In the last few years, there has been a significant increase in population growth all over the world, but particularly in many countries in Africa. This has been accompanied by intensive urbanization, an increase in industrial activities and a greater exploitation of cultivable land. These transformations have provoked a huge increase both in the quantity of discharge and the range of pollutants that could reach the river waters and have undesirable effects on fish and fisheries. A quick survey on inland water pollution was conducted in 1970 by FAO in Kenya, Tanzania, Uganda and Zambia (FAO, 1971). The study concluded that, at the moment, pollution was not a serious problem in relation to freshwater fisheries.
A more recent study was carried out in six countries (Burundi, Kenya, Malawi, Sudan, Tanzania and Zambia) (Alabaster, 1981). It was concluded that, despite the differences among the countries, problems in common now exist, although at the moment they appear to be localized. Moreover, serious gaps in qualitative and quantitative data on several subjects were identified. The need for improving legislation and for expertise was therefore recognized. This last point is of particular relevance as local authorities were in general well aware of the importance of the problem and willing to improve measures against water pollution.
The report concluded that lack of specific technical information and of monitoring facilities and research equipment were the major obstacles to effective action. The FAO Committee for Inland Fisheries of Africa, which promoted the last quoted report, consequently decided to enlarge its activities and programmed another study in five West and Central African countries: Cameroon, Ghana, Ivory Coast, Mali and Nigeria. The terms of reference were the same as for the previous study:
To identify existing and future sources of pollution affecting fisheries in the countries listed;
to examine the local capacity to deal with aspects of water pollution relating to fisheries, and
to suggest appropriate infrastructure and establish baselines for future studies and monitoring programmes in the countries.
During the short time available for the mission it was not possible to collect all the relevant information on pollution discharges. This report is therefore presented as a preliminary outline and with the understanding that a complete survey on the state of pollution in inland waters can be done only by personnel working in the country. A second aspect to be noted in the document is that there is a great disparity among the different countries and, in each country, among the various sectors of activity. This is due to several objective causes which include, among other things, the novelty of the problem, the type of administration (i.e. more or less centralized, newly-hired staff, etc.), the size of the country, the historical, geographical and demographical differences.
As a first step, information on polluting discharges was requested. Other points considered were the status of fisheries (quantity and quality) and eventually existing records of mass mortality of fish. Enquiries on possible data from analyses of fish flesh were also made, particularly on pesticide contents. As a further point, all the scientific data, or other documentation, on various subjects was collected even if only partially concerned with pollution problems (i.e. biological monitoring, point sources analysis). Finally, the last point was to obtain information on existing legislation and projects that could be relevant for future programmes and coordination of measures that would have to be taken.
The following report will go through all these lines and, whenever possible, an attempt will be made to transform qualitative information into quantitative data.
In order to evaluate the impact of pollution on fisheries, in the absence of broad scale direct studies, as is the situation in most of the countries, indirect information had to be collected from various sources and evaluated.
Data concern the theoretical pollution charges on water bodies from three main sources: sewage, industrial effluents and pesticides, including those employed in vector control. Specific discharges, whether deliberate or undeliberate, such as petroleum, had to be considered when necessary. In several cases it was possible to relate the industrial discharges to resident population units, assuming that industry is producing a waste comparable to that of a defined number of inhabitants. This assumption is particularly appropriate in the case of food-processing industries whose effluents are similar in composition to sewage discharges.
Information was collected mainly through interviews with persons in responsible positions and a number of internal reports and unpublished documents were also made available to the author. The remainder of the data is cited from scientific literature and referenced accordingly.
The Niger and its tributaries are the supporters of most of the activities in Mali. Water is used for the cultivation of rice, irrigation, potable water supply, navigation and fishing. The inland Niger delta from Ségou to Mopti is a great fishing area and also an area of intensive agricultural exploitation, including livestock raising. Fish are of great importance in Mali and more than 500 t of smoked and dried fish were exported in 1983 (FAO, 1984a).
Mali is a country with low population density, 5.5 inhabitants per square kilometer; the total population was, according to the 1982 estimate, 7 342 000. Saharian zones have the lowest density (1 inhabitant per km2), while about 20% of the inhabitants live in the area of the Niger delta. The same area also has 80% of the animals (i.e. about 4 million heads of cattle and 10 million sheep and goats).
The second most densely populated area (10% of the population) is that from Bamako to Koulikoro, where most of the industry is located. However, with the exception of Bamako, the density of the population is never very high, being around 20 per km2 in Koulikoro (106 000 on 6 000 km2), Segou (341 000 on 12 750 km2), Ke Macina (116 000 on 6 563 km2), Djenne (118 000 on 4 563 km2) and Mopti (197 000 on 9 340 km2). Bamako has 420 000 inhabitants, 30% of which are served by a sewerage system. One can therefore assume that only during the rainy season do all of the human discharges go directly to the river. Moreover, 9% of the inhabitants are connected with the public water supply taken from the Niger and chlorinated; the great majority has domestic, individual or collective, wells. A second assumption is that the per capita water consumption is low and that the drainage is limited. Obviously, domestic wells are an important limiting factor in water consumption.
A certain concern, on the contrary, could be caused by the organic load from animals. The real amount of animal wastes is difficult to evaluate although one can calculate the theoretical load by applying commonly-used conversion factors, that is 16.4 for cattle and 2.45 for sheep and goats (Gloyna, 1971). In the inland Niger delta, the animal population converted into human equivalents is therefore about 90 million (65 million for cattle and 24 million for sheep and goats). Most of the consequences of the BOD load are related to the ways and the rates by which the discharges enter the river. If the calculated load is directly released to the river, it will certainly cause considerable problems. Therefore, the possibility of keeping the animals away from the immediate vicinity of the river during certain seasons should be studied; some transhumance is, however, already practiced.
About 80 percent of the industries are located in the area between Bamako and Koulikoro. The few important industrial installations outside that area are textile and food processing industries at Ségou.
In all, there are about 20 relevant agroalimentary complexes in Mali, and among them those with the heaviest pollutant discharges of oxidizeable matter are abattoirs, oil factories, fruit juice canneries and sugar refineries. A few chemical factories (less than 10) produce or prepare paints, detergents, fertilizers and simple inorganic compounds such as sodium hypochlorite. Other industrial activities relevant to water pollution problems are a tannery, an electroplating plant and some textile complexes. However, data on the annual volume of the production of chemicals (300 t a year) do not indicate great quantities of discharges. Food processing (i.e. sugar refinery) and textile factories are certainly the most significant polluters.
As identified by local authorities, problems could be grouped in (i) the absence of treatment and direct discharge into the Niger, (ii) the ineffective means of hazard evaluation and effluent quality control, and (iii) the lack of regulations concerning industrial wastes.
The only existing treatment systems are primary settling tanks, but the primary sludges, especially in the absence of appropriate disposal, seep to the river, particularly after storms during the rainy season.
There are not enough laboratories equipped to assess the potential dangers of an effluent. This fact limits the intervention capabilities of the authorities to cases where damage has already been done and is evident, such as destruction of vegetable gardens, a strong, offensive smell, etc.
Notwithstanding the absence of regulations, local authorities are trying to persuade factories to install efficient primary treatment plants and systems to discharge the effluent indirectly through a lagoon. This is, for example, already done in a sugar refinery at Ségou, where the oxidizeable matter is discharged to irrigation channels.
Pesticides are mainly used in the Sahel zone, where the possibility of run-off is limited. The main districts are: Kayes, Nioro, Nara, north of Tombouctou and Gao.
From 1973, after the drought, to 1977, lindane has been used in relatively high quantities (130 t), but is now slowly substituted by the carbamate propoxur. This last compound has about the same toxicity to aquatic life as lindane (FAO, 1969); however, it is much less persistent and is not bioaccumulated. In 1982, fenitrothion, an organophosphorus insecticide with moderate persistence, was widely used on millet, sorghum and maize. Limited treatments against birds (Quelea quelea) have also been made with fenthion in the rice zones.
