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Abstract
Seedlings of the Chinese White Cabbage, Brassica parachinensis were grown in garden soil alone, and with two kinds of sludge, namely activated and digested sludge with l:500 and 2:500 (dry weight) application rates, respectively.
The results showed a positive effect with the addition of both types of sludge at the 1:500 and a negative effect at the 2:500. This was indicated by the total dry weight after the seedlings had been cultured for a period of 30 days.
Foliar analyses of the plants revealed a significantly higher uptake of Cd (P<0.01) in the activated sludge amended‐soil and both Cd and Mn (P<0.01) in the digested sludge amended‐soil at 1:500 application rates when compared with those grown in the garden soil alone. More heavy metals were transferred to the leaf tissues at the 2:500 application rate. However, the crops in all the pots showed no visual metal toxicity symptoms, possibly due to the short growing period and the comparatively lower content of heavy metal in the sludge.
Land application of the sludge at a smaller amount increased the soil fertility level and a higher amount depressed the growth of the crops as indicated by the lower productivity. This was mainly due to the higher uptake of various heavy metals. The need to evaluate the possibility of toxic effects through the human food chain is urged.