- Email: [email protected]
Comparative uptake of plutonium from soils by Brassica juncea and Helianthus annuus
Environmental Pollution 120 (2002) 173–182 www.elsevier.com/locate/envpol
Comparative uptake of plutonium from soils by Brassica juncea and Helianthus annuus J.H. Leea, L.R. Hossnera,*, M. Attrep Jr.b, K.S. Kungc a
Deptartment of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, USA b Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Environmental Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Received 3 September 2001; accepted 28 February 2002
‘‘Capsule’’: Extractability of Pu from soils was most affected by pH and amounts of clay, salts, and carbonates. Abstract Plutonium uptake by Brassica juncea (Indian mustard) and Helianthus annuus (sunflower) from soils with varying chemical composition and contaminated with Pu complexes (Pu–nitrate [239Pu(NO3)4], Pu–citrate [239Pu(C6H5O7)+], and Pu–diethylenetriaminepentaacetic acid (Pu–DTPA [239Pu–C14H23O10N3]) was investigated. Sequential extraction of soils incubated with applied Pu was used to determine the distribution of Pu in the various soil fractions. The initial Pu activity levels in soils were 44.40–231.25 Bq g1 as Pu–nitrate, Pu–citrate, or Pu–DTPA. A difference in Pu uptake between treatments of Pu–nitrate and Pu–citrate without chelating agent was observed only with Indian mustard in acidic Crowley soil. The uptake of Pu by plants was increased with increasing DTPA rates, however, the Pu concentration of plants was not proportionally increased with increasing application rate of Pu to soil. Plutonium uptake from Pu–DTPA was significantly higher from the acid Crowley soil than from the calcareous Weswood soil. The uptake of Pu from the soils was higher in Indian mustard than in sunflower. Sequential extraction of Pu showed that the ion-exchangeable Pu fraction in soils was dramatically increased with DTPA treatment and decreased with time of incubation. Extractability of Pu in all fractions was not different when Pu–nitrate and Pu–citrate were applied to the same soil. More Pu was associated with the residual Pu fraction without DTPA application. Consistent trends with time of incubation for other fractions were not apparent. The ion-exchangeable fraction, assumed as plant-available Pu, was significantly higher in acid soil compared with calcareous soil with or without DTPA treatment. When the calcareous soil was treated with DTPA, the ion-exchangeable Pu was comparatively less influenced. This fraction in the soil was more affected with time of incubation. The lowest extractable Pu was from a pH 6.55 Crockett soil that contained the highest clay compared to the other two soils. Extractable soil Pu was largely affected by soil pH and the amounts of clay, salt, metal oxide, and carbonate. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Accumulator; Concentration ratio; Plant uptake; Plutonium contamination; Plutonium fraction
1. Introduction Plutonium (Pu) contamination of soils, sediments, and/or water is an important consideration because this transuranic element can influence populations inhabiting the contaminated environment. A long-half life (t1/2=2.41104 year for 239Pu) and the potential health effects of Pu have resulted in extensive field and laboratory studies to resolve its environmental behavior * Corresponding author. Tel.: +1-979-845-3814; fax: +1-979-8450456. E-mail address: [email protected] (L.R. Hossner).
(Garland et al., 1981). Most of the previous research has concentrated on mechanisms by which food crops could become contaminated and risks of bioaccumulation. There has been limited research in identifying species of plants that might be suitable for phytoremediation in the specific contaminated sites. Limitations in regulatory acceptance and the long duration of time required for clean-up to acceptable levels (Schnoor, 1997) are contributing factors. Phytoremediation is a technology that should be considered for remediation of contaminated sites because of its cost-effectiveness, aesthetic advantages, and longterm applicability. This approach is well suited for use
0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(02)00167-7
174
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
at very large field sites where other methods (chemical or physical remediation) are not cost-effective or practicable. Some plants have shown the capacity to withstand a relatively high concentration of organic or inorganic contaminants without toxic effects. This technology is best applied at sites with near-surface contamination of organic, nutrient, and metal pollutants that are amenable to phytotransformation, rhizosphere bioremediation, phytostabilization, phytoextraction, or rhizofiltration (Dushenkov et al., 1995; Schnoor et al., 1995; Burken and Schnoor, 1996; Schnoor, 1997). Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) were used in this study as potential accumulator plants to investigate effective removal of 239 Pu from contaminated soils because those plants were reported as hyperaccumulators for metals (Schnoor, 1997). This process has been termed phytoextraction, the use of metal-accumulating plants to extract metals from soil and then concentrate them in the above ground shoots and leaves. It has been proposed for extraction of heavy metals and radionuclides from sites with mixed wastes. Phytoextraction offers significant cost advantages over alternative schemes of soil excavation and treatment or disposal (Cunningham and Ow, 1996; Ebbs et al., 1997; Huang et al., 1997; Schnoor, 1997; Ebbs and Kochian, 1998). Several lines of evidence point to the immobility of Pu in the soil matrix. Allard et al. (1984) described the interaction of actinide trace elements in aqueous solution with solid surfaces in terms of three basic sorption mechanisms, (1) physical sorption due to non-specific forces of attraction between solute and sorbent, (2) electrostatic adsorption due to coulombic attraction between charged solute species, and (3) chemisorption caused by the action of chemical forces. Once the Pu is in the soil or adsorbed on soil particles, Pu uptake by plants ranges between 103 and 104 of the Pu concentration in soil (Wilson and Cline, 1966). However, there can be an enormous range in concentrations of Pu present in plant tissue relative to that of the soil in which the plant was grown. The Pu concentration ratio (CR) in soil-culture systems (CR=Pu concentration in plant/Pu concentration in soil) ranged between 1010 and 103 (Wildung and Garland, 1974; Vyas and Mistry, 1978; Schulz and Ruggieri, 1981; Adriano et al., 1981; Romney et al., 1981; Garland et al., 1981; McLeod et al., 1981; Nishita, 1981; Pimpl and Schuttelkopf, 1981; Cline and Schreckhise, 1983). The CR is influenced by a number of factors including soil characteristics, particle size of Pu compounds, composition of the source material, chelation effects, and concentration of Pu in the soil. Chelates have been known to render insoluble cations more available to plants. The complexes formed in soil can increase the potential availability of elements in the root zone where the Pu is normally subjected to
hydrolysis and sorption on soil particles. Although plant uptake of Pu from soils is limited, the presence of chelating ligands and the possible formation of soluble Pu complexes with these ligands could enhance the solubility of Pu (Wallace, 1972; Lipton and Goldin, 1976; Ballou et al., 1978; Vyas and Mistry, 1980; Vyas and Mistry, 1983). As much as 85% of the added Pu was associated with the 0.1 M MgCl2 extracts following addition of Pu–diethylenetriaminepentaacetic acid (Pu– DTPA) and Pu–ethylendiaminetetraacetic acid (Pu–EDTA; Vyas and Mistry, 1984). The solubility of Pu–EDTA was less than Pu–DTPA. Lu et al. (1998) reported that chelating agents combined with reducing agents (sodium dithionite in particular) removed slightly more Pu and americium (Am) than when citrate was combined with the reducing agents. The objectives of this study were to (1) compare the uptake of Pu in Brassica juncea and Helianthus annuus from different soils contaminated with Pu complexes (Pu–nitrate, Pu–citrate, and Pu–DTPA), and (2) investigate the amounts of Pu associated with various phases in three soils with different chemical and physical properties.
2. Materials and methods 2.1. Plants and soils Two different plant species, Indian mustard (Brassica juncea ‘426308’) and sunflower (Helianthus annuus ‘Hybrid 571’), were obtained from the Regional Plant Introduction Station, Ames, Iowa, and used in this study. Crowley (acidic; fine, smectitic, hyperthermic Typic Albaqualfs), Crockett (non-calcareous; fine, smectitic, thermic Udertic Paleustalfs; only used for the sequential extraction study), and Weswood (calcareous; fine-silty, mixed, superactive, thermic Udifluventic Haplustepts) soils were collected and air-dried. The air-dried soil samples were passed through a 2-mm sieve, mixed, and stored in a plastic container. Selected chemical and physical properties of the soils are presented in Table 1. 2.2. Soil-culture study Soils (300 g, air-dry basis) were placed into a ZiplockTM plastic bag and Pu in the appropriate chelated form was added. Plutonium solutions, 8880 Bq Pu– nitrate [239Pu(NO3)4] ml1 and 9250 Bq Pu–citrate [239Pu(C6H5O7)+] ml1, were prepared. The initial Pu activity levels in soils were 44.4 and 222.0 Bq g1 of 239Pu(NO3)4 and 46.25 and 231.25 Bq g1 of 239 Pu(C6H5O7)+. The Pu–diethylenetriaminepentaacetic acid (Pu–DTPA; [239Pu–C14H23O10N3]) was prepared by addition of 239Pu(NO3)4 with 0, 10, and 50 mg DTPA g1. The Pu contaminated soil was sealed in the Zip-lockTM
175
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182 Table 1 Selected chemical and physical properties of the soils Soil
Weswood Crockett Crowley
Particle size distribution (%) Sand
Silt
Clay
67.6 39.6 56.8
25.6 23.6 19.7
6.8 36.8 23.5
Moisture content (0.03 MPa; kg kg1) 0.149 0.111 0.179
bag and taped. The bag containing the Pu contaminated soil was then enclosed in a second plastic bag and the second bag sealed with tape. The contaminated soil in double bags was thoroughly mixed by gently squeezing from outside of the second bag, incubated for 30 days at 24 1 C, and then carefully transferred to a 500-ml polypropylene container in preparation for planting. Each treatment was replicated four times. 2.3. Growing procedure for plants Seeds were soaked in distilled water for 4–6 h, spread between damp filter paper, covered, and left overnight in the dark. Sprouted seeds were planted in an uncontaminated quartz sand, provided with nutrient solution, and allowed to grow to 7 cm in height. The nutrient solution (Garland et al., 1981) contained 150 mg of KCl, 120 mg of MgSO4, 946 mg of Ca(NO3)2.. 4H2O, 68 mg of KH2PO4, 0.06 mg of ZnSO4.7H2O, 0.69 mg of H3BO3, 0.017 mg of CuCl2.2H2O, 0.024 mg of Na2MoO4.2H2O, 0.022 mg of MnCl2.4H2O, and 0.6 mg of FeCl3 per liter. Each seedling ( 7 cm) was carefully removed from the quartz sand, the roots were washed with deionized water, and two seedlings were transplanted into each labeled soil-culture container. After transferring the seedlings, strips of fiberglass were placed around the seedlings, and the proper volume of deionized water was added to bring the soil to field capacity (0.03 MPa). Clean quartz sand was used to cover the contaminated soil in the pot. Deionized water was added to wash and irrigate the plants. The plants were grown in an environmental growth chamber where the temperature was maintained at 24 2 C with a 12 h light cycle (5000– 6000 lux) and 60% relative humidity. Water lost by evapotranspiration was replaced with a solution of 0.1% (w/w) of NH4NO3. The plants were allowed to grow in the labeled soil-culture containers for 2 weeks. Plants were harvested by cutting off the shoots at the quartz sand surface. Plant tissue was dried (72 h, 50 C in a drying-oven) and weighed.