In the southern part of the country, at the border with Ivory Coast, relatively great amounts of pyrethrins have been used; however, these compounds have limited persistence and are not accumulated. Some more tonnes of pesticides are used for conditioning seeds. In the public health sector, pesticides have been widely employed in Africa to reduce, as far as possible, the impact of diseases on the populations.
Vector control is mainly carried out by chemical methods, although biological methods are increasingly being employed. DDT has been regularly used for many years in Africa, but it is difficult to make quantitative estimates. At the moment in Mali there is a pilot project on schistosomiasis applying the molluscicide niclosamine to water at the contact points with man as vector. This compound is relatively toxic to fish but it is not widely spread, since it is only used in stagnant waters or water bodies with very limited capacity for renewal.
Mali, as well as many other countries in West Africa, is involved in a vast programme of onchocerciasis control, carried out by the World Health Organization. About 800 000 km2 have been treated, and an additional 1 300 000 km2 are expected to be treated in the next few years to control the larval population of the dipteran Simulium damnosum. The pesticide most commonly used is temephos (Abate) and, in inferior quantities, chlorphoxim. This will be more widely discussed in the chapter on Ivory Coast, as Bouaké is and was an important operational center for vector control. Regarding Mali, only the southern part of the country is under treatment. There is no chemical monitoring or study on the effects on fish populations, since the local WHO office for this programme is checking only the effects on Simulium larvae and on other invertebrates. Following the treatments, all invertebrates disappeared but an almost complete recolonization was observed after a couple of weeks.
The middle Niger is intensively fished and Mopti is a centre of trade in dried and smoked fish. The yearbook of fishery statistics (FAO, 1984) attributes Mali for 1983 with 33 000 t of fish in nominal catches. 544 t of fishery products were exported to neighbouring countries (FAO, 1984a). Fish catches were much higher (about 100 000 t) and the species composition differed before the drought of 1973–74. Massive fish kills have never been observed. The only great mortality recorded concerned the freshwater manatees in the region of Gao.
At the moment, regular monitoring covers only hydrographic parameters, microbiological controls and parasites in drinking water. According to available information, analyses of pesticides were never carried out, neither in water nor in fish.
Decree 35 of 14 March 1975, in its second chapter, section 1, article 10, reads: ‘It is forbidden to discharge to water bodies substances potentially harmful to fish’, testifying the concern of the authorities but, unfortunately, without further specifications. The Direction nationale de l'hygiène publique et de l'assainissement is also in charge of water pollution control. Another group has almost completed an enquiry on the ‘Harmonization in the use of pesticides’, promoted by WHO, with the objective of recording the quantities of pesticides and how they are used throughout the whole country.
Moreover, in order to coordinate the various activities of environmental protection, a national section of Man and the Biosphere has been created recently and is in operation.
Local authorities are certainly aware of the need to protect fisheries; however, some undesirable effects of water pollution have already been observed. From the information gathered, it appears that the problem, although existing, is at the moment not too critical and could be easily managed. Now it is important is to intervene immediately and to plan well for the future.
The role of animal wastes needs to be studied. However, although amounts of human and animal wastes are significant in certain areas and seasons, they are released into a big river and problems could be avoided by optimizing discharges. For example, maximum allowable BOD could be calculated in order to avoid oxygen depletion to a level dangerous for fish, and during certain periods only immissions of controlled quantities could be permitted. Industrial discharges are point sources limited in number, and therefore relatively easy to control. Most of the wastes are composed of oxidizeable matter.
The simple measures proposed by local authorities (i.e. primary settling tanks, the avoidance of direct discharges to the river, etc.), if observed, could certainly be effective. For the future, a classification of the industries according to their contamination potential could be of great help in preventing pollution. Pesticides are not so widely used in this country, with the more persistent and bio-accumulating compounds being substituted by degradable and non-bioaccumulating insecticides. Some analyses of the contents of persistent and bio-accumulating pesticides in fish flesh should be made as a precautionary measure.
The hydrographic feature of Ivory Coast is characterized by a series of nearly parallel rivers with inconstant discharges running from the North to the Atlantic Ocean. The most important are the Bandama, the Komoé and the Sassandra. There are wide lagoons along the coast, and Abidjan was built on one of them. In the inner part of the country there are several artificial lakes.
In many large African cities sewerage systems service only a small portion of the population, most of the sewage being discharged untreated into natural water ways. Obvious consequences are bacterial contamination, eutrophication and reduction in oxygen content.
Abidjan grew from 46 000 inhabitants in 1946 to an estimated 1 600 000 today. According to an expert report (Colcanap and Dufour, 1982) only 340 000 inhabitants are served by a sewerage system.
For several years Pagès (1975) analysed the faecal contamination of the Abidjan lagoon (Lagune d'Ebrié). Several other works have been carried out more recently and the situation is now relatively well described. In fact, in a more comprehensive work, Pagès and Citeau (1978) documented the bacterial pollution and defined the situation as alarming; moreover, they observed that the opening of a common emissar would not solve the problems as traces of Abidjan solid wastes, due to currents, were found at the level of Grand-Bassam, about 50 km east of the town. Arfi et al. (1981) studied the phytoplankton and the state of eutrophication and found that several effluents were toxic to biota before dilution, while most of the bays were strongly eutrophicated. Given that the Ebrié Lagoon has an economically-important stock of fish and crustaceans and that their biological cycle is completed partly in the sea and partly in the lagoon, there is a risk of disturbing the migration of juveniles, a particularly sensitive development stage, with a consequent reduction in fishing yields.
According to Dufour and Slépoukha (1975), the bottom water oxygen saturation during low-water season is about 30 to 40% all around the town area (Marcory, Cocody, Bietri and Koumassi), in some areas as low as 20% or less. On the contrary, going west to Azito and beyond, the oxygen saturation gradually increases up to around 60%.
Zabi (1982) reviewed the existing information on the theoretical charges and hydrology and described the benthic populations in relation to pollution. This study confirmed that benthic populations have changed and that in certain areas only the oligochaetes Pachymelania aurita and Tympanotonus fasciatus can be found, both of which are considered pollution-indicating species. On the contrary, in unpolluted areas, Ethmalosa fimbriata, Acartia clausi and Corbula trigona are found: a fish, a crustacean and a mollusc typical of water in good conditions. Unfortunately, such a documentation is lacking for other towns. For example, in Bouaké, one of the most important towns, according to the administrators and public officials, contamination exists but quantitative data are not available. Bouaké does not have a sewerage system but only collecting channels. Potable water is taken from a small lake which is sometimes polluted; chlorination is therefore widely used.
With few exceptions, most of the industries in Ivory Coast are located in the coastal area, mainly around Abidjan, where they contribute significantly to increase the amount of pollution loads. Most of them produce wastes that are similar in composition to human discharges or are at least amenable to biological treatment. There are in fact several breweries, wine-bottling plants, soft drink industry, a palm oil refinery, a vegetable canning industry and an abattoir. A petroleum refinery and several textile industries there can also be considered as discharging organic wastes (Colcanap and Dufour, 1982).
The total load is calculated at about 5 200 t BOD, 75 t/a ammonia and 5 t/a phenols. The load from other industries, such as fertilizers, pesticide packaging, paints and galvanization or plating, can only be evaluated with difficulty but it includes, for example, a few tonnes per year of chromium and other metals, about 20 t/a of fluoride and about 65 t/a of phosphates (UNIDO/UNEP, 1982).
Several sugar factories, fruit canning or food processing industries are located in the inner part of the country mainly by big rivers such as the Sassandra or the Bandama and the possibilities of heavy pollution are limited.
