notice co nsultation or to submit a request for an Inventory search under the bona fide intent to manufacture provision in 40 CFR §720.25.7 As EPA cannot always judge a priori if a nanoscale substance has a molecular identity
that is identical to a substa nce listed on the Inventory, EP A may require certain data on
the nanoscale substance in order to determin e whether it is an existing chemical covered by an existing Inventory listing, or whether it is a new chemical subject to PMN reporting requirements.