# 766.3 Definitions.
The definitions in section 3 of TSCA and the definitions of §§ 704.3, 716.3, 717.3, and 790.3 of this chapter also apply to this part.
*Central Data Exchange* or *CDX* means EPA's centralized electronic submission receiving system.
*Chemical Information Submission System* or *CISS* means EPA's electronic, web-based reporting tool for the completion and submission of data, reports, and other information, or its successors.
*Congener* means any one particular member of a class of chemical substances. A specific congener is denoted by unique chemical structure, for example 2,3,7,8-tetrachlorodibenzofuran.
*Dibenzofuran* means any of a family of compounds which has as a nucleus a triple-ring structure consisting of two benzene rings connected through a pair of bridges between the benzene rings. The bridges are a carbon-carbon bridge and a carbon-oxygen-carbon bridge at both substitution positions.
*Dibenzo-p-dioxin* or *dioxin* means any of a family of compounds which has as a nucleus a triple-ring structure consisting of two benzene rings connected through a pair of oxygen atoms.
*Guidelines* means the Midwest Research Institute (MRI) publication *Guidelines for the Determination of Polyhalogenated Dioxins and Dibenzofurans in Commercial Products,* EPA contract No. 68-02-3938; MRI Project No. 8201-A(41), 1985.
*HDD* or *2,3,7,8-HDD* means any of the dibenzo-p-dioxins totally chlorinated or totally brominated at the following positions on the molecular structure: 2,3,7,8; 1,2,3,7,8; 1,2,3,4,7,8; 1,2,3,6,7,8; 1,2,3,7,8,9; and 1,2,3,4,7,8,9.
*HDF* or *2,3,7,8-HDF* means any of the dibenzofurans totally chlorinated or totally brominated at the following positions on the molecular structure: 2,3,7,8; 1,2,3,7,8; 2,3,4,7,8; 1,2,3,4,7,8; 1,2,3,6,7,8; 1,2,3,7,8,9; 2,3,4,6,7,8; 1,2,3,4,6,7,8; and 1,2,3,4,7,8,9.
*Homolog* means a group of isomers that have the same degree of halogenation. For example, the homologous class of tetrachlorodibenzo-p-dioxins consists of all dibenzo-p-dioxins containing four chlorine atoms. When the homologous classes discussed in this part are referred to, the following abbreviations for the prefix denoting the number of halogens are used:
tetra-, T (4 atoms)
penta-, Pe (5 atoms)
hexa-, Hx (6 atoms)
hepta-, Hp (7 atoms)
*HRGC* means high resolution gas chromatography.
*HRMS* means high resolution mass spectrometry.
*Level of quantitation* or *LOQ* means the lowest concentration at which HDDs/HDFs can be reproducibly measured in a specific chemical substance within specified confidence limits, as described in this part.
*Polybrominated dibenzofurans* refers to any member of a class of dibenzofurans with two to eight bromine substituents.
*Polybrominated dibenzo-p-dioxin* or *PBDD* means to any member of a class of dibenzo-p-dioxins with two to eight bromine substituents.
*Polychlorinated dibenzofuran* means any member of a class of dibenzofurans with two to eight chlorine substituents.
*Polychlorinated dibenzo-p-dioxin* or *PCDD* means any member of a class of dibenzo-p-dioxins with two to eight chlorine substituents.
*Polyhalogenated dibenzofuran* or *PHDF* means any member of a class of dibenzofurans containing two to eight chlorine, bromine, or a combination of chlorine and bromine substituents.
*Polyhalogenated dibenzo-p-dioxin* or *PHDD* means any member of a class of dibenzo-p-dioxins containing two to eight chlorine substituents or two to eight bromine substituents.
*Positive test result* means: (1) Any resolvable gas chromatographic peak for any 2,3,7,8-HDD or HDF which exceeds the LOQ listed under § 766.27 for that congener, or (2) exceeds LOQs approved by EPA under § 766.28.
*Precursor* means a chemical substance which is not contaminated due to the process conditions under which it is manufactured, but because of its molecular structure, and under favorable process conditions, it may cause or aid the formation of HDDs/HDFs in other chemicals in which it is used as a feedstock or intermediate.
*QA* means quality assurance.
*QC* means quality control.
*Reimbursement period* means the period that begins when the data from the last test to be completed under this part for a specific chemical substance listed in § 766.25 is submitted to EPA, and ends after an amount of time equal to that which had been required to develop that data or 5 years, whichever is later.
*TSCA* means the Toxic Substances Control Act, 15 U.S.C. 2601 *et seq.*
[52 FR 21437, June 5, 1987, as amended at 78 FR 72828, Dec. 4, 2013]