knowledge has emerged from pollution studies. For example, the importance of 

 atmospheric transport of organic materials from the continents to the oceans was 

 acknowledged following studies on the dispersal of DDT and the polychlorinated 

 biphenyls. The prevalence of methylated species of metals and metalloids in sea- 

 waters, sediments, and organisms was recognized from investigations that evolved 

 from the methyl mercury poisoning epidemics in Japan. 



Some of the concepts that emerged duringthis period have guided many pollution 

 studies and have provided stepping stones for developing strategies for the disposal 

 of wastes in the sea. Several of these are considered here. 



Bioaccumulation 



Some species of organisms have the unique ability to extract from their environ- 

 ment and concentrate polluting materials that can affect their own health or the 

 health of the organisms that consume them, including human beings. 



The concentration factors for marine organisms, the ratio of the concentration of 

 a given species in the organisms on a wet weight basis to the concentration in sea- 

 water, can rise to levels of hundreds of thousands. For example, ruthenium, one of 

 whose radioisotopes is involved in the laverbread story, has a concentration factor 

 for phytoplankton on the order of 200.000 ( Lowman et al„ 1971 ). As a consequence 

 of such enrichments, biological transport is an important factor in governing the 

 distribution of some elements in seawater. Lowman et al. indicate that the diurnal 

 vertical migration of organisms, fecal pellet production, moulting, and death have an 

 overall effect of moving biomass from surface to deeper waters. For pollutants that 

 are bioaccumulated, the dispersion by vertical transport, especially in highly pro- 

 ductive waters, can result in their rapid dilution. On the other hand, such mobiliza- 

 tion can carry pollutants to the benthos where they can impact upon the communi- 

 ties therein. 



Residence Times 



It is often essential to know the average period of time that a substance spends in 

 one of the reservoirs of the marine environment the water, organisms, and 

 sediments, for example — in order to predict the fate of pollutants. The concept of 

 residence time gained momentum during the initial considerations of the disposition 

 of artificially produced radionuclides in the oceans. The marine environment was 

 envisaged as consisting of a number of reservoirs or boxes, various water masses, the 

 phytoplankton, and so on. The transfer of materials from one reservoir to another 

 was assumed to occur through first order kinetics (Craig, 1957). 



Of special interest is the concept of biological residence time or half-life. Experi- 

 ments to determine half-life can develop relationships between an organism and the 

 environmental concentration. There is a wide spectrum of biological half-lives. 

 Smaller marine organisms, including phytoplankton and zooplankton, have biologi- 

 cal half-lives on the order of hours ( Lowman et al.. 1 97 1 ). For methyl mercury in a 

 human being, the value is about 90 days. Values of years or decades might be 

 expected for transuranics in human bone. Knowing a biological half-life for a sub- 

 stance and estimating future exposure levels can make possible predictions for future 

 body burdens. 



Studies of the association of a pollutant with a reservoir, be it an atmospheric wind 

 system or a water body, have emphasized the widespread dispersals of a pollutant in 

 the marine environment and have provided techniques to calculate residence times. 

 A pollutant may be injected into the environment in one country and impact upon 

 another, perhaps even in another continent. Part of the DDT sprayed upon agricul- 

 tural crops in Africa is transported by the northeast trade winds to the Caribbean. 

 Radioactive debris from the explosion of a Chinese nuclear device in May 1965 was 

 detected at sampling sites in Tokyo and Fayetville, Arizona, during two circum- 

 navigations of the earth. The average velocity of the wind transport was about 16 



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