TSCA Inventory Status of Nanoscale 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 determinations. In adopting this approach under
TSCA, EPA is not establishing a precedent on how nanotechnology issues arising under
other EPA programs, other Federal Government agencies, or other federal statutes will be
addressed.
Background
With the rapid advancement of nanotechnology and the introduction of nanoscale
substances into U.S. commerce, it has become important for the U.S. Environmental
Protection Agency (EPA) to consider the extent to which these substances may be "new
chemical substances" under the Toxic Substances 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 definition 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 considered 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 purpose, of a chemical substance not on the
Inventory, unless the substance is exempt from 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.
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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 for commercial purposes are expected to be new
chemical substances and therefore subject 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 thus intends to determine whether nanoscale substances are
new or existing chemical substances based on the case-by-case approach that the Agency
has historically applied in determining the Inventory status of chemical substances.
Note that the principles in this paper are not rules or regulations, nor do they
otherwise impose legally-binding requirements 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 substances 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 will 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 regulatory 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 substance 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 reaction or occurring in nature, and (ii) any element or
uncombined radical."
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on the Inventory); a chemical substance that has the same molecular identity as a
substance listed on the Inventory 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 principal types of chemical bonds
being the ionic, covalent, and metallic bonds.
EPA views molecular identity as being based on such structural and
compositional features as the types and number 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 compositional features to have different molecular
identities. For example, EPA considers chemical substances to have different molecular
identities for the purposes of TSCA when they:
	have different molecular formulas, i.e., they have the same types of atoms but a
different number of atoms, e.g., ethane (C2H6) and propane (C3H8), or they have
the same number of atoms but different types of atoms, e.g., bromomethane
(CH3Br) and chloromethane (CH3CI), or they differ in both the types and numbers
of atoms.
	have the same molecular formulas but have different atom connectivities, i.e.,
they have the same types and number of atoms but are structural isomers (e.g., n-
butane 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 ()-2-butene).
	have the same types of atoms but have different crystal lattices, i.e., they have
different spatial arrangements of the atoms comprising the crystals, e.g., anatase
(atoms arrayed tetragonally) and brookite (atoms arrayed orthorhombically) forms
of titanium dioxide.
	are different allotropes of the same element, 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 arranged in a tetrahedral lattice with
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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 physical 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 aggregation 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 identification of chemical substances as precisely
as practicable for listing on the TSCA Inventory. Class 1 substances can be represented
by a distinct chemical structure and specific molecular formula. Class 2 substances,
including UVCB substances (substances of Unknown or Variable composition, Complex
reaction products, and Biological materials), are 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, however, be described using either partly
indefinite names indicating variable structures (e.g., heptene), or names that are
descriptive of complex or poorly defined compositions (e.g., tall-oil fatty acids), or that
include sets of compositional characteristics (e.g., C15-18 .alpha.-alkenes). UVCB
substance names may also include a supplemental definition (e.g., pentene,
hydroformylation products, with the supplemental definition "A complex combination of
products produced by the hydroformylation of pentene. It consists predominantly of C5
olefins and paraffins, C6 alcohols and aldehydes, 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 structures, descriptive compositions, or sets of
compositional characteristics, are considered different 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 the 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 traditional chemistry these different forms of
such substances would not be considered different chemicals. However, the form in
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which a chemical is manufactured, processed, used, or disposed of may play a role in
evaluating the risk of a substance 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 Inventory approaches based
on molecular identity, rather than 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 considered to be a new chemical (i.e., not on the
Inventory). A nanoscale substance might not have a non-nanoscale counterpart with the
same molecular identity (e.g., nanotubes and carbon fullerenes), or a substance might be
found in both nanoscale and non-nanoscale forms, 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 non-
nanoscale form. When manufacture or importation commences and the substance is
added to the Inventory, the listing is considered to encompass both nanoscale and non-
nanoscale forms of the substance. Consequently, subsequent forms of the substance
manufactured or imported, whether nanoscale or macroscale, which have the same
molecular identity, would be considered existing chemical substances.
Systematic chemical nomenclature conventions 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 substances for the purposes of the TSCA
Inventory. As with existing nomenclature conventions, EPA expects that new
nomenclature conventions developed for Inventory listing of these novel substances will
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include data elements necessary to describe 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 that names assigned to these substances and
even their Inventory status may change once 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 identify 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 the 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 group of nanoscale substances to be existing
chemicals is based on the TSCA definition of "chemical substance." Although a
nanoscale substance that has the same molecular identity as a non-nanoscale substance
listed on the Inventory differs in particle size and may differ in certain physical and/or
chemical properties resulting from the difference in particle size, EPA considers the two
forms to be the same chemical substance because they have the same molecular identity.
The Inventory listing in this case is considered to represent both the nanoscale and non-
nanoscale forms of the substance and, as such, 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 chemicals, and thus whether they are subject
to PMN reporting requirements, EPA encourages companies to contact the New
Chemicals Program to arrange a pre-notice consultation or to submit a request for an
Inventory search under the bona fide intent to manufacture provision in 40 CFR 720.25.
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As EPA cannot always judge a priori if a nanoscale substance has a molecular identity
that is identical to a substance listed on the Inventory, EPA may require certain data on
the nanoscale substance in order to determine whether it is an existing chemical covered
by an existing Inventory listing, or whether it is a new chemical subject to PMN reporting
requirements.
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