333 



otherwise visible waste materials which have obvious pollutional im- 

 plications, but by far the deadliest pollutants are those which are 

 invisible and often unsuspected until the damage is done. These pol- 

 lutants can be found only by the most delicate and sensitive tests and, 

 even then, the presence of some highly dangerous materials or condi- 

 tions can only be inferred by indirect evidence. 



MATERIALS AND CX)NDITI0NS WHICH DEGRADE THE ENVIRONMBNT 



One of the major constituents of municipal and many industrial 

 wastes is decmnposable organic material. Such materials consist pri- 

 marily of carbohydrates from plants and paper, proteins from animal 

 matter, and miscellaneous fats and oils. The decomposable organics 

 are not necessarily deterimental by themselves but exert a secondary 

 effect by reducing dissolved oxygen in the water. The level of dissolved 

 oxygen is one direct index of the healthiness of the system. High levels 

 are generally indicative of a healthy system which will support a 

 diverse biota and multiple use. The lower the concentration of dis- 

 solved oxygen becomes, the sicker the system is, and the less desirable 

 it is for habitat or use. 



Another class of materials, primarily organic, that can have con- 

 siderable impact on the estuarine ecosystem are the flesh-tainting 

 substances. Generally these materials are contained in industrial waste 

 effluents and they result in offensive tastes, odors and colors of fish and 

 shellfish. 



The salts of heavy metals are fairly soluble and stable in solution. 

 Consequently, they will persist for extended length of time. Many of 

 these are highly toxic to the aquatic biota, and since many marine 

 organisms exhibit the ability to accumulate and concentrate sub- 

 stances within their cell structure, the presence of these metals in small 

 concentrations can have deleterious effects. 



Aquatic life forms require trace amounts of some minerals and 

 vitamins for growth and reproduction. Elimination of such materials 

 from the environment or their reduction below minimum levels can 

 limit the growth and reproduction of some biota. Conversely, an 

 oversupply of all necessary trace mineral salts and vitamins can stimu- 

 late growth ; providing satisfactory conditions of temperature, salinity, 

 and dissolved oxygen also exist. An oversupply of inorganic nutrient 

 salts, such as those of nitrogen and phosphorus, may be associated with 

 drastic shifts in the composition of the aquatic community. 



One of the many unfavorable effects of municipal and some indus- 

 trial wastes is the contamination of the receiving environment with 

 bacteria, viruses and other organisms of public health significance. 

 Pathogenic organisnns.^ especially those from the intestines of warm 

 blooded animals frequently persist for sufficient periods of time and 

 distance to pose a threat to the health and well-being of unsuspecting 

 water users. Secondary chances of exposure to these organisms exist 

 through the contamination of shellfish which can be harvested for food. 



Among the waste products that are frequently introduced into the 

 estuarine environment are some directly toxic to marine organisms. 



Toxic materials may exhibit a short catastrophic impact or a more 

 subtle long-term interference with growth and reproduction processes. 

 The end result is to create a biological desert in which no organism 



