POLYCHLORINATED BIPHENYLS

(PCBs)

By Jenn Corpuz

PHYSICAL & CHEMICAL PROPERTIES

C12H10-xClx MP: 340-375 C Thin, lightly colored

liquids to yellow or black waxy solids

picture from: www.epa.gov

PRODUCTION HISTORY Developed in 1929 Multiple congeners developed Used as a coolant for electrical equipment and as a

plasticizer in paints, plastics and rubber products Banned by EPA in 1979 Products manufactured before 1979 are still releasing

PCBs into the environment Most commonly known as: Aroclor, Phenoclor and

Kanechlor

MODE OF ENTRY INTO AQUATIC ENVIRONMENT

Run off Poorly maintained hazardous waste sites

containing PCBs Burning of wastes in municipal or industrial

incinerators

CHEMICAL REACTIVITY 209 known congeners

(species) Most common: Aroclor,

Phenoclors, Kaneochlors

Most toxic: coplanar mono-orthosubstituted species

Figure by Safe et. al.

CHEMICAL REACTIVITY (cont’d) Most species: insoluble in

water Solubility decreases with

increasing chlorination 0.01-0.0001ug/L Halflives: 3 wks -2 yrs (air) <6 yrs (aerobic

soils/sediments)picture from: www.epa.gov

TOXICITY TO AQUATIC LIFE Sediment bound Bioaccumulated and magnified through the

food chain Rainbow Trout LC50= 0.32ug/L

Laboratory Rats LD50= 1g/kg by weight Acute toxicity generally low Chronic toxicity gave results

TOXIC EFFECTS NOTED PCBs are known carcinogens Found to be highly associated with cancers

in the immune, reproductive and endocrine systems

Iipophilicity allows PCBs to live in animal’s tissues

MODE OF ENTRY Ingestion (most common)

gills

MODE OF INTERACTION Induces AHH and

binds to AhR Binds ARNT Leads to gene

transcription PCBs have been

linked to activation of oncogenes and inactivation of tumor suppressing genes

BIOCHEMICAL METABOLISM AND BREAKDOWN

CYP1A and CYP1B are induced

Resulting hydroxylated and methylsulfonyl PCB metabolites bind to DNA

Highly chlorinated biphenyls are metabolized very slowly if at all

Phase II (excretion) is unlikely

Figure from Tabb et. al.

DEFENSE STRATEGIES FOR DETOXIFICATION

For less chlorinated species: oxygenating chlorine sites excretion through urine

None for highly chlorinated species

BIBLIOGRAPHY www.epa.gov

www.ehponline.org

Hansen, Larry G. “Stepping Backward to Improve Assessment of PCB Congener Toxicities.” Environmental Health Perspectives. Volume 106. Feb 1998.

McConnell, Ernest. “Comparitive Toxicity of PCBs and Related Compounds in Various Species of Animals.” Environmental Health Perspectives. Volume 60. 1985. 29-33.

Neal, Robert A. “Mechanisms of the Biological Effects of PCBs, Polychlorinated Dibenzo-p-dioxins, and Polychlorinated Dibenzofurans in Experimental Animals.” Environmental Health Perspectives. Volume 60. 1985. 41-46.

Safe, Stephen, Stelvin Bandiera, Tom Sawyer, Larry Robertson, Lorna Safe, Andrew Parkinson, Paul E. Thomas, Dene E. Ryan, Linda M. Reik, Wayne Levin, Mary Anne Denomme, and Toshio Fujita. “PCBs: Structure-Function Relationships and Mechanism of Action.” Environmental Health Perspectives. Volume 60. 1985. 47-56.

Tabb, Michelle M., Vladyslav Kholodovych, Feliz Grun, Changcheng Zhou, William J. Welsh, and Bruce Blumberg. “ Highly Chlorinated PCBs inhibit the Human Xenobiotic Response Mediated by Steroid and Xenobiotic Receptor (SXR). Environmental Health Perspectives. Volume 112. 163-169.