Atlas of Contaminated Sites

Notable case, Ōkuma / Futaba, Fukushima Prefecture, Japan

Fukushima Daiichi and its fallout area

福島第一原子力発電所

The nuclear plant struck by the tsunami of 11 March 2011 and the land where its radioactive caesium fell. It is the largest decontamination of farmland and settlements ever attempted, and the place where sunflower phytoextraction was tested in the field and dropped.

Phytoremediation

Status
Remediation under way
Activity
2011–2011
People affected
164,000 (2012)2
Media
soil, surface water, sediment, groundwater, living organisms, air
Kind of site
nuclear, accident, power plant
  1. Area. There is no single official figure. Evacuation first covered a 20 km radius around the plant; the Interim Storage Facility for removed soil, in Ōkuma and Futaba, takes up about 1,600 hectares (Japanese Ministry of the Environment).
  2. People affected. Evacuees at the peak, June 2012 (Wikipedia). Ten years on, more than 40,000 were still displaced.

Contaminants

Radionuclides

Status

Remediation under way

Full-scale decontamination outside the restricted areas was completed by March 2018; by the end of July 2025 about 14.11 million m³ of removed soil and waste had been taken to the Interim Storage Facility (Ministry of the Environment). Decommissioning the plant is expected to take 30–40 years from the accident; treated water has been discharged to the sea since 2023.

Story

On 11 March 2011 the Tōhoku earthquake (magnitude 9.0) and the tsunami that followed cut power and cooling at the Fukushima Daiichi plant, between Ōkuma and Futaba. Core meltdowns and hydrogen explosions released to the air, by the estimates given in Wikipedia, 100–400 PBq of iodine-131 and 7–20 PBq of caesium-137. The accident was rated level 7 on the INES scale.

The 20 km around the plant were evacuated first, then further areas to the north-west, where fallout had been heaviest. The number of evacuees peaked at 164,000 in June 2012. On farmland the caesium stayed at the surface: according to the Ministry of Agriculture (MAFF), 95% lay in the top 2.5 cm of soil.

Decontamination therefore relied on stripping the surface layer. The removed soil and waste, about 14 million m³, have been moved since 2015 to an Interim Storage Facility of about 1,600 hectares around the plant; the law requires final disposal outside the prefecture within thirty years of the start of transport. Evacuation orders were lifted in stages; in the "reconstruction bases" inside the restricted zone they were lifted by November 2023.

Timeline

  1. 201111 March: earthquake and tsunami, loss of cooling and release of radionuclides. In September MAFF publishes the results of its farmland decontamination trials.
  2. 2012June: 164,000 evacuees, the peak.
  3. 2014December: fuel removal from the unit 4 pool is completed.
  4. 2015Transport of removed soil to the Interim Storage Facility begins (end of fiscal year 2014).
  5. 2018March: full-scale decontamination outside the restricted areas is completed.
  6. 2023August: discharge of treated water to the sea begins. November: evacuation orders lifted in the reconstruction bases of six municipalities.

Health

According to the UN scientific committee (UNSCEAR), as cited by Wikipedia, no adverse health effects directly attributable to radiation exposure have been documented among residents. Wikipedia reports 51 deaths linked to the conditions of evacuation and one worker's death from lung cancer recognised as radiation-related.

Remediation

  1. 2011topsoil removalRemoval of the surface layer of soil. In MAFF's 2011 trials, taking off 3 cm of soil together with shallow-rooted grass cut caesium by 97%; scraping 4 cm without grass by 75%; flooding, tilling and draining paddies by 36%.
  2. 2015interim storageTransport of removed soil and waste to the Interim Storage Facility in Ōkuma and Futaba: about 14.11 million m³ by the end of July 2025.
  3. 2023treated water dischargeDischarge to the sea of the treated water stored at the plant, planned over about thirty years.

Plants and fungi at this site

PhytoremediationField scale, 2011

Helianthus annuus

Trial by Japan's Ministry of Agriculture (MAFF): sunflowers grown on contaminated fields in Iitate and Kōriyama to see whether they would take up radioactive caesium from the soil. It was part of a set of farmland decontamination trials whose results were released on 14 September 2011.

Outcome It failed. With soil at 1,045 Bq/kg (Kōriyama) and 7,715 Bq/kg (Iitate), stems and flowers held 12–79 Bq/kg and roots 64–232 Bq/kg (fresh weight). The caesium sat in the top few centimetres of soil, while sunflower roots reach below one metre. MAFF concluded that plants could not be relied on for decontamination and abandoned the method.

PhytoremediationField scale, 2012

Helianthus annuus

After the MAFF result, a team led by Osamu Amano (Japan Atomic Energy Agency) had farmers in two districts of Minamisōma grow sunflowers on shallow fields that were tilled first to spread the caesium through the soil, measuring caesium in roots, stems and soil over time.

Outcome The report states that uptake was highest during the most vigorous growth, just before flowering. The amounts removed were not checked for this record.

PhytoremediationField scale

Kobayashi, Okouchi, Yamagami and Shinano grew thirteen crop species of three families (Asteraceae, Fabaceae, Poaceae) in fields ploughed to 8 and to 15 cm, to check whether plants decontaminate the soil and which species are useful.

Outcome In substance a failure: soil-to-plant transfer factors were between 0.019 and 0.13 and no species gave a noticeable decrease of radiocaesium in the soil. The abstract names the families, not the individual species.

From the literature

Species that acted on one of this site's contaminants in at least one study. The list is automatic and takes no account of this site's soil, concentrations or climate.

Plants

Fungi

Nearby

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Ashio Copper Mine

166 km

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  • Cadmium
  • Lead
  • Arsenic

Notable case, Toyama, Japan

Jinzū River basin (itai-itai disease)

346 km

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  • Zinc
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Sources

  1. Environmental Remediation: Decontamination, Ministry of the Environment, Japan, 2025
  2. Environmental Remediation: Interim Storage Facility, Ministry of the Environment, Japan, 2025
  3. Amano O. Results of Removing Radioactive Cesium from the Shallow Rice Fields by Planting Sunflower, Atomic Energy Society of Japan, 2021
  4. Sunflowers next to useless for nuclear decontamination, Asahi Shimbun (Japan Disasters Digital Archive), 2011
  5. Fukushima nuclear accident, Wikipedia, 2026

Draft compiled from public sources, not yet reviewed.