pH (1:2)
7.55 6.55 4.80
Exchangeable bases (cmol kg1) Ca
Mg
K
Na
160.0 32.5 9.0
1.67 1.67 1.58
0.38 0.36 0.13
0.04 0.04 0.04
Oxalate Fe (mg kg1)
CaCO3 (%)
58 198 798
2.45 0.26 –
Nearly dry digests were transferred to a 20-ml scintillation vial (marked at 10 and 20 ml) with 0.1 M HNO3 to the 10 ml mark followed by addition of Ultima GoldTM to a final volume of 20 ml. The mixture in the scintillation vial was sealed with a cap, shaken vigorously for 15 s, placed in a liquid scintillation counter, and counted for 30 or 60 min depending on the Pu concentration of the sample. This counting method was modified from the procedure described by Moore and Hudgens (1957). Concentration ratios (CR) were calculated for Pu uptake as follows: CR ¼ ðPu concentration in the dry plantÞ= ðPu concentration in the oilÞ
2.5. Sequential extraction Soils (40 g, air-dry basis) were placed into a ZiplockTM plastic bag. Appropriate amounts of Pu and DTPA were added to the soils to give Pu activity levels of 222.0 Bq g1 of 239Pu(NO3)4 and 231.25 Bq g1 of 239 Pu(C6H5O7)+. The 239Pu–DTPA was prepared by adding 239Pu(NO3)4 with 50 mg DTPA g1 soil. The Pu contaminated soils were sealed in Zip-lockTM plastic double-bags, taped, and thoroughly mixed. The soils were carefully transferred into a polypropylene container and closed with a perforated snap cap to allow air-exchange. The Pu contaminated soil samples were incubated in an environmental chamber at 24 1 C and 60% relative humidity. Incubated soil samples (2–3 g each) were placed into 20-ml plastic vials after 15, 30, 60, and 90 days of incubation. The samples were airdried in a ventilation hood that was especially designed for radiological work. After drying, approximately 1.0 g of the soil sample (oven dry basis) was transferred into a 50-ml polypropylene centrifuge tube and the exact weight of the soil sample determined. The sequential extraction procedure was modified from the method developed by Tessier et al. (1979), Vyas and Mistry (1984), and Loeppert and Inskeep (1996). The following extraction procedure was used:
2.4. Plutonium analysis The dried and weighed plant tissues were wet ashed in concentrated HNO3 and 30% H2O2 (Jones, 1991).
Fraction 1 (Exchangeable): 20 ml of 1 M MgCl2 (pH 7.0) were added to a polypropylene centrifuge tube containing 1.0 g of the contaminated soil sample. The
176
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
centrifuge tube was placed horizontally on an orbital shaker and shaken in a horizontal position for 1 h at a speed of 200 rpm. Fraction 2 (Bound to Carbonate): the sediment from Fraction 1 was extracted with 20 ml of 1 M NaOAC (pH 5.0). Continuous agitation was maintained for 5 h. Fraction 3 (Bound to Fe and Mn Oxides): 0.5 g Na2S2O4, 6 g Na3C6H5O7 H2O, and 20 mL deionized water were added to the sediment from Fraction 2. The mixture was continuously shaken for 16 h. Two drops of 0.2% SuperflocTM were added, the contents of the tube were vigorously shaken for 10 s, the volume was brought to 30 ml, the mixture was shaken again, and the suspended material was allowed to settle for 1 h. Fraction 4 (Bound to Organic Matter): the sediment from Fraction 3 was occasionally agitated for 2 h in 3 ml of 0.02 M HNO3+5 ml of 30% H2O2 (pH 2.0) solution at 85 2 C. The mixture was cooled, 3 ml of 30% H2O2 (pH 2.0) were added and then heated to 85 2 C for 3 h with occasional agitation. After cooling the mixture again, 5 ml of 3.2 M NH4OAC in 20% (v/v) HNO3 were added. The mixture was diluted to 20 ml and shaken continuously for 30 min. Fraction 5 (Residue): the sediment from Fraction 4 was transferred to a 100 ml TeflonTM beaker with 20– 30 ml of deionized water. The deionized water was evaporated in a ventilation hood to near dryness. The sediment was digested with 10 mL of 12 M HNO3 and 10 ml of 12 M HF at 125 C until completely dissolved. The temperature was reduced to 80 C, the digest taken nearly to dryness, and transferred into a scintillation vial with 0.1 M HNO3 to a final volume of 10 ml. The extraction of Fractions 1 to 4 was conducted in a 50-ml polypropylene centrifuge tube to avoid loss of soil. Between each successive extraction, the mixtures were centrifuged at 3000 rpm for 5 min. The centrifuge tube was turned upside down and shaken to remove soil particles from the upper inside surface of the centrifuge tube, then the mixtures were centrifuged again at 15,000 rpm (33,300g) for 20 min. The supernatant was transferred into a scintillation vial and the sediment was washed with 10 ml of deionized water followed by agitating for 10 min and centrifuging for 20 min. The second supernatant solution was discarded. 2.6. Plutonium analysis Ten milliliters of supernatant from Fractions 1 to 5 were mixed with 10 ml of Ultima GoldTM in a 20-ml scintillation vial. The scintillation vial was sealed with a cap, shaken vigorously for 15 s, placed in a liquid scintillation counter, and counted for 30 or 60 min depending on the Pu concentration of the sample. This counting
method was modified from the procedure described by Moore and Hudgens (1957).
3. Results and discussion Uptake of 239Pu by Indian mustard and sunflower was affected by Pu source and soil type (Fig. 1). The Pu concentration in shoots of Indian mustard was higher in the acidic Crowley soil when Pu–nitrate was the source compared with Pu–citrate but was not significantly different in the calcareous Weswood soil. The shoot concentration of Pu ranged from 1.50 0.40 to 25.88 3.59 Bq g1 with Pu–nitrate and from 0.96 0.20 to 8.76 0.89 Bq g1 with Pu–citrate. The concentration ratios were higher with Pu–nitrate than with Pu–citrate (Table 3). The CR ranged between (1.73 0.17)102 and (19.45 4.34)102 with Pu–nitrate and between (1.22 0.21)102 and (9.24 0.88)102 with Pu citrate. Uptake of 239Pu from the different soils by sunflower was not significantly affected by Pu source or by Pu– DTPA chelate. Plutonium uptake from Pu–citrate-treated soil was not significantly different compared with Pu– nitrate-treated soil in acidic or calcareous soils. The Pu uptake as influenced by Pu–citrate and Pu–nitrate treatments did not vary within the low and high Pu activity levels in the soils. The concentration of Pu ranged from 1.77 0.43 to 4.09 0.49 Bq g1 with Pu– nitrate treatments and from 1.96 0.14 to 6.16 0.75 Bq g1 with Pu–citrate treatments. The values of CR ranged between (0.83 0.20)102 and (5.56 1.12)102 and between (1.03 0.20)102 and (7.52 1.23)102 with Pu–nitrate and Pu–citrate treatments, respectively (Table 3). The influence of DTPA on Pu uptake and the Pu CR for Indian mustard and sunflower in the acidic Crowley soil and calcareous Weswood soil is presented in Tables 2 and 3. An increase in applied DTPA increased the Pu concentration of shoots for both low and high Pu activity levels in the soils. Plutonium uptake by Indian mustard was generally higher than by sunflower in both soils. Plutonium in the shoots of plants growing in the acid soil was always higher than for plants growing in the calcareous soil. Plutonium uptake was significantly different between different plants and soils, except in non-DTPA treatments. The CR values for Indian mustard ranged between (11.66 1.62)102 and (556.56 74.63)102 in the Crowley soil and between (1.73 0.17)102 and (369.22 18.61)102 in the Weswood soil. For sunflower, the values of CR ranged between (1.84 0.22)102 and (606.19 75.52)102 in the Crowley soil and between (0.83 0.20)102 and (93.19 17.14)102 in the Weswood soil. The concentration of Pu in the plant increased with increasing Pu activity levels for both Pu–citrate
177
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Fig. 1. Plutonium uptake by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) as affected by Pu–citrate and Pu–nitrate in soils. The Pu uptake in plants for Pu–citrate application are converted to adjust Pu activity levels from 46.25 or 231.3 to 44.40 or 222.0 Bq g1, respectively, with a conversion factor of 0.96. Bars represent one standard error of the mean values.
