by
D. Calamari and H. Naeve
Based on a recommendation of the 20th Congress of the International Association of Limnology (SIL) held in Copenhagen, a SIL-UNEP Workshop on African inland waters was held in 1979 in Nairobi, the proceedings were published as “The Ecology and Utilization of African Inland Waters” (Symoens et al., 1981).
The Workshop revealed that, compared to other areas of the world, information on African aquatic ecosystems were scarce and dispersed and certainly insufficient to produce acceptable bases for the management of aquatic resources, and concluded that:
there is an urgent need to ensure a proper scientific basis for the planning, decision-making and management of Africa's aquatic resources;
there is a real need to increase the number of African scientists trained in aquatic sciences, especially limnology, and to employ them in the utilization of the African water resources.
In 1970 FAO undertook a brief survey of inland water pollution in Kenya, Tanzania, Uganda and Zambia (Thorslund, 1971), concluding that, although water pollution was not then a serious problem in relation to freshwater fisheries, it could become so in the future as a result of increasing urbanization and industrialization.
After a decade other surveys were carried on in three more East African countries, i.e. Burundi, Malawi and the Sudan, and repeated in Kenya, Tanzania and Zambia, and in five West- and Central African countries, i.e. Mali, Côte d'Ivoire, Ghana, Nigeria and Cameroon (Alabaster, 1981; Calamari, 1985) under the following terms of reference:
to identify existing and assess potential future sources of pollution affecting fisheries in the countries listed;
to examine local capacity for dealing with fisheries aspects of water pollution; and
to suggest appropriate infrastructure and establish baselines for future studies and monitoring programmes in the countries.
The results were reported to the Committee for Inland Fisheries of Africa (CIFA), concluding that an increase of pollution loads in aquatic ecosystems was observed as well as a decrease in water quality although not to the extent of a general acute problem in all the countries. The studies did show the need for cooperation at a regional level aiming at scientifically sound water pollution control measures and at the maintenance of a water quality adequate to protect aquatic life and fisheries, identifying metals, organic pollutants with high biological oxygen demand and pesticides as major potential problems.
In 1985 CIFA decided to establish a Working Party on Pollution and Fisheries.
At the second Session of EIFAC (Paris, 1962), note was taken of a recommendation of the UN Conference on Water Pollution Problems in Europe (1961) that EIFAC should take the initiative in drawing up water quality requirements with respect to fisheries. EIFAC agreed that:
“the proper management of a river system demands that water of suitable quality be provided for each use that is made or intended to be made of it and that the attainment and maintenance of such quality is normally to be sought through the control of pollution. It was necessary, therefore, to know the standards of quality required for each particular use, in order to determine the degree of pollution control necessary and to forecast the probable effect of augmented or new discharges of effluents. It was pointed out that water quality standards for drinking water had been well defined by the Word Health Organization (WHO) and that standards for certain agricultural and industrial uses are also well defined. However, water quality criteria for fish have not received the attention that they deserve. All too often, water has been considered quite adequate for fish as long as there has been no obvious mortality which can be ascribed to known pollutants. Degradation of the aquatic habitat through pollution and decrease in the annual production and subsequent harvest of fish have often passed unnoted. With such reasoning in mind, it was agreed that the establishment of water quality criteria for European freshwater fish be undertaken by the Commission”.
In this context, a “criterion” describes a water quality, defined by means of a critical review of scientific information, which will conserve the relevant structures and functions in the aquatic ecosystem. Unlike a standard, it does not carry a connotation, nor does it imply an ideal water quality. Water quality criteria should, therefore, be based exclusively on scientifically derived evidence and not be defined in an arbitrary manner. The assumption is made that for each substance reviewed a satisfactory data base exists from which a water quality criterion can be obtained.
The Working Party on Water Quality Criteria for European Freshwater Fish, established in 1962 as a result of the deliberations cited above, agreed at the outset that:
“Water quality criteria for freshwater fish should ideally permit all stages in the life cycle 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 substance in fish to such a degree that they are potentially harmful when consumed. Indirect factors like those affecting fish-food organisms must also be considered, should they prove to be important”.