An exception exists in Bouaké, where two big factories, a cotton-spinning and textile factory and a soap and oil factory, with over 2 000 and 1 000 workers respectively, created severe pollution in the very small River Loka and caused great problems, including risks for human health (Prefecture de Bouaké, pers.comm.).
Pesticides are widely used in Ivorian agriculture, especially on the most important crops such as cotton, cocoa, coffee, banana and rice.
For example, in 1976, 300 t of DDT, 100 t of methylparathion and 30 t of other organophosphorus compounds were used on cotton fields, 600 t of lindane on cocoa. Since 1979, DDT and other chlorinated hydrocarbons were banned and replaced by organophosphorus compounds, carbamates and natural and artificial pyrethroids. An approximate idea of the actual theoretical charges could be given by assuming that about 10% of the cotton fields, that is a total of 2 000 000 ha, was treated five times per year, twice with an organophosphate associated with pyrethrins (6–10 g/ha) and three times with pyrethrin alone (12–15 g/ha).
On cocoa crops, propoxur has now replaced lindane with an application of 335 g/ha (75% active ingredients) twice a year during the period July/September. About 20% of the 1 200 000 ha are treated; it is planned to expand the treated area to 50% of the cultivation by 1987.
Before 1979, coffee was treated with DDT and lindane, now replaced by several pesticides from different chemical families. Dieldrin is still used in combination with fenithrotion against the orthopteran Zonocerus variegatus. Carbofuran is used on rice, while fenamiphos is the nematocide used on the banana cultures (6 kg/ha at the foot of the trees). There is also a certain load from fertilizer application. On 20–30% of the cultivated areas fertilizers are used, especially on coffee. The exact load, however, as well as the eutrophicating effects, are difficult to evaluate, as quantities applied are changing according to the type of soil, age of the cultivation, drainage areas, etc.
Another important field of pesticide application in Africa is the public and animal health sector associated with campaigns to curb, if not to eradicate, endemic diseases such as malaria, onchocerciasis, schistosomiasis and trypanosomiasis by means of controlling their insect or mollusc vectors.
One of the largest projects, involving 18 000 km of rivers in several countries in the Gulf of Guinea region, is the WHO anti-Simulium programme. The aquatic larvae of this dipteran are killed by spraying pesticides directly on water. Temephos (Abate) and chlorphoxim, together with the biological insecticide Bacillus thuringiensis, are the most widely applied. It is very difficult to obtain exact data for each country and each river but, as an example, one can refer to the total quantities applied per month in the dry and wet seasons.
Spraying is repeated frequently according to the river discharges and the presence of the larvae: February 1983, 3 015 l of Abate (20% a.i.), 5 666 1 of B. thuringiensis; August 1983, 13 600 1 of Abate, 24 100 1 of B. thuringiensis and 7 700 1 of chlorphoxim (20% a.i.). WHO has organized and is leading a great number of laboratory and field studies on pre-screening of new pesticides (i.e. Troubat and Lardeaux, 1982), on efficiency of the treatments and on unwanted ecological consequences.
In Ivory Coast, the research projects involved the ORSTOM (Office de la recherche scientifique et technique outre-mer) station in Bouaké and the Institut d'écologie tropicale in Abidjan. At present, on the rivers Bandama, Nzi, Maraoué and Komoé, B. thuringiensis is widely used, while on the Sassandra chlorphoxim is applied in the north and Abate in the south-east. A weekly treatment of 0.1–0.5 mg/l is the most commonly used. Many publications and reports exist on the subject and it appears that, after the use of temephos, the invertebrate population is affected but that the treated zones are readily recolonized in a short time from adjacent areas. Lévêque et al. (1982) concluded, after five years of research, that the release of temephos had no detectable effects on the fish populations in Ivorian rivers. Maslin Leny et al. (1978) arrived at the same conclusions after several years of research on the Komoé River, and similar considerations were made by Dejoux (1978). Unfortunately, since 1979, certain species of Simulium showed a resistance to Abate; this insecticide was therefore substituted by the more toxic chlorphoxim and by B. thuringiensis. This biological insecticide is considered to have only little effect on non-target species (NRCC, 1976) but, unfortunately, there are problems using it in the wet season because of the difficulty to reach the active concentration; chlorphoxim has then to be used.
During a three-year survey, Kassoum and Yte (1982) noted at several stations or rivers a decrease in catch per unit of effort and a decrease in the condition factors of the fish; however, the authors hesitated to attribute these findings totally to anti-Simulium treatment and mention, among the possible causes, the use of pesticides other than anti-vectors and the natural fluctuation of the fish populations. Elouard and Gibon (1982) investigated the possible effects of alternating applications of three insecticides on the non-target fauna of the lower course of the Maraoué. At least for the moment, the effects do not seem different from those observed after the continued application of a single insecticide.
It appears that in view of such an intensive anti-Simulium campaign, efforts to detect undesirable effects have to be continued, since the margin of safety between tolerable levels of chemicals and those provoking dramatic modifications in the environment are probably very small.
As opposed to anti-Simulium treatments, which are made directly on rivers, forests are sprayed against Glossina spp. by helicopter. This type of intervention has, in several cases, provoked mass mortality of fish (Dejoux et al., 1980); however, when the application is properly made, side-effects are certainly limited.
Everts et al. (1982) evaluated the side-effects of experimental application by helicopter of pyrethroids (permethrin and deltamethrin) in a riverine forest habitat in Bouaflé. Fish mortality was not observed, although the acute toxicity of these substance is high, but invertebrate populations were affected. Apparently, aquatic insect populations recovered quite well but certain species of crustaceans were virtually eliminated.
The total 1983 fish catches in Ivory Coast, according to FAO (1984), was about 94 000 t, of which 16% is derived from inland waters. Local estimates, however, indicate a potential for increase of inland water catches (20 000 – 40 000 t/a) by exploiting several big man-made lakes. Research projects regarding limnology and fisheries are in progress on several of these lakes. The most important ones are Kossou, Ayamé, Taabo and Buyo. Mass mortality of fish has been recorded in several lakes and the Bietri Bay due to anoxia as consequence of eutrophication, in the Aghien Lagoon and in a number of cases due to misuse of pesticides.
Pesticides are frequently abused in several African countries to illegally catch fish; in Ivory Coast paraquat is one of the more employed substances. As a consequence, several cases of intoxication have been reported after the consumption of fish and contaminated water. The authorities have taken the problem seriously and are conducting an educational campaign in the villages against this misuse (Hifognan, pers.comm.).
A preliminary work which compared the fish populations of the different polluted (Bietri and Koumassi) and unpolluted bays of the Abidjan lagoon did not reveal substantial differences (Albaret, pers.comm.). However, polluted areas showed several cases of dwarfism in fish, with sexual maturity at a size of 6–8 cm, instead of the normal 13–15 cm.
Several published results of research have been utilized in the previous sections. Zabi (1981) lists the research projects that are going on in the field of aquatic sciences at the Centre des recherches océanographiques and a number of institutes involved in pollution research and notes that, in spite of the concern on the part of the public authorities, there was not sufficient attention paid to specific research on pollution problems. To this list one must add the work of the Institut d'écologie tropicale on artificial lakes and on monitoring of unwanted ecological effects of the onchocerciasis campaign. However, in the framework of the CRO-ORSTOM activities, research is in progress on the concentration of pesticides and heavy metals in water sediments and fish at 56 sampling stations of the Abidjan lagoon.
General comprehensive legislation for water pollution control does not exist, although a number of ministries are at the moment working on the various aspects of the problem (Zabi, 1981) but in 1981 the Ministry of Environment was established to coordinate the various tasks. At the moment, negotiations with the industrial associations are at the advanced stage in order to classify industries and to establish water quality criteria, taking into account regulations which already exist in other countries.
