Li3 RADIOECOLOGY DISTRIBUTION OF ENVIRONMENTAL PLUTONIUM IN TKP TRINITY SITE ECOSYSTEM AFTER 27 YEARS Thomas E Hakonson and LaMar J Johnson Los Alamos Scientific Laboratory Los Alamos New Mexico Abstract Jesuits are presented for a radioecological survey of the Trinity Site environs where the world's first July 1945 atomic bomb was detonated The temporal behavior of the low environmental levels of the plutonium produced by this detonation are discussed ata fr°m ch s study were compared with similar data obtained in the Trinity Site environs nearly 20 years ago rh ™ojnr rfirnrr which was observed was__an ncreas_ed migration of P„ -fnt-p Concentrations of Pu in vegetation and rodents were too low to make valid comparisons Introduction eW °81CaJ wav nfT investigation of plutonium was initiated- in the fallout pat£ way of Trinity the first nuclear detonation which occurred on July 16 1945 in southern New Mexico Trinity Site was especially interesting as a study area because of the aged nature or the radioactive debris distributed in the area xeric rini sJr °f lntereSt t0 gather ecological data on plutonium in the xeric Trinity Site environs to compare with similar data being gathered in ern ew Mexico6 eC°SySteiES at the Los Alamos Scientific Laboratory in nor h- The data presented in this paper were obtained ffora samples gathered durin one sampling period in the Trinity Site environs on September 27-28 1972 The° primary objectives of this effort were to survey the plutonium content'of'a few ecosystem components and to measure the field gamma radiation intensity as a frOE1 r°Und Zer° GZ S0Ee 27 years after the detonation y facilitate the design of more intensive studies J Methods and Materials Triaity Site» a fenced area immediately around GZ is located in the semiarid northern portion of the Tularosa Basin about 40 miles of Socorro New Mexico on the White Sands Missile Range Fig 1 A general description of Site «nXh8r J rllmate vegetation and mammals of the area around 2Trinity J fcite c a n b e f o u n d m v a r i o u s r e f e r e n c e s » SW A transect was established along the reported fallout pathway of the ZilZlil Vr the det0naci0n 1 utilizing maps constructed by scientists in 1948 5 Nine sampling locations were established on the transect two in the GZ area and the remainder at 8 km in­ crements to a distance of about 56 km from GZ CaFifornla One soil core was taken at each location with a disposable 30 cm section of 2 4 cm diameter polyvinyl chloride pipe The pipe and contained core from 242 1943 felloul zone perimeter C O 4 1 i 3 0 1 Vs T «irr NCXICO White Sonde Missile Range k % New Mexico 61 __Trinify Site ground zero Fig 1 Sampling transect utilized for the radioecological resurvey of Trinity 1 each station was sealed in a plastic bag frozen on return to the laboratory and sectioned into a 0-2 5 cm 2 5-7 5 cm and 7 5-30 cm segment I A sample of the most abundant forb grass and shrub tree species was col­ lected where possible and was individually sealed in plastic bags Samples in­ cluded the above-ground portions of the grasses and forbs and the terminal leaves and stems of the shrub tree species Dust on the plant surfaces was not removed prior to analysis Rodents were collected with peanut butter baited snap-traps and were bagged and frozen for later dissection Tissues analyzed for plutonium included lungs liver hide and carcass skeleton and skeletal muscle Care was taken during the dissection to avoid cross-contaminating the soft tissues with hair from the pelt i Trinitite the fused soil material formed by the intense heat produced bN the detonation was also collected to determine its plutonium content and to identify the gamma emitters present Analytical procedures for plutonium included a combination of wet-dry ashing techniques utilizing a muffle furnace and HNO -HF solutions followed by ion exchange column separation of plutonium electrodeposition and alpha ray spectroscopy for both 238pu ancj 23ypu p g minimum sensitivity of the alpha counting system based upon background counts during a 24 hour period was 0 03 pCi 238pu or 239pu sampie 0 05 All soil and vegetation samples contained sufficient Pu and or were of sufficient mass to reduce the relative counting standard deviation on each sample to less than 25 percent 1 a However the generally low Pu content and small mass of certain rodent tissues resulted in relative counting standard deviations of as much as 100 percent The standard errors associated with the rodent data presented later reflect this fact 243 I Direct measurement of radiation in t-ha Ludlum Model 12S Count Rate to detector for in S e v „n 'l ™S accomPlished with a utilizes a Nal II scintillation meat's readout was clflibrated to rays During the survpv t-ho -t rssding with ground surface and the observed rate noted3S £ ab°Ut radi t fe meaaurements-6 values obtained from these TLD mfterlf1Tb