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While many workers have utilized various reagents for sequential extraction of soil trace metals, few studies have examined the order of extraction for key steps in the sequential procedure. In this study, several sequences involving both adsorbed and structural (occluded) metal extractants were evaluated to determine the most appropriate sequential methodology for extracting different forms of Cu, Fe, and Mn. For “specifically adsorbed” metals, Pb(NO3)2 and CH3COOH were used. The results showed that the former reagent extracted less Cu, Mn, and Fe and was probably more specific in replacing metals covalently bound to adsorption sites. Lead nitrate was therefore placed before CH3COOH extraction in the sequence. Chao's NH2OH·HCl reagent and K4P2O7, used for Mn oxide and organic metal removal, respectively, were found to solubilize significantly different amounts of Cu and Mn depending on sequence, with K4P2O7 extracting more metal when used first. As NH2OH·HCl has little effect on organic metals, it should be used before K4P2O7. Noncrystalline and crystalline Fe compounds are solubilized next, using a variety of reagents, and residual (silicate lattice) metals are dissolved in the final step. A nine‐step sequential method is proposed to characterize trace metals in agricultural, polluted, and waste‐amended soils.

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Magnetic and non-magnetic fractions of coal fly ashes from SE US electric power plants were characterized with special emphasis on the potential environmental consequences of their terrestrial disposal. Quartz and mullite were the crystalline minerals dominating the non-magnetic fractions. Magnetic fractions contained magnetite, hematite, and, to a lesser extent, quartz and mullite. Chemical analyses revealed that magnetic fractions had about 10 times higher concentrations of Fe, and 2-4 times higher concentrations of Co, Ni, and Mn. Non-magnetic fractions were enriched in K, Al and Ca. Iron content within fly ash particles was negatively correlated with elements associated with aluminosilicate matrix (Si, Al, K, Na). Solubility of most elements was higher in the non-magnetic than in the magnetic fractions of alkaline fly ashes at comparable pH. Calcium was associated with the non-magnetic fraction of the alkaline fly ashes which resulted in a higher pH buffering capacity of this fraction.

Contaminated soils can be a source for crop plants of such elements like As, Cd, Cr, Cu, Ni, Pb, and Zn. The excessive transfer of As, Cu, Ni, and Zn to the food chain is controlled by a "soil-plant barrier"; however, for some elements, including Cd, the soil-plant barrier fails. The level of Cd ingested by average person in USA is about 12 micrograms/day, which is relatively low comparing to Risk Reference Dose (70 micrograms Cd/day) established by USEPA. Food of plant origin is a main source of Cd intake by modern society. Fish and shellfish may be a dominant dietary sources of Hg for some human populations. About half of human Pb intake is through food, of which more than half originates from plants. Dietary intake of Cd and Pb may be increased by application of sludges on cropland with already high levels of these metals. Soils amended with sludges in the USA will be permitted (by USEPA-503 regulations) to accumulate Cr, Cd, Cu, Pb, Hg, Ni, and Se, and Zn to levels from 10 to 100 times the present baseline concentrations. These levels are very permissive by international standards. Because of the limited supply of toxicity data obtained from metals applied in sewage sludge, predictions as to the new regulations will protect crop plants from metal toxicities, and food chain from contamination, are difficult to make.