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Dispersion of heavy metals
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What are heavy metals?
The environmental theme ‘dispersion of heavy metals’ puts the emphasis on the eight elements considered a priority by the third North Sea conference: arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), copper (Cu), nickel (Ni) and zinc (Zn).
Heavy metals in the environment
The majority of heavy metals is naturally present in almost all soils, at levels depending on the mineralogical soilcomposition and on the erosion processes that occur. Manmade dispersion of heavy metals in the environment takes generally place via discharges in the air in the form of dust particles and as a result of discharge in the surface water. Heavy metals end up on (and in) the soil as a result of atmospheric deposition, by dumping waste or through the use of fertilizers. Once present in the soil they can permeate down to the groundwater. However, binding processes delay the movement of metals into the soil to a significant extent. They can pollute the surface water as a result of run-off. Heavy metals in the surface water can quickly settle in the watercourse sediment. However metals may be released from the watercourse sediment into the surface water over a long period.
Impact of heavy metals on plants, animals and man
Plants and animals take up heavy metals. As these are not degradable they accumulate in the environment. Man takes up heavy metals through respiration or via water or food (e.g. vegetables cultivated in a garden with heavy metals in the soil). Some elements like chromium, copper and zinc are essential to man and other living creatures in small concentrations. Heavy metals only become toxic at higher concentrations.