Cadmium global atmosphere, emissions

Fig. 4 Global metal emissions to the atmosphere by region (tonnes/year) for arsenic (As), cadmium (Cd), mercury (Hg) and molybdenum (Mo) (a) chromium (Cr), copper (Cu) and manganese Mn (b) nickel (Ni), lead (Pb), vanadium (V) and zinc (Zn) (c) and antimony (Sb), selenium (Se), tin (Sn) and thallium (Tl) (d) (data from Pacyna and Pacyna 2001)...

Cadmium (Cd) anode cells are at present manufactured based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples. Thus wastewater streams from cadmium-based battery industries carry toxic metals cadmium, nickel, silver, and mercury, of which Cd is regarded the most hazardous. It is estimated that globally, manufacturing activities add about 3-10 times more Cd to the atmosphere than from natural resources such as forest fire and volcanic emissions. As a matter of fact, some studies have shown that NiCd batteries contribute almost 80% of cadmium to the environment,4,23 while the atmosphere is contaminated when cadmium is smelted and released as vapor into the atmosphere4 Consequently, terrestrial, aquatic, and atmospheric environments become contaminated with cadmium and remain reservoirs for human cadmium poisoning. 

Cadmium is widely distributed in the earth s crust at an average concentration of about 0.1-0.2 mg/kg and is commonly found in association with zinc. Volcanic activity is major natural source of cadmium release to the atmosphere. The annual global flux from this source has been estimated to be 820 tons. Deep sea volcanism is also a source of environmental cadmium release, but the role of this process in the global cadmium cycle remains to be quantified (OECD, 1994). About 10-15% of total airborne cadmium emissions arise from natural processes (WHO, 1992a). 

Figure 3 Flux estimates of the global cadmium cycle. All fluxes are x 10 mol year . Emissions to the atmosphere are from Ref. [2], mining/smelting flux also from Ref. [16]. Atmospheric deposition and net river input (gross— loss to estuaries) to the ocean are from Ref. [18]. Loss of oceanic cadmium to marine sediments is scaled up from a cadmium accumulation rate of 0.006 nmol cm year for the Pacific from Ref. [18] and is highly uncertain. (A mass balance is not expected since the atmospheric and riverine inputs include anthropogenic increases that are recent compared to the residence time of Cd in the oceans.) Atmospheric deposition to land was calculated based on the steady-state assumption that emissions to the atmosphere equal losses to the ocean and land.

Worldwide cadmium production at present is around 17 000 metric tons/year and the global emission of cadmium compounds into the atmosphere is estimated to be 7000 metric tons/year, mainly from anthropogenic sources (Stoeppler 1991). 

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