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Phytoremediation of Radiocesium in Different Soils Using Cultivated Plants

Following the nuclear power plant disaster, more than 90 % of the radionuclides were distributed in the upper 6 cm of the soil column in wheat fields, and within 4 cm of the surface in rice paddies, orchards, and cedar forests [9]. It is well known that radiocesium is adsorbed into the soil and binds strongly to clay. As a result, it is difficult to reduce the contamination level in the soil. It was reported that phytoremediation using rice plants in a paddy field was also difficult [10]. We examined the

Fig. 13.1 Relationship between transfer factor of soil to brown rice and exchangeable K2O in the soil

Table 13.1 Yield of four plants cultivated in light-colored andosol and gray lowland soil

possibility of decontamination by means of phytoremediation using four agricultural plants such as sunflower (Helianthus annuus L.), amaranth (Amaranthus L.), sorghum (Sorghum bicolor), and buckwheat (Fagopyrum esculentum) in upland fields. The total yields of biomass cultivated in the light-colored Andosol and gray lowland soil is shown in Table 13.1. The biomass of the sorghum in the gray lowland soil (2.91 kg dry weight m−2) was five times higher than that of buckwheat cultivated in the light-colored Andosol, and the gray lowland soil was within a factor of 2.

Table 13.2 Concentration of 137Cs in plant components (Bq kg−1 dry weight)

Concentration of plant component

Cultivated soil type

Plant

Leaf

Stem

Flower

Root

Whole body

Aboveground of plant

Light-

Amaranth

184 ± 57.7

49 ± 31.6

57 ± 11.0

113 ± 48.4

50 ± 4.9

79 ± 15.8

colored

Buckwheat

104 ± 26.4

9 ± 0.1

33 ± 10.7

150 ± 9.9

22 ± 1.9

37 ± 5.4

andosol

Sorghum

72 ± 8.4

25 ± 12.5

156 ± 9.9

21 ± 4.1

42 ± 9.4

Sunflower

152 ± 28.7

46 ± 7.4

23 ± 2.5

142 ± 119.1

68 ± 9.1

48 ± 6.4

Gray

Amaranth

157 ± 10.9

11 ± 3.8

38 ± 7.5

29 ± 12.6

84 ± 14.2

51 ± 5.6

lowland

Buckwheat

41 ± 3.5

8 ± 1.3

34 ± 3.6

38 ± 2.6

43 ± 5.0

21 ± 2.5

soil

Sorghum

41 ± 7.4

5 ± 1.4

35 ± 8.7

58 ± 7.4

18 ± 4.1

Sunflower

231 ± 4.7

30 ± 8.7

11 ± 2.3

39 ± 13.9

65 ± 11.6

69 ± 11.6

Decay correction was done at harvest time, 2011; average ± SD (n = 3)

Sorghum had the highest biomass in both the light-colored Andosol and the gray lowland soil.

The concentration of 137Cs in the soil among the fields was 1,300–2,000 Bq kg−1 dry weight. The concentration of 137Cs in the plant components is indicated in Table 13.1. Among the components, the leaves exhibited the highest concentration of 137Cs, except sorghum cultivated in the light-colored Andosol. The concentration of 137Cs in the roots, including adhered soil particles, was relatively similar among the plants cultivated in each soil. However, the concentration of 137Cs in the stem differed approximately fivefold among the plants. The 137Cs concentration in the aboveground part of the plant was 36.7–78.9 Bq kg−1 dry weight in the light-colored Andosol and 18.0–69.1 Bq kg−1 dry weight in the gray lowland soil (Table 13.2).

The total content of 137Cs in the biomass among the four plants was 19.8– 132 Bq m−2 cultivated in the light-colored Andosol and 17.6–79.8 Bq m−2 cultivated in the gray lowland soil. The content in amaranth and sunflower was the highest in the light-colored Andosol and the gray lowland soil, respectively.

The removal percentage of 137Cs, which is defined as the ratio of the total content of 137Cs in the plant biomass (20–154 Bq m−2) to that in the cultivated soil of 0–15 cm depth (154,000–247,000 Bq m−2), was 0.015–0.109 % for the light-colored Andosol and 0.008–0.039 % for the gray lowland soil. The removal percentage of 137Cs for aboveground parts, excluding the root part, was 0.013–0.093 % for the light-colored Andosol and 0.007–0.038 % for the gray lowland soil. The highest values of the aboveground parts were obtained in amaranth (0.093 %) and sunflower (0.038 %) in the light-colored Andosol and the gray lowland soil, respectively (Table 13.3). The ratio of the removal of radiocesium from the surface soil to that of the cultivated biomass, that is, sunflower, amaranth, sorghum, and buckwheat, was negligible. This result indicates that it is difficult to remove radiocesium from contaminated soil by means of phytoremediation.

Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Table 13.3 Removal percentage of 137Cs by cultivated plant

References

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8. Kato N (2012) Countermeasures to reduce radiocaesium contamination in paddy rice, soybean and cabbage. In: International science symposium on combating radionuclide contamination in agro-soil environment, Fukushima, Japan, 8–10 March 2012, pp 317–318

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