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The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution.

Most analytical methods for trace element determination in plant material require decomposition of the sample. Sample decomposition procedures play an important role in ensuring that chemical analysis gives correct results. This is especially important in the determination of trace elements in plant material for environmental studies because, as a rule, plant material is not homogeneous and usually contains variable matrices. In this paper microwave digestion procedures using HNO$_3$, HNO$_3$ $+$H$_2$O$_2$, HNO$_3$ $+$HClO$_4$, HF mixtures and dry ashing $+$ HF were investigated for the analysis of Al, Ca, Cr, K, Mg, Mn, Zn, S, Pb, V, Cu, Cd, Co and Ni by ICP-AES or ICP-MS from pine needle samples. Reference samples BCR CRM 100 (Spruce Needles), BCR CRM 101 (Beech Leaves) and HUMH2 (Organic surface soil) were used to test the dissolution methods. The results showed that the sample digestion procedure is critical step for obtaining accurate results. Losses of volatile metals were notable in many cases when dry ashing was used.