EXECUTIVE SUMMARY
A general concern for timely results of toxicity tests by industrial dischargers, including members of the metal mining sector and government regulators, has resulted in the investigation of several micro/screening toxicity test procedures emerging into the market place as alternatives to methods currently in place. The purpose of this evaluation is to determine which, if any, types of micro/screening toxicity tests can be used as an alternative to the Rainbow Trout acute lethality procedures specific to the Canadian Mining sector. As more recent regulations have included the use of the Daphnia magna acute lethality toxicity test for compliance testing, the project evaluation also includes a comparison to this test organism.
This study evaluates the data generated from toxicity tests conducted on selected mine effluents of various mine types (i.e. zinc, copper/zinc, uranium, etc.) exhibiting a range of toxicity and chemical parameter characteristic of Canadian mine effluents. The report provides a comparison of toxicity tests using Rainbow Trout, Daphnia magna acute lethality bioassays with various micro/screening toxicity tests, which include the Daphnia magna IQ toxicity test™, Microtox™, Rotoxkit F, Thamnotoxkit F and Toxichromotest.
The comparison consisted of evaluating several criteria specific to each toxicity test and comparing these results to the rainbow trout toxicity test. These criteria included costs, speed, the correlation of effluent chemistry to toxicity results, the reproducibility of toxicity results including intra and interlaboratory results, the applicability of each toxicity test and the comparability of the microtoxicity test results to the comparable rainbow trout toxicity test results.
The following points summarize the main conclusions of the Canmet study:
- No one toxicity test compared directly with the rainbow trout toxicity test for both comparability of toxicity response and correlation of endpoint results to chemistry.
- Based upon the evaluation criteria the “best” toxicity test varied depending on mine types. The “best” toxicity test varied between the Thamnotoxkit, Daphnia magna IQ and Daphnia magna acute toxicity tests depending on mine type.
- When either the Daphnia magna IQ or Thamnotoxkit was selected as the “best” test, the next best test was the reciprocal procedure. When the Daphnia magna acute toxicity test was selected as the “best”, the next selection included either the IQ or Thamnotoxkit procedure.
- From the results, it has become quite obvious that the applicability of the “best” test for a specific application has to be assessed on a case by case basis. Results of the Canmet study provide direction in this assessment and would be of added value for the justification of a specific toxicity test procedure to corporate environmental mangers and/or government regulators.
- The Daphnia magna IQ and Rotoxkit demonstrated an increased toxic response for gold mine effluents compared to the rainbow trout toxicity test. This increased toxicity response may be a result of a specific toxicant(s) (i.e. cyanide) characteristic of gold mine effluents which should be investigated further.
- The highly standardized Microtox test, availability of technical reference material, ability to provide results quickly and high concordance (presence or absence of toxicity) with the rainbow trout test does make this assay procedure attractive for use at mine sites. But such things as the initial capital costs, insensitivity to various metals and reduce ecological relevance may deter its application with mining effluents. Use of the Microtox would have to be assessed on a case by case basis with regard to its applicability to address a specific application. If use of the Microtox is considered further evaluation of exposure time and osmotic adjustment agent (i.e. sucrose/NaCl or NaClO4 instead of NaCl) should be considered.
- At present, the micro or kit toxicity test kits evaluated in this study do not have any QA/QC requirements. Use of any one of these toxicity test procedures would require the inclusion of specific QA/QC procedures (i.e. reference toxicants, duplication, reporting requirements, etc.) in order to provide credibility to results, particularly if results are to be used as a replacement for the standard acute toxicity tests.
During this study, one encompassing commercial toxicity test kit could not be identified which would fulfill the requirements for acceptance and application throughout the mining sector, the scientific community and the various government jurisdictions. However, this study does contribute to the understanding of toxicity in mining discharges, the interactions of the various toxicity tests evaluated and variations of response between the various mine types and specific mining operations.
Results in this report, and the format in which they are presented, can provide the basis by which any particular site can conduct their own independent evaluation of toxicity tests specific to their effluent type, application and priorities.
AETE