The setting up of the Réseau d'observations des eaux (ROE) is also at an advanced stage as a system for monitoring the quality of the water bodies by means of mobile laboratories. The authorities are aware of the problem, and a number of activities and control measures have already been taken. See, for example, the sanitation project of the town of Abidjan (Colcanap and Dufour, 1982).
The obvious trouble spot regarding water pollution problems in Ivory Coast is the Ebrié Lagoon, with the still growing town of Abidjan. The most relevant charge are sewage and domestic wastes, with a theoretical BOD of about 37 000 t/a. Action has already been taken but the situation, as documented by a number of scientific studies, needs immediate and effective intervention to avoid arriving at the point of no return.
The situation is worsened by the presence of industrial discharges, most of them comparable to an organic charge of about 5 000 t/a. Industrialized nations have a ratio of 1 to 1 between the two types of charges, while in this country the ratio is 6 to 1. This means that it could be relatively easy to control present charges while expected new developments could be allowed only under water pollution control regulations. Concerning industrial activities and sewage discharges, the situation in the internal part of the country, with few exceptions (i.e. industrial activities in Bouaké), is certainly not critical, and remedial actions could easily be taken.
A big question mark is the consequence of the use of pesticides. The charges have been approximated, but more accurate data are needed. Unfortunately, no toxicity data are available on African fish species nor is there information on bioaccumulation under tropical conditions, and great uncertainties exist on the environmental fate of the more widely employed substances. This field is the one which needs the most research. Regarding pesticide application for vector control, a wide range of monitoring activities could probably detect undesirable effects immediately.
The water resources of Ghana are abundant. Most of the country lies in the catchment basin of the Volta River, which has been converted to a very long artificial lake. Outside that basin, the relatively long rivers Pra and Ankobra discharge into the Atlantic Ocean together with a number of smaller rivers such as the Densu, Ayensu, Nakwa and Amisa.
A few sewage treatment plants exist in Ghana, e.g. the Volta River Authority at Akosombo, University of Ghana at Legon, University of Science and Technology at Kumasi, in addition to three sedimentation tanks in the Accra-Tema metropolitan area; however, most of the raw domestic effluents are discharged directly into water bodies. Tema has the only satisfactory disposal system which collects all wastes, urban and industrial, in an outfall that discharges one mile offshore in the ocean.
The Ghana Water and Sewage Corporation, in the Accra-Tema Water Supply and Sewage Project, made an enquiry on the needs for water and the theoretical discharges of towns and industries in the area as a starting point for the sanitation plan. Results include some data on sewage quality (Takal Consulting Engineers and Architectural and Engineering Services Corporation, 1981).
For the coastal area, the report by UNIDO/UNEP (1982) estimated a theoretical charge of 22 500 t/a of BOD and 32 000 t/a suspended solids, while for Takoradi-Sekondi the load was estimated at about 5 000 t/a BOD and 7 000 t/a suspended solids.
Information on pollution caused by domestic wastes exists, but extensive and complete monitoring has been conducted only for estuaries, lagoons and coastal waters (Biney, 1982). Other investigations have been made, although of limited extent. Ofori (1978) in a study on the Densu River and the Weija dam found that both total and faecal coliform counts (at several stations) were grossly in excess of those allowed by the Ghana Drinking Water Standards. Kpekata (1978) analysed the nutrient pollution load in the Odaw River, Accra, which, in addition to sewage, also receives the discharges of a brewery. He recommended at least partial treatment before discharge into Accra Lagoon. Biney (1982) classified all the areas according to BOD level into three categories: ‘unpolluted and recovering from pollution’ (<4 mg/l), ‘doubtful and poor quality’ (4–12 mg/l) and ‘grossly polluted’ (>12 mg/l). Based on this criteria, the estuaries of the rivers Volta, Kakum, Amisa and Ayensu were classified as clean while the Densu, Nakwa, Pra and Ankobra were considered of doubtful quality. Of the 16 lagoons, 12 were considered polluted to various degrees, with Korle (Accra) and Chemu (near Tema) grossly polluted.
Industrial pollution is not widespread in Ghana, as most of the industries are placed along the coast in Takoradi, Tema and Accra. However, several big factories exist in other towns, and mining activities add to pollution.
The Water Resources Research Unit identified areas, sources and types of pollution by collecting information through questionnaires distributed to the 42 most important factories and mines asking for information on quality and quantity of their discharges (Mensah, 1976). The rivers affected included the Ofin, Birim, Volta, Densu, Ankobra and some of their major tributaries. Detailed tables report volumes of effluent discharges, composition of the effluents and in some cases chemical analysis or observations on the receiving waters. Among the types of industries mentioned are rubber, glassware and textile factories, sugar refineries, breweries, canneries and tanneries. Major mining activities include gold, diamond, manganese and bauxite. A more recent report (UNIDO/UNEP, 1982) which deals with the principal industrial establishments in the coastal area only, estimated the load at 1 400 t/a BOD and 3 500 t/a suspended solids. Among the industrial activities difficult to include in a BOD load estimate is an aluminium smelter, which has a theoretical load of 1 250 t/a of fluoride.
Some research projects have been carried out to find how the quality of inland waters has changed; a few results are mentioned, for example by Mensah (1976). Among the worst cases referred to is that of the Ankobra River basin, where 4 mg/l of cyanide were found in the Esuokofie stream, and that of the Volta River, in the lower Volta basin, where a textile factory, despite high dilution, discharges 4 400 m3/day of blackish waste water with a pH ranging from 7.6 to 10.
Since the early '70s the Institute of Aquatic Biology in Achimota, Accra, has performed special research projects on pollution problems and monitored chemically, biologically and bacteriologically some rivers (Institute of Aquatic Biology, 1970, 1974). Antwi (1973) found chemical pollution in some rivers and streams. A case history on Lomi River was done by Ofori (1980). A complete systematic survey of the quality of inland waters in Ghana in relation to industrial pollution does not exist; however, the documents and examples quoted give a certain idea of the state of water pollution in the country.
Ghana has been called a land of cocoa and minerals; in fact, cocoa cultivations cover 28% of the land, while 65% is bush and the rest is used for other cultivations. Major areas of cocoa are the south-east and the south-west on the Kumasi plateau. Until a few years ago DDT and lindane were the pesticides mainly employed; now two carbamates, propoxur and dioxicarb, are the most widely used.
Around two million ha are cultivated, but only 50–75% are treated (four times a year, with 250–500 g a.i./ha). No data are available on the possible unwanted ecological effects or residues of the use of such a high quantity of chemicals. On the other crops, different organophosphates or carbamates are used but the quantities applied are substantially less. For example, in the Great Accra region the total amount of pesticides used is about 15 000 l/a, with a tendency to favour artificial pyrethroids.
Like several other countries in the Gulf of Guinea, Ghana is involved in the Onchocerciasis Control Programme of WHO, and the Institute of Aquatic Biology in Accra is in charge of monitoring the effects of treatment on non-target fauna as well as performing laboratory studies. Several publications are available and demonstrate that the effects of Abate on invertebrate populations are limited or not detectable (Samman and Pugh Thomas, 1978, 1978a, 1979). Abban and Samman (1982) stated that no fish kills were observed that could be associated with Abate treatment of rivers but acknowledged that during the dry season fish may be exposed for longer periods than expected. Abban et al. (1982) concluded in an extensive report on the status of fish populations in Abate-treated rivers in northern Ghana that no long-term changes in fish stocks were observed. However, it would anyhow be difficult to separate effects of Abate from the changes caused by the Akosombo dam and the continuous development of the Volta Lake.
