EXECUTIVE SUMMARY – AETE
B.A.R. Environmental Inc. conducted toxicity tests involving effluents and receiving waters from Myra Falls, (Westmin Resources, B.C.), Sullivan Mine (Cominco Ltd., B.C.), Levack Mine, (Inco Ltd., ON), Onaping site (Falconbridge Ltd., ON), Dome Mine, (Placer Dome Canada, ON), Gaspé Division, (Noranda Mining and Exploration Inc., QC) and Heath Steele Division, (Noranda Mining and Exploration Inc., N.B.). The objective is to characterize the toxicity of the seven mine effluents, using the local receiving waters as dilution and control waters. The other objectives include determining if receiving waters cause toxicity to fathead minnow and Ceriodaphnia dubia, and evaluating the use of acclimation procedures for receiving waters which are found to be toxic. Toxicity studies were conducted in conjunction with field studies of the receiving environments at the seven mine sites.
Toxicity testing involved growth inhibition with Selenastrum capricornutum and Lemna minor, reproduction and survival of Ceriodaphnia dubia, growth and survival of the fathead minnow, and viability of the rainbow trout embryo. To determine if acclimation was necessary, samples of receiving waters were collected for preliminary tests with fathead minnow and Ceriodaphnia dubia. Receiving water samples for effluent tests were collected at a later time.
The acclimation procedure involves gradual introduction of the organisms to the 100% v/v receiving water. Neonate ceriodaphnids and adult fathead minnows are held for 7 days in a laboratory dilution water with pH and hardness adjusted to that of the receiving water. Newly fertilized fish eggs and with third brood ceriodaphnid neonates are then introduced to a 10% concentration of receiving water. The proportion increases each day until the organisms are in 100% receiving water, when the newly hatched fish larvae and the third brood ceriodaphnid neonates are used in toxicity tests.
Toxicity tests with effluents involved several effluent exposure concentrations, using the mine’s receiving waters as control and dilution water. The toxicity of the effluents was compared by averaging the results of the four successful toxicity tests in this study. The sensitivity of the toxicity tests was compared by ranking the IC25s.
In preliminary tests, the Sullivan receiving water was toxic to both Ceriodaphnia (30% mortality) and fathead minnows (60% mortality). The Gaspé receiving water was toxic to Ceriodaphnia only (30% mortality). The remaining receiving waters were not toxic in preliminary tests.
Ceriodaphnia were acclimated to Sullivan and Gaspé receiving water while fathead minnows were acclimated to Sullivan water only. Survival of both organisms improved during the gradual acclimation. During the acclimation procedure, all ceriodaphnids survived in the Gaspé series and 80% survived in the Sullivan series. During acclimation to the Sullivan receiving water, 87.5% of fathead minnow eggs hatched into larvae.
During effluent tests, the acclimated organisms also survived in the Sullivan and Gaspé receiving water controls, leading to valid tests. The Myra Falls receiving water was toxic to Ceriodaphnia during the effluent test, yet did not cause toxicity during the preliminary test. During the Heath Steele assay, reproduction of Ceriodaphnia in the receiving water control was significantly greater than during the preliminary test. The responses of Ceriodaphnia in Heath Steele and Myra Falls receiving waters suggest that different samples of the same receiving waters can vary in a manner that affects reproduction and/or survival of the invertebrate.
Four trout embryo tests failed. The Gaspé receiving water was slightly toxic and tests with the Dome, Sullivan and Myra Falls effluents were invalid due to poor quality eggs and/or milt, which caused excessive control mortalities.
Most effluents exhibited little toxicity. The Selenastrum, Lemna and Ceriodaphnia tests showed a similar sensitivity to the effluents while the fathead minnow assay was less sensitive. The sensitivity of the fathead minnow and trout embryo assays is similar, when data from this study and the previous Sublethal Toxicity Screening Project are combined.
