Effectiveness and Variability of Digestion Procedures for Zinc Determination in Aged, Contaminated Soils

Abstract

Abstract : Owing to the numerous advantages provided by microwave digestion, regulatory agencies are recognizing its value, yet most reported comparisons of microwave digestions with other accepted methods have used ores, laboratory- spiked soils, or soils with unexceptional, rather than elevated, metal concentrations. Objectives of this research included evaluating microwave digestion for routine laboratory use and comparing microwave, block digester, and hot-plate soil digestion techniques for determining zinc in aged, zinc- contaminated soils. Soil samples, chosen to provide a more realistic and rigorous test of the digestion procedures than would spike recovery methods and known to contain appreciable quantities of zinc, were collected from sites near a zinc smelter that had operated for more than 80 years. To obtain a range of zinc concentrations, surface (0-20 cm) samples of Weikert silt loam soil (loamy- skeletal, mixed, mesic, shallow Typic Dystrochrept) were collected from a location subject to airborne contamination from the smelter site. Very highly significant effects for digestion method, soil, and method x soil interaction were observed. Considering all the soils analyzed as a group, there was no significant difference in zinc release between two separate microwave digestions, or between the hot-plate and block digestion methods. However, microwave digestion resulted in significantly more complete metal release and greater metal concentration values than did either the hot-plate or block digestion methods. Effect of digestion method was not constant among soils. Uniformity for the microwave digestion replications was better than for either block or hot-plate methods. Contamination, Heavy metal, Trace metal.