PCBs

Introduction
PCBs Chemical Structure and Congeners
Effects on Humans
Effects on the Aquatic Environment
Monitoring Techniques and Standards
Safety Cards
Links

Introduction

*IARC: International Agency for Research on Cancer.

Polychlorinated biphenyls, (PCBs) are a group of highly toxic chlorinated industrial chemicals used as dielectrics, coolants and lubricants in electrical transformers and other electrical equipment, weatherproofers, and to prolong residual activity of pesticides. PCBs are usually released to the environment as a mixture in which other chemicals are also present. PCBs are fire-resistant, have a low volatility, and are relatively stable and persistent, making them well-suited for industrial use but also problematic in the environment. PCBs had been in use for more than 25 years when in 1966 attention focussed on PCB poisoning birds and people. By the late 1970's, evidence of the extreme persistence and adverse health effects of PCBs had resulted in bans on their manufacture in some industrialised countries. Many industrialised countries have taken, now, steps to control and restrict the flow of PCBs into the environment. The most influential force leading to these restrictions has probably been a 1973 recommendation from the Organisation for Economic Co-operation and Development (OECD), (WHO, 1993). Although they are no longer manufactured or imported into many countries, there remain seizable quantities in storage. In addition, PCB fluids are present in many older transformers, fluorescent lighting fixtures, and other electrical devices and appliances. These are vulnerable to release into the environment, as older components can leach. Other sources of PCB contamination come from improper disposal or incineration of PCBs and PCB-containing waste sites.(WFPHA, World Federation of Public Health Associations, 2000).

Because of their high persistence, and their other physical and chemical properties, PCBs are present in the environment all over the world. In past years, many thousands of samples of different foodstuffs have been analysed in several countries for contaminants including PCBs. The levels for the most important PCB-containing food items were: animal fat, 20-240 micrograms/kg of fat; cow's milk, 5-200 micrograms/kg; butter, 30-80 micrograms/kg; fish, 10-500 micrograms/kg, on a fat basis. The major foods in which contamination with PCBs needs consideration are fish, shellfish, meat, milk, and other dairy products. Median levels in fish, reported in various countries, are of the order of 100 micrograms/kg (on a fat basis). (WHO, 1993). PCBs are affecting more heavily population of cold areas of the planet. A study in the late 1980s showed that PCB levels in milk of Inuit women from the east coast of Hudson Bay in northern Quebec were approximately five times higher than in women of southern Canada. The U.S. Food and Drug Administration requires that dairy, poultry, seafood and infant products not contain PCBs in more that 0.2-3 ppm. Nonetheless, average human exposure may exceed the U.S. EPA and FDA's regulatory guidelines in many foods. (WFPHA, 2000).

PCBs Chemical Structure and Congeners

PCBs is a category, or family, of chemical compounds formed by the addition of chlorine (Cl2) to biphenyl (C12H10), which is a dual-ring structure comprising two 6-carbon benzene rings linked by a single carbon-carbon bond. The nature of an "aromatic" (benzene) ring allows a single attachment to each carbon. This means that there are 10 possible positions for chlorine substitution (replacing the hydrogens in the original biphenyl). Species with a single chlorine substituent are called "monochlorobiphenyl" (or just "chlorobiphenyl"). Species with two chlorines are called "dichlorobiphenyl", and the those with three through ten chlorines, in order, are called: "tri...", "tetra...", "penta...", "hexa...", "hepta...", "octa...", "nona...", and "decachlorobiphenyl". The positions of the chlorine substituents on the rings are denoted by numbers assigned to each of the carbon atoms, with the carbons supporting the bond between the rings being designated 1 and 1'. Any single, unique, well-defined chemical compound in the PCB category is called a "congener". The name of a congener specifies the total number of chlorine substituents and the position of each chlorine. For example: 4,4'-dichlorobiphenyl is a congener comprising the biphenyl structure with two chlorine substituents, one on each of the two carbons at the "4" (also called "para") positions of the two rings. There are 209 PCB congeners. (U.S. EPA web page on PCBs names for congeners).

