Dioxins and Dioxin-like Compounds in the Food Supply Strategies to Decrease Exposure (2003) / Chapter Skim
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3. Sources of Dioxins and Dioxin-like Compounds in the Environment
3. Sources of Dioxins and Dioxin-like Compounds in the Environment
Pages 53-70
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From page 53... ...
Five major sources of DLCs: combustion, metals smelting and refining, chemical manufacturing, biological and photochemical processes, and environmental reservoirs, are described. Quantitative information on DLCs released from each source is briefly presented and the environmental fate of DLCs, including how these compounds are transported within or to various geographic regions, is discussed.
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From page 54... ...
Combustion processes include waste incineration (e.g., municipal solid waste, sewage sludge, medical waste, and hazardous waste) , burning of various fuels (e.g., coal, wood, and petroleum products)
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From page 55... ...
Electric arc furnaces, used in secondary ferrous metal smelting and refining, have also been implicated as a source of DLCs. Chemical Manufacturing Three types of chemical manufacturing processes bleaching of wood pulp in paper manufacturing, chlorine and chlorine-derivative manufacturing, and halogenated organic chemical manufacturing lead to the production of DLCs.
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From page 56... ...
To help reduce DLCs in effluents from pulp and paper mills, EPA promulgated effluent limitations guidelines and standards for certain segments of the pulp, paper, and paperboard industries (EPA, 1998, as cited in EPA, 2000~. These industries are responsible for more than 90 percent of the bleached-chemical pulp production in the United States.
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From page 57... ...
DLCs are also found in sewage sludge; specific sources include microbial biotransformation of chlorinated phenolic compounds, runoff to sewers from contaminated lands or urban surfaces, household or industrial wastewater, and chlorination operations within wastewater treatment facilities (Cramer et al., 1995; Horstmann and McLachlan, 1995; Horstmann et al., 1992; Rappe, 1992b; Rappe et al., 1994; Sewart et al., 1995, as cited in EPA, 2000~. Evidence also suggests that DLCs can be generated by photolysis of PCPs, but this reaction has only been demonstrated under laboratory conditions (Lamparski et al., 1980; Vollmuth et al., 1994; Waddell et al., 1995, as cited in EPA, 2000)
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From page 58... ...
Since 1995, EPA has promulgated regulations limiting DLC emissions for several source categories that contribute to the DLC inventory (e.g., municipal waste combustors, waste incinerators, and pulp and paper facilities using chlorine bleach processes)
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From page 59... ...
Metals smelting and manufacturing and chemical manufacturing contributed approximately 10 percent and 5 percent, respectively, of environmental releases of DLCs from quantifiable sources in 1995. The primary environmental releases of dioxin-like PCBs are electrical equipment.
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From page 60... ...
As some DLCs are considered semivolatile, particularly the less chlorinated congeners, some small portion of deposited DLCs may reenter the atmosphere as a result of volatilization from these surfaces or bound to airborne soil particles (EPA, 2000~.
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From page 61... ...
Although the models lack quantitative and qualitative precision, they do indicate that soil is an important reservoir source for DLCs, and that degradation rates in soil and sediment may be significant determinants of the environmental transformation and fate processes of these compounds. Transport in Water As DLCs enter the water column through soil runoff and erosion or atmospheric wet or dry deposition, they adhere to particles in the water column and are ultimately removed by sedimentation.
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From page 62... ...
Additionally, PCBs suspended in fresh surface water react with hydroxyl radicals with half-lives of 4 to 11 days (Sedlak and Andren, 1991, as cited in EPA, 2000~. In soils, DLCs bind strongly to organic matter with the result that degradation below the soil surface is virtually nonexistent.
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From page 63... ...
Although microbial degradation has been demonstrated for some DLC congeners, this does not appear to be an important transformation process. Hexachlorinated congeners were degraded by 70 to 75 percent by the white rot fungus Phanerochaete sordida, with 2,3,7,8-TCDD and the pentachlorinated congeners being more resistant (Takada et al., 1994, 1996, as cited in EPA, 2000~.
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From page 64... ...
Tree bark has been shown to be a useful environmental monitor of vapor-phase PCBs (Hermanson and Hites, 1990~. Little vapor transfer of the highly chlorinated congeners from soil is expected because the vapor pressure of a homologous series of compounds, such as DLCs, decreases with increasing chlorination (Fries, 1995a)
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From page 65... ...
The data presented constitute the bulk of the general background information that the committee used to fam~lianze itself with issues related to environmental sources of DLCs and their entry into the food supply. Environmental releases of DLCs have been decreasing in recent decades.
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From page 66... ...
1991. Proposed regulation of land application of sludge from pulp and paper mills using chlorine and chlorine derivative bleaching processes.
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From page 67... ...
. Environ Sci Technol 28:1110-1115.
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From page 68... ...
eds. Chlorinated Dioxins and Related Compounds.
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From page 69... ...
1998. Model simulation of environmental profile transformation and fate of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by the multimedia environmental fate model.
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From page 70... ...
eds. Chlorinated Dioxins and Related Compounds: Impact on the Environment.
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