Zinc and health – the facts

How much zinc migrates into the environment?

Emissions of zinc from point sources (factories, sewage treatment) have decreased dramatically since the 1970’s to a level expected to be reduced by more than 80% by the early 21st Century.

Significant decreases from diffuse sources (coatings, run-off from zinc coated products) have also occurred in developed countries, particularly in Northern Europe, due to dramatic reduction in sulfur dioxide emissions, again since the 1970’s. Acid rainfall arising from high sulfur dioxide levels has not been such a problem in Australia as has been the case in the Northern Hemisphere, where environmental controls have reduced sulfur dioxide emissions by up to 90% in some industrialised regions.

It is estimated that in Sweden, where a major study has been done in the 1990’s, zinc gets into the environment from the following sources and in the following volumes:

Source                                                  Tonnes/year

Corrosion and run-off                                    400t
Tyre wear                                                      150t
Asphalt wear                                                  50t
Brake lining wear                                           50t
Sewage                                                         50t
Landfills and mining activities                       400t
Sundry sources                                             50t.
        
Zinc is the 24th most common element in the earth’s crust and is always present naturally at various levels depending on local soils and other environmental factors. In Sweden the average zinc concentration in soil is around 60mg/kg. In Australia, with its ancient soils, very low zinc levels occur in many areas that contributes to the infertility of these soils for cropping, in particular.

The Swedish investigators have estimated that about one quarter of the zinc that ends up in the waterways and lakes comes from natural sources while the balance derives from human activity.

An interesting observation made by the researchers is that the atmospheric deposition of zinc in the forested areas of the country from industrial activity has contributed to maintaining the zinc levels in the humus layer in forest soils. As pollution controls continue to reduce the atmospheric zinc levels, there is now a risk of zinc deficiency becoming an issue in the future in Sweden’s forest soils. In Australia, where 95% of the continent is not subjected to industrial activity of any kind, most soils are severely zinc depleted. As a result, most of the fertilizers used in Australia in cropping and agriculture have zinc as one of their major constituents.

Zinc Requirements for Plants, Animals & Humans
In human and plant biology, there are both essential, non-essential and toxic metals. These individual characteristics may not apply to all organisms and at all concentration levels, and even the most beneficial compounds may be toxic if their biological uptake is excessive.

Zinc is one of the essential metals and plays a central role in the function of a number of proteins in living organisms. Zinc participates in many vital biochemical reactions such as detoxification, maintenance of DNA and RNA genetic codes, protein synthesis and particularly in reproductive functions. It also plays a major part in the health of the human immune system.

Many plants are prone to zinc deficiency that dramatically reduces their fertility and productivity. The higher up the food chain, the greater the organism’s ability to regulate its zinc intake and even in high natural zinc environments, mammals (including humans) and birds do not accumulate zinc in their tissues.

It appears from research done to date, that the life forms most susceptible to toxic effects from zinc are lower forms of plant life (micro-organisms, algae). This phenomenon is used deliberately through the addition of zinc chemicals to coatings and cosmetics as an anti-fungal treatment.

It is for this reason also, that zinc is used in many ointments and medications, particularly for the treatment of skin disorders.

While the research is incomplete, current findings indicate that levels of five times the background zinc level may have detrimental impact of these lower plant life forms.

While zinc is often classified with the so called ‘heavy metals’ such as lead and cadmium when environmental standards are discussed, zinc is in fact one of the most beneficial metals. There would be ‘no life without zinc’ to quote Prof. Heinrich Vahrenkamp from the Institute of Inorganic and Analytical Chemistry, University of Freiburg, Germany from a paper of the same title presented at International Zinc Day, 1994.

The human body contains about 2.5g of zinc and more than 200 enzymes are known that require zinc to function correctly. This is a far higher number than any of the other metals essential to healthy body functions. (e.g. iron, magnesium, calcium, sodium and trace metals such as copper). Zinc has been identified as essential in wound healing, digestion, reproduction, kidney function, breathing, diabetes control, inheritance functions, tasting and skin health.

High levels of zinc are not required in humans or plants and they do not accumulate zinc, with one or two notable exceptions. Oysters have 10 times as much zinc as the next highest source (red meat), and a small flower, silene vulgaris can accumulate up to 3% of its dry weight of zinc. Some plant species can tolerate very high levels of zinc, and vulgar knotgrass (polygonum) has been found to extract over 300 kg of zinc per hectare per year from soils containing high levels of zinc..

In humans, zinc is found in the highest concentrations in the reproductive system and lowest in the nerves and brain. Mother’s milk, sperm and ova have very high concentrations of zinc and humans require around 20 mg/day of zinc, which is available in a normal balanced diet with a supply of fruit, vegetables, cereals, red meat and seafood.

The most dramatic effect of zinc deficiency is on the reproductive system in humans, particularly in the Middle East. Extreme growth retardation in adolescents and the skin disease, acroder-matitis enteropathica, which is a very painful and potentially lethal condition, have both been immediately cured by simply adding zinc supplements to severely zinc deficient diets.

Zinc in soil is vital for cereal crops and the well being of a wide range of vegetation. For this reason, zinc compounds are widely used as additives in fertilizers.

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