Table 2 Uptake of 239PU by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) from different soils as affected by Pu–nitrate with DTPA applications Pu source
Activity level of Pu (Bq g1)
Amounts of DTPA applied (g g1)
Pu uptakea Crowley soil (Bq g1)
239
Pu(NO3)4
239
Pu(NO3)4
44.40
222.0
Weswood soil (Bq g1)
Indian mustard
Sunflower
Indian mustard
Sunflower
0 10 50
8.631.92 a 208.6930.68 a 247.1133.13 a
2.47 0.50 b 137.48 6.38 b 269.15 33.53 ab
1.500.40 b 90.9510.61 c 163.938.26 c
1.770.43 b 15.022.66 d 41.387.61 d
0 10 50
25.883.59 a 338.7716.28 a 788.48104.55 a
4.09 0.49 b 168.98 11.42 b 907.83 47.67 b
3.840.38 b 273.5719.66 c 349.8564.27 c
1.840.45 b 65.824.64 d 112.177.80 d
a Pu uptake=mean valuestandard deviation (N=4), means within a row not followed by the same letter differ significantly (0.05 level) from each other as determined by Student’s t test.
and Pu–nitrate with or without DTPA treatments even though the increase was not proportional. Similar results were observed in a hydroponic system (Lee et al., 2002). Correlation coefficients (r) relating Pu uptake by Indian mustard and sunflower as affected by Pu–DTPA concentration in the acidic and calcareous soils are shown in Table 4. The Pu concentrations in the plant shoots were significantly correlated (P < 0.001) between
the low and high Pu activity levels, the plant species, and the acidic and calcareous soils. The correlation coefficient values were generally higher than 0.800. We believe that at physiological concentrations, Pu and its predominant ligands are accumulated independently and not absorbed stoichiometrically. Also, the DTPA chelated insoluble Pu-ions rendering them available to the plants and increased the mobility of Pu-ions
178
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Table 3 Concentration ratio (CR) of 239PU in the plant–soil systems as affected by Pu–nitrate with DTPA applications Pu source
Activity level of Pu (Bq g1)
Amounts of DTPA applied (g g1)
CRa102 Crowley soil Indian mustard
239
+
Pu(C6H5O7)
239
Pu(NO3)4
Pu(C6H5O7)+
Weswood soil Sunflower
Indian mustard
Sunflower
46.25
0
9.24 0.88
7.521.23
2.24 0.46
4.610.34
44.40
0 10 50
19.454.34 470.0369.09 556.5674.63
5.561.12 309.6514.37 606.1975.52
3.37 0.90 204.8423.91 369.2218.61
4.000.97 33.826.00 93.1917.14
239
231.3
0
3.94 0.40
2.890.35
1.22 0.21
1.030.20
239
222.0
0 10 50
11.661.62 152.607.33 355.1747.09
1.840.22 76.125.14 408.9321.47
1.73 0.17 123.238.85 157.5928.95
0.830.20 29.652.09 50.533.51
Pu(NO3)4
a
CR=Concentration ratio=(Pu concentration in the dry plant shoot) / (Pu concentration in the soil).
Table 4 Correlation coefficients relating Pu uptake by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) as affected by Pu–DTPA concentration in different soils Descriptiona
MC-High
MW-Low
MW-High
SC-Low
SC-High
SW-Low
SW-High
MC-Low MC-High MW-Low MW-High SC-Low SC-High SW-Low
0.849***
0.926*** –
– 0.874*** 0.948***
0.905*** – 0.982*** –
– 0.962*** – 0.769** 0.921***
0.799** – 0.919*** – 0.957*** –
– 0.969*** – 0.953*** – 0.899*** 0.928***
a N=12. Descriptions are MC, Indian mustard in Crowley soil; MW, Indian mustard in Weswood soil; SC, sunflower in Crowley soil; SW, sunflower in Weswood soil; Low, low initial activity level (44.40 Bq g1) of Pu–nitrate applied, and High=high initial activity level (222.0 Bq g1) of Pu–nitrate applied (e.g. MC-High=Pu uptake by Indian mustard in Crowley soils as applied with 222.0 Bq g1 of initial Pu activity and 0, 10, and 50 mg DTPA kg1 levels; SW-Low=Pu uptake by sunflower in Weswood soils as applied with 44.40 Bq g1 of initial Pu activity and 0, 10, and 50 mg DTPA kg1). ** P <0.01. *** P <0.001.
to roots by replenishing those taken up by the plant. Other researchers have used multidentate chelating agents, including DTPA, EDTA, ethylenediamine di-ohydroxy-phenylacetic acid (EDDHA), and nitrilotriacetic acid (NTA), as a means of supplying micronutrients to plants in intensive agriculture and in terrestrial and aquatic ecosystems (Lindsay, 1974; Vyas and Mistry, 1983). In this study, Pu uptake by the plants was increased up to 30-fold with DTPA chelation for Indian mustard and up to 200-fold for sunflower from the acidic Crowley soil when compared with Pu– nitrate and Pu–citrate. Plutonium concentration was increased up to 100-fold for Indian mustard and up to 60-fold for sunflower from the calcareous Weswood soil with the addition of DTPA. Addition of DTPA to Pu contaminated soils increased Pu concentration about a 1000-fold in pea plants (Lipton and Goldin, 19761) and increased Pu uptake by tumbleweeds (Ballou et al.,
1978). Wallace (1972) reported a 200-fold increase in Am uptake when Fe–DTPA was applied to soil. A marked enhancement in the mobility of Pu and Am through three contrasting soil types from India was observed on leaching with dilute chelating solution (Vyas and Mistry, 1980). The CR for Pu in plant shoots increased by a factor of 3–700 depending on the soil type and the complexing ligand (Vyas and Mistry, 1983). There is some indirect evidence of phytoaccumulation of Pu using sunflower and Indian mustard. Sunflower generally had a lower bioaccumulation coefficient for radiocesium (137Cs) than Indian mustard (Dushenkov et al., 1999). Accumulation of Zn by Indian mustard was significantly increased by adding EDTA chelate, but was not in oat and barley (Ebbs and Kochian, 1998). Indian mustard appears to be a better candidate for phytoremediation of Pu contaminated soils compared
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
with sunflower. However, sunflower was able to reduce elemental concentrations of manganese, chromium, cadmium, copper, and nickel to extremely low levels after only 24 h. Similar results were obtained for uranium (VI), zinc, and lead (Salt et al., 1995; Brooks and Robinson, 1998). These observations might indicate that plants selected as an accumulator might be more dependent on the target element and on the properties of the soil medium. We investigated the availability and transformation of Pu as affected by soil properties and the Pu complex added to soil (Figs. 2–4). Fractions of 1 M MgCl2 (pH 7.0) extractable Pu (assumed as ion-exchangeable Pu) were comparatively high with DTPA treatment and decreased with time of incubation. The Pu fraction that was bound to precipitated hydrous oxides and insoluble hydroxides was comparatively low with the Pu–DTPA treatment. The carbonate-bound Pu fraction (extracted with 1 M NaOAc; pH 5.0), with or without Pu–DTPA treatment, was unexpectedly detected in the acidic Crowley and non-calcareous Crockett soils. This result might be due to the dissolution of oxide-bound Pu in the soils by buffered acetate solution. Amacher (1996) reported that some dissolution of amorphous metal oxides might occur with buffered acetate solution. The residual Pu fraction was largely dependent on the amounts of Pu extracted in other fractions. More Pu was associated with this fraction, especially in those treatments without DTPA. The amount of Pu in each fraction was not different between treatments of Pu– nitrate and of Pu–citrate in the same soil. Levels of ionexchangeable Pu, with or without DTPA treatment, were much higher in the acidic Crowley soil compared
179
with the calcareous Weswood soil. The Pu level of other fractions did not show consistent trends with time of incubation but were dependent on soil properties. The extraction of Pu from soil was affected by soil pH and the amounts of clay, salt, metal oxides, and carbonates. The lowest amount of Pu was extracted from the Crockett soil, which had a near neutral pH and contained the highest clay content compared with the other two soils. When DTPA was applied to the calcareous Weswood soil, the ion-exchangeable Pu was comparatively less influenced and the amount of Pu in this fraction was more affected by time of incubation. The concentration of Pu in each fraction was higher, with or without DTPA treatment, in the acidic Crowley soil, which had an intermediate clay content. Nishita and Hamilton (1981) reported that Pu extractability was considerably lower over the entire pH range studied (pH 6–13) from soil with HCl-soluble organic matter, salts, and carbonates compared with soil without those properties. They also found that if the soil contained CaCO3 (with or without adding humic acid) and no salts, the amount of extractable Pu was markedly decreased at higher pH. In contrast, Rhodes (1957a, b) investigated Pu adsorption on a calcareous soil containing mainly montmorillonite and kaolinite and little or no organic matter. Strong adsorption of Pu (> 98%) began at pH 2 and extended to the mid range of soil pH. At higher pH values, the Pu adsorption maxium was about 80%. However, Nishita et al. (1977) explained that in most systems, Pu extractability was increased at pH 5.5 or lower, and also increased with increasing pH values over 6.5. The lowest Pu extractability occurred at pH values between 5.5 and 6.5. The extractability of Pu was
Fig. 2. Sequential extractions of Pu in Weswood soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
180
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Fig. 3. Sequential extractions of Pu in Crockett soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
Fig. 4. Sequential extractions of Pu in Crowley soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
drastically decreased in the presence of decomposing organic matter and dissolving Fe- and Mn-oxides, and CaCO3.
