SABIE RIVER IN THE KRUGER NATIONAL PARK
3.6.2 Effects of pulp and paper kraft effluent on aquatic invertebrates
Why are pulp and paper effluents toxic?
The chemical source of kraft effluent toxicity has been much debated and this is discussed at length in Section 3.1.3.
Bleaching
Despite the fact that the kraft mill investigated during this study mainly used ClO2 and ozone for bleaching, the effluent was still acutely toxic. Chlorine-free bleaching results in very little formation of polychlorinated compounds. The biological treatment further reduces the toxic potential of the kraft effluent (Haley et al., 1995; Oikari and Holmbom, 1996). Since effluents used for the study undergo primary treatment and pH stabilization before being irrigated, but not secondary treatment, organochlorines could still be contributing to effluent toxicity (Swanson, 1996). A complete substitution of chlorine dioxide has resulted in reduced impacts on aquatic ecosystems (Gullichsen, 1991; Haley et al., 1995; Landner et al., 1994; Soimasuo et al., 1998), by reducing chlorinated phenolic and dioxin/furan formation to levels at or below the detection limits (Swanson et al., 1996; Oikari and Holmbom, 1996), and altering the chemical composition of the effluent (Gullichsen, 1991; Servos et al., 1996).
Generally, bleaching effluent is acidic due to the use of strong acids and the reaction end- products during the bleaching process, and these are the major source of toxicity in kraft effluents. The acidic bleaching effluent was mixed with GKE to form IKE, and IKE is treated with CaCO3 before it is irrigated, hence the pH of IKE of this study was towards neutral. If bleaching effluents were to enter the aquatic environment, and alter the pH, this could affect the rate and type of ion exchange across the gills of organisms (Dallas and Day, 1993). Even effluent directly from the pipeline will definitely have an impact on aquatic biota should it reach the aquatic environment. Therefore, it is very important that strict precautionary measures be taken to avoid any leaks from the pipeline or overflows from the clarifying tanks.
Comparison of GKE and IKE
Toxicity results using both Probit and Trimmed Spearman-Karber analysis showed little difference in the toxicity of 1998 GKE and IKE samples, with the 1997 GKE samples being more toxic than other samples (Tables 3.5; 3.16; 3.17). Therefore, IKE was as potentially toxic to aquatic biota as the GKE during 1998. This supports the information stating that there is little difference in toxicity of bleached versus unbleached mill effluents to aquatic life (Eysenbach et al., 1990; Smith and Sprague, 1992; Robinson et al., 1994; Eklund et al., 1996). This could show that toxicity has little to do with chlorination, as effluent without chlorine was also toxic.
Effluent chemistry did not differ by a wide margin, except for sodium, chloride and sulphate levels in IKE, which were much higher than GKE.
Salinisation
Chemical analysis of surfaced groundwater indicated salinisation impacts. Exposure of test organisms to groundwater in a short-term chronic test (12 day) showed a demonstrable level of mortality. Salinisation was almost certainly linked to these lethal effects. Conductivity and TDS levels of both GKE and IKE were higher than the reference site, indicating salinity of the effluent could have contributed to test organisms’ mortality. Electrical conductivity has been found to be a major contributor to T. tinctus mortality, with sulphate having a synergestic and calcium an antagonistic effect on mortality (Scherman et al. (in press)). Sulphate levels were above the guidelines for the protection of aquatic ecosystems (DWAF, 1996f). The results of this study indicate that salinity is a major contributor to the toxicity of kraft effluent.
In this study, as in that of Robinson et al. (1994), effluent toxicity was mostly related to the degree of effluent concentrations, i.e. as the effluent concentrations increased, more organisms died. At higher effluent concentrations, all responses were acute (within 24 hrs), except for Experiments 2 and 6. This showed that if the effluent entered the river during low flow, where the dilution factor will be low, devastating impacts could occur, as happened during an accidental spill in 1989 (Kleynhans et al., 1992). At lower effluent concentrations, toxicity was reduced, indicating that the effluent must be very dilute, in order to safely enter the aquatic environment.
Treatment
In this study, pulp and paper kraft mill effluents were generally found to be acutely toxic. This could be attributed to the fact that there is no secondary treatment or any form of biological treatment of effluents in the mill, before effluent is released for irrigation. Studies have shown that untreated or inadequately treated effluents from any pulping process have the potential for significant adverse environmental impact (Ahtianen et al., 1996; Smith and Sprague, 1992;
Eklund et al., 1996). Biological treatment effectively reduces acute toxicity of the effluent (Eysenbach et al., 1990; Kovacs et al., 1995; Priha, 1996). This is supported by Zanella and Berben (1980), Hodson et al. (1992) and Ahtianen et al. (1996), who found untreated bleached effluents were toxic to fish, but that biological treatment reduced acute toxicity. The type of wood used or natural constituents of wood also influences the toxicity of the effluent produced (Ahtianen et al., 1996; Axeg@rd et al., 1993; Verta et al., 1996).
What are the environmental and biological effects of discharging kraft effluents and what end-points can be used to detect these effects?
This is not a study on environmental effects, but the exploratory investigation of groundwater indicated the potential hazards of irrigating kraft effluent. Table 3.20 and Figure 3.24 showed clearly that organisms responded negatively to the higher concentrations of groundwater. It would usually be difficult to undertake such a study because the chemistry of the groundwater is so different from surface water. However, in this case the groundwater had surfaced naturally and was collected from a surfaced spring.
The main chemical difference between groundwater and Sabie River water is salinity, particularly the sodium, sulphate and chloride levels. Although groundwater had a salinity range of 109-143 mS/m versus 13.0-15.8 mS/m in the receiving water, the implication that groundwater has been impacted by irrigation with kraft effluent is correlative. However, exposing T. tinctus to elevated salinities, Palmer and Scherman (in press) suggested that salinities above 50 mS/m would result in Class E/F conditions in the Sabie River, and thus constitute an unacceptable risk to sensitive biota. The Elands and Sabie Rivers share a similar natural salinity profile (Table 3.3), therefore it is likely that the salinisation of the groundwater to
109-143 mS/m could pose an environmental threat. The difficulty of groundwater remediation is an exacerbating factor.
A consideration of biological effects on the basis of acute toxicity results is difficult, but this study clearly showed kraft effluents have the potential to impact negatively on biota. This was demonstrated by the 1989 spill (James and Barber, 1991; Kleynhans et al., 1992), where large populations of biota were destroyed, but have since recolonised. The mill is now carefully and protectively managing the effluent, and irrigation is the only routine route of exposure. Given that in this study only one species was exposed to kraft effluent over an acute time period, and that no study was undertaken of chronic or community responses, it is necessary to determine what can be concluded about the potential biological effect of irrigation kraft effluent.
A hazard assessment approach was taken. It was assumed that the statistical information from Probit analysis around acute, lethal responses at low but measurable concentrations, could give an indication of the chronic, sub-lethal in-stream biotic response. Further, using the 95%
confidence limits around the LC1 and LC5 values allow further quantification of low, but measurable responses, at lower concentrations.
Since acute toxicity testing is relatively cost effective (Cairns, 1983; Rand, 1995), it is advantageous to infer chronic and sub-lethal effects from acute lethal data. By taking the LC1, LC5 and AEV as the basis of a hazard assessment guideline for kraft effluent disposal, we are attempting to extrapolate acute effects to the likely biological effect on the environment. We have therefore linked low levels of response to changes in feeding and breeding, as it seems reasonable to infer the possibility of these effects from actual mortality data.