A comparison study of dry and wet ashing methods used for the assessment of concentration of five heavy metals in three vegetables from Rivers State, Nigeria.

Abstract

Three commonly consumed edible vegetables from two sites in Port Harcourt, Rivers State were studied to evaluate the concentrations of five heavy metals (Pb, Ni, Cu, Mn, Co) using the dry ashing and wet ashing (digestion) methods.  Results showed that most of the metals were lost using the dry ashing method resulting in very low values when compared to those obtained from wet ashing.  Co had values of 20.1 mg/kg to 40.2 mg/kg for dry ashing and 278 mg/kg to 393 mg/kg for wet ashing followed by Ni, 24.0 mg/kg to 34.0 mg/kg for dry ashing and 138 mg/kg to 276 mg/kg for wet ashing.  Pb had values of 20.6 mg/kg to 47.2 mg/kg for dry ashing and 68.2 mg/kg to 196 mg/kg for wet ashing and Mn had values of 18.8 mg/kg to 116mg/kg for dry ashing and 63.1 mg/kg to 172mg/kg for wet ashing. For Cu, the values were 20.7 mg/kg to 35.1 mg/kg for dry ashing and 42.6mg/kg to 99.6 mg/kg for wet ashing.  Mn had high concentrations from both methods. Statistical analysis was carried out for both methods using the paired t-test. The result showed that the calculated t-value for each of the heavy metals was significantly higher than the critical value of . The result leads to the conclusion that the wet ashing method is better.

Keywords: dry ashing, wet ashing, , heavy metals, paired t-test.