ROOT UPTAKE PATHWAY RESUSPENSION EN CONTAMINATED AREAS Once radioactive material has been deposited upon soil, the main concern is to control subsequent resuspension, especially in dry, dusty areas. Whether or not the contaminating radionuclide remains in an original particulate form or undergoes chemical and physical transformations which result in its being carried by soil particles may have no particular biological consequence. Either form deposited upon the surfaces of plants becomes a source of contamination in the diet of gtazing animals. The mechanisms of resuspension and its consequences are discussed by other participants in this symposium. The subject of transuranic resuspension and the need for standards for controlling health effects from plutonium in soils is discussed in a recent treatise by Healy (1974). Optimum conditions for resuspension usually are found in arid, dusty environments, but such movement of contaminated particulate material ia not necessarily limited to those areas. In follow-up studies after the accident at Palomares, Spain, Tranzo (1968) called attention to the entrapment of plutonium by external foliage of agricultural crops harvested from contaminated soil. About one half of the contaminant could be removed by washing the foliage of tomato plants compared to from 73 to 95 per cent removed by washing fruit. Deposition on the surfaces of leaves and stems has been identified as the principal mechanism of plutonium contamination of vegetation collected from sampling locations around and adfacent to the Savannah River Plant which is situated in a humid area (McLendon et al. 1976). Some of this contamination could arise either from direct fallout deposited downwind of the source stack or from subsequent resuspension of contaminated soil. A study to measure resuspension during field preparation and planting of winter wheat at the SRP site was reported by Milham et al. (1976). Small, but detectable amounts of airborne plutonium averaged 210 fCi/m? at 7.6 m and 10 £Ci/m3 at 30.5 m distances downwind from the edge of the field under cultivation. The air at the tractor operator's face level contained 49 fCi/m?. The average concentration of plutonium in the 0-5 cm layer of «soil was 3100 fCi/g; estimated resuspension factors were of the order of 1078 m-l, Work by the Los Alamos group at the Trinity site in New Mexico showed that the horizontal distribution of plutonium in soit continued to be largely determined by the original fallout deposition pattern. The Trinity soil samples contained elevated amounts of plutonium in coarser size Fractions (> 105 pm) near ground zero and relatively larger amounts in finer fractions at increasing distances From ground Contamination of grasses within the zero (Hakonson and Nyhan 1976). fallout pattern, as a function of distance downwind from ground zero, generally followed the pattern observed in the 0-5 cm soil core fraction. The plutonium concentrations in grasses, lichens and mosses were consistently elevated above the levels observed in forb, shrub and tree This was considered to reflect higher entrapment efficiency samples. for grasses because of greater tissue surface areas (Hakonson and Johnson 1973; Hakongon and Nyhan 1976). 294 plutonium movement through plant Most soil-plant studies focusing upon n through this pathway. Concentratio roots indicate relatively low uptake from 107° to 107 ranged soil potted in grown ratios for plants ium, view of the long half-life of pluton (Plant Panel 1975). However, in concerning the extent to which ons questi g naggin with d plague one is this biologically available through the transuranics will become more indicat ing Some evidence already has appeared pathway with passing time. Am in (or mobility) of 238pu and an increased relative availability 1976; Hakonson and Johnson 1973; given situations (Essington et al. Romney et al. 1975). in between the amounts of plutonium It is difficult to differentiate and superficial contamination. uptake tract to utable attrib vegetation uptake made to accomplish this by pot Attempts, therefore, have been ltered, glasshouse conditions. experiments conducted under air-fi from the obtained from soils collected Table 3 summarizes some results soil and is made of the Pu/Am ratio in aged fallout areas at NTS. Use for comparing data (CR) ratio n tratio concen the plant samples and also The term, CR, is a conditions. representing field and glasshouse ' the activity/g. Plant from ared calcul ratio n simple concentratio activity is divided by activity/g. soil. For the field data the soil soil surface layer; the glasshouse that contained In the 0-5 cm h not, blended, potted soil, We are ghly thorou on based is ty activi because the conditions in the two systems therefore, comparing the same feed much deeper in the soil; roots of field-grown plants should What makes this field data most certainly below the top S cm layer. 0-5 cm soi] Pu/Am ratio more nearly useful in Table 3 is that the the endable material deposited on reflects that ratio for the resusp between the plutonium exists ence differ erable Consid leaf surfaces. out that tested. We should also point contents in the different soils values obtained from many CR and ratios l overal are the field data values are (n > 40) while the glasshouse samples analyzed from the field data are important findings from these The ates. replic six of means tion ratios for field soil and vegeta the similarities of the Pu/Am of principally a superficial source samples which we believe shows In addittor, the 0 field conditions. contamination on vegetation under to 10 107" ium in the field ranged from calculated CR values for pluton tests through the uptake pot our from ed obtain compared to 10-6 to 10-3 are ratios in pot-grown vegetation root uptake pathway. The Pu/Am Am indicating uptake of soit, otted the in those much lower than ,. Other data from these tests 9-240p than s amount r greate in much nds that synthetic chelating compou (Romney et_al. 19768 have shown increase to soil significantly (Pp .05) added agents lation acitdu and . root uptake of these transuranics