independent of radiation en nd 3 60 inS'CrU' Co gamma above Dosimetric la™ be »»' Provldeda basis for the correc therein tion or normalization of the Ludlum'Model 12s1 tion assumed uniform photon spectral dlstrib r normalizan of TLD-determined expose rates to the °bservad erage ratio exposure rates to the survey meter measurements was 0 70 Results and Discussion The Pu content 239PU and 238Pu of sii tance from GZ is presented in Table 1 deconatlon 1'11 35 3 function of dis- °' ecos '3 ffi components collected In the fallout zone of the Trinity Kilometers Frcn Ground 7 rro GZ — CI Vnlt_ A1 1 4 l 32 2 an V 311 331 213 125 746 175 295 668 116 34 3 0 5 1 0 60 1 9 43-3 56 4 344 3 4 278 20 62 10 1442 69 35 15 2 5 4 1 19 4 7 6 5 2 3 1 5 43 27 3 4 1 2 30 29 _5 4 5 2 7 50 45 2 8 1 1 4 7 1 6 4 Soils fCl g dry 0-2 5 ca 2 5-7 5 en 7 5-30 cn 254812 262720 61858 36 36 23 434 0 6 6 Vegetation fCl g wet Grasses Forba Shruba treei 768 169 73 6 2 2 4 9 5 11 28 5 4 0 60 2 2 26 Rodents fCl g vet Liver Lungs Bide Carcass Ko of nappies 12 11 6 4 2 2 25 19 6 8 0 96 3 2 1 2 4 11 8 1 5 6 2 3 15 8 0 5 1 3 0 3 4 1 3 0 2 0 2 0 4 2 3 0 3 1 7 3 3 0 75 0 84 1 6 2 0 3 8 2 5 Species comprising the vegetation and rodent cables are given In the text Parenthetic value represent the standard error of the determination Carcass Includes skeleton and skeletal muscle type of grass fort b 7® concentration grid ItsliZAZ found at every sampling Nation SporohMm c station W C f rt reo su™arized according to the Cral 1 T °f the lantS £re Crass species included Tridens pulchellus hS i nT lfl s WerS provide some basis for viewing Pu f°rb IIw5- £irr7rL' cm tffrlsfsmiref 1 SrabS 1d £°rb tne shruo tree species which included 244 « S°1 UdId Aohanosteohus les Atriplex canescens Larrea tridentata Lycium Anderson Jun perus monosperma and Rhus macrophylla were generally greater than 60 cm tall '— The Pu data for rodent tissues fCi g wet were also summarized without regard to species because the inadequate number of samples did not permit a species comparison and because the species composition of the catch changed with distance from GZ Species caught included Perognathus flavus Citellus spilosoma Peromyscus maniculatus» P_ truei Onychomys leucogaster Neotoma mexicana and Dipodomys ordi The Pu concentrations in many of the soil core segments Table 1 wer significantly above background Levels in GZ soils were as much as lO1 times higher than the 10-100 fCi Pu g which has been reported for several New Mexico area soils 7 A maximum of about 260 000 fCi Pu g was observed at GZ in both the 0-2 — cm and the 2 5-7 5 cm core segments The maximum concentration in non-GZ soil 1442 fCi g was measured in the 0-2 5 cm segment from the 56 4 km sampling station The Pu data for soils from the GZ and 0 1 km stations cannot be compared' with the data for the remainder of the transect because the area around GZ was mechanically disturbed shortly after the detonation in an effort to reduce sur- face radionuclide contamination Ground Zero for example was covered with at least 15 cm of uncontaminated soil and the area around the 0 1 km station was scraped to remove the Trinitite lying on the ground surface The high Pu con­ centration in the 0-2 5 cm segment of the GZ soil sample Table 1 indicates either 1 the overburdening was not successful 2 that the covered Pu had migrated to tne soil surface or 3 that the overburden had blown away over the last 27 years thus exposing the contaminated soil The Pu concentrations in the 0-2 5 cm segment generally increased toward the distal end of the sampling transect and reached a maximum at the 56 4 km station Olafson et al during efforts to map the fallout zone from Trinity also noted that the highest Pu concentration in soils vegetation and small —v mammals outside the GZ area occurred about 45 km from GZ The vertical distribution of Pu was relatively uniform in most of the core samples from GZ to the 24 1 km station This suggested that Pu which was init ally deposited on the soil surface as much as 27 years ago had migrated at least 30 cm into the soil profile On the other hand the Pu in soils from distances greater than 24 1 km was increasingly concentrated in the upper 2 5 cm Olafson et al ® and Olafson and Larson9 reported that the Pu in Trinity area soils about 20 years ago was almost exclusively confined to the top 2 5 cm of soil Many factors could account for a difference in the rate of vertical migra­ tion of Pu in soils including differences in the chemical and physical form of the Pu and or differences in the chemical physical and biological makeup of the environment 0 The Pu concentrations in grasses were consistently elevated with respect to similar measurements in other areas of New Mexico 1 9 On the other hand the Pu concentrations in forb and shrub tree samples were generally indistinguish­ able from worldwide fallout Pu levels in New Mexico vegetation