Chemical Mixtures and
Pulsed Exposure Tests

Introduction Methods Results The Bottom Line

Methods

Two sets of continuous exposure, static renewal toxicity experiments were conducted as specified by the USEPA (1989).  In the first set of experiments, the effect of the presence of suspended food solids on toxicity was evaluated by varying the timing of YCT food additions to the cups relative to organism transfer.  To establish two feeding time treatments, 0.1 ml of YCT was added to treatment cups either five minutes before or fifteen minutes after organism transfer.  Addition before transfer should allow the contaminant to bind to the food, reducing the toxicity before the organism is introduced.

In the second experiment the effects of both the amount of suspended food solids present and the maternal age on toxicity were evaluated.  Two YCT solids concentrations were established, a laboratory standard (2.54 g solids per L) and a gravity filtered lower YCT concentration (1.75 g solids per L), within the USEPA standard of 1.7 to 1.9 g solids per L of YCT.  Food solids were added five minutes prior to organism transfer.  To establish the two maternal age treatments, neonates were harvested from 7-day old adults (+36 h) and 14-day old adults (+ 36 h).
 
 

Culture cups of CeriodaphniaCeriodaphnia




Literature Cited

U.S. Environmental Protection Agency. 1989. Short-term methods for estimating the chronic toxicity of effluents and receiving waters to freshwater organisms. EPA/600/4-89/001, second edition. Environmental Monitoring Systems Laboratory, U.S. Environmental Protection Agency. Cincinnati, OH.

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