Whole-body sodium concentration in larval fathead minnows (Pimephales promelas) during and following copper exposure.

This research used whole-body sodium concentration to characterize exposure and recovery of larval fathead minnows (Pimephales promelas) from acute pulsed copper exposures. Whole-body sodium was chosen because the acute mechanism of copper toxicity to fishes is putative disruption of ion regulation, resulting in a loss of sodium and eventually leading to mortality. Whole-body sodium response in larval fathead minnows exposed to copper was both concentration and duration dependent. The loss of sodium to approximately 70% of control levels occurred within 12 h of exposure. Organisms demonstrated an ability to recover whole-body sodium within 48 h after exposure to concentrations below 0.47 microM Cu2+ for 3, 6, or 9 h. However, at higher concentrations, organisms required more than 48 h to recover. Whole-body sodium concentrations and mortality for all continuous exposures were strongly correlated. These results may facilitate development of a physiologically based model to predict the response of organisms to copper in receiving streams.

Influence of dissolved organic matter source on silver toxicity to Pimephales promelas.

In the environment, the formation of organic and inorganic silver complexes can decrease Ag bioavailability (toxicity) to aquatic organisms. However, current water quality regulations do not consider the protective effects of water quality parameters such as dissolved organic carbon (DOC) concentration. To determine the effect of DOC concentration and source on silver toxicity, nine different natural organic matter isolates were used in 96-h static-renewal toxicity tests with fathead minnow (Pimephales promelas). The 96-h dissolved silver median lethal concentrations (LC50) among different sources of dissolved organic matter varied by up to fivefold (4.5-23.3 microg/L). Further, toxicity tests with organic matter from the site with the lowest 96-h LC50 value suggested only limited additional attenuation of silver toxicity when DOC concentration was increased from 5.1 to 14.0 mg/L. With this site excluded, we found little more than a twofold difference among 96-h dissolved Ag LC50s for the remaining sources (10.1-23.3 microg/L). However, significant toxicological differences among sites remained. It was apparent that organic matter from different sources varied both chemically and toxicologically, but no conclusions could be drawn that related compositional variation to observed Ag toxicity for these isolates.