The present study was designed to derive appropriate ammonia standards for a freshwater, wooded stream on the Delmarva Peninsula (eastern shore of the United States) composed almost entirely of wastewater effluent for at least four months of the year. Representative species acute and chronic toxicity tests were performed at 20°C (summer) and 12°C (winter) to obtain seasonal standards. Acute toxicity tests using fathead minnow and Duphniu mugnu suggested that the site water had no effect on un-ionized ammonia toxicity. However, resident species appeared to be relatively insensitive to acute exposures of un-ionized ammonia. Warm-water LC5Os adjusted for pH = 8.0 and 20°C ranged between 1.02 and 2.73 mg/L for those tests in which an LC50 could be calculated. If acute no-observed-effect concentrations (NOECs) (approximately LC25) were used, bluegill was most sensitive (NOEC = 0.295 mg/L), followed by Crungonyx (amphipod) and Menidia (silverside). Warm-water chronic testing indicated that Runa (leopard frog) was most sensitive, followed by bluegill and amphipod. Cold-water acute tests yielded definitive LCSOs between 0.53 (bluegill) and 1.91 mg/L (amphipod). Hylu crucifer (spring peeper) and juvenile bluegill were most sensitive in chronic cold-water testing. Final acute values (FAVs) of 0.62 and 0.30 mg/L NH, were obtained for 20 and 12"C, respectively. The geometric mean of acute-to-chronic ratios (ACR) based on unionized ammonia were 7.2 and 5.7, for 20 and 12"C, respectively. The final chronic values (FCVs) or maximum 4-d average concentrations at 20 and 12°C were 0.09 and 0.05 mg/L NH,, respectively. Un-ionized ammonia acute toxicity to vertebrate freshwater species (fish and tadpoles) was inversely related to temperature, whereas invertebrates often exhibited the opposite trend. Chronic testing, however, suggested that most species were more sensitive to NH, at 20 than 12°C. This study suggests that the ACR developed by the U.S. Environmental Protection Agency (EPA) for warm-water streams may be overly conservative for very small streams in which species diversity is naturally low.
This study presents the results of subacute toxicity testing with the mayfly (Ephemeroptera), species Stenonema modesturn (Heptageniidae). This species is ubiquitous to many streams in the eastern United States and Canada and is associated with unpolluted sediments and water. The results show that counts of molts or exuviae over a 7-14-d exposure period can be a sensitive indicator of chronic growth effects. Molt production was a more sensitive indicator of pollutant effects than length of organism or width of head capsule measurements. Tests using coal mine effluents indicated that the 7-d molt production end point was often more sensitive than the 14-d molt or survival end point. This was due to either a short-term stimulatory effect on molting or effluent variability over time. Molt stimulation was not observed in tests using NaCl or silver nitrate. Tests with these compounds and coal mine effluents demonstrated that the methods and end points provide repeatable and relatively sensitive data. Test precision was comparable to U.S. Environmental Protection Agency 7-d short-term chronic tests. Molt production of Stenonema modestum in laboratory tests proved to be a reliable predictor of instream effects due to a metal-finishing effluent. Furthermore, simultaneous tests of sediment elutriates and ambient samples from the stream pinpointed probable mechanisms behind the observed instream impact on Stenonema modestum. This method should be amenable to other mayfly species, making it a potentially useful tool in site-specific water quality and sediment quality studies
The present study was designed to derive appropriate ammonia standards for a freshwater, wooded stream on the Delmarva Peninsula (eastern shore of the United States) composed almost entirely of wastewater effluent for at least four months of the year. Representative species acute and chronic toxicity tests were performed at 20° (summer) and 12°C (winter) to obtain seasonal standards. Acute toxicity tests using fathead minnow and Daphnia magna suggested that the site water had no effect on un‐ionized ammonia toxicity. However, resident species appeared to be relatively insensitive to acute exposures of un‐ionized ammonia. Warm‐water LC50s adjusted for pH = 8.0 and 20°C ranged between 1.02 and 2.73 mg/L for those tests in which an LC50 could be calculated. If acute no‐observed‐effect concentrations (NOECs) (approximately LC25) were used, bluegill was most sensitive (NOEC = 0.295 mg/L), followed by Crangonyx (amphipod) and Menidia (silverside). Warm‐water chronic testing indicated that Rana (leopard frog) was most sensitive, followed by bluegill and amphipod. Cold‐water acute tests yielded definitive LC50s between 0.53 (bluegill) and 1.91 mg/L (amphipod). Hyla crucifer (spring peeper) and juvenile bluegill were most sensitive in chronic cold‐water testing. Final acute values (FAVs) of 0.62 and 0.30 mg/L NH3 were obtained for 20 and 12°C, respectively. The geometric mean of acute‐to‐chronic ratios (ACR) based on unionized ammonia were 7.2 and 5.7, for 20 and 12°C, respectively. The final chronic values (FCVs) or maximum 4‐d average concentrations at 20 and 12°C were 0.09 and 0.05 mg/L NH3, respectively. Un‐ionized ammonia acute toxicity to vertebrate freshwater species (fish and tadpoles) was inversely related to temperature, whereas invertebrates often exhibited the opposite trend. Chronic testing, however, suggested that most species were more sensitive to NH3 at 20 than 12°C. This study suggests that the ACR developed by the U.S. Environmental Protection Agency (EPA) for warm‐water streams may be overly conservative for very small streams in which species diversity is naturally low.
This study presents the results of subacute toxicity testing with the mayfly (Ephemeroptera), species Stenonema modestum (Heptageniidae). This species is ubiquitous to many streams in the eastern United States and Canada and is associated with unpolluted sediments and water. The results show that counts of molts or exuviae over a 7–14‐d exposure period can be a sensitive indicator of chronic growth effects. Molt production was a more sensitive indicator of pollutant effects than length of organism or width of head capsule measurements. Tests using coal mine effluents indicated that the 7‐d molt production end point was often more sensitive than the 14‐d molt or survival end point. This was due to either a short‐term stimulatory effect on molting or effluent variability over time. Molt stimulation was not observed in tests using NaCl or silver nitrate. Tests with these compounds and coal mine effluents demonstrated that the methods and end points provide repeatable and relatively sensitive data. Test precision was comparable to U.S. Environmental Protection Agency 7‐d short‐term chronic tests. Molt production of Stenonema modestum in laboratory tests proved to be a reliable predictor of instream effects due to a metal‐finishing effluent. Furthermore, simultaneous tests of sediment elutriates and ambient samples from the stream pinpointed probable mechanisms behind the observed instream impact on Stenonema modestum. This method should be amenable to other mayfly species, making it a potentially useful tool in site‐specific water quality and sediment quality studies.
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