SABIE RIVER IN THE KRUGER NATIONAL PARK
3.6.4 Application of WET testing in South African water quality management Given that the use of a wild population of invertebrates as toxicity test organisms aims to
provide greater site-specific relevance, it would be useful to consider how the results of this study can be used in South African water quality management.
Since 1994, South African water resource management has been comprehensively reviewed, culminating in the National Water Policy (DWAF, 1997a), and the National Water Act (No. 36 of 1998). One of the main principles on which the National Water Act is based is that of resource protection to ensure sustainable resource use. Resource protection is effected by the dual application of resource-directed measures, such as quantification of the ecological Reserve and source-directed controls, such as defining the conditions for licences. In both these approaches, the SAWQG (DWAF, 1996f), and General and Special Standards (DWAF, 1991), are well placed to provide information for the management of single substances.
Acute and chronic toxicity testing of single toxicants is well established (Rand, 1995), and is the basis of SAWQG for the protection of aquatic ecosystems (DWAF, 1996f). Guidelines for the protection of aquatic ecosystems detail the procedure for the use of acute and chronic toxicity test results in the derivation of water quality management criteria (DWAF, 1996f; Roux et al., 1996). These numerical values can be used to guide and assist in the formulation of effluent discharge licenses, which, according to the National Water Act (No 36 of 1998), will be strictly enforced. The use of national criteria for the aquatic environment, which are expressed as Acute Effect Value (AEV) and Chronic Effect Value (CEV), aims to provide adequate protection with only a small possibility of over-protection (Roux et al., 1996). This however requires information on the tolerances of aquatic biota (Palmer and Scherman, in press).
However, the government gazette (No 20526 of 1999), excludes complex effluent from the General Authorization (DWAF, 1999b), thus laying the foundation for a toxicity-based approach for the management of complex effluents. This is based on the recognition that complex mixtures have integrated effects on biota, compared with the effects of their individual constituents (Grothe et al., 1996).
The decision by DWAF to include WET testing into its toxic effluent management policy (Palmer and Jooste, conf. draft) has necessitated suitable procedures to be established for use in the South African situation (Slabbert et al., 1998a; DWAF, 2000). Slabbert et al. (1998a) have developed methods for WET testing for use in South Africa. Both ecological field observations, such as biomonitoring, and toxicological studies, should be used to provide a more accurate assessment of the impact of pollution on riverine organisms (Palmer et al., 1996). According to Kovacs and Megraw (1996), a toxicological approach is a cost-effective way of assessing effluent toxicity; acute toxicity testing being the most cost-effective.
This study aimed to investigate the application of WET testing of complex kraft effluents using indigenous test organisms to assess the potential effects of these effluents on riverine ecosystems. The WET would then be used in testing results in the development of hazard-based guidelines, for the disposal of kraft effluent into the environment. The study represents a first step in developing WET testing using indigenous riverine organisms. WET testing using indigenous riverine organisms can play an important role in auditing licenses. Therefore, it is fundamentally important to have some knowledge of the relationship between the results of laboratory toxicity tests and the actual responses in the receiving water.
Since both effluents were found to be acutely toxic, this study suggests that the kraft mill should focus on Environmental Risk Assessment (ERA) as a tool for environmental decision-making. It may help the management curb the high cost of eliminating environmental risks associated with effluent impacting on the aquatic environment. It is difficult to assess the impact of this whole effluent, as the effluent is not discharged into the river but is used for irrigation. To be conservative, a move toward zero effect would be ideal because of the long-term effect of changes in the groundwater. High levels of sodium and sulphate are of concern, as they can accumulate and affect groundwater. If the groundwater with high sulphate and sodium ions reaches the in-stream environment, it will contribute to high salinity. Salinity is conservative, and therefore, if resource protection is the goal, attention should paid to the consequences of irrigation. An increase in turbidity and SS reduces light penetration, decreases primary production and food availability to organisms (Dallas and Day1993).
To conclude, the results of the study can be of use to the management of the Mpumalanga kraft mill. There is a clear indication that both GKE and IKE are variable and acutely toxic. Although the mill is using partly ozone and partly chlorine dioxide for bleaching, irrigation effluent is still toxic. This gives an indication that organochlorines are not the only possible contributors of toxicity. The fact that there is no secondary biological treatment before the effluent is used for irrigation could be contributing to the toxicity. The studies reviewed in this Chapter have indicated that secondarily treated effluent is less toxic and even non-toxic to aquatic biota.
Groundwater has been shown to have some lethal effects to aquatic biota at high concentrations, which indicated that it is impacted by the irrigation effluent. This is an indication that there is a probability that irrigation of kraft effluent will impact on the Elands River.
However, more work needs to be done to confirm the toxicity of groundwater in the area.
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