Effects on Humans

Acute effects of PCB exposure in humans were documented following ingestion of contaminated rice oil in Japan in 1968 and Taiwan in 1979. Long term studies of the more than 2,000 people who were exposed during these events revealed increased mortality due to PCB intake. A positive association was established between PCB dosing and acute liver damage, with liver disease being the cause of death in a significant number of exposed people. Acute exposure to PCBs ash also caused chloracne, a chemically induced acneform eruption. Human fetal exposures of PCBs are associated with neural and developmental changes, lower psychomotor scores, short-term memory and spatial learning effects, and long-term effects on intellectual function. Neurological dysfunction had been associated with perinatal PCB exposure in several Dutch studies.
Perinatal exposure to PCBs may impair immune responses to infection as suggested by a 20-fold higher incidence of infectious diseases and ear infections in a study of Inuit infants with high PCB exposure compared to individuals in a lesser exposed population. (WFPHA, 2000). A group of PCBs: non-and mono-ortho substituted chlorinated biphenyls, shows for their coplanar stereo structure similar biological effects, both on humans and wildlife, to 2, 3, 7, 8 TCDD. They cause hepato-, immuno, reproductive, and dermal toxicities. (Paasivirta, The handbook of environmental chemistry, Springer-Verlag, 2000).

Effects on The Aquatic Environment

PCBs have a long and documented history of adverse effects in wildlife. They have been associated with poor reproductive success and impaired immune function of captive harbour seals in the Arctic. After a major flood in the Saginaw River basin in Michigan in 1986 allowed PCB contaminants to spread through the ecosystem, the following year's hatch rate of Caspian terns in the area dropped by more than 70 percent. Hatching chicks showed developmental deformities, and none survived more than five days, Hatch ability of this Caspian tern colony did not show recovery after three more breeding seasons. (WFPHA, 2000).
In water, PCBs are adsorbed on sediments and other organic matter; experimental and monitoring data have shown that PCBs concentration in sediment and suspended matter are higher than those in associated water columns. On the basis of their water solubilities and n-octanol-water partition coefficients, the lower the chlorinated PCB congeners will sorb less strongly than the higher chlorinated isomers. Although adsorption can immobilise PCBs for relatively long periods in the aquatic environment, desorption into the water column has been shown to occur by both abiotic and biotic routes. The substantial quantities of PCBs in aquatic sediments can therefore act as both an environmental sink and a reservoir of PCBs for organisms. Most of the environmental load of PCBs has been estimated to be in aquatic sediment. (WHO, 1993). Even though many countries have controlled both use and release of PCBs and new input into the environment is on a reduced scale compared with the past, the available evidence suggests that the cycling of PCBs is causing a gradual redistribution of some congeners towards the marine environment. (WHO, 1993).

Several factors determine the degree of bioaccumulation in adipose tissues: the duration and level of exposure, the chemical structure of the compound, and the position an pattern of substitution. In general, the higher chlorinated congeners are accumulated more readily. Experimentally determined bioconcentration factors of various PCBs in aquatic species (fish, shrimp, oyster) range from 200 up to 70 000 or more. In the open ocean, there is bioaccumulation of PCBs in higher trophic levels with an increased proportion of higher chlorinated biphenyls in higher ranking predators.

Monitoring Techniques and Standards

The HSDB, Hazardous Substances Data Bank: type PCBs

This site reports a full list of information on the substance as: Human Health Effects, Animal Toxicity Studies, Environmental Fate & Exposure, Environmental Standards & Regulations, Chemical/Physical Properties, Chemical Safety & Handling, Occupational Exposure Standards, Laboratory Methods, Synonyms and Identifiers.

Toxicology report with toxicity data from the Vermont Safety Information Resources, Inc.

This site provides a list or toxicity tests results, references for toxicity literature reviews, USA standards and regulations, occupational exposure limits in different states all over the world, and reference to NIHOSH, National Institute for Occupational Safety and Health, analytical standard methods.

Safety Cards

ICSC, International Chemical Safety Cards European Union version

The International Occupational Safety and Health Information Centre (CIS) access to
International Chemical Safety Cards: two pages data sheets on pure substances from the ILO/WHO/UNEP International Program on Chemical Safety (IPCS).

ICSC, International Chemical Safety Cards U.S. National version

The National Institute for Occupational Safety and Health (NIOSH) access to
International Chemical Safety Cards.

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