Blockade by fertilisers of caesium and stronium uptake into crops: effects on the root uptake process

Abstract

The use of fertilizer application to soils as a countermeasures against the absorption of radiocaesium and radiostrontium by crop roots relies on ionic components of the added materials being able to reduce the trans-membrane flux of radionuclides into the root tissues. This paper reviews evidence which suggests that the potassium (K+) and calcium (Ca2+) ions are the most effective ‘blockers’ of caesium and strontium uptake, respectively, due to their ability to compete directly with these radioions for membrane associated uptake sites. The nature of this competition is highly concentration-dependent giving rise to non-linear soil-to-plant radionuclide transfer functions; in the case of competitive antagonism between Cs and K new evidence suggests that membrane selectivity in favour of the K+ ion may be ‘switched on’ at a threshold concentration resulting in a particularly effective potential exclusion of radiocaesium by this nutrient element. However, it is suggested that at ambient soil solution concentrations of both K and Ca, radiocaesium and radiostrontium uptake may already be so reduced in relation to its maximum potential efficiency that any fertiliser additions will have a relatively small effect in further reducing radionuclide absorption. This supports the observation that fertiliser-based countermeasures are most often effective in nutrient poor soils with a low degree of base saturation.