SECTION 11 



CHRONIC EFFECTS OF LOW LEVELS OF HYDROGEN SULFIDE 

 ON FRESHWATER FISH 



Lloyd L. Smith, Jr. 



INTRODUCTION 



The potential effects of hydrogen sulfide on fishery ecosystems have 

 not been fully realized because most survey work has measured neither con- 

 centrations below 0.5 mg/1 , nor accumulations near the sediment/water 

 interface in areas of continuous H2S production. Areas within a few 

 centimeters of the bottom where fish eggs and young fry occur are rarely 

 sampled. Since it has been assumed that levels of hydrogen sulfide po- 

 tentially dangerous to fish life occur only under conditions of low oxygen 

 concentration, it has been believed that the adverse effects of low oxygen 

 will control fish populations before the toxic effects of sulfides will 

 be manifested. Undissociated hydrogen sulfide is the toxic form. At pH 

 9.0, approximately 1 percent is undissociated, at 6.7 about 50 percent, 

 and at 5.0 about 99 percent. 



The significance of the work described in this study is primarily a 

 demonstration of the toxic effect of very low concentrations of hydro- 

 gen sulfide which frequently are found over natural organic bottoms, in 

 the vicinity of sludge beds, and in areas where hydrogen sulfide is formed 

 from waste effluents or comes directly from industrial operations. Colby 

 and Smith (1967) found levels of hydrogen sulfide within 20 mm of the 

 bottom which varied from 0.02 to 0.20 mg/1 in a river with a major wall- 

 eye ($tizoi>tcdion vWizum v.LPicum Mitchell) fishery. Dissolved oxygen at 

 these locations was adequate to maintain fish life. Here maintainance of 

 the adult population depended on inward migration of fish rather than 

 natural reproduction. In natural spawning areas for northern pike ( Ei>ox 

 lucMu, Linnaeus), Adelman (1969) reported hydrogen sulfide concentrations 

 near the bottom commonly in the range of 0.03-0.08 mg/1, and occasionally 

 as high as 0.22 mg/1 during the spawning period. Scidmore (1956) working 

 in a Minnesota lake during the winter found 0.3 and 0.4 mg/1 H S with 6.0 

 and 3.6 mg/1 , respectively. Adelman and Smith (1970) showed that eggs 

 and fry of northern pike were affected by low levels of hydrogen sulfide. 



The experiments summarized in the present report used four species of 

 fish, brook trout (SaZvctinuA ^ontinalj^, Mitchill); bluegill (LcpomiA 

 macfiockOmi Rafinesque); fathead minnow (Pvnc.pha.lte pnomclai, Rafinesque); 

 and goldfish (CaAcu>i>iui> auAatuu, Linnaeus). The purpose of this study was 



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