Page 712 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

PCBs, PBBs, Dioxin, PCDDs Chapter | 51 677

VetBooks.ir during the synthesis of certain industrial halogenated aro- 1985). PCBs, PBBs, PCDDs, and PCDFs in environmen-
PCDDs and PCDFs are byproducts that are formed
tal extracts are complex mixtures of congeners that can
vary by lot due to various physical and biological pro-
matic chemicals, byproducts from other commercial pro-
cesses, and byproducts of combustion (Safe, 1990; cesses. Thus, the impacts of these chemicals on the envi-
Kodavanti et al., 2001). Some of the important industrial ronment and biota are due to the individual components
sources of PCDDs and PCDFs have included their forma- of these mixtures, their additive, and/or nonadditive (syn-
tion as byproducts in the production of PCBs, chlorinated ergistic/antagonistic) interactions with themselves and
phenols and chlorinated phenol-derived chemicals, hexa- other classes of pollutants (Safe, 1994; Loganathan and
chlorobenzene, technical hexachlorocyclohexanes, and Masunaga, 2015).
chlorides of iron, aluminum, and copper. PCDDs and
PCDFs have also been identified in wastes and finished
paper products from the pulp and paper industry. Exposure
Emissions from municipal and hazardous waste incinera-
There are a number of ways by which animals can be, and
tors, as well as home heating systems that use wood and
have been, exposed to PCBs, PCDDs/PCDFs, and PBBs.
coal, diesel engines, forest and grass fires, and agricul-
Some of the scenarios involve ingestion of low concentra-
tural and backyard burning contain PCDDs and PCDFs
tions of these chemicals through consumption of environ-
(Safe, 1990; Huwe, 2002; Loganathan and Masunaga,
mentally or accidentally contaminated feed or feed
2015). In addition, these compounds might come from
components. During the 1940s and 1950s, silos constructed
naturally formed PCDD/Fs, which have been detected in
with concrete were sealed with a PCB-containing paint,
deep soils and clays (Safe, 1990; Huwe, 2002). which eventually peeled off from the walls, resulting in
contaminated silage. Dairy and beef cattle were exposed to
Environmental Fate the paint in the feed, resulting in accumulation of PCBs in
adipose tissue. As a result, food products such as milk and
The release of PCBs into the environment primarily has meat contained detectable concentrations of PCBs.
been the result of leaks, spills, and improper disposal. As Examples of other exposure incidents resulting in PCB resi-
stated earlier, it is estimated that approximately dues in food animals include consumption of tar paper by
370,000 tons of PCBs are present in the global environ- veal calves, consumption of fish viscera by swine, pullet
ment (Tanabe, 1988). The volatility of PCBs allows their consumption of feed containing PCB-contaminated fat
evaporation from source containers and movement added during processing, exposure of chickens to contami-
through the atmosphere, resulting in widespread environ- nated ceiling and fiberglass insulation, and treatment of
mental dispersal (Headrick et al., 1999). PCDDs and boars with a topical pesticide containing PCB-contaminated
PCDFs are released into the atmosphere primarily by oil (Headrick et al., 1999).
combustion sources and by evaporation from PCDD/ Several dioxin contamination incidents have occurred
PCDF-containing soils and water. Similar to PCBs, the in Europe. In 1998, during routine monitoring, dairy pro-
PCDDs and PCDFs can be transported long distances by ducts were identified that had dioxin concentrations that
winds, contributing both to general background concentra-
were 2 4 times higher than background concentrations.
tions and contamination of remote areas far from the orig-
The source of the contamination was traced to contami-
inal source. PCBs, PCDDs, and PCDFs are removed from
nated citrus pulp used in cattle feed, which was immedi-
the atmosphere by physical processes such as wet and dry
ately removed from the market. In another incident, PCB/
deposition and vapor uptake, and are deposited on soils,
PCDD/PCDF-contaminated oil was added to recycled fat
surface waters, and plant surfaces. Once bound to soil and
used as an additive in animal feeds. The affected feeds
sediment, these chemicals generally remain fixed, except contaminated Belgian poultry, dairy, and meat, and were
for bulk transport due to soil erosion, flooding, and dredg- discovered only after toxic effects characteristic of “chick
ing (Dickson and Buzik, 1993). Ingestion of these com- edema disease” were seen in chickens (Bernard et al.,
pounds by animals results in their preferential 2002; Huwe, 2002).
bioaccumulation and biomagnification in the food chain
(Safe, 1994). Due to their restricted manufacturing and
use, PBBs are not considered to be a significant environ- PBB Incident in Michigan
mental contaminant, with the exception of specific loca- FireMaster BP-6 was a mixture of PBB congeners contain-
0
0
0
tions in Michigan. Like PCBs, PCDDs, and PCDFs, PBBs ing 2 8 bromines with major constituents of 2,2 ,4,4 ,5,5 -
0
0
are very stable and lipophilic compounds and, therefore, hexabromobiphenyl (56%) and 2,2 ,3,4,4 ,5,5 -heptabromo-
0
persist in the environment and bioaccumulate in the food biphenyl (27%) (Damstra et al., 1982). In 1972, the formu-
chain (Damstra et al., 1982). Also, PBBs have a high lation was changed by grinding BP-6 and adding 2%
affinity for soil, and can translocate into vegetation (Fries, calcium silicate as an anticaking agent. This new