Edouard Bastarache on tue 15 jul 03
1-CADMIUM EMISSIONS
Cadmium emissions arise from two major source categories,=20
natural sources and man-made or anthropogenic sources.=20
Emissions occur to the three major compartments of the=20
environment - air, water and soil, but there may be=20
considerable transfer between the three compartments after=20
initial deposition. Emissions to air are considered more mobile=20
than those to water which in turn are considered more mobile=20
than those to soils.
2.1-Natural Cadmium Emissions
Even though the average cadmium concentration in the earth's=20
crust is generally placed between 0.1 and 0.5 ppm, much=20
higher levels may accumulate in sedimentary rocks, and marine=20
phosphates and phosphorites have been reported to contain=20
levels as high as 500 ppm (Cook and Morrow 1995, WHO
1992).=20
Weathering and erosion of parent rocks result in the transport=20
by rivers of large quantities, recently estimated at 15,000 metric=20
tonnes (mt) per annum, of cadmium to the world's oceans=20
(WHO 1992, OECD 1994).=20
Volcanic activity is also a major natural source of cadmium=20
release to the atmosphere, and estimates on the amount have=20
been placed as high as 820 mt per year (WHO 1992, OECD=20
1994, Nriagu 1980, Nriagu 1989).=20
Forest fires have also been reported as a natural source of=20
cadmium air emissions, with estimates from 1 to 70 mt emitted=20
to the atmosphere each year (Nriagu 1980).=20
The problem is distinguishing what are the expected natural levels=20
of the substances, what is from human sources, and what, if any,=20
are risks to the environment.
2.2-Example of the Influence of Soil Geochemistry:
In north central Saskatchewan and eastern and central Manitoba,=20
low cadmium and arsenic concentrations in soils reflect the=20
southward glacial transport of cadmium-poor debris derived=20
from the Canadian Shield to the north. In contrast, high=20
cadmium and arsenic concentrations in southwestern Manitoba
soils reflect glacial incorporation of trace-element-rich shale=20
bedrock forming the Manitoba Escarpment (Garrett and=20
Thorleifson 1999). In both areas, the geochemical expression=20
of the source is really more extensive in soil than in bedrock=20
as the result of glacial transport.
Where elements are readily dissolved, there can be close=20
compositional linkages between surficial materials and water.
3-Andropogenic Sources
3.1-Where does Cd come from?=20
Cadmium is a by-product of zinc, lead, and copper mining.=20
Its major feedstock, sphalerite (ZnS), contains only 0.25%=20
cadmium. Because Zn is produced in large quantities=20
(8 million metric tons in 1999), substantial amounts of cadmium=20
are produced as a by-product.This cadmium by-product can=20
be put to beneficial use in many products, or it can be discharged=20
into the environment. When the market does not absorb the=20
Cd generated by metal smelters/refiners, it is cemented and=20
buried, stored for future use, or disposed of in landfills as=20
hazardous waste.=20
3.2-Cadmium-Containing vs. Non-Cadmium Containing Products
Man-made cadmium emissions arise either from the manufacture,=20
use and disposal of products intentionally utilising cadmium, or=20
from the presence of cadmium as a natural but not functional=20
impurity in non-cadmium containing products. In the former=20
category of cadmium-containing products are included:
=B7 Nickel-Cadmium Batteries
=B7 Cadmium Pigmented Plastics, Ceramics, Glasses, Paints and Enamels
=B7 Cadmium Stabilised Polyvinylchloride (PVC) Products
=B7 Cadmium Coated Ferrous and Non-ferrous Products
=B7 Cadmium Alloys
=B7 Cadmium Electronic Compounds
In the latter category of non-cadmium containing products are included:
=B7 Non-ferrous Metals and Alloys of Zinc, Lead and Copper
=B7 Iron and Steel
=B7 Fossil Fuels (Coal, Oil, Gas, Peat and Wood)
=B7 Cement
=B7 Phosphate Fertilisers
3.3-Sources of Cd exposure to humans :
Cadmium is released into the environment from phosphate=20
fertilizers, burning fuels, mining and metal processing=20
operations, natural sources, cement production, and=20
disposing of metal products. Releases from disposed=20
cadmium products, including NiCd batteries, are minor=20
contributors to human exposures because Cd is=20
encapsulated in their structure. Most human cadmium
exposure comes from ingestion of food, and most of=20
that stems from the uptake of cadmium by plants from=20
fertilizers, sewage sludge, manure, and atmospheric=20
deposition. Van Assche (1998) has developed a model=20
for human exposure to cadmium and allocated this exposure=20
to these sources. The assumptions and the data inputs=20
for the model are based on actual data from Belgium and=20
the European Community (ERL, 1990; OECD, 1994).=20
The model estimates of the relative importance of various=20
cadmium sources to human exposure are shown in Table 1.=20
Table 1. Sources and Relative Contributions of Cd Exposure=20
to Humans (in Europe)
Phosphate fertilizers 41.3 %
Fossil fuel combustion 22.0 %
Iron and steel production 16.7 %
Natural sources 8.0 %
Non-ferrous metals 6.3 %
Cement production 2.5 %
Cadmium products 2.5 %
Incineration 1.0 %
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
Bobbruch1@AOL.COM on wed 16 jul 03
<<<<<< Edouard Bastarache writes < Cadmium emissions arise from two major
source categories, natural sources and man-made or anthropogenic
sources.........
<<<<<<3.1-Where does Cd come from? ......Cadmium is a by-product of zinc,
lead, and copper mining.
Does that mean that there is/could be a fair amount of Cadmium in the Zinc
Oxide and Copper Carb and Copper Oxide that we purchase from ceramic suppliers?
Thanks,
Bob Bruch
Edouard Bastarache on wed 16 jul 03
Bob,
" Does that mean that there is/could be a fair amount of Cadmium in the Zinc
Oxide and Copper Carb and Copper Oxide that we purchase from ceramic
suppliers?
Thanks,
Bob Bruch"
I do not think there are fair amounts of cadmium present in these materials.
Chemists and chemical engineers on this list certainly have more knowledge
than me on this matter.
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
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