The emphasis of the Working Party has always been on the preparation of critical reviews of the literature, rather than compilations of published data, by experts with proven ecotoxicological experience with specific chemicals or other aspects of water quality. Draft reports were circulated to outside reviewers and ultimately discussed and approved by the Working Party (Lloyd and Calamari, 1987).
Generally the reports cover the following aspects:
Source, form and analytical method for the substance and its occurrence in water and sediments.
Lethal effects on fish, including (a) mode of toxic action; (b) acute and chronic exposures; and (c) factors affecting toxicity, e.g. age and size of fish, water hardness, temperature, dissolved oxygen and other pollutants.
Sublethal effects on fish, including bioaccumulation.
Field observations from surveys of polluted rivers and accidental fish-kills.
Effects on invertebrates (similar to (2) above) and aquatic plants.
Overview of published data, including scope for further research.
Proposal of tentative water quality criteria taking into account the influence of specifically important modifying factors, e.g. species of fish, pH, water hardness, etc.
During the past years, the Working Party has prepared reviews on temperature, dissolved oxygen, pH, finely divided solids, ammonia, monohydric phenols, chlorine, zinc, copper, cadmium, chromium, nickel, nitrite and aluminium.
It was, however, recognized that the common pollutants rarely occurred singly, and it was possible that the water quality criteria for individual substances would need to be made more stringent to allow for the added impact of other toxicants. Therefore, a critical review was made of the various models developed to describe joint action of toxicants, and all the available literature on the toxicity of mixtures to fish, invertebrates and plants was reviewed using a concentration/addition model. The conclusion finally reached is that, for the common pollutants reviewed by EIFAC, there may be some evidence for partial joint addition at low concentrations and, therefore, the values of the individual water quality criteria may have to be slightly reduced if other pollutants are present in significant amounts. Also, for chemicals which have a common toxic action on fish (such as many organic substances), their joint toxic action is additive at all concentrations.
Finally, the EIFAC technical papers were updated and published in two books (Alabaster and Lloyd, 1982; Howells, 1994).
In parallel with the programme of the Working Party on Water Quality Criteria, a group was set up to provide advice on fish toxicity testing procedures and associated terminology. To some extent, the need for such advice arose from the variable quality of the ecotoxicological data which had been critically evaluated as part of the reviews. It was clear that tests should be carried out for well defined purposes - for initial screening of chemicals for toxicity, for enforcing effluent standards, and for monitoring river quality. Tests devised for one of these purposes were not necessarily useful for other investigations (Alabaster and Lloyd, 1982; EIFAC, 1983).
The EIFAC water quality criteria have been widely used as a basis for water quality control in Europe, and in some countries they have formed the basis for national water quality standards. Within the EEC, the criteria have formed the basis for water quality standards contained in the EC Directive on the quality of fresh water needing protection or improvement in order to support fish life (78/659/EEC) and, to a more limited extent, in the EC Directive on pollution caused by certain dangerous substances discharged into the aquatic environment of the community (76/464/EEC).
In the past, the attention of the Working Party has been directed towards common pollutants which have been identified as causing harm to fish. Because the importance of these substances has been recognized by the scientific community, a large data base was available for critical review and the tentative water quality criteria had a firm foundation. Pollution from these substances is, or should be, now under control in European rivers. The attention of regulators is now turning to the vast number of other, mainly organic, chemicals which may appear in freshwater as a result of man's activities.
This poses two main problems: First, the Working Party does not have the resources to carry out critical review on more than one or two substances a year so that progress would be much slower than that demanded by national and international political initiatives; however, this problem has been overcome to some extent by the recent preparation of some relevant critical reviews (although not generally as comprehensive as those of EIFAC in their scope) by other national or international organizations. The second problem is that, for many of these compounds, and especially for new chemicals, the data are inadequate even for the derivation of extremely tentative water quality criteria, with field data being non-existent.
Recently, attention has been given by the scientific community to the “risk assessment” approach to prevent harm being caused by pesticides or other organic chemicals to aquatic life. In this context, a risk assessment is based on a comparison between the measured toxicity of a substance to aquatic organisms and the environmental exposure (a function of concentration and duration).
