1

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. 
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 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.” 
3

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., 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 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 
4

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 
5

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 nonnanoscale form. When manufacture or importation commences and the substance is 

added to the Inventory, the listing is considered to encompass both nanoscale and nonnanoscale 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 
6

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 nonnanoscale 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. 
7

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.