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SAMPLING AT SEA. Lamont Geological Observatory's research vessel Vema samples seawater at various depths. Water is brought to the surface in the barrel and emptied into a processing tank where the carbon dioxide for C 1 4 dating is drawn off for testing in the lab. Here a Vema technician shows how the barrel's tripping system works
Fallout May Solve Sea Mystery Radiochemical studies of nu clear fallout could prove useful too! to measure mixing time of sea Today, scien tists have but a fair idea of the rate at which ocean water mixes Analytical horizontally and Chemistry vertically. To get a better picture would not only add to the scientific storehouse in this IGY-conscious world but could mean putting it to practical use. If circulation studies would show, for example, that water far below the sur face takes a very long time to reach up per levels, then deep water might be the spot to dispose of radioactive waste —waste will have decayed before it floats to the surface where it might endanger human life. T. T . Sugihara of Clark University's department of chemistry suggests that ACS NATIONAL MEETING
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MEANWHILE BACK AT THE LAB. This counter filling assem bly for carbon dioxide at Lamont's geochemistry laboratory at Palisades, N . Y., is used to determine the specific activity of sample carbon, as part of the carbon-14 analysis project of the U. S. IGY oceanography program. Here a technician transfers C 0 2 from storage to a sample counter
radiochemical studies of fallout fission products in the ocean promises to be a new a n d possibly powerful tool to measure mixing time of the sea. He told the Symposium on Radiochemical Analysis sponsored by the Division of Analytical Chemistry that he and two colleagues have worked out a way to isolate strontium-90, cesium-137, cerium-144, and promethium-147 from ocean waters. Those working with him on the proj ect are E. J. Troianello, also of Clark, and V. T. Bowen, Woods Hole Oceanographic Institution. • Top W a t e r Mixes Quickly. The top 100 to 200 meters of the ocean in most areas are mixed rapidly by wind and waves. Water below, however, is much older; that is, it was at the surface years ago. Sugihara's group thinks sur face waters at a given site will have the same concentration of strontium-90. But deeper waters should contain much less. (Cerium-144 and promethium147 are colloidal at p H 8, and their movement in the sea may differ from that of strontium-90 and cesium-137.) The amounts of radioactivity in sea water are very small, Sugihara states. Using the most sensitive detector for
activity, 50 to 100 liters of water must be processed to get as much as one count per minute. To get reasonably accurate measurements, a way had to be found to separate the elements in question from the large bulk of sea water, and in a relatively simple step, according to Sugihara. And since t h e men wished to detect very small amounts of radioactivity, they had to find a trick to keep the separated ma terial from being contaminated b y radioactivity. "Both these objectives have been satisfied for the fallout radioactivities in question," says Sugihara. First step—separating the elements from large volumes of sea water—calls for precipitating strontium with calcium as the mixed carbonates. Coprecipitating cesium with potassium sodium cobaltinitrite comer next. Carrier-free in the ocean, t h e rare earths cesium, cerium, and promethium are carried on ferric hydroxide for t h e analysis. The second series of steps frees the elements of unwanted con tamination. Strontium carbonate is precipitated repeatedly in the pres ence of ethylenedinitrilotetraacetate ion ( E D T A ) to free it of the bulk of cal cium. More calcium comes out b y
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the precipitation of strontium nitrate. > Scavenging Removes Contamin a n t s . Barium-chromate-ferric hydroxide scavenging removes radiochemical contaminants, such a radium, lead-210, a n d t h e actinides. T h e strontium-90 present is measured indirectly by isolating a n d counting its daughter n u clide, 64-hour yttrium-90. Cesium gets freed of most of the potassium and sodium in the mixed cobaltinitrite precipitated by precipitation of cesium silicotungstate. After converting the latter to the perchlorate, a phenol-sulfonic cation exchanger absorbs it. Potassium-40 and rubidium-87 are the chief radiochemical contaminants. After washing with 0.3M hydrochloric acid, rubidium and lighter alkali metals show up on bands well apart from t h a t of cesium. In the case of the rare-earth fraction, 10 mg. each of cerium ( I I I ) , neodymium, a n d samarium are added to a solution of the ferric hydroxide precipitate. Iron stays in solution by precipitating the rare earth fluorides. Scavenging with barium sulfate removes radium and lead-210. Anion exchange on Dowex-1 removes uranium and protactinium in concentrated hydrochloric acid; thorium in 7.5M nitric acid, Cerium is finally isolated in pure form as ceric iodate. Promethium is obtained by a cationexchange separation on Dowex-50. Positions of the samarium and neodymium bands define the promethium band. Promethium is carried on neodymium for counting purposes. Sugihara lists typical yields from these procedures: strontium, 7 0 % ; cesium and cerium, 60%; and p r o methium, 8 0 % . T h e promethium yield is estimated by averaging the yields of neodymium and samarium. A cylindrical, flow Geiger counter, V 4 inch in diameter and 2l/2 inches long, does the counting for the tests. Its background inside 7 inches of iron and with anticoincidence shielding is about 0.22 count a minute. Yttrium-90 is identified by its characteristic halflife, and the others can be positively identified with a beta absorption curve. Sugihara reports t h a t t h e strontium-90 level in Atlantic surface waters is about 0.1 disintegration per minute per liter. And the corresponding cerium-144 activity measures about t h e same. T h e cerium-144 to promethium147 ratio is about three. Cesium samples have not yet been counted.
