Pollution is the poisoning of air, land and water with detrimental substances such as pesticides, sewage and heavy metals. Most pollutants cannot be seen, smelt or tasted. However, while it is easy to believe they are not there, pollutants produce a measurable change in the environment and affect human health, plants and animals.

The increase in the amount of discharges and types of pollutants in the Zambezi Basin is due to population growth, intensive urbanisation, as well as increased industrial and agricultural activities.

Pollution may originate from definite, single sources called point sources such as industrial processes, mining activities, and sewage effluent, or from sources that are not easily located, called non-point sources such as from agricultural land and traffic.

Point source pollution

Industrial processes

Industry is the primary source of pollution in the Zambezi Basin, producing huge amounts of liquid effluents that often find their way into water bodies; solid waste, which is often dumped illegally on the land; and emissions that pollute the air.

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, chemical and steel industries and others.

These industrial processes produce large quantities of different kinds of pollutants. In steel manufacturing, for example, raw materials used include lime, iron ore and coal. The crushing and cleaning of the limestone and ore produces sludge and its disposal can pose problems. In the processing of the ore, other chemicals such as coke, sulphuric acid and tar are produced. The effluent from these processes contributes to pollution.

Wastewater from steel plants is not suitable for drinking or irrigation. Such effluent can also affect groundwater. For example, pollution by a Kwekwe-based steel company in Zimbabwe is said to discharge high quantities of iron, sulphate, oil and tar into the Kwekwe River, making the water unsuitable for irrigation and drinking.

The effects of the pollution are felt, as far afield as Lake Kariba where it is, for example, suspected to stiffen the trunks of elephants. In coastal areas, most industries dispose of untreated wastes directly into streams or rivers running into the oceans.

Power Generation

Thermal power generation is the largest source of transboundary air pollution in southern Africa with some of the plants located in the Zambezi Basin. Burning coal and coal-bed methane mainly generates thermal power in the region.

Gases emitted by the thermal power plants include carbon dioxide, nitrogen dioxide and sulphur dioxide.

Table 1: Carbon dioxide (CO2) emissions in the Zambezi Basin countries, 1995

No information is available for Namibia.
*    For comparison within the SADC Region
** For comparison with a developed country
Source: WRI, 1998 -99. World Resources: a Guide to the Global Environment, Oxford University Press, 1998.

Mining

The main effect from mining is the contamination of water bodies by soluble substances and toxic liquid effluent that are produced during mineral processing. Mining creates serious environmental problems in localised places within the Zambezi Basin. Most of the Basin's mining-related pollution comes from Zambia's copper mines, concentrated in the Copperbelt area.

In 1996-97, the copper mining industry produced over 17 million tonnes of solid waste, comprising mainly of overburden, waste rock, tailings and slag. Effluents from the mining operations discharged into the Kafue River and its tributaries, are high in suspended solids, copper, sulphates, zinc cobalt and iron.

Waste disposal

Approximately 95 percent of all the waste in the Zambezi Basin countries are disposed on land. It is therefore, essential that effective control mechanisms and guidelines be created for safe and acceptable land disposal practices. Problems with illegal dumping and littering require immediate attention.

The level of urbanisation in the basin worsens waste disposal problems. Harare, for example, generates more than 124,000 tonnes of solid waste annually. Besides poor waste disposal methods, another problem associated with such huge amounts of waste is that some of it comprises of plastics and metal cans that cannot decay or be recycled at present.

Sewage effluent

Sewage treatment facilities are largely inadequate in all the urban centres and are a major source of water pollution in the Zambezi Basin. Lake Chivero, outside Zimbabwe's capital Harare, for example, is highly eutrophic because sewage effluent is discharged into it from the city.

The lake is also the principal water supplier. In Zambia, the Kafue District Council discharges sewage into the Kafue River which drains into the Zambezi. In Livingstone (Zambia) and Victoria Falls town (Zimbabwe) treated effluent is discharged into the Zambezi River.

The problems, associated with pollution of Lake Chivero, are fish deaths and water hyacinth, which has covered the lake. It has also extended to Lake Kariba, threatening the lake's fishing and recreational activities.

Non-point sources

Leachate from landfills

Landfills constitute potential sources of groundwater pollution since they may contain organic micropollutants, heavy metals and high salt levels.

