Cadmium: From Toxicity to Essentiality

Volume 11 of the series Metal Ions in Life Sciences pp 31-62


Biogeochemistry of Cadmium and Its Release to the Environment

  • Jay T. CullenAffiliated withSchool of Earth and Ocean Sciences, University of Victoria Email author 
  • , Maria T. MaldonadoAffiliated withDepartment of Earth and Ocean Sciences, University of British Columbia

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Cadmium is at the end of the 4d-transition series, it is relatively mobile and acutely toxic to almost all forms of life. In this review we present a summary of information describing cadmium’s physical and chemical properties, its distribtion in crustal materials, and the processes, both natural and anthropogenic, that contribute to the metal’s mobilization in the biosphere. The relatively high volatility of Cd metal, its large ionic radius, and its chemical speciation in aquatic systems makes Cd particularly susceptible to mobilization by anthropogenic and natural processes. The biogeochemical cycle of Cd is observed to be significantly altered by anthropogenic inputs, especially since the beginning of the industrial revolution drove increases in fossil fuel burning and non-ferrous metal extraction. Estimates of the flux of Cd to the atmosphere, its deposition and processing in soils and freshwater systems are presented. Finally, the basin scale distribution of dissolved Cd in the ocean, the ultimate receptacle of Cd, is interpreted in light of the chemical speciation and biogeochemical cycling of Cd in seawater. Paradoxically, Cd behaves as a nutrient in the ocean and its cycling and fate is intimately tied to uptake by photosynthetic microbes, their death, sinking and remineralization in the ocean interior. Proximate controls on the incorporation of Cd into biomass are discussed to explain the regional specificity of the relationship between dissolved Cd and the algal nutrient phosphate (PO\(^{3-}_{4} \)) in oceanic surface waters and nutriclines. Understanding variability in the Cd/PO\( ^{3-}_{4} \) is of primary interest to paleoceanographers developing a proxy to probe the links between nutrient utilization in oceanic surface waters and atmospheric CO2 levels. An ongoing international survey of trace elements and their isotopes in seawater will undoubtedly increase our understanding of the deposition, biogeochemical cycling and fate of this enigmatic, sometimes toxic, sometimes beneficial heavy metal.


anthropogenic emissions biogeochemistry cadmium cadmium/phosphorus ratio marine biogeochemistry pollution trace metal