Trace-Element Geochemistry of Coal Resource Development Related to Environmental Quality and Health (1980)

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1 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS SUMMARY AND CONCLUSIONS The U.S. coal resources are estimated at approximately 3.6 trillion metric tons, of which an estimated 396 billion metric tons can be mined economically. Annual consumption of coal in the United States is currently about 600 million metric tons, of which about two thirds are used in electric power qeneration. The production and use of coal in the United States is projected to double in the next decade. Electric power utilities are the major users of coal, and most of the projected increase will also be for the qeneration of power. Minor increases in coal use as a chemical feedstock to replace petroleum sources is anticipated, but not in the next few years. The use of coal in cokinq will probably remain at about the present level. Because of the way it was formed, coal may contain every naturally occurrinq element. Except for the major elements (carbon, hydroqen, oxyqen, nitroqen, sulfur, silicon, iron, aluminum, potassium, calcium, and maqnesium), most elements are present in coal in trace amounts. The chemical composition of coal is site- and source-specific and varies with rank and location in a coal bed, as well as between beds. Of the trace elements in coal, only boron, mercury, lead, molybdenum, arsenic, cadmium, antimony, and selenium are commonly more abundant in coal than in the averaqe composition of the earth's crust. However, not all are concentrated in coals from the various coal-mininq reqions of the United States. Generally, coals from the western United States contain lower concentrations of sulfur and certain other trace elements than do coals from other reqions in the country. In the future, more of the hiqh- and medium-sulfur coals (>l percent) will underqo cleaninq and processinq before use, primarily to reduce sulfur and inorqanic matter concentrations. In the process of coal cleaninq, trace-element concentrations are usually lower in comparison with those in uncleaned coals. Because western coals are qenerally low in sulfur (<l percent), they are not expected to require coal cleaninq on a broad scale. The handlinq of coal durinq mininq, cleaninq, storaqe, and transportation produces materials that may release trace elements with possible health effects. Information on these trace-element releases is sparse. Coal cleaninq qenerates some dust problems, but most critical 1 

2 is the proper control of slurries or residues produced durinq the washinq and preparation processes. The slurries are acidic and have elevated trace-element concentrations, especially of arsenic, lead, zinc, manqanese, qallium, and selenium. Coal dust is a major problem encountered in storaqe and transport of coal. Aqueous solutions of surface-active aqents are often used to minimize windblown dust. Soils near coal storaqe areas and alonq heavily used coal-haulaqe routes can, however, contain elevated trace- element concentrations because of additions of windblown coal dust or because of the leachinq and dispersal action of rainfall. Direct health impacts of dust or leachates from coal durinq cleaninq, storaqe, or transportation are relatively unknown, but dust inhalation could present a problem if not controlled. Dust-control measures currently used in the United States are expected to prevent severe health hazards. Residues remaininq from coal cleaninq and preparation usinq current methods are site-specific problems dependent on local qeochemical conditions, climatic conditions, and the type of coal treated. Careful monitorinq, neutralization, and disposal should effectively control potential health problems. Unless new and currently unknown health-related problems emerqe, present requlations and controls for coal cleaninq, storaqe, or transportation with existinq technoloqy appear to be adequate to accommodate increased coal consumption. Combustion of coal in power-qeneratinq plants produces a variety of residues and emissions (bottom ash, boiler slaq, fly ash, flue-qas desulfurization sludqe, and noncaptured qases and particulates). The relative amount of each residue depends on the power-plant confiquration and emission-control devices used. Trace elements oriqinatinq from the source coal are redistributed amonq the various residue streams. For example, the concentrations of most inorqanic trace elements are hiqher in ash residues than in the coal. Elements that are volatile at combustion temperatures (e.q., selenium, molybdenum, mercury, boron) may or may not exhibit hiqher concentrations in fly ash than in coal. Fly-ash residues captured in baq filters or electrostatic precipitators, which currently represent the qreater percentaqe of solids collected, contain most of the trace-element burden. Research has demonstrated that when fly ash is incorporated in soil it is beneficial to crop qrowth because it serves as a source of some elements essential to plants, such as sulfur, calcium, molybdenum, boron, zinc, and possibly manqanese. Fly ash is substantially alkaline in nature, and its potential as an inexpensive amendment to neutralize acidic soils has been demonstrated. Field. and qreenhouse studies, however, have shown possible detrimental effects on plant qrowth and crop quality where fly ash has been added to soils at rates qreater than approximately 4 percent by weiqht. In particular, concentrations of total dissolved salts and boron may reach levels that are toxic to plants. Foraqe crops qrown on fly-ash-amended soils may accumulate levels of molybdenum and selenium considered unsafe for livestock consumption. Data available indicate that hazardous accumulations of certain additional trace elements (such as cadmium, arsenic, lead, and mercury) by plants qrown on fly-ash-amended soils will not occur. 

