Challenges with the current methodology for conducting Endangered Species Act risk assessments for pesticides in the United States.

The US Environmental Protection Agency (USEPA or the Agency) is responsible for administering the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The Agency is also required to assess the potential risks of pesticides undergoing registration or re-registration to threatened and endangered (i.e.

Acute dysprosium toxicity to Daphnia pulex and Hyalella azteca and development of the biotic ligand approach.

The toxicological understanding of rare earth elements (REEs) in the aquatic environment is very limited but of increasing concern. The objective of this research is to compare the toxicological effect of the REE dysprosium to the freshwater invertebrates Daphnia pulex and Hyalella azteca and in the more sensitive organism, understand the toxicity modifying influence of Ca, Na, Mg, pH and dissolved organic matter (DOM). Standard methods (Environment Canada) were followed for testing and culture in media of intermediate hardness (60mg CaCO3 mg/L) at pH 7.