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SUMMARY

As part of a study on the use of young barley plants to monitor accumulations of toxic elements arising from sludge or waste disposal, we have examined the interactions between Cu, Ni and Zn in young barley.

We find that Cu has little effect on the amount of Ni or Zn that reaches the shoots or vice versa: Ni uptake is raised by critical levels of Zn; Zn uptake is raised by sub-critical and critical levels of Ni. These effects are small and may be ignored when monitoring sub-toxic accumulations. At higher concentrations the interactions are larger and more complex.

A significant part of the quantity of any one of these elements that has been translocated to the photosynthesising tissues of the barley test plant, up to a threshold concentration [T]x, is not toxic, alone or in combination with the other two elements. Toxic effects become apparent from a critical tissue concentration [T]c, above which yield decreases in proportion to increases in log [T]. [T]x/[T]c∼ 1/2 – 2/3. Values of [T]x and [T]c are presented.

The toxic effects of Cu and Zn appear to be antagonistic (effect less than expected) when the tissue concentrations of both are above their critical levels. Apart from this the toxic effects of the elements above their threshold concentrations are directly additive or slightly less than additive.

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Values are presented for K, k, M and m and the critical values of Ia and Ib.

In their general form these results are very similar to those of similar studies on the toxicity of mixed solutions to fish.