The influence of solution concentration of aluminium, arsenic, boron and copper on root growth in relation to the phytotoxicity of pulverised fuel ash

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Abstract
To find whether the concentrations of aluminium, arsenic, boron or copper and soluble sulphate salts which have previously been found in the aqueous phase of water saturated pulverised fuel ash (PFA) are sufficiently high to restrict growth, lettuce seedlings were grown on filter paper saturated with a solution containing various concentrations of each of the different ions. Over a period of five days root growth was reduced by half when the concentration of aluminium was increased to 2.0 mg/litre, arsenic (As3+) to 1.6 mg/litre, boron to 90 mg/litre or copper to 0.3 mg/litre or when the soluble sulphate salts were increased to 100 mEq/litre (conductivity 8 × 10−3 ohm−1 cm−1 at 20°C). The concentrations of ions in the aqueous phase of wet PFA depend on pH which varies greatly from one batch of ash to another. The concentrations of aluminium and copper in equilibrium with acid batches of ash and those of arsenic in equilibrium with alkaline batches of ash were sufficiently high to restrict growth. The concentrations of boron and soluble salts were always at phytotoxic levels irrespective of the pH of the ash.