EXECUTIVE SUMMARY
The objective of the laboratory screening study was to evaluate nine sublethal toxicity tests through the testing of eight representative mining effluents. The evaluation considered the sensitivity, cost, and applicability of the tests.
The toxicity tests included the Microtox chronic test, the Ceriodaphnia survival and reproduction test, the larval fathead minnow survival and growth test, the rainbow trout embryo survival test, the nematode survival and growth/maturation test the algal growth inhibition test with Selenastrum capricornutum, growth inhibition of the duckweed Lemna minor and the multi-species microplate algal growth inhibition test, and the Mutatox test. Receiving waters were used as control and dilution water in the assays with Ceriodaphnia, fathead minnow, trout embryo, Selenastrum capricornutum, and Lemna minor, and in the multi-species microplate algal test.
Three assays were excluded from consideration: the nematode test, due to serious faults in the test design and protocol, the Mutatox test, since test results were of an “all or none” format, and the trout embryo test, because few of the tests were valid and the sensitivity of the test could not be evaluated.
The inhibitory concentrations for a 25% effect (IC25) were calculated and used to compare sensitivities. IC25s were compared non-parametrically (Friedman ANOVA and Kendall concordance) and by a simple ranking system. The most sensitive tests were the Selenastrum and phytoplankton microplate assays, followed by the Lemna minor and Ceriodaphnia tests, which are of roughly equal sensitivity, and the fathead minnow test. The Microtox chronic test is least sensitive, taking into account the stimulatory responses observed.
The relationship between effluent toxicity (IC25s) and effluent chemistry was examined by the calculation of correlation coefficients (nonparametric Spearman R). There were few significant correlations between the IC25s and the chemical parameters, possibly because of the small sample size. In addition, many analytical results were less than the limit of detection, suggesting that the sensitivities of the chemical methods used were too low for these samples.
Costs of the bioassays were estimated based on the costs of labour (number of hours allocated for testing, reporting, culturing and quality assurance/quality control) and disposable materials. The Selenastrum and Lemna minor growth inhibition tests were the least expensive assays (< $100.00 per sample, followed by the Microtox chronic and multispecies phytoplankton tests (< $200.00 per sample), and the Ceriodaphnia and fathead minnow tests (< $400.00 per sample). The cost of the rainbow trout embryo test is almost $700.00 per sample.
Points for applicability were awarded based on relevance and practicality of the tests. Points for relevance were awarded if the test organism was native to Canada and if the test protocol permitted the use of receiving water as a dilution water. Practicality was rated by summing the volumes of effluent and/or receiving water required to perform the tests. The most applicable tests were the Selenastrum, Ceriodaphnia and multispecies phytoplankton tests, followed by the Lemna minor, fathead minnow and trout embryo assays, and lastly the Microtox chronic test.
In conclusion, this report recommends the following tests for future studies involving mine effluents: growth inhibition of the freshwater alga Selenastrum, growth inhibition of the duckweed Lemna minor, survival and reproduction of Ceriodaphnia dubia and survival and growth the larval fathead minnow. The multi-species microplate phytoplankton growth inhibition test was the most sensitive assay, yet the Selenastrum test is preferred due to the availability of a standard test method. It was not possible to rank the rainbow trout embryo assays, as the sensitivity of the test could not be evaluated.
AETE
