Toxicants reference

Dorn, P.B., Rodgers. J.H.. Jr.. Jop,K.M.,Raia,J.C., and Dickson, K.L. Hexavalent chromium as a reference toxicant in effluent toxicity tests. Environ. Toxicol. Chem., 6(6) 435-444, 1987a. 

Hickey, C.W. Martin, M.L. Relative sensitivity of five benthic invertebrate species to reference toxicants and resin acid contaminated sediments. Environ. Toxicol. Chem. 1995, 14, 1401 -1409. 

As part of this field study, relevant quality assurance/quality control (QA/QC) criteria and guidelines (SETAC, 1993 JAMP, 1998a,b) have to be set to insure the quality of data generated during the assessments. The development of QA/QC criteria for this study involved conducting a series of replicate bioassays with each of the methods. Samples tested included a control sediment, contaminated sediments and reference toxicants. Based on the results of the bioassay replicates, the variability associated with the tests was quantified and we were able to determine what we considered acceptable QA/QC criteria for these methods. 

Environment Canada (1990) Guidance document on control of toxicity test precision using reference toxicants, Report EPS l/RM/12, Environment Canada, Ottawa, 85 pp. 

The Microtox assay which measures light inhibition with the bacterium Vibrio fisheri is a well known and useful aquatic toxicity test (see Chapter 1, volume 1 of this book). As previously reported (Blaise et al., 1994) and based on our own experience, it appears more appropriate to determine 60 min IC50 for waste leachates, as opposed to 15 min or 30 min endpoints. IC50s measured after 60 min on MIOM leachates were clearly more sensitive and reproducible than those measured at 30 min and 15 min (Ferrari et ah, 1999). Since WASTOXHAS was applied on (poly)metallic matrices in this study, we also found it more suitable to use zinc sulphate as a reference toxicant to periodically verify the sensitivity of the Microtox bacterial light reagent. 

Solution used to prepare the reference toxicant or effluent dilutions required for toxicity testing. Volume 1(6). 

Selected chemical employed to measure the sensitivity of the test organisms in order to establish confidence in toxicity data obtained for a given test sample (or a batch of test samples). In most instances, a toxicity test with a reference toxicant is performed i) to confirm that test organisms (or cells) are in good physiological health for bioanalytical purposes at the time the test sample is evaluated, and ii) to assess the precision and reliability of results obtained by the laboratory for that reference toxicant. The toxicant selected should meet different properties as defined by Environment Canada, 1990. Volume 1(2,3,6,7,14), Volume 2(11). 

Test conducted using a reference toxicant in conjunction with a toxicity test to appraise the sensitivity of the organisms and the precision and reliability of results obtained by the laboratory at the time the test material is evaluated. Deviations outside an established normal range indicate that the sensitivity of the test organisms (and/or the performance and precision of the test) are suspect. Volume 1(2,7,10). 

Standardization Imposition of rules permitting to check or validate the accuracy of a test using live organisms. For example, the use of a well-defined experimental procedure and the use of a reference toxicant are important rules to standardize a test. Test standardization also requires that the test be feasible by many laboratories and yield comparable results with the same test substance. Volume 1(14). 

Graph used to follow changes over time, in the endpoints for a reference toxicant. Date (or number) of the test is on the horizontal axis and the effect-concentration is plotted on the vertical logarithmic scale. Volume 1(2). 

The same procedure above may be applied for simultaneous shorler-lenn exposures to several chemicals. For drinking water exposures, 1- and 10-day Hcallli Advisories can be used as reference toxicity values. Depending on available data, a separate hazard index might also be calculated for developmental toxicants (using RfDj,s), wliich might cause adverse effects following exposures of only a few days. 

Reference toxicants often are used to determine the health of the test species. There is no widely used reference toxicant several that have been used include dodecyl sodium sulfate (anionic surfactant), sodium chloride, sodium pentachlorophenol, and cadmium chloride. 

Sodium pentachlorophenate (NaPCP) is the reference toxicant that has been suggested for toxicity tests using daphnids. The use of a reference toxicant is important in confirming the health of the daphnia and the quality of the water and test methodology. 

Why is the use of a reference toxicant important in the daphnia toxicity test ... 

To attain a measure of reproducibility of the MARA test repeated testing on different days using a suitable reference toxicant (3,5 dichlorophenol) was implemented. 

Figure 2.1 Probability density functions for EC50/IC50 values derived from an interlaboratory ring-test for Daphnia and Microtox tests using 3,4-dichloroaniline as a reference toxicant.

A conventional response to issues of variability in bioassays is to construct Shewhart Control Charts based on the results achieved in repeat tests within a laboratory using a reference toxicant. This effectively describes the range of results typically found within the laboratory and hence can be used to define limits within which the laboratory normally expects to operate. However, there is a flaw in such internal quality control because the more variable a laboratory s reference toxicant test results are, the wider the limits of acceptability will be. Indeed, it can serve merely to reinforce high variability or bias. 

We can then calculate the limits, expressed as concentrations of the reference toxicant, within which we would expect 95% of EC50 estimates to lie. 

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