Abstract |
Since humic substances are ubiquitous, but highly variable, components of the chemical matrix of freshwater ecosystems, and are assumed to affect the toxicity and bioavailability of metals, any attempt to derive water quality criteria or standards for metals must take into account interactions between humic materials and those metals. Unfortunately, at present, it is impossible to predict the effects of humic substances on the toxicity or bioaccumulation of metals. Although, for example, the most recent U.S. EPA water quality criteria for cadmium and copper (U.S. EPA 1980a,b) acknowledge that naturally occurring organics will alter toxicity, no data on the effects of such organics on metal toxicity were available for incorporation into the criteria. In view of the very minimal data available on the effects of humic substances on acute toxicity and the lack of data on effects on chronic toxicity, the objectives of the present study were to evaluate, using D. pulex and D. magna as models, the effects of humic acid on the acute and chronic toxicity and bioaccumulation of Cd and Cu. |