Sublethal toxicity tests

Barata C, Alanon P, Gutierrez-Alonso S, Riva MC, Fernandez C, Tarazona JV (2008) A Daphnia magna feeding bioassay as a cost effective and ecological relevant sublethal toxicity test for environmental risk assessment of toxic effluents. Sci Total Environ 405(l-3) 78-86... 

CANMET (1997b) Laboratory screening of sublethal toxicity tests for selected mine effluents, Aquatic Effects Technology Evaluation (AETE) Program, Project 1.2.2, Canada Center for Mineral and Energy Technology (CANMET), Mining Association of Canada (MAC), Ottawa, Ontario, pp. 1-69. 

Both methods have been shown to be effective in illustrating the relationships between laboratory sublethal toxicity tests (using fish, invertebrates, and algae) and receiving environment measurements of fish and benthic invertebrates. The applications, strengths, and weaknesses of both the ZPE and LTF methods are discussed and compared. 

The potential effects based on results of sublethal toxicity tests are illustrated by zones superimposed on the industrial effluent plume and then compared to field survey components of a monitoring program. The field survey components of a monitoring program are rated on a similar scale as the sublethal toxicity tests for weight-of-evidence comparison. 

Step 2. Determine the lowest IC25 from a battery of sublethal toxicity tests. Step 2. Assign an LTF rating of 1 to 5 to the fish survey based on the percentage of potentially effluent-related effects relative to all the endpoints measured. 

Sublethal toxicity tests that use species of relatively low sensitivity (z. e., fathead minnow) reduce the usefulness of both EEM Hazard Assessment Schemes to estimate potential effects observed in the field. Insensitive laboratory measurements can lead to an underestimation of potential field effects and reduce the strength of laboratory toxicity tests as good estimators of effects. 

Rating the relationship between ZPE andfield measurements The relationship between sublethal toxicity tests and field measurements can be rated on the basis of zones of potential effect (Environment Canada, 1999). The following points describe the criteria used for rating the relationship between zones of potential effect for each sublethal test (lowest IC25) and potential effluent-related effects on fish or the benthic invertebrate community (Moody, 1992). 

Table 6. Sublethal toxicity tests for secondary treated ASB final effluent collected at...

Sublethal toxicity test Fish survey Benthic survey... 

Table 10. Sublethal toxicity tests, EEM Cycles 1 and 2, for secondary treated final effluent collected at Provincial Papers.

Using the ZPE scheme, the study of effluent discharge situations at 16 Ontario pulp and paper mills demonstrated a majority of strong or moderately strong relationships between sublethal toxicity tests and ecosystem indicators (fish populations and benthic invertebrate communities). The locations of effects in benthic organisms corresponded in 100% of cases with zones predicted by the Ceriodaphnia test and in 81% of cases with predictions from the Selenastrum test. The fathead minnow test did not perform as well, predicting effects on fish in only 53% of cases (Moody, 2000). 

Table 14. Summary of relationship between sublethal toxicity tests and field studies using the ZPE and LTF methods at 16 Ontario Pulp and Paper Mills1.

The application of these schemes illustrates how sublethal toxicity tests can be used to estimate the potential for effects in the receiving water environment. Both ZPE and LTF use laboratory sublethal toxicity data and statistically significant field observations for a more comprehensive or weight-of-evidence approach for regulatory monitoring of industrial effluents. 

Sublethal toxicity tests that are relatively less sensitive can reduce the usefulness of both ZPE and LTF. In addition, confounding factors such as the presence of other discharge sources can complicate the interpretation of both hazard assessment schemes. 

Borgmann, A., Moody, M. and Scroggins, R. (2004) The Lab-to-Field (LTF) Rating Scheme A New Method of Investigating the Relationships between Laboratory Sublethal Toxicity Tests and Field Measurements in Environmental Effects Monitoring Studies, Journal of Human and Environmental Risk Assessment, August 2004. 

Because nominal concentrations overestimate, sometimes by orders of magnitude, measured concentrations, they are not representative of effects concentrations. Analytically determined initial chemical concentrations more accurately represent the effects concentrations, especially when the toxic response occurs shortly after exposure initiation. Rapid manifestation of toxicity is expected for TNT and its major transformation products as these chemicals reach steady state in small organisms very quickly (see review in Chapter 6). Lethal effects of TNT were observed during the initial few days of exposure in sediment toxicity tests [11,13], Therefore, the use of short exposure duration for the evaluation of the effects of sediment-associated explosives is desirable. For sublethal toxicity testing requiring longer exposure periods that allow greater transformation of parent compound with the concomitant decrease in toxicity, multiple analytical determinations of sediment concentrations should be conducted to determine the appropriate exposure concentration associated with the observed effects [11],... 

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