Zinc - A Natural Element

Zinc like all metals, is a natural component of the earth’s 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 – 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 man’s 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).

Zinc - Essential for Man and the Environment

Zinc is essential for all life. It plays a specific role in various biological reactions of all living organisms - humans, animals, plants and the smallest microorganisms.

Organisms take up the essential elements they need from their environment, that means directly from air, water, soil, and from food. When their cellular requirements for these elements are satisfied, growth and development are optimal. When uptake is too low, deficiency occurs and adverse effects can be observed. On the other side, uptake of too much of an essential element can lead to toxicity. Between these two extremes, each organism has an optimal concentration range for each essential element within which it can regulate its internal zinc level so that its metabolic requirements are satisfied.

(Van Assche et al.1996)

The amount of zinc available varies significantly geographically and seasonally and zinc deficiency is a widespread problem. It is estimated that zinc deficiency affects one third of the world’s population. In the World Health Report 2002 WHO says that zinc deficiency is one of the leading causes of illness and disease in low-income countries. It ranks 5th among the leading 10 risk factors. Even on a global scale zinc deficiency ranks 11th out of the 20 leading risk factors. WHO attributes 800,000 deaths worldwide each year to zinc deficiency and over 28 million healthy life years lost. Zinc deficiency is responsible for approximately 16% of lower respiratory tract infections, 18% of malaria and 10% of diarrhoeal disease. WHO points out that zinc deficiency is largely related to inadequate intake or absorption of zinc from the diet and zinc supplementation and fortification both prove to be very cost-effective interventions in all regions of the world.

Zinc deficiency in agricultural soils and crops is also a common phenomenon and constitutes a major problem in many parts of the world as crop yields are reduced and the quality of crops is often impaired. Relatively small amounts of zinc compounds can cure deficiency and last for several years before they need to be repeated.