A Risk-Management Strategy for PCB-Contaminated Sediments (2001) / Chapter Skim
Currently Skimming:
PCBs in the Environment
PCBs in the Environment
Pages 23-51
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 23... ...
Polychiorinated biphenyis have between 1 and 10 chlorine atoms substituting for hydrogen atoms on the biphenyl rings (Figure 2-11. The various number and positions of the chlorine atoms on the biphenyl molecule result in up to 209 possible chemical structures designated as congeners in the scientific literature.
|
From page 24... ...
These conditions and properties favor the production of specific congeners; thus, there are different relative proportions of congeners within given in(lustrial mixtures. These mixtures exist as liquids to viscous solids.
|
From page 25... ...
PCBs in the Environment 25 monochlorobiphenyJa ~1 hi> dichJorobiphenyJs CI~' pen tachiorobipheny/s Cl itCI ~C! \CI \CI Clew Cl\ CI ~CI \CI Cl\ CI Cl~ Cl Cl CI\ CI~C Cl Cl Cl\ 'Cl ~CI Ct Cl FIGURE 2-2 Examples of PCB homologues.
|
From page 26... ...
comparison of the shape and size of a coplanar chlorinated biphenyl to 2,3,7,8-TCDD. last two numbers of which generally, but not always, refer to the percent by weight of chlorine in the mixture.
|
From page 27... ...
Due to the Tong service life of this equipment, considerable amounts of PCBs are likely to remain in use for many TABLE 2-1 Domestic Uses of PCBs Category Type of Product Closed electrical systems Nominally closed systems New Total Use Open-end applications Transformer, capacitors, other (minor) electrical insulating and cooling applications Hydraulic fluids, heat transfer fluids, lubricants Plasticizers, surface coatings, ink and dye carriers, adhesives, pesticide extenders, carbonless copy paper, dyes 61% before 1971; 100% after 1971 13% before 1971; 0°/O after 1971 26% before 1971 0% after 1971 Source: NRC (1979~.
|
From page 28... ...
The National Toxics Inventory, an inventory conducted every 3 years by EPA under the Clean Air Act Amendments of 1990, reports atmospheric releases of hazardous air pollutants, including PCBs, from mobile and stationary sources. Point source air emissions of PCBs were 136 pounds per year from 127 maximum achievable control technology sources, which included utility boilers, industrial boilers, waste incineration, sewerage sludge incineration, Portland cement manufacturing, municipal landfill, and other biological incineration (EPA 2000b)
|
From page 29... ...
Materials that might contain PCBs include automobile and truck parts (e.g., nonmetallic parts such as glass and plastic) , military equipment (e.g., ship parts)
|
From page 30... ...
Particles suspended in the water column are affected by hydrodynamic conditions. PCBs that are freely dissolved or associated with DOC can cross the sediment-water interface and move between the deeper sediments (below the bioturbation or bioactive surface sediment)
|
From page 31... ...
can cause relative proportions of some congeners to increase while others decrease (Boon and Eijgenraam 1988; Boriakoglu and Walker 1989~. Because the susceptibility of PCBs to degradation end bioaccumulation is congener specific, the composition of PCB congener mixtures that occur in the environment differs substantially from that ofthe original industrial mixtures released into the environment (Zell ant!
|
From page 32... ...
For example, PCBs can enter the aquatic food web via uptake by benthic invertebrates that are in close contact with the contaminated sediments. These invertebrates are eaten by other aquatic organisms, such as fish, and thus the PCBs migrate up the food
|
From page 33... ...
PCBs in the Environment 33 TABLE 2-2 Global Atmospheric PCB Concentrations in Ambient Outdoor Air Location Concentration (ng/m3) 0.06-0.2 0.1-0.3 0.02-0.5 0.1-5 0.1-2 0.5-30 0.2 Reference Antarctic coast Canadian Arctic (81° N)
|
From page 34... ...
. Fish can accumulate PCBs by direct absorption through the gills and by eating contaminated sediments, insects, and smaller fish.
|
From page 35... ...