Although there is some general international agreement on the basic data package required for such an assessment, no guidance has been given on the way in which the data are evaluated in order to arrive at an assessment. For example, it is obviously unnecessary to obtain data from detailed and lengthy ecotoxicological studies on a chemical whose maximum predicted concentration in the aquatic environment based on very conservative estimates is many orders of magnitude lower than the acute toxic concentrations for fish and Daphnia. It is only when this margin safety is small that refined estimates have to be made of both, the toxicity of the substance and the predicted environmental concentration. The former may be readily carried out using well-tried techniques, but the latter is more uncertain. Although several models have been produced to predict the distribution of a substance in various environmental compartments, rates of biodegradation in the natural environment may be critical and difficult to quantify.
Within this rapidly developing and complex field, the scientific community is now focusing its attention on one aspect of aquatic toxicity prediction - the use of quantitative structure-activity relationships (QSAR). Basically, in this context, QSAR is the correlation of the toxicity of a compound with its physico-chemical properties.
During 1991/92 FAO, in a Technical Cooperation Project, used risk assessment as a tool to identify environmental problems in the Kenyan waters of Lake Victoria (Calamari et al., 1994).
Such an exercise was considered of high interest and the Committee of Sponsoring Agencies of the Onchocerciasis Control Programme of the World Health Organization commissioned a similar study to assess the environmental impact of the recolonisation of the oncho free areas in the upper Léraba Basin, Burkina Faso, Côte d'Ivoire and Mali (Baldry et al., 1994).
After the CIFA Working Party on Pollution and Fisheries had been established in 1985, it was decided that its first report should be devoted to discussing the Scientific Bases for Pollution Control in African Inland Waters, taking into account the traditional experience of the industrialized world on pollution control and the new emerging approaches such as the risk assessment procedures and the preventive strategies which take care of the evolution of the pollution problems. This report was prepared in 1986 and published (Biney et al., 1987).
Taking into consideration that relevant pollution problems had never been reviewed on at continental scale and existing information were scarce and scattered, it was decided to prepare critical reviews on the state of pollution in Africa looking at the three major contaminants identified in 1985 at the Sixth Session of CIFA, namely organic loads with elevated content of BOD (sewage and wastes from agro-alimentary industries), metals and pesticides.
The first two reviews were prepared in 1989 and 1991 and published (Saad et al., 1990; Biney et al., 1994). Pesticides, the third item identified, was considered a too complex subject and should have been subdivided. After a preliminary literature survey, however, documentation found was insufficient for most of the classes of pesticides, except for chlorinated hydrocarbon substances. It was therefore decided to limit the review to this group only. The review was prepared in 1993 and published (Osibanjo et al., 1994).
In the meantime, regarding the state of the African freshwater environment, useful information on the impact of vector control operations have been reported and were reviewed by Dejoux (1988), in particular, the assessment of environmental impact of onchocerciasis control operations have been described (Lévêque et al., 1989, Yameogo et al., 1992).
In the eight years of its existence, the CIFA Working Party on Pollution and Fisheries produced a document on the scientific bases for planning intervention and management of water resources in relation to pollution. Moreover three documents were prepared, collecting data on organic loads, metals and chlorinated hydrocarbon pesticides in African inland waters and reviewing the level of contamination by these three groups of contaminants. Finally, it promoted a study on risk assessment from land based sources in an important African lake that could be used as a model for other similar studies.
During its activities the Working Party involved several African scientists from various countries (Burundi, Cameroon, Côte d'Ivoire, Egypt, Ghana, Kenya, Nigeria, Seychelles and Tanzania), attempting to respond to the two recommendations from the SIL/UNEP workshop, an authoritative scientific group, cited at the beginning of this introduction.
The Working Party achieved its major goals in outlining the scientific bases for water pollution control and management and in evaluating the state of the African aquatic environment, reviewing the major groups of pollutants that could have negative impact on aquatic life and fishery resources.
The papers and reports prepared by the CIFA Working Party on Pollution and Fisheries have been re-edited and are presented in this volume.
