40 



not evolved an ability to decompose or degrade them rapidly. We are still un- 

 certain as to their i>ersistence in the marine environuit-ut, but the available 

 evidence suggests that they would be fouud tor decades, perhaps centuries, even 

 it ail further additions to the environment couid be stopi>ed. Uil pollution is an 

 increasing threat to the marine environment because of our ever-increasing de- 

 mands for energy and the increased sea transport of oil in tankers. Mortality 

 of marine organisms, sometimes extensive, has been found wherever accidental 

 oil spills have been studied, and recovery from the high concentrations pro- 

 duced in these accidental spills may take months, years or decades depenaing 

 upon the amount of oil spiiied and how rapidly the oil is disi>ersed and diluced 

 to non-toxic concentrations. Domestic pouution consists of the natural products 

 of human metabolism and can be rapidly decomposed by natural marine processes. 

 There ai'e two critical problems connected with the disposal of domestic pollution 

 to the marine environment, however. 



First, in many of our estuaries the quantity which must be discharged exceeds 

 the receiving capacity of the body of water to which ic is added, and second, 

 many sewage ehiuents contain toxic materials from industrial additions or from 

 urban runoff. Proper treatment methods can remove most of these from the efflu- 

 ent, but they will remain in the sludge which also must be disposed of in some 

 manner. The disiwsal of solid wastes of our civilization also poses increasing 

 problems. Even though much of the solid waste is non-toxic, large quantities are 

 involved. Some of this material is being disposed of in our coastal waters, such as 

 the sewage sludge and dredging six>ils disposal in the New York Bight and other 

 areas. These substances have clearly caused deterioraiion of the environment 

 where they are dumped. Each of these categories of iK>llutants will be discussed in 

 greater detail below. 



First, however, it may be desirable to comment in general upon the term tox- 

 icity, which is difl5cult to define and not always well understood. Any substance 

 on earth is toxic if the concentration is great enough in the wrong environment. 

 For exuiaple, a characteristic of the marine environment is the salt content of 

 the water, but most marine organisms can survive only within a narrow range of 

 salinity. Estuarine organisms, accustomed to brackish water, may not be able to 

 survive in the open seat where the salinity is higher. Even pure water can be 

 considered toxic since marine organisms cannot sur\'ive in fresh water and man 

 cannot survive for long in pure water which is few inches above his nose. We are 

 all accustomed to temperature fluctuations, but organisms cannot survive in an 

 environment that is either too hot or too cold. The substances which are of the 

 greatest concern, however, are those which are lethal in concentrations of parts 

 per million (mg/1) or less. The toxic heavy metals, the chlorinated hydrocarbons 

 and i>etroleum hydrocarbons are toxic at these low concentrations, and it is be- 

 cause of this that they are of greatest concern. 



MARINE POLLUTANTS OF GREATEST CONCERN 



Heavy metals 



A list of eleven heavy metals which are toxic to marine organisms and which 

 are reaching the environment is considerable quantities is presented in Table 1. 

 All elements reach the marine environment in varying amounts as a result of the 

 weathering of the continents and their transport by the rivers to the estuaries 

 and ultimately to the sea. Many elements are also present in coal and petroleum 

 and are released in varying amounts to the atmosphere as we bum these fossil 

 fuels. Estimates of the rates of supply from these two sources are given in Table 1, 

 which also lists the toxic concentrations in sea water. A relative critical index is 

 computed by dividing the rate of sui)ply by the toxic concentration. Actually, this 

 index gives the volume of sea water (in cubic kilometers) which would receive an 

 annual increment of the element equal to the listtni toxic concentration. The con- 

 centration of the element already present in sea water is not taken into consider- 

 ation because, in some cases, the concentration is so low that it would not modify 

 the calculation, and in some cases the ab.solute concentn\tion in the sea water is 

 not accurately known. 



