Trace element hazards

Concern over the release of hazardous trace elements from the burning of coal has been highlighted by the 1990 Clean Air Act Amendments. Most toxic elements are associated with ash-forming minerals in coal (5). As shown in Table 1, levels of many of these toxic metals can be significantly reduced by physical coal cleaning (6). 

Mineralisation leads to the strongest fixation of the C02 in the aquifer. Whether, and at what reaction rate, it occurs depends on the specific geochemical situation. It should be noted that mineralisation of C02 is considered as desirable, since it leads to a strong fixation but could have adverse effects too. The mineralisation processes usually go hand in hand with dissolution of other parts of the rock matrix. So mineralisation could lead to an increased concentration of hazardous trace elements in the brine that were formerly bound to the rock matrix. 

Sloss, L. L. Davidson, R. M. 2001. Pardoning of potentially hazardous trace elements in coal combustion. Proceedings of 18th Annual International Pittsburgh Coal Conference. CD Rom. 

Research indicates that a significant fraction (50-90% ) of mercury is volatilized and lost during coal combustion (10, 11, 12) and that many of the potentially hazardous trace elements appear concentrated upon finer particulate emissions (13, 14). Several investigators have observed enrichment of these hazardous elements upon particulates in urban areas... 

Ren, D., Xu, D. and Zhao, F. (2004) A preliminary study on the enrichment mechanism and occurrence of hazardous trace elements in the Tertiary lignite from the Shenbei coalfield, China. International Journal of Coal Geology, 57(3-4), 187-96. 

Wagner, N.J. and Hlatshwayo, B. (2005) The occurrence of potentially hazardous trace elements in five Highveld coals, South Africa. International Journal of Coal Geology, 63(3-4), 228-46. 

Zhang, J., Ren, D Zhu, Y. el at. (2004) Mineral matter and potentially hazardous trace elements in coals from Qianxi Fault Depression Area in southwestern Guizhou, China. International Journal of Coal Geology, 57, 49-61. 

Coal contains most of the elements of the periodic table, the majority of which are present in concentrations of 100 ppm or less. Many of these trace elements are toxic to plant and animal life, even at low levels. Because U.S. power plants consune on the order of 600 million tons of coal annually for the production of electricity (1), coal combustion can mobilize thousands of tons of potentially hazardous trace elements into the environment each year. Due to the large quantities of coal combusted, even trace amounts of toxic elements present in the coals can accumulate to hazardous levels. Also, potentially deleterious effects of particulate emissions from coal combustion may be enhanced since many trace elements are surface-enriched (2) and concentrate preferentially in the smaller, more respirable particle sizes (3). Substantial amounts of some elements, such as As, Hg, and Se, are in the vapor phase in flue gases from coal combustion and are essentially unaffected by most particle control devices. Aside from the potential detrimental environmental aspects, trace elements in coal can pose adverse technological... 

The largest and most obvious minerals in coal are the epigenetic minerals that have precipitated in the cleat and fractures subsequent to coal formation. These minerals include sulfides, carbonates, and kaolinite. They are common but volumetrically minor constituents. Nevertheless, the epigenetic sulfide minerals can have a profound impact on the utility of the coal, because they contain potentially hazardous trace elements. 

The analysis of coal ash (Chapter 8) for environmentally hazardous trace elements is but one example of how the data might be used. The mineral portion of coal has been ignored for too many years. It must be considered an integral part of the coal structure and so the ash (and its contents) must also be given consideration when a use is designed for coal. 

For example trace elements in milk powder are not consumed as milk, and moisture in transformer oil is not used in transformers, yet matrix reference materials based on milk are imported as food and are subject to health certification requirements and sometimes import quotas. Likewise a matrix based on oil is identified as fuel or lubricating oil and is both classified as a hazardous material and subject to mineral oil tax. These problems arise because RMs are frequently incorrectly classified by specific title of their matrix (as Reference Material of Trace Elements in Rice is classified as rice) and not as reference material which is the intended use. 

Trace element characterization represents concentrations of elements that are contaminated in materials or their leachates in a trace level, generally reported in units of mg/kg or mg/L. Although in minimum quantities, trace elements need to be characterized to assess the hazardous impact of the... 

Anaerobic mineralization processes in the sediment or bottom water alter water composition (e.g. by removal of nitrate, production of reduced substances such as Mn " ", Fe ", NHi" and H2S hazardous release of trace elements from sediments)... 

First, we analyzed samples for a large number of elements to Identify any elements, regardless of toxicity or typical concentration, that would provide signals for the presence of material from certain types of sources. Both ambient samples and particles from sources were analyzed by Instrumental neutron activation analysis (INAA), by which one can often measure about 35 elements In Individual samples (17), As the Important elements Pb, N1 and Cd are not consistently, If ever, observed by INAA, they were often measured by other methods. As INAA Is sensitive to very small amounts of obscure elements, we have obtained reliable data for elements such as Ga, Hf, Sc, In, W and many rare earths which pose no known health hazard at present levels and contribute Insignificant amounts of mass to TSP. However, as discussed below, many trace elements have already been shown to be Important In receptor... 

