The contamination of agricultural areas by fission products from nuclear events is a possibility, and would in turn lead to contamination of plants. Of special importance is the long-lived strontium-90, as it has been shown1 that this isotope is taken up by plants to a much greater extent than any of the other long-lived fission products. Much work2–5 has, therefore, been concerned with the possibility of bringing down the strontium-90 uptake by plants through ploughing or through the addition of lime or fertilizer to the soil. Another factor, the effect of ageing on the availability of strontium, has been considered6,7. In general, these methods appear to be of little practical value, except for deep ploughing and the liming of acid soils, both of which will reduce the strontium uptake by a factor of 3–4.