Effects of hardness, chloride, and acclimation on the acute toxicity of sulfate to freshwater invertebrates

The acute toxicity of sulfate to Ceriodaphnia dubia, Chironomus tentans, Hyalella azteca, and Sphaerium simile was assessed to support potential updates of Illinois (USA) sulfate criteria for the protection of aquatic life. The mean lethal concentrations to 50% of a sample population (LC50s), expressed as. mg SO₄^2-/L, in moderately hard reconstituted water (MHRW) were as follows: 512 mg/L for H. azteca, 2,050 mg/L for C. dubia, 2,078 mg/L for S. simile, and 14,134 mg/L for C. tentans. At constant sulfate (∼2,800 mg/L) and hardness (106 mg/L), survival of H. azteca was positively correlated with chloride concentration. Hardness also was found to ameliorate sodium sulfate toxicity to C. dubia and H. azteca, with LC50s for C. dubia increasing from 2,050 mg SO₄^2-/L at hardness = 90 mg/L to 3,516 mg SO₄^2-/L at hardness = 484 mg/L. Using a reformulated MHRW with a similar hardness but higher chloride concentration and different calcium to magnesium ratio than that in standard MHRW, the mean LC50 for H. azteca increased to 2,855 mg/L, and the LC50 for C. dubia increased to 2,526 mg/L. Acclimation of C. dubia to 500 and 1,000 mg SO₄^2-/L for several generations nominally increased mean LC50 values compared with those cultured in standard MHRW.