Antwi (1983) found no differences in acetylcholinesterase (AchE) activity in fish taken from the White and the Red Volta, which received aerial treatments of Abate for 3 and 5 years respectively. However, he noticed an inhibitory effect on AchE in caged Tilapia left in the Maraoué River, Ivory Coast, after a treatment of chlorphoxim, one of the substitutes for Abate. This effect is probably reversible, as no reduction in AchE activity was observed in fish caught in the Bandama and the Nzi Rivers, which received chlorphoxim treatments for 10 months but where the treatments had been suspended 7 months ago.
In most coastal town of Ghana, fishing is the main occupation. According to FAO (1984) less than 20 per cent of the total annual catch (228 000 t in 1983) are derived from freshwater fisheries, which come mainly from Lake Volta, also a good source of brood stocks of fish for aquaculture.
Several fish kills have been reported in the mining areas, especially in the Ankobra River basin. As in many other African countries, fish kills due to intentional misuse of pesticides are reported, one of the last recorded was a massive kill in Weija Lake, where DDT was used for fishing.
The Hydro Division of the Architectural and Engineering Service Corporation has data, although not always complete, on the most important rivers, but unfortunately only until 1977. Chemical analysis includes the following parameters: colour, turbidity, pH, alkalinity, chlorides, nitrites, nitrates, ammonia, hardness, Ca, Mg, Fe, carbonates, sulphates, Mn and suspended solids.
Studies on eutrophication in Lake Volta and monitoring of the consequences of the Onchocerciasis Control Programme are still in progress but, in general, research on pollution problems is reduced due to economic constraints. However, the most relevant cases such as discharges of mining activities in the Ankobra basin and aluminium smelter wastes in Tema are included in the research programmes.
A Water Pollution Control Decree has to be completed and complemented on the basis of a project begun in 1979. This Decree will give the Environmental Protection Council the power to control water pollution and to develop programmes and methods for monitoring. No uniform discharge standards are prescribed; there will be a case-by-case intervention instead.
At the moment a Water Pollution Control Committee is acting. Some measures have already been taken; for example, the big textile complex on the Volta River has built a sedimentation tank, and a number of industries have been made aware of the danger they are causing and have been requested to take appropriate measures. There are no regulations on pesticides.
In a few relevant cases, such as the gold mine on the Ankobra River and the Korle Lagoon, the Council has established an Environmental Impact Assessment Team. This team has to consider all the facets of the problem, including air pollution, environmental management, and socio-economic aspects.
A number of activities which have been quite well documented for lagoons and estuaries are underway in order to minimize the effects of urban discharges in Ghana. Sanitation systems are projected, and data for planification are available.
Relatively simple measures could be effective in most of the cases of industrial pollution, considering the amount of water in the country. As a first measure, a simple acute toxicity test with fish could help limiting the most obvious and significant damages provoked by industrial or mining wastes.
With regard to the wide use of pesticides on cocoa crops, no data are available and therefore research needs to be undertaken on three major areas: toxicity on indigenous species of fish and invertebrates, probability of bioaccumulation, and the environmental fate of the substances under tropical conditions.
The situation in relation to the use of pesticides for vector control looks very much like the one in Ivory Coast. Applications of Abate over several years did not cause evident negative effects while the necessary change to chlorphoxim seems to cause more worry. However, the research and survey team now in operation could possibly detect the most significant unwanted changes at an early stage and allow the implementation of suitable measures.
The hydrography of Nigeria is dominated by the Niger River, which enters the country from the north-east and flows into the Atlantic Ocean through a wide and very complex delta region. Small effluents flow into the river from the West, while from the East the Benue River contributes significantly. Some short rivers flow directly to the Atlantic. In the North, the Komadugu River collects the waters of the catchment basin of Lake Chad.
According to recent estimates Nigeria has about 82 million inhabitants. The largest town is the capital, Lagos, with about 4 million inhabitants and a theoretical annual charge of 95 000 t/a of BOD and 136 000 t/a of suspended solids.
According to a national report (Nigeria, 1982) the prevailing situation in most Nigerian towns and cities is very unsatisfactory as central sewerage systems are almost non-existant. However, small modern sewage treatment plants can be found in large establishments and institutions in the larger towns. The main methods employed at present in the disposal of human wastes are: septic tanks, the traditional ‘salanga’ system (pit latrines) and the pail latrine. Even in Lagos, night soil is collected in metal pails and simply dumped in the lagoon. Projects have been prepared for the installation of central sewerage systems in Lagos, at least in the new urban areas such as Amuwo-Odofin, Victoria Island or the Lekki peninsula.
Analytical data on the Lagos Lagoon do not exist; it is therefore difficult to draw any conclusion on what effects the entering water may have. However, the Lagos Lagoon, once very productive in fish, is now considered a bad place for fishing (Adeyanju, 1979).
As far as the interior of the country is concerned, a few investigations have been carried out and published by the University of Ibadan. Oluwande et al. (1983) made a survey on five rivers and streams for over three years generating physical, chemical and bacteriological data. Human and industrial discharges deteriorated the water quality. The BOD was relatively high in the main stream, the presence of coliforms was detected and the oxygen level was in certain areas near zero.
Ajayi and Osibanjo (1984) studied the self-purification constants for a stream in the Ibadan area and concluded that the capacity was quite high.
It has been estimated that about 75 per cent of the industrial activity is situated along the coast with about 50% in Lagos. The total theoretical industrial charge from these regions was estimated at 17 000 t/a BOD and 24 000 t/a suspended solids (UNIDO/UNEP, 1982). The most relevant contributors to pollution are breweries, textile industries, pulp and paper mills and petroleum refineries.
Within the framework of a broad project aiming at highlighting the major environmental problems, build-up of a data base, creating public awareness and diffusing basic information, a survey on waste management in industry in Nigeria was carried out by the Environmental Planning and Protection Division of the Federal Ministry of Housing and Environment (Nigeria, 1981). In 1971, there were 840 major industrial establishments, the great majority of them in Lagos and the western states. Among them are 40 textile mills (counted in 1980), mainly situated in Lagos (7) Kano (11) and Kaduna (8). Their waste management is described, giving analytical data on the water quality of effluents and receiving streams. Colour, total solids and BOD seem to cause the major problems in the receiving streams.
Waste management in two big breweries, one in Lagos and the other in Ibadan, as well as in a paper mill and a sugar refinery, both in the Kwara State, are discussed and taken as case histories for water pollution control problems.
An enquiry was made through a pilot test questionnaire to survey waste management practices in the industries in the Lagos metropolitan area; however, its results were considered not completely satisfactory. The Ministry therefore wants a more precise quantification and qualification of the discharges and consequently a comprehensive study on the Lagos Lagoon and the Five-Cowrie Creek has been initiated. A study on contamination of ground water by infiltration of industrial and urban wastewaters in the Lagos metropolitan area showed higher-than-normal levels of mercury, iron and manganese. Finally, an accident is reported, where a sewer collecting and drawing industrial effluents to a treatment plant in the Ikeja Industrial estate in Lagos broke and wastewater caused damage to residential areas. This survey, although incomplete, gives a good picture of the pollution problem in the country and suggests approaches towards the prevention and control of pollution by industrial wastes in Nigeria.
Diazinon, fenitrothion, methidathion and fenthion are bought and distributed by the Federal Office of Pest Control Service in quantities as high as 20–25 000 t/a each, but each State Administration has its own office and buys more of these and other compounds. Data for individual states were not available. However, as a reason for the wide use of pesticides, it was claimed that insect spraying programmes have increased the yield of cotton tenfold.
