Description of Work The sensitivity of various species of freshwater mussels (Unioidea) to range of inorganic and organic chemicals has been evaluated in acute toxicity tests and the sensitivity of freshwater mussels to a range of inorganic chemicals has been evaluated in chronic toxicity tests. However, the chronic toxicity of organic chemicals has only been evaluated with a limited number of mussel species or for a limited number of organic chemicals. The objective of this study will be to evaluate methods for conducting 90-d water only exposures with juvenile mussels and conducted chronic 28-d toxicity tests with at least organic chemicals of concern and two commonly tested species of mussels (Lampsilis siliquoidea, fatmucket and [...]