MATERIALS AND METHODS
2.9.4 Hazard assessment
Toxicity test results have been used in this study to describe site-specific hazard-based guidelines for the effluents tested, which could be used in Ecological Risk Assessments (ERA). This approach, detailed in Palmer and Scherman (in press), should be considered preliminary. ERA and the toxicity-based hazard assessment are new tools available in South Africa for the protection of water resources, and are used to support sustainable environmental management. The hazard-based guidelines include the concept of “risk to the organisms”, and would be used in ERA after the likelihood of exposure to the hazard is determined. Risk, defined as the likelihood that adverse effects will result from exposure (SETAC, 1997), is a fundamental component of DWAF’s water resource protection policy (NWA, 1998), and is used in determining effects of impacts on environmental ecosystems. Because of the complexity of ecosystems, the concept of risk incorporates both the variability and uncertainty inherent to biological data (SETAC, 1997).
Palmer and Scherman (in press) have developed a method which relates toxicity test data (which describes the hazard), to resource classification. This method was applied to both kraft and textile mill WET test results. Each river reach can be classified in a
state of health ranging from natural (Class A), to highly modified with levels of water resource-use such as water abstraction and effluent disposal (Class D). If resource-use is causing ecosystem degradation beyond a sustainable level, the system may be classified as a Class E or F. These classes are defined by the “present state” condition of water quality, quantity, instream habitat, riparian habitat and the biota (Palmer, 1999). The class-related definitions for water quality and biota are given in Table 2.1 (modified from Palmer, 1999).
TABLE 2.1
WATER QUALITY AND BIOTIC CRITER IA WHICH MAY BE USEDTO CLASSIFY AQUATIC ECOSYSTEM CONDITION IN SOUTH AFRICA (FROM PALMER, 1999) Class A
Water quality Unmodified. Allow minimal risk to sensitive species. Remain within the target water quality range (TWQR, sensu DWAF, 1996f) for all constituents.
No modification from reference conditions as defined by the rapid Bioassessment procedure SASS (South African Scoring System) (Chutter, 1994; 1998).
Class B
Water quality Use Aquatic Ecosystems guideline values (DWAF, 1996f) such as Chronic Effect Value (CEV) and TWQR to set objectives that pose a slight ris k to intolerant organisms.
Biota May be slightly modified from reference conditions. Especially intolerant biota may be reduced in numbers or extent of distribution.
Class C
Water quality Use Aquatic Ecosystems guideline values (DWAF, 1996f) such as Acute Effect Values (AEV), CEV, and TWQR to set objectives that allow moderate risk only to intolerant biota.
Biota May be moderately modified from reference condition. Intolerant organisms may be absent from some locations.
Class D
Water quality Use Aquatic Ecosystem guideline values (AEV, CEV, TWQR) to set objectives that may result in high risk to intolerant biota.
Biota May be highly modified from reference conditions. Intolerant biota unlikely To be present.
When toxicity results were analyzed using the EPA Probit programme, LC1, LC5 and LC50 values, with their 95% confidence limits, were generated. Each of these values (or toxicity test end-points) can be associated with a particular hazard description (Table 2.2; modified from Palmer and Scherman, in press). The toxicity test end- points were then ranked according to the percentage response, and then related to the resource classification system (Table 2.1; Palmer, 1999; Palmer and Scherman, in press). Table 2.2 shows selected end-points and associated hazard assessment descriptions (Palmer, 1999).
TABLE 2.2
EXAMPLES OF SELECTED TOXICITY END-POINTS AND
ASSOCIATED HAZARD DESCRIPTIONS. SIMILAR DESCRIPTIONS CAN BE DERIVED FOR ANY LC VALUE OF THOSE LISTED HERE, THE LC50 IS THE MOST ACCURATE, AND THE LC5 AND LC1 INDICATE
LOW HAZARD CONCENTRATIONS (PALMER, 1999)
Tolerance end-point Hazard description
Below the low 95% confidence limit for the LC1
Concentrations at which there is a 95% probability that each nymph has <1% chance of mortality Below the low 95% confidence limit
for the LC5
Concentrations at which there is a 95% probability that each nymph has <5% chance of mortality
LC1 Best estimate of concentration where each nymph has
a 1% chance of mortality
LC5 Best estimate of concentration where each nymph has
a 5% chance of mortality
LC50 Best estimate of concentration where each nymph has
a 50% chance of mortality
The AEV were calculated in each case according to DWAF (1996f), except that LC1 values for a single test species were used instead of the mean LC50 values of a wide range of species, as recommended in DWAF (1996f) and Roux et al. (1996). Table 2.3 shows an example of how to calculate the acute effect value using whole effluent acute toxicity results. LC1 values were used to calculate the AEV values. Chronic effect values were not calculated, as no chronic tests were conducted.
TABLE 2.3
EXAMPLE OF THE CALCUL ATION OF ACUTE EFFECT VALUE (AEV) USING WHOLE EFFLUENT TOXICITY TEST RESULTS FROM THE EXPOSURE OF THE MAYFLY T.
TINCTUS TO GENERAL AND IRRIGATION KRAFT EFFLUENT 1.Acute Effects Value (AEV)
Step 1.
Calculate the Final Acute Value (FAV) – using the LC1 for acute tests 4 Day exposure:
e.g. Experiment 1 (GKE)
LC1 = 3.8% effluent concentration Step 2
2.Calculate the Acute Effects Value (AEV) where AEV = FAV/2 LC1 – based AEV = 1.9% effluent concentration
In this study, chronic testing was not undertaken, so the CEVs and chronic LC values were not available. However, chronic testing would be essential for a comprehensive set of hazard assessment guidelines. This method was applied to each batch of effluent, so that the percentage concentration of effluent with a particular chemical profile could be related to the instream hazard to the ecosystem. The mill manager could manage conservatively, as if it were the most toxic case in each instance. The application of this method is dealt with in detail in Chapters 3 and 4.
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