to determine "no-effect" levels of hydrogen sulfide based on long-term 

 tests, and to relate them to acute toxicity levels. 



MATERIALS AND METHODS 



The work described here was done at the University of Minnesota labor- 

 atories using well water (Table 1). Continuous flow-through apparatus was 

 used in all tests. Small species and early life history stages were 

 tested in equipment described by Colby and Smith (1967), and Mount and 

 Brungs (1967). Adult fish of larger species were tested in fiberglass 

 tanks and all other tests were done in glass or acrylic test chambers. 

 Molecular hydrogen sulfide concentrations were maintained with sodium sul- 

 fide solutions, and pH was adjusted to provide the desired test concentra- 

 tion. Analyses of water from the center of each test chamber were made 3 

 times each day in acute tests and every 2 days in chronic tests. Using 

 Method C of Standard Methods of Water Analysis (1971), undissociated 

 hydrogen sulfide was determined by calculation. Bluegills and some fat- 

 head minnows were wild stock from local lakes or streams. Other fish 

 were hatchery stock or laboratory reared. The LC50 values were cal- 

 culated by standard methods using probit techniques. 



Acute Toxicity 



Acute tests were made with 4 to 5 concentrations of hydrogen sulfide 

 arranged in a logarithmic series and one control. Temperature in various 

 tests ranged from 6.1 °C to 26 °C depending on species, life history 

 stages, and specific objectives (Table 2). Duration of tests was from 4 

 to 12 days to determine the 96-hr LC50 and tne threshold LC5Q. The 

 threshold value was considered to be attained when no death occurred in 

 48 hours. Eggs, sac fry, swim-up fry, juveniles, and adults of fish 

 species were tested. The LC50 at 96-hr varied from 0.515 mg/1 H2S at 

 6.1 °C with fathead minnow sub-adults, to 0.007 mg/1 H2S at 24 °C with 

 fathead fry. Values ranged between these limits for other species, life 

 history stages, and temperatures (Table 2). 



The effect of temperature on resistance was large in fathead minnows. 

 The 96-hr LC50 concentration increased from 0.021 mg/1 at 24 °C to 0.515 

 mg/1 at 6.1 °C (Table 2). This twenty-five fold change in tolerance 

 occurred principally between 10 and 6.1 °C. Goldfish tested at tempera- 

 tures between 14.1 and 26 °C showed 96-hr LC50 values varying from 0.145 

 mg/1 H 2 S at the lowest, to 0.063 mg/1 H2S at the highest temperature 

 (Adelman and Smith, 1972). 



Threshold LC50 concentrations were lower than those for 96-hr in most 

 tests, but not markedly so, except in the goldfish at lower temperatures. 

 Threshold values for the various life history stages had the same general 

 relationships to each other as the 96-hr LC50 values. 



Long-Term Tests at Low Concentrations 



Since acute toxicity of a material may be a poor index of long-term 

 effects of sub-acute concentrations of a toxicant on a fish population, a 



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