The potency with which individual PCB congeners elicit dioxin-like effects (compared with the potency of TCDD itself) gives rise to the concept of TCDDtoxic equivalents, or toxic equivalence factors (TEE)
|
From page 36... ...
The Yusho incident occurred in Japan in 1968 and involved more than 1,600 individuals ingesting rice oil contaminated with PCBs. Reported health effects ofthose exposed included acneform dermatitis, hyperpigmentation of the skin, aches and pain, peripheral nerve damage, and severe headaches.
|
From page 37... ...
A similar incident occurred in 1979 in Taiwan, where about 2,000 people consumed rice oil contaminated with PCBs (Erikson ~ 997~. It was called Yucheng, which means ''oil disease" in Chinese.
|
From page 38... ...
However, as noted previously, these commercial mixtures differ substantially from the composition of PCBs typically found in sediments and from those to which humans are exposed through the consumption of contaminated fish and other foods. Thus, the toxicity characteristics of the Aroclors and sediment PCB mixtures are different, as are the possible interactions between the various congeners.
|
From page 39... ...
, and the National Toxicology Program classified PCBs as reasonably anticipated to be a human carcinogen (NTP 1998~. The mechanism or mechanisms by which PCBs induce tumors in rodents remain unresolved.
|
From page 40... ...
At each higher trophic level, certain PCB congeners are selectively enriched or depleted because of selective metabolism and excretion of metabolites. As a result, organisms at the top of the food chain are generally at the greatest risk of adverse effects due to exposure to PCBs.
|
From page 41... ...
1998~. As discussed previously, the difference is due to the changes in the composition of PCB mixtures over time after release into the environment because of several processes collectively referred to as "environmental weathering." The weathered multicomponent mixtures might have significant differences compared with Aroclor standards; the degree and position of chlorine substitution not only influences the physical and chemical properties of the PCB congeners but also their toxic effects.
|
From page 42... ...
Thus, both processes, reductive dechlorination and selective sorption of coplanar PCB congeners, tend to reduce the toxicity of the mixture, relative to technical Aroclor mixtures, during the weathering process. As was discussed above, the most accurate method of estimating the relative toxic potency of PCB mixtures is to measure the concentrations of individual congeners in tissues of receptors and correct their toxic potency by use of toxic potency factors.
|
From page 43... ...
It must be understood by all affected parties that even if the risks at a site are managed such that a specific sediment concentration of PCBs is achieved, over time PCB concentrations will slowly change due to numerous factors including atmospheric inputs from other sources and biodegradation. Although considerable new information has become available in the past 2 decades and new information from field and laboratory studies is reported regularly, the committee finds that further research is particularly warranted in the following areas: · Additional data are needed on the toxicological effects of exposure to multiple chemicals—PCBs plus PAHs, PCDDs, and metals and to "realworId" mixtures of PCBs.
|
From page 44... ...
1992. Polychlorinated Biphenyls indoor air contamination due to thiokol-rubber sealants in an office building.
|
From page 45... ...
l995b. Isomer-specific analysis of polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs)
|
From page 46... ...
1999a. Draft Mercury, Polychlorinated Biphenyls, Alkyl Lead, and Benzo~a~pyrene and Hexachlorobenzene Reports published in reponse to the United States' committment in "The Great Lakes Binational Toxics Strategy; Canada-United States Strategy for the Virtual Elimination of Persistent Toxic Substances in the Great Lakes.
|
From page 47... ...
I: Concentrations of organo chlorine insecticides, polychlorinated biphenyls, dioxin equivalents, and mercury.
|
From page 48... ...
1993. Isomer-specific analysis and toxic evaluation of polychlorinated biphenyls in striped dolphins affected by an epizootic in He western Mediterranean sea.
|
From page 49... ...
1994b. Atmospheric concentrations of polychlorinated biphenyls at Bloomington, Indiana.
|
From page 50... ...
1997. Polychlorinated Biphenyl Contamination of Tree Swallows in the Upper Hudson River Valley, New York.
|
From page 51... ...
1989. The relation of Polychlorinated biphenyls to birth weight and gestational age in the offspring of occupationally exposed mothers.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.