which measure about 1-5 fCi g wet sample 1 7 The Pu data for grasses as a function of dis­ tance from GZ generally followed the pattern which was observed for the 0-2 5 cm soil core segment Table 1 The maximum Pu concentration in grasses 76$x fCi g wet was observed at GZ and decreased to a minimum of 5 1 fCi g at the 24 1 km station Pu concentrations in grasses then generally increases with distance 245 The Pu data for rodent tissues in Table 1 show a considerable variability Sources of this variability would include among other things species differ ences the low Pu content of the tissues yielding generally poor counting statis tics and an insufficient number of samples In general rodent lungs had the highest mean Pu concentrations and exhi- J bited a pattern with distance from GZ that was similar to the 0-2 5 cm layer of soil and the grass Lung deposition of Pu suggested that resuspension of soil may be an important mechanism in the biological redistribution of Pu Other investigators have noted high lung concentrations in small free-roaming ii i mammals The activity ratios 239Pu 238Pu for all sample types are summarized in Table 2 The ratios for the 0-2 5 cm and 2 5-7 5 cm core segments averaged 19 and 18 respectively while the 7 5-30 cm segment averaged 9 The mean values for vegetation were about 8-12 and about 0 5-2 for rodent tissues The sign ficance of the decreasing 239Pu 238Pu ratio from soils t02 Set Cl° tissues is not clear at this time It may indicate that 238Pu in the Trinity environs is more mobile than 3yPu Table 2 The 239Pu 238Pu ratio ir seme ecosystem compo­ nents collected in the fallout zone o the Trinity detonation »Pu 238 u Nc Saxoies Soils 0-2 5 era 2 5-7 5 cm Remainder 19 18 9 0 3 2 1 7 2 3 9 7 12 7 6 5 0 2 0 1 9 1 6 13 10 9 6 Vegetation Grasses Forbs Shrubs Rodents Liver Lungs Bide Carcass S E 0 44 1 0 1 8 1 7 0 10 0 28 0 89 0 65 5 6 16 20 standard deviation ™ number oi samples The Pu content of three samples of Trinitite from GZ measured 32 nCi g 1 5 nCi g and 1 2 nCi g with an average 239Pu Pu ratio of 21 0 8 1 These Pu concentrations are about an order of magnitude higher t an centrations in GZ soils The 241 concentrations of the Trinitite samples measured 0 5 nCi g 0 024 nCi g and 0 033 nCi g Preliminary data fron -J ecological studies at Los Alamos1 indicated that Am may enter biological systems to a greater degree than Pu and consequently may be o equal o greater importance than Pu as a contaminant in natural e systems A wide variety of additional radionuclides were identified in Trinitite including 133Ba IM 155Eu 60Co 137Cs and 90Sr-90Y The average gross gamma radiation measurements obtained outside the GZ area were not significantly different from the measurements tions or what could be considered to be the natural background for the central New Mexico area 7 Measured values of radiation also fall witl 246 asSS r™-2 «ssisa ss j there has been an increased migration of Pu into the soils since the last 4 S e made abOU 20 years ag°Concentrations of Pu in aU t™ r t p of the present study were generally similar to the findings of lT£l l££ ite- H°WeVer' thG limited tTlrZ ade-aCa sample 20 vear samples analyzed In the -d -» refined studiL Literature Cited 1 Hakonson T E J W Nyhan L J Johnson and K V Bostick Lg M-m Alamos 1973 Eco- °f radioactlve materials in waste discharge areas at Los Alamos Scientific Laboratory Report LA-5282-MS Basil' LFm -943 EcoloSical distribution of mammals in the Tularosa Basin New Mexico Contr Lab Vert Biol Univ of Michigan 20 1-24 2' V 3' J L Leltch' W F- D nn J- W Keel J H Olafsor E E Held™ KT T to the 1 948 v w rSS' A • Bellamy- 1«1 Alpha activity due Univ of1 £ iff v detonation at Trinity Alamogordo New Mexico Univ of -California Report UCLA-108 4 Zonation of vegetation within the Tularosa Basin New wi Jf ™' New Mexico The Southwest Naturalist 1 2 49-680 5' 1951' rt ' '-1 Nummary of the radiological findings in animals from ReporruCLA-m 3 °f 1947' 1948' 49 195° Un±V- °f Cal«°tnia — 6 Scientiff f 197f' EnviTronir'aatal monitoring in the vicinity of the Los Alamos cientific Laboratory Los Alamos Scientific Laboratory Report LA-4970 7 L' J 1 I2' L°S Alamos land 2 eas environmental radiation 1972 C Los Alamos Scientific Laboratory Report LA-5097-MS 8 toni ™ JrtH i N± hita and K H Larson- 1957 The distribution of pluV £he soil® of central and northeastern New Mexico as a result of the atomic bomb test of July 16 1945 Univ of California Report UCLA-406 9' mpnffT n J H and K H Larson« 1961 Plutonium its biology and environpersistence Univ of California Report UCLA-501 10 review2' j' f' n Pdut onill 1 in soils and uptake in plants a review J Environ Quality 2 1 67-70 11 Larson K H 1958 12' Unpublished data Cited in reference 9 Colorado Fl1973' adioacol°gy of some natural organisms and systems U3 Pr°8rCSS ReP°rt °n Contract ATai-1 -1156 C°-isSi°» M ra HUllooTLyfN 011 h 8™ ' 247 '