4. Conclusions Plutonium uptake from soil by Indian mustard and sunflower was increased with increasing Pu activity level. A difference in Pu uptake between treatments of Pu–nitrate and Pu–citrate without chelating agent was observed only with Indian mustard in acidic Crowley
soil. Plutonium uptake by the plant was increased with increasing concentrations of DTPA in soils containing both low and high levels of Pu activity. Plutonium in the shoots of plants was significantly higher from the acid Crowley soil compared with the calcareous Weswood soil, especially in those treatments with DTPA chelation. The Pu concentration of Indian mustard was higher than that of sunflower. Also, the Pu concentration of the plant shoots was significantly correlated between the low and high Pu activity levels, plant species, and the acidic and calcareous soils. The shoot Pu concentration did not increase in proportion to the applied Pu–DTPA rates to
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
soils. Therefore, Pu and its predominant ligands are apparently accumulated independently and not absorbed stoichiometrically by the plants. Levels of exchangeable Pu were higher in acidic Crowley soil than in neutral Crockett and calcareous Weswood soils with or without DTPA treatment. The exchangeable Pu fraction initially increased with DTPA treatment but then decreased with time of incubation. When DTPA was added along with Pu to the calcareous Weswood soil, exchangeable Pu was less influenced and this fraction was more affected by time of incubation. Plutonium was unexpectedly detected in the carbonate bound fraction of the non-calcareous soils apparently because the buffered acetate solution may extract or dissolve oxide-bound Pu from the soils. The Pu fraction that was bound to precipitated hydrous oxides and insoluble hydroxides was comparatively lower. More Pu was associated with the residual Pu fraction when the soil was not treated with DTPA. The Pu levels of other fractions did not provide consistent trends with time of incubation and there was no difference in the levels of Pu in the various fractions when Pu–nitrate and Pu–citrate were added to the same soil. The extraction of Pu from these soils was mostly affected by soil pH and the amounts of clay, salts, and carbonates. The lowest amount of extractable Pu was from Crockett soil, which had the highest clay content and moderate pH (6.55) compared with the other two soils.
Acknowledgements The authors acknowledge the financial support of the Amarillo National Resource Center for Plutonium, 600 South Tyler, Amarillo, TX 79101 under agreemet UTA960043.
References Adriano, D.C., McLeod, K.W., Ciravolo, T.G., 1981. Plutonium, curium, and other radionuclide uptake by the rice plant from a naturally weathered, contaminated soil. Soil Sci. 132 (1), 83–88. Allard, B., Olofsson, U., Torstenfelt, B., 1984. Environmental actinide chemistry. Inorganica Chemica Acta 94, 205–221. Amacher, M.C., 1996. Nickel, cadmium, and lead. In: Sparks, D.L. (Ed.), Methods of Soil Analysis, Part 3—Chemical Methods. Number 5 in the SSSA of America Book Series. SSSA and ASA, Madison, WI, pp. 739–768. Ballou, J.E., Price, K.R., Gies, R.A., Doctor, P.G., 1978. The influence of DTPA on the biological availability of transuranics. Health Phys. 34, 445–450. Brooks, R.R., Robinson, B.H., 1998. Aquatic phytoremediation by accumulator Plants. In: Brooks, R.R. (Ed.), Plants that Hyperaccumulate Heavy Metals: Their Role in Phytoremediation, Microbiology, Archaeology, Mineral Exploration and Phytomining. CAB International, New York, pp. 203–266. Burken, J.G., Schnoor, J.L., 1996. Phytoremediation: Plant uptake of atrazine and role of root exudates. J. Environ. Eng. Nov. 958–963.
181
Cline, J.F., Schreckhise, R.G., 1983. Comparative plant uptake of plutonium-239 added to soil in the oxide vs. the nitrate form. In: Pinder III, J.E. (Ed.), Environmental Research on Actinide Elements. Proceeding of a Symposium held at Hilton Head, South Carolina, 7–11 November. Office of Scientific and Tech. Information, DOE, 1987, Oak Ridge, TN, pp. 73–81. Cunningham, S.D., Ow, D.W., 1996. Promises and prospects of phytoremediation. Plant Physiol. 110, 715–719. Dushenkov, S., Mikheev, A., Prokhnevsky, A., Ruchko, M., Sorochinsky, B., 1999. Phytoremediation of radiocesium-contaminated soil in the vicinity of Chernobyl. Kraine. Environ. Sci. Tech. 33 (3), 457–469. Dushenkov, V., Kumar, P.B.A.N., Motto, H., Raskin, I., 1995. Rhizofiltration: the use of plants to remove heavy metals from aqueous streams. Environ. Sci. Tech. 29, 1239–1245. Ebbs, S.D., Kochian, L.V., 1998. Phytoextraction of zinc by oat (Avena sativa), barley (Hordeum vulgare), and Indian mustard (Brassica juncea). Environ. Sci. Tech. 32 (6), 802–806. Ebbs, S.D., Lasat, M.M., Brady, D.J., Cornish, J., Gordon, R., Kochian, L.V., 1997. Phytoextraction of cadmium and zinc from a contaminated soil. J. Environ. Qual. 26, 1424–1430. Garland, T.R., Cataldo, D.A., Wildung, R.E., 1981. Absorption, transport, and chemical fate of plutonium in soybean plants. J. Agric. Food Chem. 29 (5), 915–920. Huang, J.W., Chen, J., Berti, W.R., Cunningham, S.D., 1997. Phytoremediation of lead-contaminated soils: role of synthetic chelates in lead phytoextraction. Environ. Sci. Tech. 31, 800–805. Jones Jr., J.B., 1991. Plant tissue analysis in micronutrients. In: Mortvedt, J.J., Cox, F.R., Shuman, L.M., Welch, R.M. (Eds.), Micronutrients in Agriculture, second ed. SSSA, Madison, WI, pp. 477– 521. Lee, J.H., Hossner, L.R., Attrep Jr., M., Kung, K.S., 2002. Uptake and translocation of plutonium in two plant species using hydroponics. Environ. Pollu. 117 (1), 61–68. Lindsay, W.L., 1974. Role of chelation in micronutrient availability. In: Carson, E.W. (Ed.), Plant Roots and its Environment. University Press of Virginia, Charlottesville, VA, pp. 507– 524. Lipton, W.V., Goldin, A.S., 1976. Some factors influencing the uptake of plutonium 239 by pea plants. Health Phys. 31, 425–430. Loeppert, R.H., Inskeep, W.P., 1996. Iron. In: Sparks, D.L. (Ed.), Methods of Soil Analysis, Part 3—Chemical Methods. Number 5 in the SSSA of America Book Series. SSSA and ASA, Madison, WI, pp. 639–644. Lu, N., Kung, K.S., Mason, C.F.V., Triay, I.R., Cotter, C.R., Pappas, A.I., Pappas, M.E.G., 1998. Removal of plutonium-239 and americium-241 from Rocky Flats soil by leaching. Enviro. Sci. Tech. 32 (3), 370–374. McLeod, K.W., Adriano, D.C., Ciravolo, T.G., 1981. Uptake of plutonium from soils contaminated by a nuclear fuel chemical separation facility. Soil Sci. 132 (1), 89–98. Moore, F.L., Hudgens Jr., J.E., 1957. Separation and determination of plutonium by liquid–liquid extraction. Anal. Chem. 29 (12), 1767–1770. Nishita, H., 1981. Relative adsorption and plant uptake of 238PU and 239 Pu in soils. Soil Sci. 132 (1), 66–70. Nishita, H., Hamilton, M., 1981. The influence of several soil components and their interaction on plutonium extractability from a calcareous soil. Soil Sci. 131 (1), 56–59. Nishita, H., Haug, R.M., Rutherford, T., 1977. Effect of inorganic and organic compounds on the extractability of 239Pu from an artificially contaminated soil. J. Environ. Qual. 6 (4), 451–455. Pimpl, M., Schuttelkopf, H., 1981. Transport of plutonium, americium, and curium from soils into plants by root uptake. Nuclear Safety 22 (2), 214–225. Rhodes, D.W., 1957a. Adsorption of plutonium by soil. Soil Sci. 84, 465–471.
182
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Rhodes, D.W., 1957b. The effect of pH on the uptake of radioactive isotopes from solution by a soil. Soil Sci. Soc. Am. Proc. 21, 389– 392. Romney, E.M., Wallace, A., Schulz, R.K., Kinnear, J., Wood, R.A., 1981. Plant uptake of 237Np, 239,240Pu, 241Am, and 244Cm from soils representing major food production areas of the United States. Soil Sci. 132 (1), 40–59. Salt, D.E., Blaylock, M., Kumar, N.P.B.A., Dushenkov, V., Ensley, B.D., Chet, I., Raskin, I., 1995. Phytoremediation: a novel strategy for the removal of toxic metals from the environment using plants. Bio/Tech. 13, 468–474. Schnoor, J.L., 1997. Phytoremediation (Technology Evaluation Report, TE-98–01). Ground-Water Remediation Technologies Analysis Center, Pittsburgh, PA. Schnoor, J.L., Licht, L.A., McCutcheon, S.C., Wolfe, N.L., Carreira, L.H., 1995. Phytoremediation of organic and nutrient contaminants. Environ. Sci. Tech. 29 (7), 318A–323A. Schulz, R.K., Ruggieri, M.R., 1981. Uptake and translocation of neptunium-237, plutonium-238, plutonium-239,240, americium-241, and curium-244 by a wheat crop. Soil Sci. 132 (1), 77–82.
Tessier, T., Campbell, P.G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51 (7), 844–851. Vyas, B.N., Mistry, K.B., 1978. Studies on the uptake of plutonium from major Indian soils and its distribution in plants. J. Environ. Qual. 7 (4), 533–536. Vyas, B.N., Mistry, K.B., 1980. Studies on the mobility of plutonium239 and americium-241 in three major Indian soils. J. Nuclear Agric. Biol. 9, 85–88. Vyas, B.N., Mistry, K.B., 1983. Influence of chelating agents on the uptake of 239PU and 241Am by plants. Plant and Soil 73, 345–353. Vyas, B.N., Mistry, K.B., 1984. Studies on transformation of plutonium-239 and americium-241 in three major Indian soils. Sci. Total Environ. 32, 183–195. Wallace, A., 1972. Increased uptake of 241Am by plants caused by the chelating agent DTPA. Health Phys. 22, 559–562. Wildung, R.E., Garland, T.R., 1974. Influence of soil plutonium concentration on plutonium uptake and distribution in shoots and roots of barley. J. Agr. Food Chem. 22 (5), 836–838. Wilson, D.O., Cline, J.F., 1966. Removal of plutonium-239, tungsten185, and lead-210 from soils. Nature 209, 941–942.