3 In Figure 1, trace elements that are of concern in coal and residues produced from coal resource development have been placed in five categories: of greatest concern; of moderate concern; of minor concern; radioactive elements generally considered to be of minor concern but adequate information is lacking for proper assessment; and of concern but with negligible concentrations in coal and coal residues. • Besides the troublesome gaseous compounds of carbon, nitrogen, and sulfur, the elements of greatest concern are arsenic, boron, cadmium, lead, mercury, molybdenum, and selenium. These eight elements commonly occur in coal and in residues from coal cleaning and combustion at concentrations greater than those encountered on the average in the earth's crust. The elements carbon, nitrogen, and sulfur and their compounds, although considered to be of greatest concern, are beyond the scope of this report and are not discussed here. Arsenic, cadmium, mercury, and lead are highly toxic to most biological systems when they occur in available form at concentrations above certain critical levels. Levels of molybdenum and selenium derived from airborne deposits resulting from coal development produce concentrations in soil and water that should present no adverse impact on the health of humans or plants. Even if molybdenum and selenium become somewhat enriched in soils, they .----- r- -- 3 H Li 4 Be 1.,.11._... , ero11~ 5 B ... ;;i ~ c c...... 7 N o.,... 0 h iilllfOOf" 8 II 10 He ...,.... Ne ..... II 12 13 14 15 16 17 18 Na Mg - Al Si p s .._ Ar _ Cl ...... _ lllllrl•·~ .,_ ...... s.- ~ ... $1,ilf_w: '"'°''~ 19 K Ca ..Sc Ti 20 21 22 __ ff!Va:l l~~ E Cr~ :.1 25 26 Mn. Fe Co fNm a.,u n Ga ,............. As Se Br Kr s.10, ..... .. ...... ..... . 27 31 ~ 34, 35 36 ""'·~ _-- ColCIW9i fit~ '•"·~ C.OOJf Atitrt!C' C•rPIOll 47 _ 37 38 39 40 41 42 43 44 45 46 '18 49 50 51 52 53 54 Rb S,r y Zr .Nb. Mo Tc ....Ru Rh Pd Ag (<id.,_ In Sn Sb Te ...... Xe Cd I ....... ""1.IHf..m '"°""'_,.. $tfM! ...... YHt.._ Z•c.,..._ Mol•tidilrvt '"' 83 PallOCSIWll S•i..-et ll'ld.lliMl'I 4ftl•ltiO!l't h lUlllllll 57 72 74 75 ~ r~11 55 56 73 76 77 78 79 00 81 82 85 Cs ~a L.,._ Hf Ta w ..... Os ... Pt Au Hg Tl Ph Bi c•.- La Re Qr .l~ ,,. Ir ,.,."""" .... l'fllm11119o '°"'' ..... W11lfltllft _At _ """'- ~' CJl!!''I 1M ll•~ L••~ 911.lluiJTft AUOHN ~j.~ 87 89 I04 Fr Ac 58 59 60 61 62 63 64 65 66 67 68 69 70 71 ·-- iicl•_,.. Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ~ ~ ~ % ~ ~ ~ ~ ~ m m lilY ...,'""°""' Ur u Np ,.,"' Pu Am Cm Bk P11o11on"""' Amitie""" c..-111"' Cf Es Fm Md No Lw ltr•e•'Wfft CeUtcr,._ Eifttttif'll-..m "''"''""' •U'ft ,..Ii""" lo.r-"CVll II ELEMENTS OF GREATEST CONCERN mm! ELEMENTS OF MODERATE CONCERN D ELEMENTS OF MINOR CONCERN llIIIIll RADIOACTIVE ELEMENTS, GENERALLY CONSIDERED TO BE OF MINOR CONCERN BUT ADEQUATE INFORMATION IS LACKING FOR PROPER ASSESSMENT [] ELEMENTS OF CONCERN, BUT WITH NEGLIGIBLE CONCENTRATIONS IN COAL ANO COAL RESIDUES D ELEMENTS OF NO IMMEDIATE CONCERN FIGURE 1 Potentially hazardous elements in coal resource development. 

