TSCA Inventory Status of Nanoscale Substances – General Approach 

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.  

	

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 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….”  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 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 (CH3Cl), 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 (E)-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 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 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 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. 
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.  

 Certain categories of chemical substances are not subject to TSCA. 
Examples include foods and food additives, pesticides, drugs, cosmetics,
tobacco, nuclear material, or munitions.

− (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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