Comparative uptake of plutonium from soils by Brassica juncea and Helianthus annuus J.H. Leea, L.R. Hossnera,*, M. Attrep Jr.b, K.S. Kungc a
Deptartment of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, USA b Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA c Environmental Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Received 3 September 2001; accepted 28 February 2002
‘‘Capsule’’: Extractability of Pu from soils was most affected by pH and amounts of clay, salts, and carbonates. Abstract Plutonium uptake by Brassica juncea (Indian mustard) and Helianthus annuus (sunflower) from soils with varying chemical composition and contaminated with Pu complexes (Pu–nitrate [239Pu(NO3)4], Pu–citrate [239Pu(C6H5O7)+], and Pu–diethylenetriaminepentaacetic acid (Pu–DTPA [239Pu–C14H23O10N3]) was investigated. Sequential extraction of soils incubated with applied Pu was used to determine the distribution of Pu in the various soil fractions. The initial Pu activity levels in soils were 44.40–231.25 Bq g1 as Pu–nitrate, Pu–citrate, or Pu–DTPA. A difference in Pu uptake between treatments of Pu–nitrate and Pu–citrate without chelating agent was observed only with Indian mustard in acidic Crowley soil. The uptake of Pu by plants was increased with increasing DTPA rates, however, the Pu concentration of plants was not proportionally increased with increasing application rate of Pu to soil. Plutonium uptake from Pu–DTPA was significantly higher from the acid Crowley soil than from the calcareous Weswood soil. The uptake of Pu from the soils was higher in Indian mustard than in sunflower. Sequential extraction of Pu showed that the ion-exchangeable Pu fraction in soils was dramatically increased with DTPA treatment and decreased with time of incubation. Extractability of Pu in all fractions was not different when Pu–nitrate and Pu–citrate were applied to the same soil. More Pu was associated with the residual Pu fraction without DTPA application. Consistent trends with time of incubation for other fractions were not apparent. The ion-exchangeable fraction, assumed as plant-available Pu, was significantly higher in acid soil compared with calcareous soil with or without DTPA treatment. When the calcareous soil was treated with DTPA, the ion-exchangeable Pu was comparatively less influenced. This fraction in the soil was more affected with time of incubation. The lowest extractable Pu was from a pH 6.55 Crockett soil that contained the highest clay compared to the other two soils. Extractable soil Pu was largely affected by soil pH and the amounts of clay, salt, metal oxide, and carbonate. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Accumulator; Concentration ratio; Plant uptake; Plutonium contamination; Plutonium fraction
1. Introduction Plutonium (Pu) contamination of soils, sediments, and/or water is an important consideration because this transuranic element can influence populations inhabiting the contaminated environment. A long-half life (t1/2=2.41104 year for 239Pu) and the potential health effects of Pu have resulted in extensive field and laboratory studies to resolve its environmental behavior * Corresponding author. Tel.: +1-979-845-3814; fax: +1-979-8450456. E-mail address: [email protected] (L.R. Hossner).
(Garland et al., 1981). Most of the previous research has concentrated on mechanisms by which food crops could become contaminated and risks of bioaccumulation. There has been limited research in identifying species of plants that might be suitable for phytoremediation in the specific contaminated sites. Limitations in regulatory acceptance and the long duration of time required for clean-up to acceptable levels (Schnoor, 1997) are contributing factors. Phytoremediation is a technology that should be considered for remediation of contaminated sites because of its cost-effectiveness, aesthetic advantages, and longterm applicability. This approach is well suited for use
0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(02)00167-7
174
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
at very large field sites where other methods (chemical or physical remediation) are not cost-effective or practicable. Some plants have shown the capacity to withstand a relatively high concentration of organic or inorganic contaminants without toxic effects. This technology is best applied at sites with near-surface contamination of organic, nutrient, and metal pollutants that are amenable to phytotransformation, rhizosphere bioremediation, phytostabilization, phytoextraction, or rhizofiltration (Dushenkov et al., 1995; Schnoor et al., 1995; Burken and Schnoor, 1996; Schnoor, 1997). Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) were used in this study as potential accumulator plants to investigate effective removal of 239 Pu from contaminated soils because those plants were reported as hyperaccumulators for metals (Schnoor, 1997). This process has been termed phytoextraction, the use of metal-accumulating plants to extract metals from soil and then concentrate them in the above ground shoots and leaves. It has been proposed for extraction of heavy metals and radionuclides from sites with mixed wastes. Phytoextraction offers significant cost advantages over alternative schemes of soil excavation and treatment or disposal (Cunningham and Ow, 1996; Ebbs et al., 1997; Huang et al., 1997; Schnoor, 1997; Ebbs and Kochian, 1998). Several lines of evidence point to the immobility of Pu in the soil matrix. Allard et al. (1984) described the interaction of actinide trace elements in aqueous solution with solid surfaces in terms of three basic sorption mechanisms, (1) physical sorption due to non-specific forces of attraction between solute and sorbent, (2) electrostatic adsorption due to coulombic attraction between charged solute species, and (3) chemisorption caused by the action of chemical forces. Once the Pu is in the soil or adsorbed on soil particles, Pu uptake by plants ranges between 103 and 104 of the Pu concentration in soil (Wilson and Cline, 1966). However, there can be an enormous range in concentrations of Pu present in plant tissue relative to that of the soil in which the plant was grown. The Pu concentration ratio (CR) in soil-culture systems (CR=Pu concentration in plant/Pu concentration in soil) ranged between 1010 and 103 (Wildung and Garland, 1974; Vyas and Mistry, 1978; Schulz and Ruggieri, 1981; Adriano et al., 1981; Romney et al., 1981; Garland et al., 1981; McLeod et al., 1981; Nishita, 1981; Pimpl and Schuttelkopf, 1981; Cline and Schreckhise, 1983). The CR is influenced by a number of factors including soil characteristics, particle size of Pu compounds, composition of the source material, chelation effects, and concentration of Pu in the soil. Chelates have been known to render insoluble cations more available to plants. The complexes formed in soil can increase the potential availability of elements in the root zone where the Pu is normally subjected to
hydrolysis and sorption on soil particles. Although plant uptake of Pu from soils is limited, the presence of chelating ligands and the possible formation of soluble Pu complexes with these ligands could enhance the solubility of Pu (Wallace, 1972; Lipton and Goldin, 1976; Ballou et al., 1978; Vyas and Mistry, 1980; Vyas and Mistry, 1983). As much as 85% of the added Pu was associated with the 0.1 M MgCl2 extracts following addition of Pu–diethylenetriaminepentaacetic acid (Pu– DTPA) and Pu–ethylendiaminetetraacetic acid (Pu–EDTA; Vyas and Mistry, 1984). The solubility of Pu–EDTA was less than Pu–DTPA. Lu et al. (1998) reported that chelating agents combined with reducing agents (sodium dithionite in particular) removed slightly more Pu and americium (Am) than when citrate was combined with the reducing agents. The objectives of this study were to (1) compare the uptake of Pu in Brassica juncea and Helianthus annuus from different soils contaminated with Pu complexes (Pu–nitrate, Pu–citrate, and Pu–DTPA), and (2) investigate the amounts of Pu associated with various phases in three soils with different chemical and physical properties.
2. Materials and methods 2.1. Plants and soils Two different plant species, Indian mustard (Brassica juncea ‘426308’) and sunflower (Helianthus annuus ‘Hybrid 571’), were obtained from the Regional Plant Introduction Station, Ames, Iowa, and used in this study. Crowley (acidic; fine, smectitic, hyperthermic Typic Albaqualfs), Crockett (non-calcareous; fine, smectitic, thermic Udertic Paleustalfs; only used for the sequential extraction study), and Weswood (calcareous; fine-silty, mixed, superactive, thermic Udifluventic Haplustepts) soils were collected and air-dried. The air-dried soil samples were passed through a 2-mm sieve, mixed, and stored in a plastic container. Selected chemical and physical properties of the soils are presented in Table 1. 2.2. Soil-culture study Soils (300 g, air-dry basis) were placed into a ZiplockTM plastic bag and Pu in the appropriate chelated form was added. Plutonium solutions, 8880 Bq Pu– nitrate [239Pu(NO3)4] ml1 and 9250 Bq Pu–citrate [239Pu(C6H5O7)+] ml1, were prepared. The initial Pu activity levels in soils were 44.4 and 222.0 Bq g1 of 239Pu(NO3)4 and 46.25 and 231.25 Bq g1 of 239 Pu(C6H5O7)+. The Pu–diethylenetriaminepentaacetic acid (Pu–DTPA; [239Pu–C14H23O10N3]) was prepared by addition of 239Pu(NO3)4 with 0, 10, and 50 mg DTPA g1. The Pu contaminated soil was sealed in the Zip-lockTM
175
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182 Table 1 Selected chemical and physical properties of the soils Soil
Weswood Crockett Crowley
Particle size distribution (%) Sand
Silt
Clay
67.6 39.6 56.8
25.6 23.6 19.7
6.8 36.8 23.5
Moisture content (0.03 MPa; kg kg1) 0.149 0.111 0.179
bag and taped. The bag containing the Pu contaminated soil was then enclosed in a second plastic bag and the second bag sealed with tape. The contaminated soil in double bags was thoroughly mixed by gently squeezing from outside of the second bag, incubated for 30 days at 24 1 C, and then carefully transferred to a 500-ml polypropylene container in preparation for planting. Each treatment was replicated four times. 2.3. Growing procedure for plants Seeds were soaked in distilled water for 4–6 h, spread between damp filter paper, covered, and left overnight in the dark. Sprouted seeds were planted in an uncontaminated quartz sand, provided with nutrient solution, and allowed to grow to 7 cm in height. The nutrient solution (Garland et al., 1981) contained 150 mg of KCl, 120 mg of MgSO4, 946 mg of Ca(NO3)2.. 4H2O, 68 mg of KH2PO4, 0.06 mg of ZnSO4.7H2O, 0.69 mg of H3BO3, 0.017 mg of CuCl2.2H2O, 0.024 mg of Na2MoO4.2H2O, 0.022 mg of MnCl2.4H2O, and 0.6 mg of FeCl3 per liter. Each seedling ( 7 cm) was carefully removed from the quartz sand, the roots were washed with deionized water, and two seedlings were transplanted into each labeled soil-culture container. After transferring the seedlings, strips of fiberglass were placed around the seedlings, and the proper volume of deionized water was added to bring the soil to field capacity (0.03 MPa). Clean quartz sand was used to cover the contaminated soil in the pot. Deionized water was added to wash and irrigate the plants. The plants were grown in an environmental growth chamber where the temperature was maintained at 24 2 C with a 12 h light cycle (5000– 6000 lux) and 60% relative humidity. Water lost by evapotranspiration was replaced with a solution of 0.1% (w/w) of NH4NO3. The plants were allowed to grow in the labeled soil-culture containers for 2 weeks. Plants were harvested by cutting off the shoots at the quartz sand surface. Plant tissue was dried (72 h, 50 C in a drying-oven) and weighed.
