Thecadmium cycle is abiogeochemical cycle ofdispersion anddeposition of cadmium through theatmosphere,biosphere,pedosphere, andhydrosphere. Cadmium typically exists in the environment with an oxidation state of +2 but can be found with an oxidation state of +1 (though quite uncommon).^[1]

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Biogeochemical cycles
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Related topics Biogeochemistry geochemical cycle chemical cycling environmental chemistry Biosequestration Deep biosphere Ocean acidification acid rain Biogeochemical planetary boundaries
Research groups DAAC GEOTRACES IMBER NOBM SOLAS
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Atmospheric sources are dominated byanthropogenic emissions (non-ferrous metal production,fossil fuel combustion, iron and steel production,waste disposal, and cement production), with minor introduction of cadmium through natural emissions (volcanoes, dust, biomass burning, andsea spray).^[1] Cadmium introduced as powders and aerosols through anthropogenic sources and natural sources can be detected in almost all corners of the globe. Cadmium is highly soluble and cadmium concentrations are rapidly depleted after wind transport as particles, aerosols, and water droplets.^[1] Typically, cadmium deposition decreaseslatitudinally from the source.

The majority of cadmium deposition to soils and freshwater is due to anthropogenic atmospheric emissions,contaminants inbiosolids, and contaminants infertilizers.Dry deposition accounts for 30-70% of terrestrial inputs.^[1] Cadmium is highly mobile in soils and becomes mineral-associated over time. Higher pH and temperature favor cadmium incorporation into minerals, while lower pH and temperature makes cadmium more soluble. Dissolved cadmium circulates through freshwater systems before introduction to larger bodies of water. In rivers, dissolved cadmium ranges from nanomolar to micromolar concentrations.^[1]

The vast majority of marine cadmium (80-90%) comes fromwet deposition.^[1] Cadmium behaves similarly tonutrients such asphosphate andzinc: dissolved concentrations depend heavily on uptake, assimilation, and deposition byphytoplankton anddiatoms.^[2] Dissolved cadmium concentrations are sub-nanomolar in the surface ocean and increase with depth, with a maximum in thethermocline.^[1] Like other nutrients, cadmium is lowest in theNorth Atlantic (~0.3 nM). Higher concentrations (up to 1 nM) occur in the deepIndian,Southern, andPacific oceans due to water mass aging duringthermohaline circulation.^[1] Coastal waters range from 0.2 to 0.9 nM, denoting a significant terrestrial input.^[1]

• Cadmium
• Carbonic anhydrase
• Diatoms

• Biogeochemical cycle
• Cadmium