UPPER CRITICAL LEVELS OF TOXIC ELEMENTS IN PLANTS

Abstract

Summary: This study examined the effect of Cu, Ni, Zn or Cd in the leaves and shoots of young barley on their yield of dry matter. As expected, the yield of dry matter, or the uptake of heavy metals from a given solution, varies considerably with growing conditions. However, the minimum concentrations of these elements in the plant tissue that was necessary before the yield of dry matter was reduced by their toxic effects (‘upper critical level’) proved to be independent of growing conditions varied enough for the control plants to have required 14–31 days to reach the five‐leaf stage, and for the weights of the control plants to have ranged from 76 to 214 mg. This being so it is suggested that if young barley plants were used to monitor accumulations of heavy metals in the soil environment, the quantity would provide a good measure of the hazard of any accumulation relative to the onset of toxicity, where To and Tc are standard values for the background (unpolluted) and the upper critical level of the element in plant tissue, and Tits level in a test crop. This reduces to [m. Log 10T/n] and if T is measured in ppm of dry matter, m and n are approximately, image A graph of Relative Hazard against tissue concentration is presented.