pH (1:2)
7.55 6.55 4.80
Exchangeable bases (cmol kg1) Ca
Mg
K
Na
160.0 32.5 9.0
1.67 1.67 1.58
0.38 0.36 0.13
0.04 0.04 0.04
Oxalate Fe (mg kg1)
CaCO3 (%)
58 198 798
2.45 0.26 –
Nearly dry digests were transferred to a 20-ml scintillation vial (marked at 10 and 20 ml) with 0.1 M HNO3 to the 10 ml mark followed by addition of Ultima GoldTM to a final volume of 20 ml. The mixture in the scintillation vial was sealed with a cap, shaken vigorously for 15 s, placed in a liquid scintillation counter, and counted for 30 or 60 min depending on the Pu concentration of the sample. This counting method was modified from the procedure described by Moore and Hudgens (1957). Concentration ratios (CR) were calculated for Pu uptake as follows: CR ¼ ðPu concentration in the dry plantÞ= ðPu concentration in the oilÞ
2.5. Sequential extraction Soils (40 g, air-dry basis) were placed into a ZiplockTM plastic bag. Appropriate amounts of Pu and DTPA were added to the soils to give Pu activity levels of 222.0 Bq g1 of 239Pu(NO3)4 and 231.25 Bq g1 of 239 Pu(C6H5O7)+. The 239Pu–DTPA was prepared by adding 239Pu(NO3)4 with 50 mg DTPA g1 soil. The Pu contaminated soils were sealed in Zip-lockTM plastic double-bags, taped, and thoroughly mixed. The soils were carefully transferred into a polypropylene container and closed with a perforated snap cap to allow air-exchange. The Pu contaminated soil samples were incubated in an environmental chamber at 24 1 C and 60% relative humidity. Incubated soil samples (2–3 g each) were placed into 20-ml plastic vials after 15, 30, 60, and 90 days of incubation. The samples were airdried in a ventilation hood that was especially designed for radiological work. After drying, approximately 1.0 g of the soil sample (oven dry basis) was transferred into a 50-ml polypropylene centrifuge tube and the exact weight of the soil sample determined. The sequential extraction procedure was modified from the method developed by Tessier et al. (1979), Vyas and Mistry (1984), and Loeppert and Inskeep (1996). The following extraction procedure was used:
2.4. Plutonium analysis The dried and weighed plant tissues were wet ashed in concentrated HNO3 and 30% H2O2 (Jones, 1991).
Fraction 1 (Exchangeable): 20 ml of 1 M MgCl2 (pH 7.0) were added to a polypropylene centrifuge tube containing 1.0 g of the contaminated soil sample. The
176
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
centrifuge tube was placed horizontally on an orbital shaker and shaken in a horizontal position for 1 h at a speed of 200 rpm. Fraction 2 (Bound to Carbonate): the sediment from Fraction 1 was extracted with 20 ml of 1 M NaOAC (pH 5.0). Continuous agitation was maintained for 5 h. Fraction 3 (Bound to Fe and Mn Oxides): 0.5 g Na2S2O4, 6 g Na3C6H5O7 H2O, and 20 mL deionized water were added to the sediment from Fraction 2. The mixture was continuously shaken for 16 h. Two drops of 0.2% SuperflocTM were added, the contents of the tube were vigorously shaken for 10 s, the volume was brought to 30 ml, the mixture was shaken again, and the suspended material was allowed to settle for 1 h. Fraction 4 (Bound to Organic Matter): the sediment from Fraction 3 was occasionally agitated for 2 h in 3 ml of 0.02 M HNO3+5 ml of 30% H2O2 (pH 2.0) solution at 85 2 C. The mixture was cooled, 3 ml of 30% H2O2 (pH 2.0) were added and then heated to 85 2 C for 3 h with occasional agitation. After cooling the mixture again, 5 ml of 3.2 M NH4OAC in 20% (v/v) HNO3 were added. The mixture was diluted to 20 ml and shaken continuously for 30 min. Fraction 5 (Residue): the sediment from Fraction 4 was transferred to a 100 ml TeflonTM beaker with 20– 30 ml of deionized water. The deionized water was evaporated in a ventilation hood to near dryness. The sediment was digested with 10 mL of 12 M HNO3 and 10 ml of 12 M HF at 125 C until completely dissolved. The temperature was reduced to 80 C, the digest taken nearly to dryness, and transferred into a scintillation vial with 0.1 M HNO3 to a final volume of 10 ml. The extraction of Fractions 1 to 4 was conducted in a 50-ml polypropylene centrifuge tube to avoid loss of soil. Between each successive extraction, the mixtures were centrifuged at 3000 rpm for 5 min. The centrifuge tube was turned upside down and shaken to remove soil particles from the upper inside surface of the centrifuge tube, then the mixtures were centrifuged again at 15,000 rpm (33,300g) for 20 min. The supernatant was transferred into a scintillation vial and the sediment was washed with 10 ml of deionized water followed by agitating for 10 min and centrifuging for 20 min. The second supernatant solution was discarded. 2.6. Plutonium analysis Ten milliliters of supernatant from Fractions 1 to 5 were mixed with 10 ml of Ultima GoldTM in a 20-ml scintillation vial. The scintillation vial was sealed with a cap, shaken vigorously for 15 s, placed in a liquid scintillation counter, and counted for 30 or 60 min depending on the Pu concentration of the sample. This counting
method was modified from the procedure described by Moore and Hudgens (1957).
3. Results and discussion Uptake of 239Pu by Indian mustard and sunflower was affected by Pu source and soil type (Fig. 1). The Pu concentration in shoots of Indian mustard was higher in the acidic Crowley soil when Pu–nitrate was the source compared with Pu–citrate but was not significantly different in the calcareous Weswood soil. The shoot concentration of Pu ranged from 1.50 0.40 to 25.88 3.59 Bq g1 with Pu–nitrate and from 0.96 0.20 to 8.76 0.89 Bq g1 with Pu–citrate. The concentration ratios were higher with Pu–nitrate than with Pu–citrate (Table 3). The CR ranged between (1.73 0.17)102 and (19.45 4.34)102 with Pu–nitrate and between (1.22 0.21)102 and (9.24 0.88)102 with Pu citrate. Uptake of 239Pu from the different soils by sunflower was not significantly affected by Pu source or by Pu– DTPA chelate. Plutonium uptake from Pu–citrate-treated soil was not significantly different compared with Pu– nitrate-treated soil in acidic or calcareous soils. The Pu uptake as influenced by Pu–citrate and Pu–nitrate treatments did not vary within the low and high Pu activity levels in the soils. The concentration of Pu ranged from 1.77 0.43 to 4.09 0.49 Bq g1 with Pu– nitrate treatments and from 1.96 0.14 to 6.16 0.75 Bq g1 with Pu–citrate treatments. The values of CR ranged between (0.83 0.20)102 and (5.56 1.12)102 and between (1.03 0.20)102 and (7.52 1.23)102 with Pu–nitrate and Pu–citrate treatments, respectively (Table 3). The influence of DTPA on Pu uptake and the Pu CR for Indian mustard and sunflower in the acidic Crowley soil and calcareous Weswood soil is presented in Tables 2 and 3. An increase in applied DTPA increased the Pu concentration of shoots for both low and high Pu activity levels in the soils. Plutonium uptake by Indian mustard was generally higher than by sunflower in both soils. Plutonium in the shoots of plants growing in the acid soil was always higher than for plants growing in the calcareous soil. Plutonium uptake was significantly different between different plants and soils, except in non-DTPA treatments. The CR values for Indian mustard ranged between (11.66 1.62)102 and (556.56 74.63)102 in the Crowley soil and between (1.73 0.17)102 and (369.22 18.61)102 in the Weswood soil. For sunflower, the values of CR ranged between (1.84 0.22)102 and (606.19 75.52)102 in the Crowley soil and between (0.83 0.20)102 and (93.19 17.14)102 in the Weswood soil. The concentration of Pu in the plant increased with increasing Pu activity levels for both Pu–citrate
177
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Fig. 1. Plutonium uptake by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) as affected by Pu–citrate and Pu–nitrate in soils. The Pu uptake in plants for Pu–citrate application are converted to adjust Pu activity levels from 46.25 or 231.3 to 44.40 or 222.0 Bq g1, respectively, with a conversion factor of 0.96. Bars represent one standard error of the mean values.
