SOIL ACIDIFICATION EFFECTS ON THE BIOAVAILABILITY OF ZN AND CD AND ACCUMULATION IN TWO INDICATOR SPECIES

A pot experiment with four different soils was conducted with varying degree of Zn and Cd contamination and modified each of them to three different pH levels: A(0) (original soil pH), moderately acidic A(1) (4.5) and highly acidic A(2) (3.5). Two indicator plant species, Taraxacum officinale and Plantago lanceolata, were planted on each of soil treatments and were grown for 75 days. Decreasing soil pH increased Ca(NO3)(2) extractability of Zn and Cd. Similarly in planted pots increased uptake of Zn and Cd was found for A(1) acidity level but no plants were able to grow on A(2) level. Interestingly in two soils, A(1) produced more biomass (2.30 and 1.15 times more) as compared to original pH treatment (A(0)). In DGT samplers, significantly increased amounts of Zn and Cd were found due to increasing soil solution concentration of Zn and Cd with decreasing pH. Due to soil acidification the resupply was significantly decreased, clearly reflected by DGT derived R values. Both Ca(NO3)(2) extract and DGT data nicely predict the high uptake and hence accumulation of Zn and Cd in AI (pH 4.5 soil) as compared to Ao (original soil pH). Acidification could clearly increase the uptake of Zn and Cd in plants but it is strongly recommended that the soil acidification should not decrease below 4.5 pH level to avoid toxicity effects of heavy metals and Aluminium.