U.S. EPA, TSCA Inventory Representation for Chemical Substances of Unknown or Variable Composition, Complex Reaction Products, and Biological Materials: UVCB Substances (1995) (ELR Order No. AD-3999)

• Author: Carolyne R. Hathaway/William K. Rawson/Ann Claassen/Julia A. Hatcher
• Pages: 299-303

TSCA Inventory Representation for Chemical Substances of Unknown or Variable Composition Page 299

Toxic Substances Control Act

Inventory Representation for

Chemical Substances of Unknown

or Variable Composition, Complex

Reaction Products and Biological

Materials: UVCB Substances

I. Introduction

is paper is a compendium of inform ation related to

the broad class of chemica l substances referred to as

UVCBs: Unknown or Variable compositions, Com-

plex reaction products and Biologica l materials. ese

chemical substa nces cannot be represented by unique

structures a nd molecula r formulas.  is paper is a

companion paper to other nomenclature papers i nclud-

ing “Combinations of two or more substanc es: Com-

plex reaction products” and “Products conta ining two

or more substances: Formulated and st atutory mix-

tures.” e Agency’s goal in developing t his paper is to

make it easier for the user s of the Inventory to interpret

listings for U VCB products and to underst and some

of the considerations that go into na ming new UVCB

substances for the Inventory.

Fundamental to the Inventory a s a whole is the prin-

ciple that entries on the Inventory are identie d as

precisely as possible for the commercia l chemical sub-

stance, as repor ted by the submitter. Substances that

are chemically i ndisting uishable, or even identical, may

be listed dierently on t he Inventory, depending on the

degree of knowledge th at the submitters possess and

report about such substance s, as well as how submit-

ters intend to represent the chemical identities to t he

Agency and to cus tomers. Althoug h these chemically

indistingu ishable substances are named di erently on

the Inventory, this is not a “nomenclature” issue, but

an issue of substance re presentation. Submitters should

be aware that their c hoice for substance repres entation

plays an important role in t he Agency’s determin ation

of how the substance wil l be listed on the Inventory.

II. Def‌initions

A. Class 1, Class 2 and UVCBs

Substances on the TSC A Inventory are div ided into

two classe s for ease of identic ation. Class 1 substances

are those single compound s composed of molecules

with particu lar atoms arranged in a denite, know n

structure. E xamples of Class 1 substances include:

acetone, iron, benzene and dimet hylmercury. ese

substances have di screte molecular formulas and fully-

dened structu ral diagrams. ey are inc luded in the

molecular formula index of t he printed Inventory and

are searchable in ma ny computerized dat abases by

molecular formula, na me or structural fragments.

Many commercial subst ances that are subject to TSCA

are not Class 1 substa nces, however. ey may have

unknown or vari able compositions or be composed of a

complex combination of dierent molecules. es e are

designated Class 2 sub stances.

Class 2 substanc es can be further divided into th ree

subgroups. e rst subgroup includes subst ances that

can be represented by denite Hi ll ordered molecu-

lar formulas but have var iable structural diagra ms.

An example of thi s rst subgroup is xylene, in which

the location of the substituent groups is va riable. e

second subgroup includes substanc es that can be

represented by denite molecular formu las but have

unknown str uctural diagrams, suc h as aluminum

cerium nickel sulde , AlCe3NiS7. e third subgroup

includes substances t hat have no denite molecular

formula representation and either par tial structural

diagram s or no structu ral diagrams. ese are t he

UVCB substances . Each name for a UVCB substance

includes more than one molecula r entity: as suc h, each

UVCB can be considered to be a c ategory of mol-

ecules, often closely re lated. An example of this kind

of substance is “Light oil (coal), coke- oven” (CASRN

65996-78-3* ), which is dene d on the Inventory as:

“the volatile organic liquid ex tracted from the

gas evolved in the hig h temperature (greater

than 700°C (1292°F)) destructive di stillation of

coal. Composed prima rily of benzene, toluene

and xylenes. May contai n other hydrocarbon

constituents.”

B. Natural Products: Product Combinations

that are Generally Chemical Substances

A combination that occur s in nature is a chemical sub-

stance and not a mix ture. If the natural product is pro-

cessed for commercia l purposes u sing only techniques

from the restricted li st below, the resulting subst ance is

considered to be included implicitly on the Inventory

NOTICE: e policies set out in this doc ument are

not nal Agency a ction, but are intended solely as

guidance. ey a re not intended, nor can they be relied

upon, to create any rights enforceable by a ny part y in

litigation with the United States. E PA ocials may

decide to follow the guidanc e provided in thi s docu-

ment, or to act at variance with t his guidance, based

on an analysis of spe cic circumstances.