In Nigeria there is an increase in the use of herbicides as is demonstrated by a booklet of instructions for the use of herbicides in small and middle-sized farms (Nigeria, 1983), but total quantities applied are not known. Campaigns against quelea birds (Quelea quelea) have been conducted in the north. Regarding vector control, very large tracts of land have been cleared of dangerous parasites by means of pesticides. In northern Nigeria 72 000 km2 have been made available for crop production and animal husbandry by exterminating the Glossina sp., a carrier of trypanosomiasis. Apparently, DDT and endosulfan are still in use for these purposes in a quantity of 50 000 kg/a. Koeman et al. (1971, 1978) studied the effects of insecticide application on the fauna of marshes in Nigeria and analysed the levels of pesticides in the brain, liver and fat of different aquatic birds, fish and snakes. Levels of 0.1 mg/kg of dieldrin were found in the fish while DDT was much lower, not exceeding 0.05 mg/kg. In the proceedings of a National Conference on Water Pollution and Pesticide Residues in Foods, held at the University of Ibadan, three papers were presented on this subject (Odeyemi, 1980; Odu, 1980; Osibanjo and Jensen, 1980).
In 1971 Nigeria became the tenth largest producer of petroleum in the world, but in succeeding years production has increased and the country has moved up to the eighth position. In 1981, the total production was 71.1 million t, with a decrease in 1982 (63.8 million t). There are two refineries along the coast and a big petrochemical complex at Warri.
The amount of oil lost to the environment has been estimated by UNIDO/UNEP (1982) to be 53 500 t/a. However, the same report claims that an American Petroleum Institute separator (a simple treatment plant) was operating as an integral part of the oil refining process.
The concern of the Nigerian Authorities for the problem of pollution was reflected in three symposia on ‘Petroleum Industry and the Nigerian Environment’, of which two volumes of proceedings have been published (Nigeria, 1979; Thomopulos, 1983) and the third is in preparation.
The transportation and distribution of oil involves a very complex network spread all over the delta region, which is very rich in fish and shrimps. Imevbore (1979) reported widespread pollution in the delta, the creeks and estuaries of the various rivers, causing the death of a great number of specimens of Callinectes gladiator and C. latimanus, two species of edible crabs, but no quantitative data were available. A reduction in the diversity and density of life in the cleared mangrove forest swamps was also cited. Two years later, Imevbore and Adeyemi (1983) presented a map of the Niger Delta showing the isopleths of oil concentration as measured by infrared spectrography, thus improving the information available a great deal, although not to full satisfaction.
A detailed analysis of oil spill accidents, which discussed the frequency and magnitude, spill size, monthly distribution, causes and companies involved was made by Awobajo (1983). From 1976 to 1980, 784 spills were reported, of which 588 were of minor scale and 11 involved more than 1 500 t. The total oil spilled was calculated to be 293 020 t. In an ecological study after a big oil spill, Ekekwe (1983) found that 1.45% of the local mangrove forest was killed and that edible crabs and winkles were killed or tainted. Odu (1983) presented a study of the degradation and weathering of crude oil in the laboratory and in the field under tropical conditions. All these studies show that under tropical conditions oil degrades more rapidly than in temperate regions. The Nigerian Institute of Oceanography and Marine Research also made investigations both in the laboratory (Ajao et al., 1983) and in the field (Onuoha, 1980). Laboratory studies indicated that undiluted wastewater effluents were toxic to mullets (Mugil sp.) but at 10% dilution the toxicity was highly reduced. In the field the effect of oil pollution was studied in the Niger Delta along the Bonny River for a period of six months. It was shown that primary production was reduced in respect to a control area and the algal species distribution was different.
The most relevant result of this scientific activity was obviously an enforcement of pollution control measures, a long-term comprehensive monitoring plan and an oil pollution contingency plan. An Environmental Sensitivity Index based on geomorphic, ecological and socio-economic criteria was prepared for Nigerian areas that may be involved in oil accidents.
The total nominal catches of Nigeria for 1983 have been estimated to be about 515 000 t of which inland waters contribute about 125 000 t (FAO, 1984).
According to the opinion of the Fisheries Department in most of the country, with few exceptions, pollution is at the moment not a problem; however, the risk is rapidly increasing.
Massive fish mortality has been observed due to industrial effluents and to the illegal use of pesticides, particularly paraquat, for catching fish. A case of mass poisoning of people eating contaminated fish which had been caught with pesticides is reported by Imevbore (1972). Oil spills, either directly in the rivers or in the temporary ponds formed in the flood plains have led to tainting of fish which consequently could not be marketed. An area where fisheries are certainly at risk is the Niger delta, but no accurate data are available (Imevbore, 1979).
Most of the activities performed or planned are in the framework of a plan of action organized by the Environmental Planning and Protection Division of the Federal Ministry of Housing and Environment. In the Lagos area, the Division is undertaking a big pilot project with four phases:
Preparation of a register of contamination sources;
sampling and analysis of the quality and the quantity of contaminants;
research on possible effects, and
preparation and diffusion of effluent guidelines to control pollution at point sources. This project would later be extended to cover all eleven River Basin Authorities.
Moreover, a four-year project has begun to study the impact of pesticides on the Nigerian environment and the problem of pesticide residues as a basis for legislation.
Other institutions working on pollution problems are the Nigerian Institute for Oceanography and Marine Research (NIOMR) and the universities of the country. For example, the University of Lagos is working on microbial pollution of the lagoon from domestic wastes, and the universities of Port Harcourt and Calabar on an impact assessment of petroleum residues on the mangrove ecosystems of the Niger delta. In the coastal area a study has been undertaken for establishing the rate of recovery after an oil spill caused by a fire in an extraction tower. Particularly active in these matters is obviously the Nigerian National Petroleum Corporation, which is funding research and is organizing seminars on the subject ‘The Petroleum Industry and the Nigerian Environment’, three of them having already been held in 1979 (Nigeria, 1979), in 1981 (Thomopulos, 1983) and in 1983 (report in preparation).
Data on hydrology are available on an annual basis from the Federal Ministry of Water Resources. The same ministry is also analysing ground water.
The National Fisheries Development Committee, composed of the directors of fisheries of all the State Governments, has proposed in 1983 a draft of an inland fisheries decree. The text mentions explicitly the need to protect fisheries from pollution and wants to prohibit ‘any discharge of any chemical substances or drugs, poisons or any noxious or polluting substance in any waters frequented by fish or that flow into such waters’.
In a more general framework, an Environmental Control Agency Bill is in the process of being ratified, and related regulations will be based on the Lagos pilot project described under 6.3. In the meantime, a policy of educating concerned parties about pollution problems is actively being pursued. Two seminars have been organized by the Environmental Planning and Protection Division: an Environmental Awareness Seminar for National Policy Makers and one on Environmental Awareness for Media Practitioners (Ijalaye, 1982; Nwuneli and Opubor, 1983). In the first of these workshops a review is made of the laws which concern the environmental problems of Nigeria. A review of legislation concerning the operations of the oil industry has also been published (Ojikutu, 1979).
Nigeria is subject to the same problems as the other African countries but on a wider scale due to its greater development and higher number of inhabitants. Sewerage systems are almost nonexistant and organic wastes cause the direct deoxygenation of the water through the oxidation of organic matter or by the enrichment in nutrients which causes eutrophication problems. Most of the industries are discharging substances with a high BOD, provoking the same type of damage. Research projects are presently being carried out and laws have been passed for water pollution control management.
Also in this country the possible consequences of the use of massive quantities of pesticides have never been evaluated or measured.
Nigeria is unique in respect to the other African countries for its contamination by the petroleum industry as Nigeria is one of the biggest producers in the world. The Niger delta contains one of the largest mangrove swamp areas of the world, is rich in fish, shrimps and molluscs and has a very wide area used for oil extraction, transport and refining. Pollution can be found all over the Niger delta area but severe effects seem to be limited to a few accidents with serious repercussions. However limited, the damages observed have spread to the whole area. Administrative Authorities are actively intervening in order to ensure that resources are utilized while safeguarding the environment and the fisheries.