Table 2 Uptake of 239PU by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) from different soils as affected by Pu–nitrate with DTPA applications Pu source
Activity level of Pu (Bq g1)
Amounts of DTPA applied (g g1)
Pu uptakea Crowley soil (Bq g1)
239
Pu(NO3)4
239
Pu(NO3)4
44.40
222.0
Weswood soil (Bq g1)
Indian mustard
Sunflower
Indian mustard
Sunflower
0 10 50
8.631.92 a 208.6930.68 a 247.1133.13 a
2.47 0.50 b 137.48 6.38 b 269.15 33.53 ab
1.500.40 b 90.9510.61 c 163.938.26 c
1.770.43 b 15.022.66 d 41.387.61 d
0 10 50
25.883.59 a 338.7716.28 a 788.48104.55 a
4.09 0.49 b 168.98 11.42 b 907.83 47.67 b
3.840.38 b 273.5719.66 c 349.8564.27 c
1.840.45 b 65.824.64 d 112.177.80 d
a Pu uptake=mean valuestandard deviation (N=4), means within a row not followed by the same letter differ significantly (0.05 level) from each other as determined by Student’s t test.
and Pu–nitrate with or without DTPA treatments even though the increase was not proportional. Similar results were observed in a hydroponic system (Lee et al., 2002). Correlation coefficients (r) relating Pu uptake by Indian mustard and sunflower as affected by Pu–DTPA concentration in the acidic and calcareous soils are shown in Table 4. The Pu concentrations in the plant shoots were significantly correlated (P < 0.001) between
the low and high Pu activity levels, the plant species, and the acidic and calcareous soils. The correlation coefficient values were generally higher than 0.800. We believe that at physiological concentrations, Pu and its predominant ligands are accumulated independently and not absorbed stoichiometrically. Also, the DTPA chelated insoluble Pu-ions rendering them available to the plants and increased the mobility of Pu-ions
178
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Table 3 Concentration ratio (CR) of 239PU in the plant–soil systems as affected by Pu–nitrate with DTPA applications Pu source
Activity level of Pu (Bq g1)
Amounts of DTPA applied (g g1)
CRa102 Crowley soil Indian mustard
239
+
Pu(C6H5O7)
239
Pu(NO3)4
Pu(C6H5O7)+
Weswood soil Sunflower
Indian mustard
Sunflower
46.25
0
9.24 0.88
7.521.23
2.24 0.46
4.610.34
44.40
0 10 50
19.454.34 470.0369.09 556.5674.63
5.561.12 309.6514.37 606.1975.52
3.37 0.90 204.8423.91 369.2218.61
4.000.97 33.826.00 93.1917.14
239
231.3
0
3.94 0.40
2.890.35
1.22 0.21
1.030.20
239
222.0
0 10 50
11.661.62 152.607.33 355.1747.09
1.840.22 76.125.14 408.9321.47
1.73 0.17 123.238.85 157.5928.95
0.830.20 29.652.09 50.533.51
Pu(NO3)4
a
CR=Concentration ratio=(Pu concentration in the dry plant shoot) / (Pu concentration in the soil).
Table 4 Correlation coefficients relating Pu uptake by Indian mustard (Brassica juncea) and sunflower (Helianthus annuus) as affected by Pu–DTPA concentration in different soils Descriptiona
MC-High
MW-Low
MW-High
SC-Low
SC-High
SW-Low
SW-High
MC-Low MC-High MW-Low MW-High SC-Low SC-High SW-Low
0.849***
0.926*** –
– 0.874*** 0.948***
0.905*** – 0.982*** –
– 0.962*** – 0.769** 0.921***
0.799** – 0.919*** – 0.957*** –
– 0.969*** – 0.953*** – 0.899*** 0.928***
a N=12. Descriptions are MC, Indian mustard in Crowley soil; MW, Indian mustard in Weswood soil; SC, sunflower in Crowley soil; SW, sunflower in Weswood soil; Low, low initial activity level (44.40 Bq g1) of Pu–nitrate applied, and High=high initial activity level (222.0 Bq g1) of Pu–nitrate applied (e.g. MC-High=Pu uptake by Indian mustard in Crowley soils as applied with 222.0 Bq g1 of initial Pu activity and 0, 10, and 50 mg DTPA kg1 levels; SW-Low=Pu uptake by sunflower in Weswood soils as applied with 44.40 Bq g1 of initial Pu activity and 0, 10, and 50 mg DTPA kg1). ** P <0.01. *** P <0.001.
to roots by replenishing those taken up by the plant. Other researchers have used multidentate chelating agents, including DTPA, EDTA, ethylenediamine di-ohydroxy-phenylacetic acid (EDDHA), and nitrilotriacetic acid (NTA), as a means of supplying micronutrients to plants in intensive agriculture and in terrestrial and aquatic ecosystems (Lindsay, 1974; Vyas and Mistry, 1983). In this study, Pu uptake by the plants was increased up to 30-fold with DTPA chelation for Indian mustard and up to 200-fold for sunflower from the acidic Crowley soil when compared with Pu– nitrate and Pu–citrate. Plutonium concentration was increased up to 100-fold for Indian mustard and up to 60-fold for sunflower from the calcareous Weswood soil with the addition of DTPA. Addition of DTPA to Pu contaminated soils increased Pu concentration about a 1000-fold in pea plants (Lipton and Goldin, 19761) and increased Pu uptake by tumbleweeds (Ballou et al.,
1978). Wallace (1972) reported a 200-fold increase in Am uptake when Fe–DTPA was applied to soil. A marked enhancement in the mobility of Pu and Am through three contrasting soil types from India was observed on leaching with dilute chelating solution (Vyas and Mistry, 1980). The CR for Pu in plant shoots increased by a factor of 3–700 depending on the soil type and the complexing ligand (Vyas and Mistry, 1983). There is some indirect evidence of phytoaccumulation of Pu using sunflower and Indian mustard. Sunflower generally had a lower bioaccumulation coefficient for radiocesium (137Cs) than Indian mustard (Dushenkov et al., 1999). Accumulation of Zn by Indian mustard was significantly increased by adding EDTA chelate, but was not in oat and barley (Ebbs and Kochian, 1998). Indian mustard appears to be a better candidate for phytoremediation of Pu contaminated soils compared
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
with sunflower. However, sunflower was able to reduce elemental concentrations of manganese, chromium, cadmium, copper, and nickel to extremely low levels after only 24 h. Similar results were obtained for uranium (VI), zinc, and lead (Salt et al., 1995; Brooks and Robinson, 1998). These observations might indicate that plants selected as an accumulator might be more dependent on the target element and on the properties of the soil medium. We investigated the availability and transformation of Pu as affected by soil properties and the Pu complex added to soil (Figs. 2–4). Fractions of 1 M MgCl2 (pH 7.0) extractable Pu (assumed as ion-exchangeable Pu) were comparatively high with DTPA treatment and decreased with time of incubation. The Pu fraction that was bound to precipitated hydrous oxides and insoluble hydroxides was comparatively low with the Pu–DTPA treatment. The carbonate-bound Pu fraction (extracted with 1 M NaOAc; pH 5.0), with or without Pu–DTPA treatment, was unexpectedly detected in the acidic Crowley and non-calcareous Crockett soils. This result might be due to the dissolution of oxide-bound Pu in the soils by buffered acetate solution. Amacher (1996) reported that some dissolution of amorphous metal oxides might occur with buffered acetate solution. The residual Pu fraction was largely dependent on the amounts of Pu extracted in other fractions. More Pu was associated with this fraction, especially in those treatments without DTPA. The amount of Pu in each fraction was not different between treatments of Pu– nitrate and of Pu–citrate in the same soil. Levels of ionexchangeable Pu, with or without DTPA treatment, were much higher in the acidic Crowley soil compared
179
with the calcareous Weswood soil. The Pu level of other fractions did not show consistent trends with time of incubation but were dependent on soil properties. The extraction of Pu from soil was affected by soil pH and the amounts of clay, salt, metal oxides, and carbonates. The lowest amount of Pu was extracted from the Crockett soil, which had a near neutral pH and contained the highest clay content compared with the other two soils. When DTPA was applied to the calcareous Weswood soil, the ion-exchangeable Pu was comparatively less influenced and the amount of Pu in this fraction was more affected by time of incubation. The concentration of Pu in each fraction was higher, with or without DTPA treatment, in the acidic Crowley soil, which had an intermediate clay content. Nishita and Hamilton (1981) reported that Pu extractability was considerably lower over the entire pH range studied (pH 6–13) from soil with HCl-soluble organic matter, salts, and carbonates compared with soil without those properties. They also found that if the soil contained CaCO3 (with or without adding humic acid) and no salts, the amount of extractable Pu was markedly decreased at higher pH. In contrast, Rhodes (1957a, b) investigated Pu adsorption on a calcareous soil containing mainly montmorillonite and kaolinite and little or no organic matter. Strong adsorption of Pu (> 98%) began at pH 2 and extended to the mid range of soil pH. At higher pH values, the Pu adsorption maxium was about 80%. However, Nishita et al. (1977) explained that in most systems, Pu extractability was increased at pH 5.5 or lower, and also increased with increasing pH values over 6.5. The lowest Pu extractability occurred at pH values between 5.5 and 6.5. The extractability of Pu was
Fig. 2. Sequential extractions of Pu in Weswood soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
180
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Fig. 3. Sequential extractions of Pu in Crockett soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
Fig. 4. Sequential extractions of Pu in Crowley soil; Plutonium sources are N=Pu(NO3)4, D=Pu–DTPA, and C=Pu–citrate; Soil and Pu were incubated for 15, 30, 60, and 90 days.
drastically decreased in the presence of decomposing organic matter and dissolving Fe- and Mn-oxides, and CaCO3.
