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Giardia - and other water pollutants


by John Walsby


7K drawing of Giardia by J. Walsby

When we turn on a tap we usually take it for granted that the water will be clean and safe to drink but throughout much of the world there is a constant danger that any fresh water will be contaminated by diseases and toxic chemicals. When aid programmes are set up to help disadvantaged people in Third World countries, one of the main needs is always to improve both the quantity and quality of the drinking water supply.

Where water is drawn from wells or bores there is always a danger that the underground reservoirs might be contaminated because of poor management of both land and water resources by the same people that need the clean water. In residential areas the effluent from septic tanks seeps down and mixes with the groundwater and even where there is mains sewerage there is a risk of fractured pipes and weeping joints.

At vehicle service stations the large steel tanks buried in the ground for safe bulk storage of petrol and diesel quite frequently rust. Small but steady fuel leaks can then contaminate the ground water.

From nearby industrial areas chemical spills or careless disposal of solvents and other wastes, frequently poison the soil and may drain down to the water table. Chemicals also seep into underground water supplies from rubbish tips, particularly those in gullies which also serve as catchment basins for rainwater.

In the country agricultural and horticultural pesticides and fertilisers leach through the soil. Wherever people live, work and travel, there is a danger of contamination. Water supplies that look crystal clear often contain unwanted dissolved chemicals or organisms that cannot be seen with the naked eye. Both can cause sickness and some can cause serious illness.

Even in New Zealand's remote areas where mountain stream water has always been regarded as pure and palatable there is now a danger of infection from a single celled micro-organism called giardia (Giardia intestinalis). This protozoan animal thrives on food being digested in the guts of people and other mammals. Its waste products interfere with food absorption and frequently result in the host suffering from diarrhoea, vomiting and body cramps.

The minute animal swims freely about the intestine propelled by eight whip-like fibrils called cilia. It absorbs the simple soluble food substances released from complex foods by the hosts digestion and multiplies rapidly by repeated division. They also produce ovoid cysts which pass out with the hosts faeces to contaminate the vegetation and water that other animals may eat and drink.


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