Zinc is part of nature. Most rocks and many minerals contain zinc in varying amounts and zinc exists naturally in air, water and soil. The average natural level of zinc in the earth's crust is 70 mg/kg (dry weight), ranging between 10 and 300 mg/kg. (Malle 1992)
Zinc is a Natural Element
At some locations, zinc has been concentrated to much higher levels by natural geological and geochemical processes. Such concentrations, found at the earth's surface and underground, are being exploited as ore bodies. The most commonly found zinc mineral is sphalerite (ZnS). Zinc metal is produced both from ores and from recycled zinc products. In fact, 30% of the world zinc supply today comes from recycled zinc.
Due to natural erosion processes like the weathering and abrasion of rock, soils and sediments by wind and water, a small but significant fraction of natural zinc is continuously being mobilised and transported in the environment. Volcanic eruptions, forest fires and aerosol formations above seas also contribute to the natural transport of zinc. These processes cause cycling of zinc in the environment, resulting in natural background levels in the air, surface waters and soil.
Just as the natural amount of zinc in soil varies, the zinc concentration in water depends on a multitude of factors such as the nature and age of the geological formations through which the water flows, together with biological and physicochemical conditions. Seasonal variations also influence zinc concentration in water. Nonetheless, some general categories of surface waters can be defined, which are characterised by a range of natural background zinc levels. These general categorised, called habitat-types, are where communities of organisms - ecosystems - dwell, which are conditioned to the zinc levels present. The European alluvial lowland rivers, the U.S. Rocky Mountains streams, and the Great Lakes in North America are examples of freshwater habitat-types with different natural ranges of zinc concentration.
Zinc-tolerant plants are found in zinc-enriched environments.