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111 0.3% deicer solution. In addition, no significant change in BOD could be observed as a result of the addition of salt and sand (0.6% by mass). 9. Tadpoles of the boreal toad were subjected to biotoxicity testing under controlled laboratory conditions through exposure to a range of concentrations of 1996-97 deicer. The boreal toad is of particular interest because of its status as an endangered species, and its presence in aquatic environments near roadways that receive deicer. The tadpoles showed no mortality over 96-hour intervals at deicer concentrations of 0.1%, which is close to the expected median concentration of deicer concentrations in runoff as it exits the roadway. The concentration of deicer required to cause 50°,4 mortality (LD$0) among tadpoles over a 96-hour period was estimated as 0.32%. Tadpoles were similarly affected by solutions of pure magnesium chloride (LD50--0.65%). Repetition of testing with 1997-98 deicer produced similar results. A sublethal (physiological stress) test was added for 1997-98 deicer; it showed physiological stress at or above 0.1% deicer. The no effect concentration for the sublethal test probably lies in the vicinity of 0.02% deicer. 10. Juvenile rainbow trout were tested with 1996-97 deicer for response to varying concentrations of deicer. The threshold for mortality over 96-hour exposure intervals was approximately 0.5%. The LDS0 for rainbow trout was estimated as 1.4% magnesium chloride deicer. Results were similar for 1997-98 deicer. 11. The aquatic invertebrate Ceriodaphnia was tested for response to a range of magnesium chloride deicer solutions over an interval of 48 hours. The threshold of mortality for Ceriodaphnia was approximately 0.1%. The LDS0 for Ceriodaphnia was estimated as 0.19°,4 (48 hours). A test of reproductive capability was also performed on Ceriodaphnia. The reproductive test indicates the onset of negative physiological effects for Ceriodaphnia at about