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

Elevated nitrate (NO3 ) and sulfate (SO4 ) in surface water are a global concern and studies are needed to generate toxicity data to develop environmental guideline values for NO3 and SO4 . The present study was designed to fill existing gaps in toxicity databases by determining the acute and/or chronic toxicity of NO3 (tested as NaNO3 ) to a unionid mussel (Lampsilis siliquoidea), a midge (Chironomus dilutus), a fish (rainbow trout Oncorhynchus mykiss), and 2 amphibians (Hyla versicolor, Lithobates sylvaticus), and determine the acute and/or chronic toxicity of SO4 (tested as Na2 SO4 ) to 2 unionid mussels (L. siliquoidea, Villosa iris), an amphipod (Hyalella azteca), and 2 fish species (fathead minnow Pimephales promelas, O. mykiss). Among the different test species, acute NO3 EC50s ranged from 189 to >883 mg NO3 -N/L and chronic NO3 EC20s based on the most sensitive endpoint ranged from 9.6 to 47 mg NO3 -N/L. The midge was the most sensitive species and the trout was the least sensitive species in both acute and chronic NO3 exposures. Acute SO4 EC50s for the 2 mussel species (2071 and 2064 mg SO4 /L) were similar to the EC50 for the amphipod (2689 mg SO4 /L) whereas chronic EC20s for the 2 mussels (438 and 384 mg SO4 /L) were >2-fold lower than the EC20 of the amphipod (1111 mg SO4 /L), indicating the high sensitivity of mussels in chronic SO4 exposures. However, the fathead minnow, with an EC20 of 374 mg SO4 /L, was the most sensitive species in chronic SO4 exposures while the rainbow trout became the least sensitive species (EC20 >3240 mg SO4 /L). The high sensitivity of fathead minnow was consistent with the finding in a previous chronic Na2 SO4 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 Na2 SO4 toxicity to the minnow. This article is protected by copyright. All rights reserved.