4 should not be toxic to plants. However, the disposal of fly ash on soils used to produce forage crops could lead to accumulations of these elements in the forage and render it unsafe for consumption by animals. Adverse impacts of excess boron contamination are limited to possible phytotoxic effects. However, atmospheric deposition of boron onto plants or soil is small, and the probability of encountering levels sufficiently elevated to cause phytotoxicity is remote. • Elements considered by the Panel to be of moderate concern include chromium, vanadium, copper, zinc, nickel, and fluorine. The Panel's rationale for grouping these elements in this category is that they are potentially toxic and occur at elevated concentrations in some residues produced during coal combustion, but the probability of adverse impact is considered less than for the elements of greatest concern. Also, vegetation and animal health problems that could occur from excesses of these elements are reversible and can be corrected economically. Copper, nickel, and zinc, in certain site-specific situations, could accumulate over the years in soils to levels that are phytotoxic. Fluorine is a highly volatile element, and, in areas where its deposition onto vegetation is great, the forage may not be suitable for consumption by animals • • Those elements considered to be of minor concern include barium, strontium, sodium, manganese, cobalt, antimony, lithium, chlorine, and bromine. Although these elements frequently occur in fly ash at concentrations greater than in the normal geochemical environment, the probability of a specific adverse impact that could not be easily corrected is regarded as remote • • The radioactive elements n•u, usu, and u2Th are present in coal in small quantities and are released into the environment as airborne effluents, in collected residues [fly ash, bottom ash, and flue-gas desulfurization (FGD) sludge], and in mine tailings during the course of coal utilization. Because levels of radioactivity associated with these elements during coal resource development are not significantly different from those commonly found in nature, and because they are in a geochemically immobile form, their effects on health ar= thought to be negligible. Available information on other radioactive elements such as radon, radium, and polonium suggests that the effects of their radioactivity associated with coal resource development are minimal1 however, because adequate information is lacking, the Panel has classed these radioactive elements in a category requiring additional information for conclusive assessment. • Although there are other elements in the periodic chart with known and documented relationships to health, many of them have only negligible concentrations in coal and are commonly rendered inert in coal residues; therefore, potential hazards associated with coal development from these elements are considered to be remote. Elements in this category include tin, beryllium, thallium, silver, and tellurium. Environmental exposure resulting from coal resource development of the other remaining elements, not otherwise cited, is not generally regarded as hazardous to health. Residues from the coal combustion process include those materials collected by the emission-control devices and those that escape these devices and enter the atmosphere. The noncaptured particulates entering 

