100 



ID 20 

 CONCENTRATION IN 



30 40 50 

 PARTS PER THOUSAND 



Figure 400. — Depression of the activity of ciliated 

 epithelium of oyster gill by increased concentration of 

 pulp mill effluent (black liquor) of specific gravity 

 1.0028. From Galtsoflf, Chipman, Engle, and Calder- 

 wood, 1947. 



by other investigators (Seydel, 1913; Veselov, 

 194S) on the toxicity of crude oil to fishes. 



Determination of the toxicity of some pollutants 

 is difficult because they may be present in such low 

 concentrations that they are near or below the 

 threshold of sensitivity to chemical methods. 

 Their presence in even mmimal quantities should 

 be considered potentially dangerous to sedentary 

 animals unable to avoid them. Another detection 

 problem is that in many industrial plants the dis- 

 charge of effluents is not contmuous but is fre- 

 quently interrupted or made during the night and 

 early hours of the morning. Pollution studies 

 must include taking composite samples of water 

 with automatic samplers over a period of several 

 hours. Some contaminants are unstable; after 

 being discharged into sea water they are graduallj' 

 oxidized, precipitated, neutralized, and become 

 less harmful. The rate of this self-purification of 

 water depends on many conditions, temperature, 

 salinity gradient, sedimentation, and currents. 

 To avoid inconsistencies in results, toxicity tests 

 with such materials should be carried out only with 

 stabilized samples (Odlaug, 1949). 



Bioassays made within a few days indicate the 

 presence or absence in water of a physiologically 

 active substance but do not determine whether the 

 pollution is lethal to the animal. Long-term field 

 and laboratory' observations are needed to deter- 



mine the lethal effects of a low concentration of 

 pollutants. 



Ecological studies in polluted waters show that 

 under certain conditions the normal environment 

 may be modified by the contaminant and become 

 unsuitable for growth and reproduction of oysters. 

 Pollution of Shelton Bay, Puget Sound, Wash., 

 with red liquor discharged by a local pulp mill 

 boosted the production of the diatom Melosira sp. 

 to such an extent that the beds of 0. lurida in the 

 bay became covered with a thick layer of this 

 fouling plant. A similar effect occurred in labora- 

 tory tests with red liquor made by Odlaug (1949). 

 Oysters affected by red liquor were useless because 

 of then poor quality and poor taste; their repro- 

 duction stopped completely. Normal conditions 

 were restored after discharge of the pollutant was 

 discontinued (McKernan, Tartar, and Tollefson, 

 1949). 



The biologist who studies pollution of natural 

 water should remember that there is no harmless 

 pollution. All types of pollution are harmful to 

 marine populations; only the degree of their effects 

 differs. Frequently it is claimed tliat the enrich- 

 ment of sea water by phosphates, nitrates, carbo- 

 hydrates, and other organic matter is beneficial 

 and will tend to increase productivity. In the 

 case of water pollution by duck farms in Moriches 

 Bay, Long Island, N.Y., indiscriminate pollution 

 by duck manure caused an imbalance of nutrient 

 salts and boosted the outbreak of microorganisms 

 which had an adverse effect on shellfish (Redfield, 

 1952). LTseful enrichment of sea water can be 

 achieved only by controlled and balanced fertiliza- 

 tion. 



Oxidation is important in reducing or destroying 

 the toxicity of certain contaminants of sea water 

 (Galtsoff, Chipman, Engle, and Calderwood, 1947). 

 The efficiency of oxidation is influenced by tem- 

 perature and by the manner in whicn the pollutant 

 is added to the water. Preliminary storage in 

 tanks is helpful in removing objectionable solids, 

 and cascading the effluent from storage tanks to 

 tlie place of discharge will expedite its oxidation. 

 Tlie U.S. Public Health Service found that 10,400 

 factory outlets in 1950 were pouring their waste 

 into natural waters of the United States; only 657 

 of them had waste treatment plants of adequate 

 capacities. In about 30 percent of tlie plants, the 

 method of treatment was unsatisfactory. The 

 number of plants which at present discharge their 



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FISH AND WILDLIFE SERVICE 



