The impact of some chemicals on ecosystems may not be measured directly by the types of toxicity tests discussed above. Some chemicals are known to bioaccumulate either directly from the water (bioconcentrate) or through steps in the food chain (biomagnifiy). The concentrations of chemicals with these characteristics may not be acutely toxic and the classic endpoints of chronic toxicity tests may not show the impacts. The classic example of this type of toxicity is the eggshell thinning from biomagnified chlorinated hydrocarbons that resulted in lowered hatching success for certain bird species, most notably the Bald
Eagle. The concentrations of chlorinated hydrocarbons in the environment did not suggest direct toxicity and this pathway for toxicity was not understood for a long time.
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