The territory of Cameroon is divided into five hydrographic basins: Chad, Niger, Congo, Sanaga and the Atlantic coastal area. The Sanaga is the hydrographic axe of the country, flowing from the centre to the ocean. Several shorter rivers discharge directly to the ocean: The Nyong, the Wouri, the Mungo and the Ntem. In the north of the country, rivers have very variable, but in general scarce, flow; the most important are the Bénoué and the Logone.
Cameroon has about 9.2 million inhabitants (according to 1983 estimates) who tend to live concentrated in the towns. At the moment sewerage systems are practically non-existent, with rare exceptions in the newly-constructed areas in Yaoundé and Douala. These two towns, with about 0.5 and 0.6 million inhabitants, produce a waste water discharge with a BOD load of 11 700 and 14 000 t/a respectively. In Douala, the Wouri estuary is considered a polluted area but no quantitative data were available.
In Yaoundé a study has started on Mfundi River, its affluents (Abiergué and Ekozoa) and the artificial lake in the town centre. Preliminary results of the biological monitoring and a number of basic physico-chemical analyses are available. The problem of pollution is under study, and sanitation projects have been started by the Ministry of Mines and Energy (Cameroun, 1980). In Yaoundé some treatment plants are already in operation (i.e. Palais des Congrès). Sewerage system projects have also been started for Limbé and Garoua. However, notwithstanding the primitive state of the sanitation systems, the bacteriological analyses conducted by the Hygiene and Sanitation Service of the Ministry of Public Health demonstrated that cases of contamination of potable waters by E. coli have been very rare.
In Cameroon, as for most of the African countries, there are a number of industries such as breweries, sugar refining, food transformation and processing plants and tanneries, with a heavy discharge of organic wastes. At Mbandjok and Nkoteng sugar refineries discharge directly in the Sanaga without any treatment. A tannery in Ngaounderé and breweries in Bafussam, Yaoundé and Douala are also directly discharging to rivers. On the contrary, one positive example of the growing awareness of the necessity of pollution control is the tobacco and cigarette manufactury in Yaoundé which has good treatment facilities both for air and wastewater. Another example is a large pulp mill in Edéa, with a theoretical BOD load of 25 000 t/d which applies secondary (biological) treatment. A dam is foreseen on the Sanaga in order to provide enough dilution for the residual discharge during the dry season. Moreover, a survey will be performed in cooperation with water pollution control authorities in order to optimize the treatment and to be sure that undesirable effects will not occur.
There is a second important industry in Edéa, with a high theoretical pollution charge, an aluminium smelter that discharges 500 t/a of suspended solids and 333 t/a of fluoride, mainly into the air, however. In Douala, the theoretical BOD from industry is not high compared to the urban load (2 000 t/a and 14 000 t/a respectively). However, in most cases, industries discharge effluents without any treatment (breweries, chemical industry, abattoirs, textile bleaching and printing factories, paint and varnish factories, etc.).
In Limbé, a paper mill and a palm oil factory discharge directly into the sea, while a big refinery complex is ready to start operating with direct discharge into coastal waters.
Most of the theoretical charges from industrial sources have been calculated and reported in a document by UNIDO/UNEP (1982); others can be calculated from the number of personnel employed and the type of production. At the moment analytical data on rivers or estuaries for the whole of Cameroon do not exist. It is, however, to be mentioned that the Ministry of Mines and Energy has started a project for evaluating the actual discharge, under the framework of Law 76/372, which regulates industries whose activities could cause danger, health problems or other disturbances.
A detailed catalogue of all the activities, classified according to the possible danger, has already been issued for the Departments of the Wouri, with the town of Douala, and Sanaga Maritime, with Edéa.
The crops on which pesticides are most abundantly used are cocoa and coffee. Lindane is still employed in cocoa cultures (2 l/ha) but is more and more being substituted by heterocyclic organophosphate derivates, such as diazinon (0.5 l/ha).
Endosulfan was previously used on coffee, but now fenitrothion is applied. High-quality cocoa and coffee plantations cover 300 000 and 100 000 ha respectively, and the total quantity of pesticides used is approximately 100 000 l of diazinon, 145 000 l of fenitrothion and 186 000 l of chlorpyrifos as commercial formulations. However, pesticides are used within the framework of integrated pest management. Tests are made before the treatments to define to degree of infestation and to ascertain which species are present and to what percentage; also, attention is given to beneficial insects.
A few campaigns against birds (Quelea quelea) have been conducted in the north of the country.
The Conseil phytosanitaire interafricain of the OUA has set up an African Scientific Committee on Pesticides to prepare guidelines for formulating regulations common to all African countries. As a preparatory measure, they are making an inventory of the existing parasites, crops and methods of treatment. Recommendations will be made for the pesticides to be homologated.
Freshwater fisheries in Cameroon are important and catches are estimated for 1983 at 40 000 t, compared to 44 000 t of marine catches (FAO, 1984). It is therefore particularly important to protect inland fishery resources from pollution. Unfortunately, several mass mortalities in partiallymanaged river areas near Bafussam have been recorded. They were caused by oxygen depletion by a large organic load which provoked anoxia in fish. In the industrial area of Ngaounderé fish have disappeared from several parts of local waters. Finally, the practice of pesticide abuse for fishing is quite diffused, a practice the Fisheries Service is well aware of, but no information is available on the type of pesticides employed.
A laboratory for water pollution control analysis is planned in the framework of the implementation of Law 76/372. This will allow the numerous qualitative information already existing to be quantified.
An interdisciplinary group has started work at the University of Yaoundé, although in Cameroon pollution problems are believed not to be critical yet. A memorandum (Bopelet, 1983) exists which lists all current activities and outlines future research. The general goal is to have sufficient information on the ‘zero level’ conditions throughout the country. Within the same framework, the Fisheries Research Station at Limbé, at the moment working only on fisheries problems, has been requested to undertake water pollution studies in coastal waters.
In Cameroon specific laws on environmental protection do not exist but in different sectors a number of laws or regulations deal with environmental aspects. A good review of the existing legal framework has been prepared by the local MAB Committee (Cameroun, 1983). Specific mention should be made of Law 76/372 of July 1976 which allows the Ministry of Mines and Energy to intervene to control water pollution. As quoted before, a classification is made of all the activities which are considered dangerous or which could cause various types of deleterious effects and which will consequently be subjected to special regulations.
There are several point sources of pollution of industrial origin in Cameroon but, looking at the country as a whole, water pollution problems seem to be mainly due to an absence of sewerage systems, which are however planned in most of the big towns.
Qualitative data are available and could allow intervention and control. These actions will certainly be improved when quantitative data will be produced by the planned laboratory or by the university. As for many other African countries, the environmental fate of pesticides, their undesirable side effects and the possible residues in vegetables or animals, including fish, remains the big question mark in Cameroon. The need for data in this field is apparent.
The report shows an increase of the theoretical charges and a decrease in water quality, although not to the extent of a general acute problem in all of the countries visited.
Pollution of inland waters and coastal lagoons is serious in the vicinity of most big towns (i.e. Abidjan, Accra, Lagos) but measures are being taken to improve sanitary standards and to reduce the eutrophication problems where they exist (i.e. Ebrié Lagoon).
Most of the countries have planned or started sanitation projects at various levels which do not necessarily amount to a complete sewerage system, but various activities have been undertaken in that direction.
Industrial pollution has a certain impact, though limited in space as it is virtually confined to a few areas, mainly in the coastal region, where control measures to avoid undersirable effects on aquatic biota and the environment in general could be taken.
Two cases of pollution not generated by typical industrial effluents call for particular attention: the mining activities in Ghana and the extraction and transport of petroleum in Nigeria.