Landfills can either be open dumps or sanitary trenches, which are lined and can later be capped when full. Leachate from landfills impacts on water resources mainly because all landfills in the basin are not well planned and managed to monitor leachate production.

Use of pesticides and insecticides

Agriculture relies heavily on chemicals to kill unwanted disease, insects, plants and animals. The degree of environmental concern for a particular pesticide depends on how long it lasts in the environment, and how much is used.

In general terms, wildlife near commercial farms are more exposed to pesticides than those in remote areas.

DDT (dichlorodiphenyltrichloroethane) was one of the major pesticides used to control pests such as tsetse fly in the basin. Due to many risks associated with DDT and other such compounds, use has been limited and banned for many agricultural purposes.

Gold panning

The proliferation of riverbed and alluvial gold panning has resulted in serious damage to the basin's rivers, posing serious consequences on future water supplies. During heavy rains, the riverbanks often collapse, resulting in loss of vegetation, erosion and river siltation.

Siltation of rivers from gold panning can reduce river conveyance and the storage capacity of reservoirs, as well as the operational life of water bodies. A 1992 report reveals that half of Zimbabwe's dams are 50 percent silted and that for some rivers it was no longer economically viable to construct new dams.

Transport

Road, air and water transport cause various forms of pollution, including noise, air and water pollution. Vehicles driven by fossil fuels emit, for example, nitrogen oxides (NOX), carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs) and heavy metals. Ground level ozone (O3) that reduces agricultural productivity and the growth of trees is formed from the reaction of NOX, VOCs and sunlight.

Noise pollution from aircraft is mainly restricted to airport termini, which in most areas of the Zambezi Basin tend to be located far away from residential areas. Noise from road transport is worsening due to the growth in the number of vehicles and the absence of regulations that limit the amount of noise produced by cars.

The regulations are also silent on the permissible levels and types of fumes, which cars can emit.

Storm water runoff

Urban runoff can easily pollute water sources if the towns are not well planned to contain drainage. Drainage water is dirtier than the partially treated sewage effluent, and is difficult to manage since it emanates from non-point sources.

Runoff from towns and cities contributes to high concentrations of lead (from vehicle exhaust fumes), phosphorous and nitrogen (from decaying matter), and spillages from sewage works due to storm water entry into sewers.

Effects of pollution

Ecological effects

Pollutants degrade water quality and can harm aquatic life by interfering with photosynthesis, respiration, growth, and reproduction.
For example, pollution of water bodies can impair reproduction in fish, retard their growth or even kill them.

One of the major consequences of water pollution is the worsening of eutrophication of lakes and reservoirs. Eutrophication of water bodies causes the proliferation of aquatic weeds.

Until recently, the Kariba weed Salvinia molesta was the most widespread within the Zambezi basin. The water hyacinth (Eichhornia crassipes) has since become the most problematic weed in the basin, and it is found in nearly every water body within the Zambezi catchment area.

The water hyacinth weed invaded Lake Kariba five years ago. Other important weeds found within the Zambezi Basin include the water fern (Azola species) and water lettuce (Pistia stratiotes).

Health effects

Water bodies such as rivers and reservoirs ultimately receive wastewater from cities and other urban areas within the Zambezi Basin.

The wastewater, which contains both pathogenic and non-pathogenic viruses, bacteria and parasites, is usually diluted with large amounts of clean water. In some cases, the wastewater is treated before the water bodies receive it.

Among the organisms that are found within water bodies are pathogens that pose the greatest threat to public health, especially when the receiving water is used for domestic, recreational or agricultural purposes.

A study conducted in the town of Victoria Falls showed that the Zambezi River is highly polluted from the Victoria Falls sewage outfall to the 18.6 km peg downstream.

Actions and challenges to control pollution

Environmental legislation

Effective environmental legislation to regulate pollution and waste management is critical. In general terms, the legislation and administration of pollution control and waste management has lost sight of the need to maintain a holistic outlook on pollution regulations.

The impact of certain actions on all three environments (air, water and land) needs to be constantly borne in mind. The aim is to ensure that all three environments are considered in environmental control.

The chief method for achieving this is to move towards adopting the Best Practical Environmental Option (BPEO) standard and depart from the more traditional Best Practical Means (BPM) standard in imposing regulatory controls. Nearly all the countries in the basin have some air pollution control policies.