Pectin Plugs Cause Wilts Wisconsin researchers shed light on mechanism o f v a r i ous fungus diseases of tomatoes / b a n a n a s By producing wilt diseases in ACS NATIONAL p l a n t s , f u n g i MEETING cause millions of dollars worth of damage a year. Food Chemistry These losses could be reduced if there were a basic understanding of how fungi operate. At stake is the possibility of eradicating tomato wilt, a severe problem in many sections of the U. S. and Europe. Also possible is the prevention of oak wilt, a destructive disease throughout the Midwest, and Panama disease, one of the greatest hazards in the growing of bananas. Insights into how these disease-producing fungi behave in plants are provided by Mark A. Stahmann and John C. Walker of the University of Wisconsin. As Stahmann told the ACS Division of Agricultural a n d Food Chemistry, their research so far has been focused mainly on tomato wilt. In this fungus disease, the lower leaves of the plant gradually turn yellow, wilt, and die. The plant is stunted and becomes permanently wilted. T h e Fusarium fungus, a cause of wilt, enters the plant through the roots and passes into the vascular system. There, the fungus produces two enzymes, pectin methylesterase and pectic depolymerase. These enzymes, says Stahmann, hydrolyze some of the pectin in the vascular cell walls. The pectin is d e g r a d e d to a point where soluble fragments go into the vascular stream. I n this stream, the pectin fragments react with calcium or other ions to form pectin gels. These gels accumulate sufficiently to block the transport of water and nutrients to the upper parts of t h e plant. This blockage, Stahmann explains, causes the plant to wilt. Of the two types of enzymes responsible for t h e partial breakdown of pectin, the most important is pectic depolymerase. Pectin methylesterase alone causes very little vascular plugging and thus very little wilting. Fungi-produced enzymes capable of degrading pectin may be key factors in the biochemistry of Fusarium wilt of
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FUNGI DID IT. Tomato w i l t is caused by pectin gels that plug t h e conducting vessels of t h e plant and block off water and nutrients, says Mark A. Stahmann, University of Wisconsin. Cutting he holds at left has been wilted by fungusproduced pectic enzymes cotton, Fusarium and Verticillium wilt of tomatoes, Dutch elm disease, oak wilt, and other fungus diseases, Stahmann says. • Mechanism of Resistance. But why are certain plants resistant to wilt diseases and others are not? H o w is it possible, for example, that some tomato plants are immune to Fusarium wilt? T h e answer, Stahmann believes, is that resistant plants are able to reduce the amount of pectin-splitting enzymes formed by the attacking fungi. In a resistant t o m a t o plant, the amount of depolymerase secreted by t h e fungus is only one third that produced in a susceptible plant. In a resistant plant, some substance may be continuously produced t h a t is toxic to t h e fungus or may reduce enzyme formation. This resistance mechanism, Stahmann says, is closely related to the respiratory system of the plant. When the system is blocked by a respiratory inhibitor, such as 2,4-dinitrophenol, a resistant plant loses its immunity. Recent work at t h e Wisconsin laboratory suggests that P a n a m a disease of bananas is also caused by the forming of pectin plugs in the vascular system. Control of this highly destructive disease of bananas can best b e achieved, Stahmann says, by selecting and breeding resistant varieties, as has already been done successfully with tomatoes and other plants. • APRIL
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