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Assessment of heavy metals contamination in soils surrounding a gold mine: comparison of two digestion methods

This study investigated two digestion methods (USEPA 3051: microwave, HNO3 or Hossner: hot plate, HF–H2SO4–HClO4) for heavy metals analysis in contaminated soil surrounding Mahad AD'Dahab mine, Saudi Arabia. Moreover, contamination metal levels were estimated. The Hossner and USEPA 3051 methods showed, respectively, average total contents of 17.2 and 18.1 mg kg−1 for Cd, 11.6 and 10.6 mg kg−1 for Co, 45.7 and 34.7 mg kg−1 for Cr, 1030 and 1100 mg kg−1 for Cu, 33,300 and 27,400 mg kg−1 for Fe, 963 and 872 mg kg−1 for Mn, 33.2 and 22.8 mg kg−1 for Ni, 791 and 782 mg kg−1for Pb, and 6320 and 2870 mg kg−1 for Zn. A lack of significant differences and a high correlation coefficient (>90%) for Cd, Pb and Cu between the two digestion methods suggest that the total-recoverable method (USEPA 3051) may be equivalent to the total-total digestion method (Hossner) for determining these metals in the studied soil. However, significantly higher concentrations of Cr, Fe, Ni and Zn were found by the Hossner method comapred with the USEPA 3051 method. The soil samples have very or extremely high levels of Zn, Cu, Cd and Pb contamination, indicating very high potential ecological risk.