RADISH AS AN INDICATOR PLANT FOR DERELICT LAND - UPTAKE OF ZINC AT TOXIC CONCENTRATIONS

Radish was grown in glasshouse experiments. Two experiments involved mixing varying ratios of calcareous zinc (Zn) mine waste with soil and in the third, radish was grown in culture solution supplemented with Zn. Zinc toxicity was seen at higher treatment concentrations. From curves for substrate Zn versus % yield the toxic threshold was estimated as 343 mug Zn/g soil which compares favourably with the British ''trigger concentration'' of 300 mug Zn/g. Small yields of hypocotyls were obtained at 1000 mug Zn/g. A 50% yield reduction occurred at tissue Zn concentrations from 36.1 - 1013 mug/g. The shape of Zn uptake curves suggested that hypocotyls were ''indicators'' of Zn uptake but leaves were ''excluders''. The relative ease with which radish is grown in terms of climate and supervision together with its growth properties on contaminated soil suggest it is suitable as a monitor crop for derelict land.