All living organisms need zinc.
Zinc and living organisms
Zinc is an essential element for all living organisms. Zinc is necessary and indispensable for human, animal and plant life.
There is an optimal zinc concentration range for each living organism. Within this concentration range, living organisms can regulate their internal concentration in order to meet the requirements of their metabolism.
If these optimal conditions are not met and there is a deficit, zinc deficiency can result, likewise, in the event of excess, ecotoxicological problems arise.
Human beings are not usually exposed to an excess of zinc but they can experience zinc deficiencies.
On the other hand, ecosystems are rarely subjected to a lack of zinc but can be subjected to an excess of zinc.
Zinc and human beings
Zinc is an important metal element for humankind as it ranks 3rd, after magnesium and iron.
Zinc plays an essential role in health. It is essential for growth, brain development, protecting the skin, the proper functioning of the immune system, digestion, reproduction, taste, smell and many other natural processes.
The human body is unable to synthesise the zinc it needs. It therefore draws zinc from its food. The World Health Organisation (WHO) recommends a daily zinc intake of 10 mg/day for children, 12 mg/day for women and 15 mg/day for men. Certain population groups have a higher zinc requirement and are therefore more at risk of zinc deficiency: children and adolescents, pregnant women, elderly people, etc.
The symptoms related to the risk of deficiency are: a reduction in the senses of taste and smell, skin problems, mental lethargy and a reduction in fertility.
Variety in a person's diet depends primarily on their culture and standard of living. Since the amount of zinc varies according to the type of food, on a global scale many adults and children have a diet that is too low in zinc. In developing countries, zinc deficiency ranks 5th among the leading 10 risk factors for human health; the World Health Organisation (WHO) attributes 800,000 deaths worldwide each year to zinc deficiency and over 28 million healthy life years lost (¹).
Zinc and ecotoxicology
Zinc is naturally present in the environment: rocks, soil, water and air have always naturally contained variable concentrations of it. During the course of their evolution, all living organisms have used the zinc available in their environment for specific functions of their metabolism. So, zinc is an essential element, which is necessary and indispensable for all living organisms in all ecosystems.
Living organisms are adapted to the natural concentration of zinc in their ecosystem. Furthermore, they have developed mechanisms to maintain optimum living conditions when this concentration level varies from the natural norm. But if the zinc concentration radically changes, living conditions are no longer optimum and the functioning of the ecosystem can be affected.
For this reason ecotoxicological studies can be conducted to assess the risk to the environment of an excess of zinc.
In these ecotoxicological studies, only the concentration of dissolved zinc should be taken into account because the insoluble part has no effect. The concentration of dissolved zinc is affected by properties of its environment such as pH, water hardness, dissolved organic carbon and temperature. So any study of the environmental impact of zinc must take into account the specific features of the ecosystem concerned and the concentration of dissolved zinc, not the total zinc concentration.
Ecotoxicological studies have shown that zinc concentrations in European ecosystems, originating either from human activities (such as atmospheric corrosion of rolled zinc and galvanised steel, wear and tear of vehicle tyres, fertilisers and animal feed, etc) or natural emissions (mainly from the earth's volcanic activity), remain within the limits of optimal living conditions. A good example of this is the current levels of zinc in the Rhine (extreme values from 3 to 25 µg/L) which are within the optimal range for zinc (3).