5 the atmosphere from stacks are of submicrometer size. Hiqh percentaqes may remain airborne for extended periods of time; similarly, some elements (e.q., fluorine and mercury) are released in a qaseous form from stacks and remain airborne for some time. Current best-available technoloqy is such that more than 99 percent of the solid residues from coal combustion are collected (Fiqure 2). Therefore, in the future the trace-element burden associated with coal resource development in terms of total quantities is one of proper disposal or recyclinq of the collected residues (Fiqures 3 and 4). New power plants should represent only a neqliqible contribution to the trace-element burden from airborne sources. However, power plants not equipped with modern control devices will continue to emit to the atmosphere considerable quantities of trace elements until they are phased out or required to install up-to-date equipment. The trace-element enrichment in soils and veqetation around these plants will continue to be localized and will occur in reqions close to the source, qenerally within a few kilometers. Current annual production of fly ash from the combustion of coal by electric utilities is 56 million tons, of which less than 15 percent is used in industrial operations. As relatively small amounts of the fly ash produced are used, and the amounts qenerated will increase as coal use increases, fly ash will accumulate and intensify disposal problems. Approximately 36 percent of the fly-ash disposal is by truckinq to storaqe areas, presumably landfills, and the remainder is sluiced to disposal ponds. Leachate from unsealed disposal ponds could contaminate qroundwater. Likewise, dust from dry ash storaqe areas, if left unstabilized, could contaminate soils in adjacent areas. Volunteer qrowth of native veqetation also may accumulate certain trace elements (molybdenum and selenium) to levels unsafe for consumption by wildlife. Current information on the potential problems associated with the disposal of fly ash is inadequate. Knowledqe required to assess the impacts of fly-ash disposal, therefore, should be developed. Once developed, criteria for the safe disposal of fly ash should be formulated. The submicrometer-sized particles emitted to the atmosphere from power plants (even thouqh equipped with modern control devices) include those that, when inhaled, may be deposited in the lunq. Concern has therefore been expressed over possible lonq-term, subacute, chronic poisoninq from certain trace elements in the vicinity of coal-burninq plants. The current data show that the contribution of particulates from a power plant to the trace-element concentration in air surroundinq such plants is small, much less than other sources of natural and man- made atmospheric contamination, and because of particle size considerations inhalation of these submicrometer-sized particles should not be iqnored. . Near-term development of coal in the United States will be principally at western sources where surface mininq is widely practiced. In the process of topsoil removal, overburden removal, coal extraction, overburden and topsoil replacement, and reqradinq, the porosity of the displaced material is increased. This increased porosity may allow additional leachinq of trace elements by qroundwater or surface water. Because, except for boron, the solubilities of the trace elements of qreatest concern in the neutral to alkaline rocks and soils of the western reqion are small, the transport of trace elements via this 

6 FIGURE 2 The 2700-MW, coal-fired Bruce Mansfield Plant at Shippingport Pennsylvania, is the world's largest electric generating station with ' comprehensive environmental controls. (Photo courtesy Pennsylvania Power Company.) pathway should be limited to short distances. On a localized basis, certain specific imbalances may cause reduced productivity and adverseiy affect the quality of new crops planted on the reclaimed land. saits could accumulate, and soil salinization could occur and cause reduced productivity. Because of increased exposure and porosity from strip mining, boron concentrations in surface waters and groundwater couid reach levels that would damage boron-sensitive crops. Molybdenum and selenium also could be rendered more available to plants and cou1d accumulate to such an extent in forage as to make it unsafe for animai consumption. There are insufficient data from actual field situations to make proper assessments of these potential problems. When they occur, such problems are site specific and may be mitigated through proper soil management. The term synthetic fuels refers to liquid and gaseous fuels Produc d by the thermal processing of coal. Liquefaction and gasification e 

7 ~ubber system for units 1 and 2 at the Bruce Mansfield l to remove 99.8 percent of the fly ash and 92.1 percent >xide. The scrubbers require 5 percent of each unit's cost approximately $13 million a year per unit to ~ain. (Photo courtesy Pennsylvania Power Company.) tl conversion in the United States are still in the 1e. There are no large-scale commercial synthetic-fuel operating within the United States, and only a few riew of unit operations in liquefaction and gasification Eined the stages where trace-element concentrations and :ur. Data on the fate of trace elements in synfuel 1inninq to emerge but are currently insufficient to Le assessment related to health. >ssible emissions from coal-handling facilities and , escape of trace elements from synfuels plants should The processing of co~l in these plants occurs in \nd most of the trace ~iements in the feed coals will i.c waste streams, whicl\ can be disposed of or treated to )f trace elements to tile environment. 

