Effect on Daphnia pulex (de geer) of daily pulse exposures to copper or cadmium

Abstract
The most recent U.S. EPA water quality criteria indicate that chronic exposures to pulses of the LC50 concentration of a metal will cause no damage to freshwater animals as long as the average daily concentration does not exceed the chronic, no‐observable‐effect concentration. We have tested this concept by exposing Daphnia pulex to such pulses of copper and cadmium. The exposures to cadmium for periods of up to 70d, caused no adverse effects. However, 70‐d exposures to daily pulses of copper resulted in significant reductions in survival, growth and reproduction. Although the two‐number criterion has not been tested for other chemicals, it is probable that the success of this approach in protecting freshwater animals from chronic exposures to chemicals will be as variable among other chemicals as we have shown it to be between copper and cadmium.

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