Combustion of coal and other fossil fuels is a major source in the envi- ronment of trace elements that are hazards to human health. Toxic elements such as Hg, As, Sb, F, Se, and T1 are volatilized during coal combustion and are emitted directly into the atmosphere or concentrated in the fly ash (1, 2, 3). Most elements in coal occur at only parts per million levels, but large tonnages of coal are consumed each year in the United States. In addition, coal conversion processes, which could vastly increase coal use are now being considered seriously. The fate of trace elements during these processes is largely unknown. 

Kentucky. The cadmium appears to be so distributed in the coal that removal of the high specific gravity fraction of the coal does not affect the cadmium concentration in the remaining coal. This result is different from that encountered with the other trace elements. Other coals will be studied to see if they exhibit the same cadmium distribution as the Hazard No. 4 coal. 

T he ash content and trace element distribution in oils produced from coal are of concern for two different reasons—they bear on possible environmental hazards from the use of the oil and they determine the suitability of the oil for firing in gas turbines. Some trace element analyses of oils produced by the catalytic liquefaction of three coals are reported, together with analyses of the solid residues from the process. The data are neither comprehensive nor particularly accurate and are offered at this time because, in the absence of better information from other laboratories, they seem to be of some interest. 

The paucity of available information on the biological consequences of coal use emissions has been underlined recently by Dixie Lee Ray (8) in her energy report to the President and during a conference sponsored jointly by the American Academy of Pediatrics and the Committee on Environmental Hazards (9). The lag in knowledge of coal-related trace element emissions and their environmental impact has been attributed in large part to belated federal funding (10, 11). 

The hazard of coal-related trace element pollution must be considered in conjunction with similar pollution from other sources. There is nothing toxicologically unique about the trace element composition of coal. It is geochemically similar to the makeup of the earths crust... 

There is an interesting group of trace dements, called ultratrace elements because they are needed, if at all. at not more than 1 ppm in food, probably less than SO ppb. These ultratrace elements include arsenic and nickel, certainly essentia] at these low concentrations, and cadmium and lead, probably not essential. Many of these elements (e.g., Ni. As, Cd, and Pb) are quite toxic at any concentration much above an ultratrace level. Naturally, determination of the essentiality of an ultratrace element is even more difficult than for ordinary trace elements.1— Life used and adapted to those elements and those concentrations available to it (see next section). When humans started mining, using, and releasing these elements into the err. Tnmenl. the ecosystem was faced with hazards it had never before encountered, and to which it had, therefore, never adapted. 

Deficiency syndromes of Zn, Cu, Cr, Se and Mo have occurred in patients on total parenteral nutrition (TPN). There is still much research to be done in assessing the nutritional status of many elements and understanding their metabolism, so that normal dietary intake may be supplemented for health benefits. Table 2 is a summary of the amounts required, the functions and the nutritional (usually dietary) imbalances in humans, where known, of the essential trace elements.31-33 (Note that this summary does not attempt to include imbalances related to environmental toxicology and occupational hazards.) Several trace elements have important functions in the immune system. Some are associated with nucleic acid. Others have structural roles, such as Si in cartilage, F and Zn in bone. They may be parts of vitamins, such as Co in vitamin B12, or hormones, such as iodine in thyroid hormones, Zn and Cr have a role in the synthesis and action of insulin.31-33... 

Underwood EJ. 1979. Interactions of trace elements. In Oehme FW, ed. Hazardous and toxic substances. Vol. 2, New York, NY Marcel Dekker, Inc., 641-668. 

Bamford, S.A., D. Wegrzynek, E. Chinea-Cano, et al. 2004. Application of X-ray fluorescence techniques for the determination of hazardous and essential trace elements in environmental and biological materials. Nukleonika, 49 87-95. 

Trace Elements of Environmental Concern. In a list prepared by a panel o scientists and engineers involved with environmental aspects of coal utilization, As, B, Cd, Hg, Mo, Pb, and Se were considered to be of primary environmental concern (8j. The elements Cr, Cu, Ni, V, and Zn were of moderate concern, while Ba, Co, Ge, and toi were believed to be of minor concern. Despite the toxicity of Ag, Be, Sn, and Tl, the panel believed concentrations of these elements in coal and coal residues are negligible and that the likelihood of health hazards associated with these constituents is remote. This list served as a guide in choosing the elements to be determined in raw and treated coals in this study. However, some of the elements, such as B, were not studied in this work due to the inherent difficulties with the analytical procedures and instrumental methods employed. 

The principal health hazards is instead associated with the chemical constituents of the initial wastewaters which can therefore produce contamination of crops or groundwaters. Cu, Cr, Zn and Se are essential trace elements however, they are PTEs, and above certain concentrations may interfere with or inhibit the actions of cellular enzymes. After the treatment, even if toxic materials are not present in the sludge in concentrations likely to affect humans, they might well be at phytotoxic levels, which would limit their agricultural use (Table 11.5). Furthermore, Hillman (1988) has drawn attention to the particular concern attached to the cumulative poisons, principally PTEs, and carcinogens, mainly organic chemicals. World Health... 

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