4. Conclusions Plutonium uptake from soil by Indian mustard and sunflower was increased with increasing Pu activity level. A difference in Pu uptake between treatments of Pu–nitrate and Pu–citrate without chelating agent was observed only with Indian mustard in acidic Crowley
soil. Plutonium uptake by the plant was increased with increasing concentrations of DTPA in soils containing both low and high levels of Pu activity. Plutonium in the shoots of plants was significantly higher from the acid Crowley soil compared with the calcareous Weswood soil, especially in those treatments with DTPA chelation. The Pu concentration of Indian mustard was higher than that of sunflower. Also, the Pu concentration of the plant shoots was significantly correlated between the low and high Pu activity levels, plant species, and the acidic and calcareous soils. The shoot Pu concentration did not increase in proportion to the applied Pu–DTPA rates to
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
soils. Therefore, Pu and its predominant ligands are apparently accumulated independently and not absorbed stoichiometrically by the plants. Levels of exchangeable Pu were higher in acidic Crowley soil than in neutral Crockett and calcareous Weswood soils with or without DTPA treatment. The exchangeable Pu fraction initially increased with DTPA treatment but then decreased with time of incubation. When DTPA was added along with Pu to the calcareous Weswood soil, exchangeable Pu was less influenced and this fraction was more affected by time of incubation. Plutonium was unexpectedly detected in the carbonate bound fraction of the non-calcareous soils apparently because the buffered acetate solution may extract or dissolve oxide-bound Pu from the soils. The Pu fraction that was bound to precipitated hydrous oxides and insoluble hydroxides was comparatively lower. More Pu was associated with the residual Pu fraction when the soil was not treated with DTPA. The Pu levels of other fractions did not provide consistent trends with time of incubation and there was no difference in the levels of Pu in the various fractions when Pu–nitrate and Pu–citrate were added to the same soil. The extraction of Pu from these soils was mostly affected by soil pH and the amounts of clay, salts, and carbonates. The lowest amount of extractable Pu was from Crockett soil, which had the highest clay content and moderate pH (6.55) compared with the other two soils.
Acknowledgements The authors acknowledge the financial support of the Amarillo National Resource Center for Plutonium, 600 South Tyler, Amarillo, TX 79101 under agreemet UTA960043.
References Adriano, D.C., McLeod, K.W., Ciravolo, T.G., 1981. Plutonium, curium, and other radionuclide uptake by the rice plant from a naturally weathered, contaminated soil. Soil Sci. 132 (1), 83–88. Allard, B., Olofsson, U., Torstenfelt, B., 1984. Environmental actinide chemistry. Inorganica Chemica Acta 94, 205–221. Amacher, M.C., 1996. Nickel, cadmium, and lead. In: Sparks, D.L. (Ed.), Methods of Soil Analysis, Part 3—Chemical Methods. Number 5 in the SSSA of America Book Series. SSSA and ASA, Madison, WI, pp. 739–768. Ballou, J.E., Price, K.R., Gies, R.A., Doctor, P.G., 1978. The influence of DTPA on the biological availability of transuranics. Health Phys. 34, 445–450. Brooks, R.R., Robinson, B.H., 1998. Aquatic phytoremediation by accumulator Plants. In: Brooks, R.R. (Ed.), Plants that Hyperaccumulate Heavy Metals: Their Role in Phytoremediation, Microbiology, Archaeology, Mineral Exploration and Phytomining. CAB International, New York, pp. 203–266. Burken, J.G., Schnoor, J.L., 1996. Phytoremediation: Plant uptake of atrazine and role of root exudates. J. Environ. Eng. Nov. 958–963.
181
Cline, J.F., Schreckhise, R.G., 1983. Comparative plant uptake of plutonium-239 added to soil in the oxide vs. the nitrate form. In: Pinder III, J.E. (Ed.), Environmental Research on Actinide Elements. Proceeding of a Symposium held at Hilton Head, South Carolina, 7–11 November. Office of Scientific and Tech. Information, DOE, 1987, Oak Ridge, TN, pp. 73–81. Cunningham, S.D., Ow, D.W., 1996. Promises and prospects of phytoremediation. Plant Physiol. 110, 715–719. Dushenkov, S., Mikheev, A., Prokhnevsky, A., Ruchko, M., Sorochinsky, B., 1999. Phytoremediation of radiocesium-contaminated soil in the vicinity of Chernobyl. Kraine. Environ. Sci. Tech. 33 (3), 457–469. Dushenkov, V., Kumar, P.B.A.N., Motto, H., Raskin, I., 1995. Rhizofiltration: the use of plants to remove heavy metals from aqueous streams. Environ. Sci. Tech. 29, 1239–1245. Ebbs, S.D., Kochian, L.V., 1998. Phytoextraction of zinc by oat (Avena sativa), barley (Hordeum vulgare), and Indian mustard (Brassica juncea). Environ. Sci. Tech. 32 (6), 802–806. Ebbs, S.D., Lasat, M.M., Brady, D.J., Cornish, J., Gordon, R., Kochian, L.V., 1997. Phytoextraction of cadmium and zinc from a contaminated soil. J. Environ. Qual. 26, 1424–1430. Garland, T.R., Cataldo, D.A., Wildung, R.E., 1981. Absorption, transport, and chemical fate of plutonium in soybean plants. J. Agric. Food Chem. 29 (5), 915–920. Huang, J.W., Chen, J., Berti, W.R., Cunningham, S.D., 1997. Phytoremediation of lead-contaminated soils: role of synthetic chelates in lead phytoextraction. Environ. Sci. Tech. 31, 800–805. Jones Jr., J.B., 1991. Plant tissue analysis in micronutrients. In: Mortvedt, J.J., Cox, F.R., Shuman, L.M., Welch, R.M. (Eds.), Micronutrients in Agriculture, second ed. SSSA, Madison, WI, pp. 477– 521. Lee, J.H., Hossner, L.R., Attrep Jr., M., Kung, K.S., 2002. Uptake and translocation of plutonium in two plant species using hydroponics. Environ. Pollu. 117 (1), 61–68. Lindsay, W.L., 1974. Role of chelation in micronutrient availability. In: Carson, E.W. (Ed.), Plant Roots and its Environment. University Press of Virginia, Charlottesville, VA, pp. 507– 524. Lipton, W.V., Goldin, A.S., 1976. Some factors influencing the uptake of plutonium 239 by pea plants. Health Phys. 31, 425–430. Loeppert, R.H., Inskeep, W.P., 1996. Iron. In: Sparks, D.L. (Ed.), Methods of Soil Analysis, Part 3—Chemical Methods. Number 5 in the SSSA of America Book Series. SSSA and ASA, Madison, WI, pp. 639–644. Lu, N., Kung, K.S., Mason, C.F.V., Triay, I.R., Cotter, C.R., Pappas, A.I., Pappas, M.E.G., 1998. Removal of plutonium-239 and americium-241 from Rocky Flats soil by leaching. Enviro. Sci. Tech. 32 (3), 370–374. McLeod, K.W., Adriano, D.C., Ciravolo, T.G., 1981. Uptake of plutonium from soils contaminated by a nuclear fuel chemical separation facility. Soil Sci. 132 (1), 89–98. Moore, F.L., Hudgens Jr., J.E., 1957. Separation and determination of plutonium by liquid–liquid extraction. Anal. Chem. 29 (12), 1767–1770. Nishita, H., 1981. Relative adsorption and plant uptake of 238PU and 239 Pu in soils. Soil Sci. 132 (1), 66–70. Nishita, H., Hamilton, M., 1981. The influence of several soil components and their interaction on plutonium extractability from a calcareous soil. Soil Sci. 131 (1), 56–59. Nishita, H., Haug, R.M., Rutherford, T., 1977. Effect of inorganic and organic compounds on the extractability of 239Pu from an artificially contaminated soil. J. Environ. Qual. 6 (4), 451–455. Pimpl, M., Schuttelkopf, H., 1981. Transport of plutonium, americium, and curium from soils into plants by root uptake. Nuclear Safety 22 (2), 214–225. Rhodes, D.W., 1957a. Adsorption of plutonium by soil. Soil Sci. 84, 465–471.
182
J.H. Lee et al. / Environmental Pollution 120 (2002) 173–182
Rhodes, D.W., 1957b. The effect of pH on the uptake of radioactive isotopes from solution by a soil. Soil Sci. Soc. Am. Proc. 21, 389– 392. Romney, E.M., Wallace, A., Schulz, R.K., Kinnear, J., Wood, R.A., 1981. Plant uptake of 237Np, 239,240Pu, 241Am, and 244Cm from soils representing major food production areas of the United States. Soil Sci. 132 (1), 40–59. Salt, D.E., Blaylock, M., Kumar, N.P.B.A., Dushenkov, V., Ensley, B.D., Chet, I., Raskin, I., 1995. Phytoremediation: a novel strategy for the removal of toxic metals from the environment using plants. Bio/Tech. 13, 468–474. Schnoor, J.L., 1997. Phytoremediation (Technology Evaluation Report, TE-98–01). Ground-Water Remediation Technologies Analysis Center, Pittsburgh, PA. Schnoor, J.L., Licht, L.A., McCutcheon, S.C., Wolfe, N.L., Carreira, L.H., 1995. Phytoremediation of organic and nutrient contaminants. Environ. Sci. Tech. 29 (7), 318A–323A. Schulz, R.K., Ruggieri, M.R., 1981. Uptake and translocation of neptunium-237, plutonium-238, plutonium-239,240, americium-241, and curium-244 by a wheat crop. Soil Sci. 132 (1), 77–82.
Tessier, T., Campbell, P.G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51 (7), 844–851. Vyas, B.N., Mistry, K.B., 1978. Studies on the uptake of plutonium from major Indian soils and its distribution in plants. J. Environ. Qual. 7 (4), 533–536. Vyas, B.N., Mistry, K.B., 1980. Studies on the mobility of plutonium239 and americium-241 in three major Indian soils. J. Nuclear Agric. Biol. 9, 85–88. Vyas, B.N., Mistry, K.B., 1983. Influence of chelating agents on the uptake of 239PU and 241Am by plants. Plant and Soil 73, 345–353. Vyas, B.N., Mistry, K.B., 1984. Studies on transformation of plutonium-239 and americium-241 in three major Indian soils. Sci. Total Environ. 32, 183–195. Wallace, A., 1972. Increased uptake of 241Am by plants caused by the chelating agent DTPA. Health Phys. 22, 559–562. Wildung, R.E., Garland, T.R., 1974. Influence of soil plutonium concentration on plutonium uptake and distribution in shoots and roots of barley. J. Agr. Food Chem. 22 (5), 836–838. Wilson, D.O., Cline, J.F., 1966. Removal of plutonium-239, tungsten185, and lead-210 from soils. Nature 209, 941–942.