Comparison of four USEPA digestion methods for trace metal analysis using certified and Florida soils

It is critical to compare existing sample digestion methods for evaluating soil contamination and remediation. USEPA Methods 3050, 3051, 3051a, and 3052 were used to digest standard reference materials and representative Florida surface soils. Fifteen trace metals (Ag, As; Be, Be, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, and Zn), and six macro elements (AI, Ca, Fe, K, Mg, and P) were analyzed. Precise analysis was achieved for all elements except for Cd, Mo, Se, and Sb in NIST SRMs 2704 and 2709 by USEPA Methods 3050 and 3051, and for all elements except for As, Mo, Sb, and Se in NIST SRM 2711 by USEPA Method 3052. No significant differences were observed for the three NIST SRMs between the microwave-assisted USEPA Methods 3051 and 3051a and the conventional USEPA Method 3050 except for Ng, Sb, and Sc. USEPA Method 3051a provided comparable values for NIST SRMs certified using USEPA Method 3050. However, fur method correlation coefficients and elemental recoveries in 40 Florida surface soils, USEPA Method 3051a was an overall better alternative for Method 3050 than was Method 3051. Among the four digestion methods, the microwave-assisted USEPA Method 3052 achieved satisfactory recoveries for all elements except As and Rig using NIST SRM 2711. This total-total digestion method provided greater recoveries for 12 elements Ag, Be, Cr, Fe, K, Mn, Mo, Ni, Pb, Si,, Se, and Zn, but lower recoveries for Mg in Florida soils than did the total-recoverable digestion methods (3050, 3051, and 3051a).