jumped tenfold since tetraethyl lead was first used in gasoline 45 years ago. 

 While some 4,000 to 5,000 tons of mercury are estimated to enter the oceans 

 annually by natural erosion, man introduces an equivalent amount. The ele- 

 ment accumulates in fish and plants. 



One of the most abundant of the manmade pollutants in the sea is DDT, 

 which is transported in the form of agricultural run ofT. Like many other 

 manmade substances DDT does not degrade readily in water; nature's 

 natural decomposing forces cannot break it down. Some scientists believe 

 that two-thirds of the 1.5 million tons of DDT produced by man may still 

 be adrift. Moreover, DDT concentrates in the food chain and today is 

 found in all oceans and all marine organisms as well as man. 



Other forms of environmental degradation result from man's activities. 

 Physical modifications, such as dredging and filling, construction of dams, 

 diversions, jetties, groins, hurricane barriers and heavy waste disposal, alter 

 natural processes and cause pollution. Heating of coastal waters by industry 

 decreases the oxygen carrying capacity of water, adversely affecting marine 

 life. Seabirds catch their necks in plastic soft drink holders; plastic bags 

 clog water intakes; lost synthetic fishing nets which do not sink or disinte- 

 grate continue to catch and destroy fish for years. 



Effects of Ocean Pollution 



The current effects of marine pollution are harbingers of the serious 

 problems which lie ahead if it is not curbed. Domestic sewage disposal ha> 

 already spoiled large areas of U.S. shoreline, sections of Lake Erie's accessi- 

 ble shoreline are now off limits to swimmers and fishermen; many estuarine 

 areas in other parts of the country face similar restrictions. 



The long-range consequences of pollution are visible in the Great Lakes, 

 especially Lake Erie. The lake is suflFocating to death as a result of man- 

 made pollution over the past 50 years. By dumping detergent phosphates, 

 fertilizer nitrates and other pollutants into the lakes, an enormous growth 

 of algae has been generated consuming the oxygen and choking off other 

 life in the process. In five decades the lake has aged the normal equivalent 

 of 15,000 years. Though the cause is not completely known, similar condi- 

 tions are found today in the shallow Baltic Sea where the dissolved oxygen 

 has decreased in lower depths and dissolved phosphorus has increased. 



The hazards to animal life are severe. The shellfish in an estimated 1.2 

 million acres, or 8 percent, of the Nation's shellfish grounds have been 

 declared unsafe for human consumption. Fish kills in the United States 

 resulting from identifiable pollution sources, principally in fresh water 

 and estuarine areas, are mounting. In 1968 alone, an estimated 15 million 

 fish were killed by pollutants, 31 percent more than the previous year. 

 Municipal sewers and treatment plants, industrial waste and transportation 

 accidents were the main causes. In 1969, a chemical spill in the Rhine River 

 killed an estimated 40 million fish. 



The long-range consequence of many pollutants is not clear. The effect 

 of the ocean's increased lead content upon marine life is unknown, as is 

 the long-range impact of the accumulation of solid smoke particles in ocean 



22 



