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Dissolved organic compounds

Natural organic compounds have been present in the environment for millions of years. Many synthetic chemicals are harmless to living things, but some interfere with biochemical processes. Some of these synthetic chemicals are purposely introduced into the environment to kill insects. Some organic compounds pollute waterways. They are especially dangerous if they are not biodegradable. Some, like DDT, are concentrated by passage through a food chain.

Acidic pollutants

A source of acidic inorganic pollutants is the drainage of water from mines. Water flowing from underground mines is usually highly acidic. In lakes and rivers, the acids react with carbonate ions to form carbon dioxide. A raised level of carbon dioxide in the water makes it more difficult for animals to respire. Extreme acid pollution kills aquatic plants and animals.

Cyanides

Cyanides are widely used in industry for cleaning metals. Cyanides enter waterways in effluents from industries. The toxic effect of cyanide is due to the formation of a complex with iron.

Aluminium

Aluminium ions are present in the water supply because aluminium sulphate is used in water treatment. There is evidence of a correlation between Alzheimer’s disease and the aluminium content of drinking water. The rate of Alzheimer’s disease in districts where the concentration of aluminium in drinking water exceeds 0.11mg/L (1mg=0.001g, 1L=1dm³) is higher than the rate in districts where the aluminium concentration is less than 0.01mg/L.

Cadmium

Pollutant cadmium in water may came from industrial discharges. Heavy metals are serious water pollutants. Cadmium is highly toxic, with a recommended upper limit of only 10ppb (part per billion, 1000ppb=1ppm).

Lead

Leaded petrol is a source of lead in the atmosphere. Particles of soot and lead compounds from vehicle exhausts can fall on land and contaminate. Lead come from lead pipes and solders, from lead glazes on pottery and glasses. The World Health Organisation recommends that the limit for lead in drinking water should be 50 ug/L.

Mercury

Mercury compounds are found in nature in low concentrations in rocks and soils. However, we find a variety of uses for mercury which add mercury to the environment. Mercury comes from mercury cathode electrolysis cell, from fungicides, paints, coal and disinfectants. It has accumulated in a number of lakes. Mercury is slowly converted into dimethylmercury and methylmercury which are soluble and can be ingested by animals. Sludge from sewage treatment plants contains about 1ppb of mercury.

Chromium

Chromium compounds are toxic and irritating. They are present in wastes from electroplating plants and tanneries.

Nickel

Nickel compounds came from electroplating plants and cause damage to brain.

Copper

Copper compounds are toxic. If the dose is high enough. It can damage brain and eyes.

Zinc

Zinc enters the water supply from galvanising plants. It is relatively non-toxic, but large doses cause vomiting.

Arsenic

Contamination by agricultural pesticides has occasionally been a source of arsenic poisoning. It comes from the combustion of fossil fuels and is concentrated in food chains. The level of arsenic in natural water is 2ppb. Ingestion of 100mg of arsenic by an adult is fatal. The recommended upper limit for drinking water is 50 ppb

Thermal pollution

The rise in temperature of the water is called thermal pollution. Water is taking from waterways, used for cooling, and returned to waterways. It decreases the solubility of oxygen, increase the metabolic rate of organism,… If the temperature rises sufficiently, fish may die.

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