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POLLUTION

Pollution of land and water resources and the atmosphere are major environmental problems in the Zambezi Basin. Although the severity and impacts of some of the pollution is not well researched and documented, it is believed that the quality of vegetation, soils and water is adversely being affected by pollution.

Urban areas such as Harare and Lusaka are facing serious problems of air pollution caused mainly by industrial activity and the over-dependence on fossil fuels. Sulphur dioxide, suspended particulate matter, nitrogen oxides, carbon monoxide and lead, are the most common, as well as most harmful pollutants in the basin. If the growth in demand for energy and vehicular transport is to be met using current technologies, the Zambezi Basin will witness emissions from thermal power stations increasing eleven-fold and from vehicles five-fold by the year 2003. The use of mainly leaded fuel in vehicles throughout the basin is a major concern, which coupled with the ageing fleet of cars, is worsening the levels of lead pollution in the basin.

The high rates of urbanisation and industrialisation in the basin, which are not being matched with adequate waste treatment facilities, have resulted in water pollution in some of these areas. Consequently, gastro-enteric diseases such as cholera and dysentery have become prevalent due to faecal contamination of drinking water supplies.

Sources of pollution

The major sources of the pollution are:

• Point source pollutionsewage effluent, industrial processes, power generation, and mining activities.
• Non-point source pollutionnatural pollution, stormwater runoff, agricultural activities, leachate from landfills, soil erosion, and gold panning.

Point source pollution
Sewage effluent

Urbanisation is probably the biggest threat in terms of pollution in the Zambezi Basin because of the problems of sewage disposal. The largest and closest settlement to the Zambezi River is Livingstone, in Zambia, with a population of 100,000. In Livingstone, six wastewater oxidation ponds were commissioned in 1995, prior to which raw sewage was being discharged into the Zambezi River. Despite the ponds, some limited discharge into the Zambezi River, still occurs.

In Zimbabwe, Victoria Falls with a population of more than 30,000 is the most popular tourist destination in southern Africa, with a monthly visitor population averaging 32,000. The growth rate of Victoria Falls is estimated at 14 percent annually. Victoria Falls town discharges 8,000 cu m of wastewater into the Zambezi River. The discharge of effluent by the town into the Zambezi River was condoned under the Water (Effluent and Waste Water Standard) Regulations because the town's population was, until 1998, considered small. The town's sewage treatment facilities are also overloaded and subject to frequent breakdowns, forcing the town to discharge raw sewage effluent into the river through the Masume River.

Sewage treatment facilities are largely inadequate in all the urban centres and are a major source of water pollution in the Zambezi Basin. Chitungwiza town, south of Harare, has high levels of pollution due to poor disposal of sewage. The town has grown rapidly since 1980, with annual population growth rates of 3.5-7 percent, resulting in serious overload of sewage treatment facilities. The town has more than 350,000 residents making it one of the largest urban areas in Zimbabwe. The town is a significant pollution threat to the Manyame River, which drains into the Zambezi. The major consequence of discharging partially treated sewage effluent into any aquatic ecosystem is eutrophication due to high levels of nitrates and phosphates. A recent survey showed that total phosphate and nitrogen levels in the final effluent at Victoria Falls, Livingstone, Kariba and Kasane exceeded permissible limits by Zimbabwean standards. The total coliform count was also high.

Industrial pollution

Sources of industrial effluent range from pulp-and-paper mills to fertiliser factories and granulation plants; abattoirs; textile manufacturing, using dyes and noxious cleaning chemicals; cloth manufacturers; various chemical industries; water treatment plants; steel industries and others. These industrial processes produce large quantities of different kinds of pollutants.

Industrial pollutants from poorly designed solid waste dumpsites find their way into the environment through direct discharge and leaching into aquifers. Studies along the Zambezi Valley found that metal and batteries dominated the industrial solid waste in Kariba, contributing 60 percent and 10 percent of the total waste, respectively. Livingstone's solid waste was predominantly food remains (73 percent) and metal (nine percent), while in Victoria Falls, paper (34 percent) and plastic (22 percent) dominated the solid waste.

Major pollution effects due to industry occur in the highly urbanised parts of the Zambezi catchment area, which includes the Manyame, Kafue, and the Kwekwe/Sanyati river systems. The Kafue River, for example, is the lifeline for 40 percent of Zambia's population, in addition to being the hub of the country's industrial activity. Industrial activities include mining, chemical, fertiliser and textile manufacturing. More than 93,000 tonnes of industrial waste are produced annually, and most of it finds its way into the Kafue and eventually the Zambezi River.

Mining activities

Mining is a major cause of pollution in the Zambezi Basin, causing water acidification and discharging a variety of highly toxic metals such as arsenic, mercury, cadmium and lead. The disposal of solid mine waste also presents serious problems.

