eee ee SE j. J. KORANDA ND 3 Cactus Crater (Table 1) does not appear to be of ADAMs, related to the current level of tritium in the soil conclusion urce of the water (509 T.U.) beneath that plant. Because the total loose water of a woody stem may oil samples aLOW and contain water that is not involved in the current uanspirational stream, the loose-water tritium in nuclear he Nevada value for wood is not expected to be in equilib- “ent in the nd moves physiolog- rum with soil-water tritium levels. However, the loose waterofthe leaves of the Messerschmidia tree at Cactus Crater contained 442 T.U. which is within the range of expected equilibrium with the soil-water tritium (509 T.U.) indicated by experimental studies. The variation in the boundtritium content of exhibit a the Cactus Crater area within 30 ft of each other ~- .p to inter. -9. These the Afesserschmidia and Scaevola trees growing in isno doubt related to the usual variation in soil moisture conditions (whenever they are considered micro-topographically). ) with the tration of cted in a The high tissue-boundtritium values of plant amples at Cactus Crater indicate that not only content of is tritium present under the current environmental conditions, but also that it occurred in n fallout ation site ly bound higher concentrationsin the available soil water in periods preceding this survey and subsequent to the detonations. The higher level of bound stonation ritium in the inner growth rings or older wood cimen or ofMesserschmidia indicates greater concentrations at earlier times, even if exchange mechanisms are considered. The tissue-bound tritium content of the Cactus Craterlitter samples, when compared to the tissue-boundtritium values for grecn leaves from the sametree,also indicates a sin their )2-15 months. yorted in Table 4. aalysis of es show varying concentration of tritium during the general, e sample Sinceit mples in ted with On Engebi and Sandildefonso Islands, loose water in plants and the soil had a low tritium content also. Previous to the sampling, however, available water must have contained more tritium because tissue-bound tritium levels are as much as thirty times (Scaevola litter) the current loose soil water. ie that in samples Because of the low level of tritium in the available soil water in the presence of the large tritium aterials, water of level of sources boundin thesoil, the levels occurring in the organic matter as tissue-boundtritium seem to be anomalous. The following sequence of events should explain the conditions described iced an er of the te loose- above. The tritium levels in the soil water will veadily increase if it is » ‘ moving through the 0 T.U.) — wil rapidly, as it would conceivably be in the 1455 rainy season. After heavy precipitation and in very porous soil materials such as coral sand, rainwater moves quickly through the soil profile and washes the shallow root zones of the atoll plants, lowers the loose-water tritium content, and leaves it with the same tritium content as the rainwater. The shallow root system of Messerschmidia was described by Kenapy@® who found that a 4ft high tree had lateral roots which extended 60 ft from the crown within 2-6 in. of the surface of the ground. Becausé the plant absorbs large quantities of water daily, the loose water of the leaves will quickly adjust to the low tritium content of the new soil water, while the tissue-bound tritium of the same plant confirms that previously, tritium was more abundantin the waterofits root zone. BLUMENsTOCK and REx"!”) give an average value of 6.93in. of rain on Eniwetok Island for August which wasthe time of samplecollection. This would account for the lower loose-water tritium content in soil water at this time. In Table 3, the tritium analyses of samples collected on four other islands on Eniwetok Atoll are reported. These islands have been contaminatedbyclose-in fallout which contained large particles. Like the other islands, a large source of tritium is present, bound in soil materials. Also the loose soil water has a lower tritium concentration, and loose-water tritium values in plants, except for coconuts, were generally between 50 and 150 T.U. Higher levels were present in the tissue-bound tritium of the plants. The elevated tritium concentrations in the coconuts from Japtan and Igurin Islands would indicate that the tree had been exposed to water of much higher tritium concentration during the formation of the coconut. Thetritium content of water samples collected at Eniwetok Atoll is given in Table 5. Because of the frequent exchange of the lagoon water with the open sea and the vigorous mixing of the lagoonitself, the water in the lagoon is apparently uniform in its tritium content from surface to bottom. Von Arx"#)estimated the exchange of Bikini lagoon water with the open seas as once every 13-39 days depending upon the season. In spite of the frequent exchange of the lagoon with the open sea and the occurrence ofintralagoon mixing, there is a local concentration of