Zinc in the environment
Zinc –Natures Part in Hot Dip Galvanising
Zinc occurs naturally in the environment and is the 17th most common element in the earth’s crust.
Most rocks contain zinc in varying amounts and zinc exists naturally in air, water and soil. Due to natural weathering and erosion of rocks, soils and sediments together with volcanic eruptions and forest fires, a small but significant fraction of natural zinc is continuously being mobilised and transported in the environment.
The natural concentrations of zinc in different environments are referred to as background levels and can vary considerably between locations. The animal and plant species within a particular area have evolved to take up zinc from their environment and use it for specific functions in their metabolism. Consequently, all organisms are conditioned to the bio-available zinc concentrations in their environment that are not constant but subject to seasonal variations. Organisms have mechanisms to regulate their internal zinc levels. If uptake levels drop too low, deficiency can occur and adverse effects may be observed.
What happens to Zinc in the environment?
A major part of zinc present in surface waters ends up deposited in sediments of rivers, estuaries and coastal areas where it binds to organic and inorganic matter; which reduces its mobility and bio-availability.
Only a finite amount of zinc can be dissolved in a given amount of water depending on many factors such as temperature and pH. It is only the dissolved zinc and not the total zinc that is bio-available and therefore of ecological significance. Zinc bound in suspended organic matter will generally settle so that top sediment layers mirror the zinc levels in the overlying water.
Studies of ice cores from Greenland show the levels of atmospheric zinc deposition as well as other metals going back thousands of years. Since the late 18th century industrial activity has resulted in anthropogenic (man-made) input of zinc to the environment. The results obtained show that this reached a peak in the 1960’s and has markedly decreased since then. This downward trend is a direct result of more efficient emission control within the zinc industry and ambient air zinc levels seem to be returning to pre-industrial levels.
Environmental Risk Assessment
Risk assessment determines the possibility of a substance having an adverse effect on human health or on the functioning of an ecosystem. To achieve this it is necessary to derive two values:
- The critical level at which adverse effects can be expected and
- The true exposure to the substance in the environment
If the results of the risk assessment show that the value (1) is greater than the value (2) then there is no risk to man or the environment. If they are equal or (2) is greater; then a risk exists.
WHO/IPCS Zinc Task Force Position
Recently, the International Programme on Chemical Safety (IPCS) a world forum under the auspices of the WHO (World Health Organisation), the ILO (International Labour Organisation) and UNEP (United Nations Environment Programme) - formed a Task Force on Zinc to establish Environmental Health Criteria For Zinc. Among its conclusions, the Task Force states:
“Zinc is an essential element in the environment. The possibility exists for both a deficiency and excess of this metal. For this reason it is important that regulatory criteria for zinc, while protecting against toxicity are not set so low as to drive zinc levels into the deficiency area.”
Zinc – Essential for Health and the Environment
Zinc is essential to life. It is a natural element found in all plants and animals and plays a crucial part in the health of our skin, teeth, bones, hair, nails, muscles, nerves and brain function. Zinc and its chemistry is found in over 200 enzymes and hormones in man.
Zinc is essential for growth. It is used to control the enzymes that operate and renew the cells in our bodies. The formation of DNA, the basis of all life on our planet, would not be possible without zinc.
Zinc and zinc compounds are of major importance in skin care. Some of its vital uses are:
- To soothe nappy rash and itching thanks to its astringent and drying properties.
- As a sun-block to protect the skin from the sun’s harmful rays.
- As an effective treatment for acne.
- In the relief of cold sore symptoms.
- To aid the healing of wounds, like surgical incisions, burns and other skin irritations. Many adhesive plasters contain zinc oxide for this reason.
- As an anti-inflammatory to relieve the discomfort from sunburn, blisters and gum disease.
- As an insect repellent.
- Helping to protect body tissue from damage by stimulating the transport of Vitamin A from the liver to the skin,
- As bactericides in high quality cosmetics and toiletries.
- To help heal leg ulcers through addition to the diet.
In respect of efficient protection of the environment and prudent use of natural resources, the Hot Dip Galvanising process stands up to scrutiny and can be considered as a major contributor towards sustainable construction.