Aquatic toxicology

Dr Patsy Scherman

Centre for Aquatic Toxicology of the Institute for Water Research, Rhodes University, South Africa

Collecting riverine invertebrates in the Sabie River, for toxicity testing in artificial streams.Aquatic toxicology is the study of toxic effects of chemicals on living organisms in the aquatic environment. In the past, South Africa has generally relied on chemical monitoring for water quality management: this is a combination of end-of-pipe discharge standards for polluters (e.g. industries), and collecting water chemistry measurements from water bodies (e.g. rivers and dams). The Department of Water Affairs and Forestry (DWAF) therefore has developed an extensive water quality network for SA, based on routine sampling of water bodies and analysing samples for their chemical profile.

Although this information is very valuable, it is not sufficient to assess the actual impact of pollution on aquatic biota. Information on the chemical and physical structure of a pollutant will therefore not indicate its toxicity (or how poisonous it is) to aquatic organisms. If this information is required, laboratory-based experiments, called toxicity tests, should be carried out using organisms which are sensitive to pollution, e.g. certain species of fish, algae and riverine macroinvertebrates (or river insects), and the water flea Daphnia.

These tests then provide scientifically-derived limits for particular chemicals or effluents which, provided they are not exceeded, will protect aquatic resources. In-stream bioassessment surveys, commonly referred to as biomonitoring, are used to assess the health of water resources. The in-stream indicators monitored during a biomonitoring survey act as signals of deteriorating conditions or "red flags"; thereby indicating a problem, but without providing any definite causal links. Toxicological data are therefore used to interpret water chemistry information by determining concentrations at which organisms respond, and provide a powerful basis for the interpretation of biomonitoring data.

Applications of toxicological data

The National Water Act (No. 36 of 1998) of South Africa has provided the legal framework for resource protection, particularly with the provision for the ecological Reserve. The ecological Reserve is "the quality and quantity of water requires to protect aquatic ecosystems in order to secure sustainable development and use of the relevant water resource (National Water Act No. 36 of 1998, Chapter 1, Section 1.1.xviii.b)". The resource protection policy will be enacted by implementing both resource-directed measures and source-directed controls. Resource-directed measures include the development of water quality guidelines for the protection of aquatic ecosystems, the development of a classification system to assess degrees of resource-use and consequent ecological health or degradation, the development of a national River Health Programme with appropriate biomonitoring methods, and the development of methods to quantify the ecological Reserve. Source-directed controls are exemplified by licenses which specify allowable resource-use, such as water abstraction, effluent discharge, and land-uses which result in stream-flow reduction.

Aquatic toxicity data can be used in both these applications, to control pollution of water bodies. The South African Water Quality Guidelines for Aquatic Ecosystems were derived from international toxicological databases, and there are options for site-specific modifications of national guidelines based on using local indigenous organisms in toxicity tests. Methods for quantifying ecological requirements for water quality, as part of ecological Reserve assessments, include requirements for toxicity data. The development of guidelines and procedures for the release of complex industrial wastewaters, which will include toxicological procedures, has been initiated and is likely to be undertaken within the next two years. 

Users of toxicological technology Aquatic toxicology, particularly applied within Ecological Risk Assessment (ERA), is of most use to those who discharge wastewaters or whose activities contribute to non-point source pollution. Industry, agriculture, and sewage works would all be potential users of the technology of aquatic toxicology. Water resource managers, such as DWAF, as well as water boards and irrigation boards, could make use of this technology both in developing and refining water quality guidelines, setting site-specific guidelines, investigating the effects of single variables and/or whole effluents, and including toxicological end-points in discharge licenses. Industries which produce effluent that are discharged into river directly, or via municipal sewage works, could be required to use toxicological methods to check compliance with license conditions. In-stream testing of indigenous organisms could be used by resource managers, in conjunction with biomonitoring, to check whether resource objectives have been met.

CAT-IWR at Rhodes University The Centre for Aquatic Toxicology of the Institute for Water Research (CAT-IWR) was launched at Rhodes University on 8 November 1999, with partial sponsorship from Lever Ponds, South Africa. The aim of establishing CAT-IWR was to establish a centre of excellence for training in aquatic toxicology and ERA, and to develop an aquatic toxicology laboratory for routine and commercial toxicity testing. An annual introductory course in aquatic toxicology was initiated in 2000, and is rapidly gaining popularity among industry and regulators alike. Research and consulting within the fields of aquatic toxicology, risk assessment, biomonitoring and water quality are core tasks of CAT-IWR. The main toxicological research focus since 1992, mostly funded and supported by the Water Research Commission and DWAF, has been the development of methods for using indigenous riverine macroinvertebrates in artificial streams, particularly for assessing the effects of increasing salinisation of South African rivers (as a result of mining and agricultural activities) on aquatic biota.

This work culminated in the production of a protocol of standard methods, available from CAT-IWR and the Institute for Water Quality Studies, DWAF. The use of aquatic toxicology in water resource management is common world-wide, and toxicology is a well-established science. There is a pool of technical expertise in South Africa, and there is a well developed policy and legal framework within which to apply the data from toxicity testing. However, toxicology is not yet formally included in DWAF policy (although this should change shortly), and is used infrequently by user groups such as industry, possibly because users are reluctant to invest in a technology and in training that is not required by law. A centre such as CAT-IWR provides training capacity building, research facilities and consulting expertise to meet the needs of both resource-management and resource-use organisations, specifically in the field of aquatic toxicology, but also in the wider field of water quality management.

For further information, contact the CAT-IWR web page at or e-mail staff at

September 2001