In all the countries, under different legal frameworks, a register of point sources has been completed or is in an advanced stage of completion. Such registers are very important as the obvious first step to be undertaken in the control of water pollution. With only few exceptions, data on the quality of effluents and the status of receiving waters are absolutely scarce.
The second step, in the long-term strategy for water pollution control, should therefore be based on the activity of laboratories which have to characterize analytically the discharges and to make a survey of the present situation of the water bodies in each country. A good example of this is the work done on estuaries and lagoons in Ghana, limited, however, to organic wastes.
In some countries such water pollution laboratories do exist, but with insufficient means; elsewhere universities are used (i.e. Nigeria) and in other countries specialized laboratories are planned or being constructed (i.e. Ivory Coast and Cameroon). Scientists from the region have suggested improving the structures and the equipment of existing fishery laboratories rather than building new structures. As economic aspects are at all times and everywhere very important (African countries are no exception), the knowledge of the exact quality and quantity of discharges could allow the use of the assimilative capacity of the receiving waters. It is obvious that by giving a role to natural self-purification and dilution processes, the construction of expensive treatment plants could be avoided, and this would be a great advantage. A classic and simple example could be the calculation of the oxygen depletion (sac-curve) in a river after an immission of BOD discharge of urban or industrial origin.
As an immediate short-term measure for industrial effluents with toxic potential, an acute toxicity test with fish could be employed to limit the most dangerous discharges and to avoid immediate damage and fish kills. However, efficient water pollution control should involve the use of water quality criteria, established upon definition of water quality requirements which depend on the intended use of the water, with human utilization and aquatic life being the most demanding uses. Several national and international organizations have gained considerable experience in establishing water quality criteria, usually by reviewing available scientific information and critically defining a limit not to be exceeded. As an example, according to EIFAC/FAO, quality criteria for aquatic life, and in particular for freshwater fish, should meet the following requirements:
‘Water quality criteria for freshwater fish should ideally permit all stages in the life cycles to be successfully completed and, in addition, should not produce conditions in a river water which would either taint the flesh of the fish or cause them to avoid a stretch of river where they would otherwise be present or give rise to accumulation of deleterious substances in fish to such a degree that they are potentially harmful when consumed. Indirect factors such as those affecting fish-food organisms must also be considered, should they prove to be important’.
Reports on individual substances are usually prepared by working groups that discuss the chemistry of the pollutant in the water, its lethal action on fish, its sublethal effects, the type of toxic action, the factors which influence lethal levels, field observations of polluted waters and data regarding toxicity on algae and invertebrates. Reports are concluded with a tentative quality criterion for aquatic life. In the few cases where a verification of such criteria in the field was possible the results were positive.
The direct application to African waters of water quality criteria produced in Europe or North America would be scientifically incorrect, since the experimental data for the reviews have been obtained mainly, if not exclusively, from European or North African species of organisms and very little attention has been dedicated until now to the tropical environment. It would, however, be an impossible task to produce in a short time enough data to prepare water quality criteria for African fish. A solution to the problem could be to generate a limited quantity of toxicity data for a few representative species such as Orechromis niloticus, Tilapia zillii, etc. Comparing these data derived from a few acute tests with some selected toxicants, with the numerous data existing for some European species, e.g. Salmo gairdneri, one could make extrapolations and could thus apply the already existing water quality criteria to African conditions.
As reported throughout the document, pollution by pesticides is one of the more serious problems. The use of pesticides is widespread and the quantities applied are very high, while data on their toxicity to African aquatic biota, on their environmental fate and their residues are scarce. It could be possible that the tropical environment is much less sensitive to these compounds than other areas but this has certainly to be verified. Finally, as the contamination originates from diffuse, non-point sources, control is very difficult and environmental protection has mainly to be undertaken by preventive measures. Information is therefore urgently needed to assess the environmental impact of pesticides on fisheries through the evaluation of their toxicity for aquatic life, their transformation kinetics, fate and residues.
Balk and Koeman (1984) prepared a report on land-use development and pesticide use with special reference to West Africa and South-East Asia. Unfortunately most of the information refers to the region as a whole and therefore cannot be utilized easily in the context of this report. They confirm, however, the need to generate data on the quoted problems. The consultation of that report is highly recommended to anybody interested in the problem at regional level. It contains an abundance of data on the application of pesticides in agriculture (mostly from FAO sources), on recent developments in disease vector control and on the ecology of the region.
The only well-studied case is the one connected with the Onchocerciasis Control Programme in which temephos appeared to be safe in all aspects, while chlorphoxim is suspected to be potentially dangerous. However, the 6th Session of the Ecological Group of the Onchocerciasis Control Programme stated, in April 1985, that to-date no significant irreversible pressure was being placed on any of the vertebrate or invertebrate fauna or on aquatic flora. It is for sure not possible to study to the same extent all other pesticides used in high quantities, but for at least ten substances experimental data on acute toxicity for African freshwater organisms, on environmental fate and on residues in tropical conditions should be generated. It should also be mentioned that, in addition to the listed common problems, each country has its own special problems or ‘hot’ areas. For example, in Mali the role of animal wastes as water pollutant has to be evaluated; in Nigeria the ‘hot’ area of the Niger delta, with its petroleum extraction, requests special attention, and in the Abidjan Lagoon eutrophication is the particular problem.
The FAO Committee for Inland Fisheries of Africa promoted this report which identifies sources of pollution, evaluates local capacities of dealing with fisheries aspects of water pollution and identifies as the major constraint the lack of homogeneous quantitative data on effluents and receiving waters, particularly with regard to pollution by pesticides. The need for laboratories for pollution control and research is stressed.
The basic infrastructures for biological and fisheries studies do exist in many West and Central African States but not specifically for pollution work. Moreover, equipment for chemical analyses is frequently lacking or, when present, cannot work due to the absence of basic services and reagents (i.e. pure carrier gas for gas-chromatography).
Training of specialized scientists, another prerequisite for pollution research, should preferably be carried out by foreign experts to work in laboratories in the region, since training abroad frequently does not take into account the real needs in developing countries.
CIFA could satisfy certain needs through its Working Party on Pollution and Fisheries, for example by preparing appropriate documents or circulating analytical methods. CIFA should also solicit funds for limited research projects and invite African scientists to promote research on water pollution in their own countries, since the generation of some basic data is the absolute requirement for a scientifically-sound intervention on pollution problems. The Working Party on Pollution and Fisheries should specifically work on the following subjects:
Scientific bases for pollution control in African inland waters
A review of current strategies for environmental regulatory actions and their possible application to African countries.
Manual of methods for calculating the assimilative capacity of African inland waters for organic wastes
The current techniques for calculating the minimum level of oxygen after an organic discharge can be reviewed, and models and examples proposed to show how to minimize the impact of wastes. A critical combination of elements from already existing manuals could probably be sufficient.
Methods for toxicity testing of African fish
In the absence of equipment for chemical analyses a toxicity test with fish is a simple useful instrument for water pollution control. Effluent tests and screening tests (i.e. for pesticides, oil dispersants, etc.) modified for African species of fish should be developed. Small research projects may probably be necessary.
Water quality criteria for African inland waters
In a research project, a limited number of chemicals should be tested by short-term bioassays with a few African fish species to compare their sensitivity with that of European and North American species. Results could allow to establish by extrapolation water quality criteria for Africa.
Assessment of the impact of pesticides on African inland waters
In a more complex research project, based on proposals (3) and (4), toxicity testing with African fish species is combined with chemical analysis of pesticide residues in fish and in sediments. Such a project would best be carried out in a restricted pilot area and could be concluded with a theoretical study on environmental distribution and fate of pollutants in selected areas.
Acknowledgements
This report has been made possible by the persons listed in the Appendix, their information, their expertise, their patience and their help in finding documents, in organizing travels and visits. The author is deeply indebted to all of them.
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