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

Elevated nitrate (NO 3 ) and sulfate (SO 4 ) in surface water are of global concern, and studies are needed to generate toxicity data to develop environmental guideline values for NO 3 and SO 4 . The present study was designed to fill existing gaps in toxicity databases by determining the acute and/or chronic toxicity of NO 3 (tested as NaNO 3 ) 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 4 (tested as Na 2 SO 4 ) 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 3 median effect concentrations (EC50s) ranged from 189 to >883 mg NO 3 ‐N/L, and chronic NO 3 20% effect concentrations (EC20s) based on the most sensitive endpoint ranged from 9.6 to 47 mg NO 3 ‐N/L. The midge was the most sensitive species, and the trout was the least sensitive species in both acute and chronic NO 3 exposures. Acute SO 4 EC50s for the 2 mussel species (2071 and 2064 mg SO 4 /L) were similar to the EC50 for the amphipod (2689 mg SO 4 /L), whereas chronic EC20s for the 2 mussels (438 and 384 mg SO 4 /L) were >2‐fold lower than the EC20 of the amphipod (1111 mg SO 4 /L), indicating the high sensitivity of mussels in chronic SO 4 exposures. However, the fathead minnow, with an EC20 of 374 mg SO 4 /L, was the most sensitive species in chronic SO 4 exposures whereas the rainbow trout was the least sensitive species (EC20 > 3240 mg SO 4 /L). The high sensitivity of fathead minnow was consistent with the finding in a previous chronic Na 2 SO 4 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 2 SO 4 toxicity to the minnow. Environ Toxicol Chem 2020;39:1071–1085. © 2020 SETAC