[Illustration: _The Nansen bottle, shown being attached to a hydrographic wire, is one of the standard tools of oceanology. When a bottle reaches a desired depth, a sliding weight tips it upside down to collect seawater samples. Thermometers on the sides of the bottles record temperature. The device was designed by the Norwegian oceanographer and explorer, Fridtjof Nansen._ (_See photo on page 56._)] In order to evaluate the effects of these materials in the ocean environment, it is necessary to know many things. Just how much radiation is introduced? In what form? Where geographically? How are these radionuclides dispersed or concentrated physically, chemically, biologically, and geologically? What is the net result in each case now, and what will it be many years hence? These questions are not answered easily. There is, as yet, no satisfactory laboratory substitute for the open ocean. Research for the most part must be conducted at sea, where tests and measurements are difficult at best, and where results therefore are often suspect. Further, if we are to study the effects of man-induced changes in a natural environment, it would have been advantageous to have known the nature of that environment before the changes were introduced—which, by and large, in the case of the ocean we do not. So we must start with a contaminated environment and try to separate what we have put there ourselves from what would have been there anyway. It isn’t an easy task to make the physical and biological observations that will make this distinction. Table II CONCENTRATION AND AMOUNTS OF 42 OF THE ELEMENTS IN SEAWATER Element Concentration Amount of element in Total amount in (mg/l) seawater (tons mile³) the oceans (tons)