There is a considerable amount of mining in the Zambezi Basin, including copper mining in the Kafue sub-basin in Zambia; and tin, gold and coal mining in Zimbabwe and Mozambique. Coal and copper are, however, the major minerals mined within the Zambezi Basin. Both open and underground mining methods are used in the extraction process, wasting vast tracks of land through excavations of the ground and deposition of mine dumps. The Kafue River has over 90,000 ha of land under mining, 11 percent of which is occupied by solid waste dumps. The solid waste, which in 1996-97 amounted to 17 million tonnes, comprises of overburden, waste rock, tailings and smelting slag.

Non-point source pollution
Agricultural and forestry activities

Pollutants from agricultural and forestry activities include nitrogen, phosphorous, insecticides, herbicides, as well as poisonous residues contained in irrigation seepage water and livestock feedlots. Such sources of pollution are difficult to control due to their diffuse nature.

The agricultural industry takes up the greatest proportion of activities in the Zambezi Basin, requiring the extensive use of both organic and inorganic fertilisers and pesticides. DDT has been extensively used in the basin, not only for agricultural purposes, but human health as well through the campaign to eradicate tsetse flies during the period 1961-91. For example, 127 tonnes of DDT were used for tsetse control in the Binga, Gokwe and Hurungwe areas of the Zambezi operational front on the Zimbabwe side in 1983 alone.

The tsetse control operations are probably the main reason for the current levels of DDT in the aquatic fauna of Lake Kariba. An analysis of DDT and its metabolites in fish, mussels and birds in Lake Kariba showed that the pesticide bioaccumulates in living organisms. One symptom of DDT poisoning is eggshell thinning in birds, leading to reduced hatching. The Fish Eagle is one such species, which is seriously affected by DDT in Lake Kariba. Besides causing eggshell thinning, the following impacts were also observed in woodland birds:

• Progressive population declines in some bird species in sprayed areas.
• Mortality among some bird species following spray operations.
• Fewer bird species in sprayed areas (only six in sprayed areas compared to 23 species in unsprayed areas).
• Eighty-eight percent decline in Black Chat population over 33 months after cessation of spraying in the sprayed area compared to 13 percent decline in unsprayed area.
• Decline in population and high nest desertion in the African Goshawk in sprayed areas. One study found DDT levels in excess of 130 ppm in theAfrican Goshawk.

A study in which DDT has been found to damage the brain, leading to death in large mammals has helped dispel the misconception that the pesticide does not harm large mammals.

Gold panning

The proliferation of riverbed and alluvial gold panning has resulted in serious damage to the basin's rivers, exposing water supplies to serious pollution. About 57 percent of the gold panners, numbering hundreds of thousands throughout the Zambezi Basin use the most destructive horizontal tunneling method of extracting the mineral. During heavy rains, the riverbanks often collapse, resulting in loss of vegetation, erosion and siltation. Chemicals such as mercury are often used adjacent to the water bodies, contaminating rivers and streams.

Management of pollution

The basin is witnessing growing pollution problems resulting from industrial and energy-related pollution, deforestation and overuse of natural resources. Other issues of concern in terms of pollution and waste management include:

• Proper management of waste is not a priority by both local and central governments of the basin when compared to issues of economic development, housing and employment.
• There is a general lack of awareness regarding the impact of waste on the environment and human health in the basin.
• Legislation and regulations relevant to pollution and waste management are in most cases inappropriate, incomplete or diffuse.
• There is inadequate enforcement of existing regulations, and this is worsened by limited monitoring capacity.
• Existing industrial processes are inefficient, resulting in excessive waste generation and inordinate resource and energy consumption.
• Small to medium-scale enterprises, which do not have adequate finances and technical know-how to manage their pollution and waste, are set to worsen pollution and waste management problems in the Zambezi Basin.

Pollution monitoring is increasingly gaining prominence in the basin with countries such as Zambia and Zimbabwe undertaking legal reforms to strengthen monitoring. Both countries have set up units responsible for the physical inspection of all sources of pollution.

Several pieces of legislation covering water and air pollution are in place throughout the Zambezi Basin, despite problems of poor enforcement and weak institutional set-up. Other laws are so outdated as to become obsolete. Zimbabwe's Atmospheric Pollution Act (1971), for example, allows industries that were in existence before the promulgation of the act to continue using outdated equipment even if the industries are major polluters.

Water pollution control is fairly covered by national legislation, including Zimbabwe's Water Act (1998) and Zambia's Effluent or Wastewater Regulation (1993). The Zambian legislation sets out limits for effluent quality based on bacteriological, chemical and physical parameters.

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