The effect of the solution pH was studied at Au concentrations of 100 and 1000 ppm. Fig. 4a shows the pH dependent uptake of both plants. The highest Au concentration in the plant was observed at pH3. This is consistent with Girling and Peterson [29]whoobserved increased uptake of Au at acidic pH. Au uptake in MS was always higher than in BJ, although BJ showed a 6-fold increase in uptake at pH 3 compared to pH 6. The effect at 1000ppm was inconclusive
for both MS and BJ (Fig. 4b). Maximum uptake of 75mgAu g−1 dry weight in MS and 41mgAu g−1 dry weight in BJ was observed. The Au concentration in the shoots of both BJ and MS was not significantly influenced by a reduction in pH, hence translocation of Au from roots to shoots was pH independent. This result is consistent with the findings of Rodriguez [17].