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in living tissue in quantities substantially above that of natural back- 

 ground, is recognized as injurious (IV.5.1). Since some isotopes 

 may be extremely long-lived, and radionuclides may be cycled through 

 the food chain or recycled to the environment if the host expires, the 

 biological magnification factor is important. The potential conse- 

 quences of each particular radioisotope discharge must be evaluated 

 individually. The best rule is to minimize the amount of these materials 

 cycling in the environment. 



Toxic materials directly kill the biota, interact in the food chain, 

 or deleteriously affect the reproduction or growth processes. The ulti- 

 mate damage is to stress or eliminate parts of the energy-conversion 

 chain in the estuarine environment (fig. IV.5.6). 



HEAT 



The preceding discussion emphasized the many environmental fac- 

 tors affecting the impact of various types of wastes on the estuarine 

 environment. Water temperature was mentioned in almost every in- 

 stance. Tlius the addition of large quantities of heat from industrial 

 cooling water constitutes a form of pollution which must be considered 

 (fig.IY.5.7). 



The impact of heat pollution on the environment appears in several 

 different ways: 



( 1 ) Heat affects the physical properties of water such as density, 

 viscosity, vapor pressure, and solubility of dissolved gases. Con- 

 sequently, such processes as the settling of particulate matter, 

 stratification, circulation, and evaporation can be influenced by 

 changes in temperature. Since the solubility of oxygen in water 

 decreases as temperature increases, thermal pollution reduces the 

 oxygen resources. Most aquatic organisms depend on dissolved 

 oxygen to maintain growth and reproduction. 



(2) Heat affects the rate at which chemical reactions progress, 

 and it can speed up the formation of undesirable compounds or 

 change dynamic chemical equilibria. It also affects biochemical 

 reactions and can result in a more rapid depletion of the oxygen 

 resources. If sufficient heat is added, temperatures can be elevated 

 enough to sterilize the environment by killing all living organisms. 



(3) Environmental temperatures are important to the living 

 resources. Physiological processes such as reproduction, develop- 

 ment, and metabolism are temperature dependent. The range of 

 many species of fishes and the species composition of communities 

 are governed to a great extent by the environmental temperature. 

 Temperature anomalies also can block the passage of anadromous 

 fish, greatly reducing future populations. 



(4^ An increase in temperature can result in synergistic action ; 

 that is, the simultaneous effects of separate agents is greater than 

 the total sum of individual effects. Prime examples are increased 

 toxicity of some materials, increases in susceptibility of fish to 

 diseases, and increased virulence of fish pathogens. 



(5) Thermal pollution affects other aquatic organisms such as 

 the aquatic plants, the benthos, and the bacterial populations. In- 

 creased temperatures may reduce the numbers of species in the 



