Aquatic Toxicity Monitoring

The toxicity monitoring task for the ETTP BMAP includes tests of effluent from treatment facilities, effluent from storm drains (SD170, SD180, SD190), and surface water from six sites within Mitchell Branch. 

Ambient toxicity tests using fathead minnows and Ceriodaphnia found intermittent occurrences of acute toxicity prior to 1991.  Dechlorination of the Storm-Drains (SD) eliminated much of the ambient toxicity.

More recent tests were generally negative for acute toxicity, with any ambient toxicity related to discharges from SDs 170 or 190.

Evaluations of SDs during the 1994-1999 period, found evidence of intermittent chronic toxicity at SD 190 more frequently than at SD 170 (Figure 1).  Reproduction or survival of Ceriodaphnia was often less than 20% in full-strength effluent from SD 190.  Survival in tests of SD 180 were generally above 80%, although reproduction was often affected.

Figure 1. Ceriodaphnia survival (%) at end of chronic toxicity tests of stormwater effluent.

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Last Modified: April 17, 2001