may have detrimental effects. Probably more im- 

 portant, however, is the fact that the greater the 

 blood CO2 concentration, the less readily will the 

 animal's hemoglobin combine with dissolved oxy- 

 gen. Thus the presence of much CO2 raises the 

 minimum oxygen concentration which is tolerable. 

 Since the combination of oxygen with hemoglobin 

 is inversely related to temperature, it is obvious 

 that CO2, temperature, and oxygen are closely 

 related. Insufficient data are available at present 

 to permit us to state the greatest amount of dis- 

 solved carbon dioxide that all types of aquatic 

 organisms can tolerate and how these tolerable 

 concentrations vary with temperature and dis- 

 solved oxygen. Studies of the effect of CO2 on 

 the oxygen requirements of several species of fish 

 indicate that CO2 concentrations of the order of 

 25 mg/1 should not be detrimental, provided the 

 oxygen concentration and temperature are within 

 the recommended limits. 



Recommendation: According to our rather meagre 

 knowledge of the subject, it is recommended that the 

 free CO2 concentration should not exceed 25 mg/1. 



Oil 



Oil slicks are barely visible at a concentration of 

 about 25 gal/sq mi (Amer. Petroleum Inst. 1949). 

 At 50 gal/sq mi, an oil film is 3.0x10" inches 

 thick and is visible as a silvery sheen on the sur- 

 face. Sources of oil pollution are bilge and ballast 

 waters from ships, oil refinery wastes, industrial 

 plant wastes such as oil, grease, and fats from the 

 lubrication of machinery, reduction works, plants 

 manufacturing hydrogenated glycerides, free fatty 

 acids, and glycerine, rolling mills, county drains, 

 storm-water overflows, gasoline filling stations, and 

 bulk stations. 



Wiebe (1935) showed that direct contact by fish 

 (bass and bream) with crude oil resulted in death 

 caused by a film over the gill filaments. He also 

 demonstrated that crude oil contains a water-solu- 

 ble fraction that is very toxic to fish. Galtsoff, et al. 

 (1935) showed that crude oil contains substances 

 soluble in sea water that produce an anaesthetic 

 effect on the ciliated epithelium of the gills of 

 oysters. Free oil and emulsions may act on the 

 epithelial surfaces of fish gills and interfere with 

 respiration. They may coat and destroy algae and 

 other plankton, thereby removing a source of fish 

 food, and when ingested by fish they may taint 

 their flesh. 



Setteable oily substances may coat the bottom, 

 destroy benthic organisms, and interfere with 

 spawning areas. Oil may be absorbed quickly by 

 suspended matter, such as clay, and then due to 



wind action or strong currents may be transported 

 over wide areas and deposited on the bottom far 

 from the source. Even when deposited on the bot- 

 tom, oil continuously yields water-soluble sub- 

 stances that are toxic to aquatic life. 



Films of oil on the surface may interfere with 

 reaeration and photosynthesis and prevent the 

 respiration of aquatic insects such as water boat- 

 men, backswimmers, the larvae and adults of 

 many species of aquatic beetles, and some species 

 of aquatic Diptera (flies). These insects surface 

 and carry oxygen bubbles beneath the surface by 

 means of special setae which can be adversely af- 

 fected by oil. Berry (1951) reported that oil films 

 on the lower Detroit River are a constant threat to 

 waterfowl. Oil is detrimental to waterfowl by de- 

 stroying the natural buoyancy and insulation of 

 their feathers. 



A number of observations made by various 

 authors in this country and abroad record the con- 

 centrations of oil in fresh water which are dele- 

 terious to different species. For instance, penetra- 

 tion of motor oil into a fresh water reservoir 

 used for holding crayfish in Germany caused the 

 death of about 20,000 animals (Seydell, 1913). 

 It was established experimentally that crayfish 

 weighing from 35 to 38 g die in concentrations of 

 5 to 50 mg/1 within 1 8 to 60 hours. Tests with two 

 species of fresh water fish, ruff (small European 

 perch), and whitefish (fam. Coregonidae) showed 

 that concentrations of 4 to 16 mg/1 are lethal to 

 these species in 18 to 60 hours. 



The toxicity of crude oil from various oil fields 

 in Russia varies depending on its chemical com- 

 position. The oil used by Veselov (1948) in the 

 studies of the pollution of Belaya River (a tribu- 

 tary in the Kama in European Russia) belongs to a 

 group of methano-aromatic oils with a high con- 

 tent of asphalt, tar compounds, and sulfur. It 

 contains little paraffin and considerable amounts 

 of benzene-ligroin. Small crucian carp (Carassius 

 carassius) 7-9 cm long were used as the bioassay 

 test animal. This is considered to be a hardy fish 

 that easily withstands adverse conditions. The 

 water soluble fraction of oil was extracted by 

 shaking 15 ml of oil in 1 liter of water for 15 

 minutes. The oil film was removed by filtration. 

 Dissolved oxygen was controlled. A total of 154 

 tests were performed using 242 fishes. The average 

 survival time was 17 days at the concentration of 

 0.4 ml/1 of oil but only 3 days at the concentration 

 of 4 ml/1. Further increase in concentration had no 

 appreciable effect on fish mortality. 



Seydell (1913) stated that the toxicity of Rus- 

 sian oil is due to naphthenic acids, small quantities 

 of phenol, and volatile acids (Veselov, 1948). 



45 



