Acute and Chronic Toxicity of Sodium Nitrate and Sodium Sulfate to Several Freshwater Organisms in Water-Only Exposures.

Elevated nitrate (NO ) and sulfate (SO ) in surface water are of global concern, and studies are needed to generate toxicity data to develop environmental guideline values for NO and SO . The present study was designed to fill existing gaps in toxicity databases by determining the acute and/or chronic toxicity of NO (tested as NaNO ) to a unionid mussel (Lampsilis siliquoidea), a midge (Chironomus dilutus), a fish (rainbow trout, Oncorhynchus mykiss), and 2 amphibians (Hyla versicolor and Lithobates sylvaticus), and to determine the acute and/or chronic toxicity of SO (tested as Na SO ) to 2 unionid mussels (L. siliquoidea and Villosa iris), an amphipod (Hyalella azteca), and 2 fish species (fathead minnow, Pimephales promelas and O. mykiss). Among the different test species, acute NO median effect concentrations (EC50s) ranged from 189 to >883 mg NO -N/L, and chronic NO 20% effect concentrations (EC20s) based on the most sensitive endpoint ranged from 9.6 to 47 mg NO -N/L. The midge was the most sensitive species, and the trout was the least sensitive species in both acute and chronic NO exposures. Acute SO EC50s for the 2 mussel species (2071 and 2064 mg SO /L) were similar to the EC50 for the amphipod (2689 mg SO /L), whereas chronic EC20s for the 2 mussels (438 and 384 mg SO /L) were >2-fold lower than the EC20 of the amphipod (1111 mg SO /L), indicating the high sensitivity of mussels in chronic SO exposures. However, the fathead minnow, with an EC20 of 374 mg SO /L, was the most sensitive species in chronic SO exposures whereas the rainbow trout was the least sensitive species (EC20 > 3240 mg SO /L). The high sensitivity of fathead minnow was consistent with the finding in a previous chronic Na SO study. However, the EC20 values from the present study conducted in test water containing a higher potassium concentration (3 mg K/L) were >2-fold greater than those in the previous study at a lower potassium concentration (1 mg K/L), which confirmed the influence of potassium on chronic Na SO toxicity to the minnow. Environ Toxicol Chem 2020;39:1071-1085. © 2020 SETAC.