Assessment of Metal - Induced Inhibition of Soybean Urease as a Tool for Measuring Heavy Metals in Aqueous Samples

Inhibition of soybean (Glycine max) urease by heavy metal ions has been investigated with a view to developing a method for the indirect determination the heavy metals. Urease activity was assayed as a function of metal concentration in the presence of Cd 2+ , Cr 3+ , As 3+ , Cu 2+ , Pb 2+ and Zn 2+ . Our results revealed concentration dependent inhibition of urease activity within the range of 0.001 -10 mg/L for Cu 2+ , As 3+ , Cr 3+ and Cd 2+ and 0.1 -10 mg/L for Zn 2+ and Pb 2+ . The inhibitory strengths of the metals as evaluated from their IC50 values showed the following ranking: Cu 2+ > As 3+ > Cr 3+ > Cd 2+ >Zn 2+ > Pb 2+ . Assays for multi-metal solutions revealed similar findings as the single-metal systems but with higher inhibitory strengths. The calibration plots of % inhibition against concentration displayed different linear ranges for the investigated metals; Cu As, Cr and Cd showed linearity within the range of 0.01 -10mg/L while Zn and Pb plots were linear within 0.1 -10 mg/L. The applicability of the assay for the quantitative determination of heavy metals was evaluated by analysing synthetic water samples and comparing the results with a standard method (AAS). T-test examination revealed 74% agreement between the two methods. The results of this study show that soybean urease can be valuable for the inhibitive determination of heavy metals in aqueous samples.