EFFECTS OF AMELIORATIVE TREATMENTS APPLIED TO RADIOCAESIUM CONTAMINATED UPLAND VEGETATION IN THE UNITED KINGDOM

摘要

Relatively high levels of ~(137)Cs have persisted in some upland areas of the United Kingdom following the Chernobyl accident. The ~(137)Cs deposition in the British Isles was related to rainfall patterns, and deposition was highest in areas of heavy rainfall, including Cumbria and north Wales. Because of the peat soils, low nutrient status and semi-natural vegetation of these upland areas, the radiocaesium deposited has remained available for plant uptake and transfer to livestock. The radiocaesium concentration in lambs grazing this contaminated vegetation continues to exceed the statutory level of 1000 Bq/kg live weight, and restrictions on the movement, sale and slaughter of livestock remain in force. The ability of soil treatments to reduce the radiocaesium concentration in vegetation via immobilization in soil and/or competition of caesium and potassium for plant uptake was investigated. Field plots in north Wales and Cumbria were treated with potassium, ammonium ferric hexacyanoferrate (AFCF), bentonite and clinoptilolite in 1990, and the radiocaesium concentrations of vegetation and soil were monitored for three years following application. The ~(137)Cs concentration of vegetation on both treated plots and control plots exhibited a strong seasonal variation, with the peak concentration being in early summer. The variation in ~(137)Cs concentration between different plant species was large, and the response to treatments also varied between plant species. The potassium treatment produced reductions in the radiocaesium concentration of the natural vegetation, especially in the initial years after treatment. Clinoptilolite and AFCF treatments also produced reductions in radiocaesium concentration, with some plant species showing greater responses to the various treatments. Potassium, clinoptilolite and AFCF have shown some potential for use as soil ameliorative treatments for ~(137)Cs reduction on upland peat soils with grazed semi-natural vegetation.