Table 2: Regulatory framework for air pollution in the Zambezi Basin

Source: Chenje M, Reporting the Southern African Environment: A media handbook, SADC/IUCN/SARDC, Maseru/

Environmental education
There is need for public education on environmental matters at different levels.

The public is not fully informed on matters such as littering, technological aspects and the pros and cons of so called "green" products that have lesser environmental impacts than other products.

Access to information

In some cases, information does not exist, and in other cases it is regarded as confidential. This situation is exacerbated by statutory provisions specifically protecting information from public scrutiny, for example, the Atmospheric Pollution Prevention Act in countries such as Zambia and Zimbabwe.

Conclusion

Pollution within the Zambezi River Basin is a serious problem. Education of managers, workers and the public should help raise awareness of the dangers of pollution.

Better pollution monitoring, integrated pest management and stricter enforcement of pollution control legislation are needed. For example, farmers may reduce pesticides use by introducing non-chemical methods of pest control such as crop rotation, biological control or at least, selective use of chemicals.

Another way to minimise pollution is to recycle waste material such as wastewater, cans, glass and paper.

The most desirable solution is preventing exposure in the first place. Prevention is less costly.

Glossary

Contamination is the introduction of any undesirable substance - physical, chemical or biological - into an ecosystem.

Effluents are liquid waste materials that are a byproduct of human activities such as liquid industrial discharge or sewage.

Eutrophication or nutrient enrichment is a process of overfertilisation of a body of water by nutrients that produce more organic matter than the self-purification reactions can overcome.

Leaching is a process by which a substance is washed out of the soil by water passing through it. Leachate from landfills may contain organic pollutants such as PCB, heavy metals such as led, and high salt levels, which all are a potential cause of groundwater pollution.

Pathogen is an agent (germ, virus, etc) which causes a disease.

Pollution is the poisoning of land, air or water with anything that reduces its ability to support life.

Siltation is the deposition of sediments by water in a lake or river-channel causing it to chock or fail in conveyance.

Volatile organic compounds (VOCs) are a chemically diverse group of compounds that have at least one carbon atom and are highly volatile.

Sources

University of Botswana
Department of Chemistry 
P. Bag 0022, Gaborone    
Botswana  
Tel: 267-351151  
Fax: 267-356591      
       

Ministry of the Coordination of Environmental Affairs  
Department of Environmental Quality   
C.P. 2020, Maputo   
Mozambique   
Tel: 258-1-466059   
Fax: 258-1-465849  
       
   
Zambezi River Authority  
P.O Box 30233   
Lusaka 
Zambia   
Tel: 260-1-228401 
Fax: 260-1-227498   

SADC - Environment and Land Management Sector (ELMS)   
Private Bag A284, Maseru 100
Gaborone 
Lesotho   
Tel: 266-312158  
Fax: 266-310190   

Department of Water Affairs    
P. Bag 13193    
Windhoek   
Namibia  
Tel: 264-61-2963025
Fax: 264-61-2963023  

Ministry of Mines, Environment and Tourism  
Department on Natural Resources   
P.O. Box 4033 Harare
Zimbabwe   
Tel: 263-4-705661/71
Fax: 263-4-793123   

Department of Environmental Affairs   
Private Bag 394, Capital City Lilongwe 3  
Malawi   
Tel: 265-781111 / 783171
Fax: 265-783379   

Environment Council of Zambia (ECZ)  
P.O. Box 35131   
Lusaka  
Zambia  
Tel: 260-1-286453/224009  
Fax: 260-1-223123   

University of Zimbabwe  
Department of Biological Sciences   
P.O. Box Mp 167, Mt Pleasant Harare 
Zimbabwe  
Tel: 263-4-303211
Fax: 263-4-303544/333407  

Bibligraphy

Chenje, M., Sola, L., and Paleczny, D. (eds.), The State of Zimbabwe's Environment 1998, Government of the Republic of Zimbabwe, Ministry of Mines, Environment and Tourism, Harare, 1998.

Sanyanga, R.A. and Masundire, H, "Waste Management in Major Population Centres in the Zambezi Valley", Unpublished Project Report CIDA-ECEP 32PP, 1998.

Feresu, S.B. and van Sickle, J, "Coliforms as a Measure of Sewage Contamination of the River Zambezi", Journal of Applied Bacteriology, 68, 397-403, 1990.