338 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



replicates were used to determine soil chemical changes at various times during the 

 180-day duration of the study. 



After 50 days of equilibration, the pots were transferred into a water bath located in 

 a glasshouse. A 1 -cm-thick sheet of glass fiber was placed on top of the soil surface to 

 prevent the soil particles from adhering to lower plant portions during irrigation. Two 

 Bahia grass seeds were placed in each of three holes, cut in the fiber equidistant from 

 each other and the pot perimeter. On the 70th day, the plants were tliinned to three per 

 pot, one for each hole, and watered with deionized water as required. The plants were 

 chpped at the 100th, 130th, and 180th day after equiUbration. This gave a plant growth 

 time of 50, 30, and 50 days for the first, second, and tliird clipping periods, respectively. 

 The plants were clipped 2.5 cm from the glass-fiber surface. They were then cut into 

 shorter pieces, placed in paper bags, and dried to constant weights. 



Rice Experiments. Only the Do than soil was used in these experiments. A total of 

 5 kg of soil was placed in each black plastic pot (top diameter, 22 cm; bottom diameter, 

 18 cm; height, 20 cm), and 2 /uCi of ^'''Am was added either by the soil-layering 

 technique earlier described or by injection to the ponded water used in the flooded 

 experiment. 



In the first experiment ^'^^ Am, dissolved in O.IA^ HNO3 , was chelated by adding a 

 ^^^ AmCNOaJa aliquot to 50 ml of DTPA solution. Chelated or nonchelated ^^ ' An. "'-'■ 

 added to the ponded water at three various stages of growth: booting stage, flowering 

 stage, and dough ripening stage. 



In the second experiment DTPA and OM (Bermuda grass hay) were premixed with 

 the whole soil to give 40 ppm DTPA and 5% OM by weight. The nonchelated 

 radionuclide was added to only the top 1 kg of soil by the layering technique. Two rice 

 varieties were grown, one under flooded condition and the other under nonfiooded 

 condition. 



All pots were supplemented once with reagent-grade NH4NO3, KH2PO4, and KNO3. 

 All treatments were replicated five times. The plants were grown to maturity in a water 

 bath in a glasshouse, harvested, separated into various plant parts, cut into shorter pieces, 

 and dried. 



The dried- plant tissues from all experiments were placed in counting tubes and 

 counted for at least 50 min for ^'^^ Am with a 7.6- by 7.6-cm Nal well crystal interphased 

 to a multichannel analyzer. Concentration ratios were calculated from the soil and plant 

 tissue radioactivity data. 



Pot-Culture Experiments with Soils Representing the Desert 

 Environments of the Western United States 



Some areas of the test-range complex in Nevada (NTS) were contaminated by fallout 

 debris during separate liigh-explosive (nonnuclear) detonations of devices containing 

 plutonium more than 20 yr ago. The ratios of plutonium to americium in soils and 

 vegetation collected in the field indicated that at least americium was taken up via roots 

 from the soil (Romney et al., 1976). Considerable amounts of plutonium and americium 

 have moved to the root zone in the soils involved. The soils in these areas are sandy desert 

 calcareous soils with pH values averaging about 8.0 (Leavitt, 1974). Sampling locations 

 were selected with a portable gamma spectrometer [FIDLER (field instrument for the 

 determination of low-energy radiation)] , which measures the 60-keV gamma radiation 

 emitted from ^"^^ Am. Radiochemical data of representative soil samples collected from 



