Zinc - A Natural Element
Zinc like all metals, is a natural component of the earths crust and an inherent part of our environment. Zinc is present not only in rock and soil, but also in air, water and the biosphere C plants, animals and humans.
Zinc is constantly being transported by nature, a process called natural cycling. Rain, snow, ice, sun and wind erode zinc-containing rocks and soil. Wind and water carry minute amounts of zinc to lakes, rivers, and the sea, where it collects as sediment or is transported further. Natural phenomena such as volcanic eruptions, forest fires, dust storms and sea spray all contribute to the continuous cycling of zinc through nature. It is estimated that these natural emissions of zinc amount to 5.9 million metric tonnes each year. In comparison anthropogenic emissions of zinc to the atmosphere as a result from mans activity (metal production, waste disposal, fossil fuel combustion, etc.) are estimated at 57,000 metric tonnes per year worldwide.
The amount of zinc present in the natural environment varies from place to place and from season to season. For example, the amount of zinc in the earth's crust ranges between 10 and 300 mg/kg. In some areas zinc has been concentrated to much higher levels by natural geological and geochemical processes. Such concentrations are being exploited as ore bodies. Zinc in rivers varies from less than 10 micrograms per liter to over 200 micrograms. Similarily, falling leaves in autumn lead to a seasonal increase in zinc levels in soil and water.
During the course of evolution, all living organisms have adapted to the zinc in their environment and used it for specific metabolic processes.
Zinc-tolerant plants are found in zinc-enriched environments.
The photo shows Viola calaminaris which thrives in the naturally
zinc-rich area of La Calamine in Belgium (photo: F. Van Assche).
For references, see Van Assche et al (1996).
Natural zinc levels (total zinc) in the environment
RANGE
Air (rural) (ug/m3)
0.01 - 0.2
Soil (general) (mg/kg dry weight)
10 - 300
Rocks (ppm)
- basaltic igneous
- granitic igneous
- shales and clays
- sandstones
- black shales
48 - 240
5 - 140
18 - 180
2 - 41
34 - 15000
Ore Bodies (%)
5 -> 15
Surface Waters (ug/l)
Habitat-type:
- Open ocean (surface)
0.001 - 0.06
- Coastal seas/inland seas
0.5 - 1
- Freshwater:
- Alluvial lowland rivers
rich in nutrients and oligo
elements (e.g. European
lowland)
5 - 40
- Mountain rivers from old
strongly leached geological
formations (e.g. Rocky
Mountains)
< 10
- Large lakes (e.g. Great Lakes)
0.09 - 0.3 (dissolved)
- Zinc-enriched streams
flowing through
mineralization areas
> 200
For references, see Van Assche et al (1996).
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