epa presentation to the moffett field restoration advisory board on may 15, 2008, giving background...
TRANSCRIPT
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