Sublethal toxic effects testing

Acute toxicity studies are often dominated by consideration of lethaUty, including calculation of the median lethal dose. By routes other than inhalation, this is expressed as the LD q with 95% confidence limits. For inhalation experiments, it is convenient to calculate the atmospheric concentration of test material producing a 50% mortaUty over a specified period of time, usually 4 h ie, the 4-h LC q. It is desirable to know the nature, time to onset, dose—related severity, and reversibiUty of sublethal toxic effects. 

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... 

By far the most comprehensive research into AHR-related effects of PCDD/Fs on fish was a retrospective analysis of Lake Ontario lake trout reproductive impairment due to AHR-mediated early life stage mortality [16]. This includes blue sac disease as well as sublethal effects, which may increase susceptibility of sac fry and alevins to increased mortality and predation during swim-up. Lake trout are more susceptible to AHR-mediated toxic effects than any other Great Lakes species, with the possible exception of mink. WHO TEFs for fish were used to calculate the 2378-TCDD equivalent (TECegg or TEQ) concentrations in lake trout eggs. The validity of the additive toxicity equivalence model was established through early life stage trout toxicity tests. The WHO fish TEFs are likely to be fairly robust for lake trout, since they were determined primarily from relative potency values for effects in embryos of a related salmonid, rainbow trout, even if the relative sensitivity of the species to 2378-TeCDD toxicity may be different. 

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. 

To estimate the extent of the toxic effects from effluent discharged to an aquatic receiving environment. To examine the relationship between effluent sublethal toxicity results from laboratory testing and field biological measurements at a specific EEM study site. 

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). 

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). 

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. 

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. 

Acute effect Overt adverse effect (lethal or sublethal) induced in test organisms within a short period of exposure to a test material. Acute effects often induce highly toxic responses (e.g., mortality or assessment endpoints related to mortality). See also Acute exposure and Acute toxicity. Volume 1(1,2,3,5,10), Volume 2(5,8,11). 

Toxicity — The capability of a poisonous compound or toxin to produce adverse effects in organisms. These effects include alteration of behavioral patterns or biological productivity, which is referred to as sublethal toxicity, or, in some cases, death or lethal or acute toxicity. The toxic capability of a compound is frequently measured by its acute LC50 with a standard test organism such as rainbow trout. This is the concentration that will result in death in 50% of the test organisms over a given time period, usually 96 hours. The most immediately toxic compounds in crude oils or refined petroleum products are the aromatics such as benzene. (See also Aromatics, LCS0.)... 

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],... 

---