Polychlorinated Biphenyls (PCBs)

Patrick Wilson, Ph.D., M.P.H.Senior Regional Toxicologist

U.S. EPA

Restoration Advisory Board Former NAS Moffett Field

All Substances are Poisons.

There is None Which is Not a Poison.

The Right Dose Differentiates a Poison and a Remedy

Paracelsus (1493-1541)

THE DOSE MAKES THE POISON

PCB PHYSICAL PROPERTIES•Colorless

•Odorless

•Low vapor pressure

•Viscous liquid or solid

•Low electrical conductivity

• Flame Retardant

• Lipophilic (mix easily with oil or fat)

• Very Stable

PCBs CHEMICAL PROPERTIES

6'5'

4'

6

2'3'

4

2 3

5

meta

metameta

meta

parapara

ortho

ortho ortho

ortho

Structure of Polychlorinated Biphenyl (PCB) Molecule

PCB Molecular Structure

Fully-Chlorinated PCB MoleculeFully-Chlorinated PCB Molecule

Cl

Cl

Cl

Cl

Cl Cl Cl

Cl

Cl

Cl

Cl

Cl

Cl Cl Cl

Cl Cl Cl

Key ConceptsPolychlorinated biphenyls (PCBs): a mixture of compounds containing the biphenyl structure with varying numbers (i.e., one to ten) and arrangements of chlorine atoms attached.

Aroclor: One of nine commercial PCB mixtures, with varying levels of chlorination, formerly produced in the United States. The percent of chlorine content varies across the different Aroclors, depending on their intended uses. Generally, samples of pure Aroclorexhibit a distinct pattern of congener concentrations, but transformations during routine use and/or weathering can alter these patterns.

Key Concepts

Congener: One of the 209 possible PCB molecules, each distinguished by the number and arrangement of chlorine atoms. Commercially-produced PCB mixtures collectively include about 175 congeners, some at concentrations so low they are not detectable in environmental samples. One hundred and ten of the 209 congeners typically constitute 98 percent of PCB mass measured in samples.

Dioxin-Like Congener: One of 12 PCB congeners that exhibits toxicity similar to that of dioxin as the result of structural similarity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). The 12 dioxin-like PCB congeners are: 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189.

Key ConceptsDioxins and Furans: Two families of chemicals related by their similar physical and biological characteristics. Several hundred different compounds exist among the chlorinated dibenzo-p-dioxins (CDDs) and the chlorinated dibenzofurans (CDFs). The term “dioxin” is often used to refer to the most toxic dioxin compound, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). CDDs and CDFs are products of combustion created by anthropogenic activities and natural processes.

Weathering: Physical, biological, or chemical processes that can alter the chlorination pattern of a PCB molecule, and thereby change the congener composition of environmental mixtures of PCBs.

• Persistent in the environment

• Bioaccumulation and bioconcentrationeffects

• Found in virtually all human fat tissueHumans 2300 ng/g (ppb)

Human Breast Milk 1200 ng/g (ppb)

Why Were PCBs Banned??

• Cancer• Non-cancer Toxicity

KidneyLiverSkinImmune SystemNervous SystemDevelopmental\Reproductive System

Toxicities of Concern

What Are the Acute Health Effects of PCBs?

Chloracne (reversible)

Irritation of eyes, face & skin

What Are the Chronic Health Effects of PCBs?

Group A - Human Carcinogens

Group B - Probable Human Carcinogen

Group C - Possible Human Carcinogen

Group D - Not Classifiable

Group E - Negative Evidence

EPA Risk Assessment Guidelines for Carcinogens

POTENTIAL FOR HUMAN EXPOSURE

Superfund Sites With PCB Contamination

National PCB Fish Advisories

Bioaccumulation/Biomagnification

Mean Concentration of PCBs in Human Breast Milk

Serum PCB Concentrations

Serum PCB Concentrations

PCB Half Lives

How Are PCBs and Dioxins Related?

•Chemical structural similarity

•Dioxin-like PCBs pr Coplanar PCBs (CPCBs) are similar dioxins

•Preliminary test data indicate correlation between chemical structure and toxicity

•Products of Incomplete Combustion (PICs) of PCBs

•Dioxins

•Dioxin-like chlorinated polycyclic aromatic hydrocarbons (PAHs)

•Presence of dioxins or dioxin-like chlorinated PAHs results in risk regardless of route of formation

Exhibit A-2TOXIC EQUIVALENCY FACTORS (TEFs) FOR THE DIOXIN-LIKE PCBS

CongenerHumans/

Mammals1 Fish2 Birds2

77 0.0001 0.0001 0.0581 0.0003 0.0005 0.1

105 0.00003 <0.000005 0.0001114 0.00003 <0.000005 0.0001118 0.00003 <0.000005 0.00001123 0.00003 <0.000005 0.00001126 0.1 0.005 0.1156 0.00003 <0.000005 0.0001157 0.00003 <0.000005 0.0001167 0.00003 <0.000005 0.00001169 0.03 0.00005 0.001189 0.00003 <0.000005 0.00001

1 WHO TEFs for humans and mammals were updated in 2005 (Van den Berg, et al., 2006).2 WHO TEFs for fish and birds were published most recently in Van den Berg, et al. (1998).

PCB Congeners Toxicity

Intelligence is about making decisions based upon imperfect knowledge and among partially good choices.

Douglas R. HofstadterPulitzer Prize Winner