8 FIGURE 4 The gypsumlike waste from the Bruce Mansfield Plant is deposited in the valley behind the dam. The capital cost of this waste- disposal system is reported to be $90 million. (Photo courtesy Pennsylvania Power Company.) In conclusion, the volume of chemical analytical data on u.s. coal is now considered large enough to provide the needed broad assessment of trace elements in coal and related problems. The major problem now is to identify the types of studies and possible regulatory actions needed to control those relatively few trace elements of known health concern in those particular coal beds and combustion plants that contain such trace elements in appreciable amounts. For example, arsenic and mercury are of no concern for coal mines and coal-fired power plants in the Northern Great Plains; however, close monitoring and possible regulation of arsenic in mines in the Appalachian and Interior provinces and of mercury in the Appalachian, Interior, and Gulf provinces may be necessary. Clearly, adequate information on coal is now available to use the bed-specific, site-specific approach in assessing related health hazards. 

9 RECOMMENDATIONS 1. Determinations of the exact chemical and mineralogical form of the relatively few trace elements of health concern in specific coal beds and coal-use processes should be made (or confirmed) as soon as practical so that appropriate physical and chemical treatment measures for their removal and control can be developed. 2. Adequate information on the health effects of radioactive elements associated with coal resource development on which to make a reliable judgment should be gathered and assessed. Although available data suggest that these effects are minor, this assumption should be either substantiated or corrected by appropriate agencies. 3. A single federal agency, such as the U.S. Geological Survey with its National Coal Resources Data System, should be designated to maintain a single trace-elements-in-coal data bank, to which pertinent data would be submitted routinely by all government, university, and industry groups. 4. More data are needed on the chemical form and solubility of trace elements in the topsoil, the overburden, and the underclay associated with site-specific coals, before and after the coal is mined. These data would provide the basis for an improved prediction of mining results, particularly with respect to the new underclay-spoil interface and the porosity, density, permeability, and surface area of the materials disturbed, which will provide the basis for theoretical and empirical assessments of the effects of these changes on the mobility of trace elements. Such collections should be begun soon by both environmental and regulatory agencies. 5. More and better information on the mass balance and on the migration pathways of trace elements through major coal gasification and liquefaction processes is urgently needed; efforts to improve such data should be initiated and vigorously pursued by the appropriate agencies. Specifically, the concentrations of trace elements in hydrocarbon liquids produced from coal must be studied. The fate of these elements in subsequent uses of the liquids should also be investigated. 6. In addition to the Standard Reference Material for bituminous coal (NBS SRM 1632a) and subbituminous coal (NBS SRM 1635), standard samples of other coals, with certified critical trace-element concentrations, should be established on a priority basis by the National Bureau of Standards. Standard reference samples for lignite and anthracite are needed and should be made readily available. 7. The Panel also recommends that individual researchers in academic, industrial, and government organizations and administrators responsible for planning federal agency programs give particular attention to the following research and data needs that would improve the safe and effective exploitation of coal resources (the sequence of listing is not intended to signify relative priorities): • Research is needed to facilitate industrial and agricultural uses of coal ash, and to identify and implement additional uses, including the development of techniques to alter the properties of the ash thus rendering it more conducive to beneficial uses • • Data are needed on leaching of salts, boron, fluorine, molybdenum, selenium, chromium, and possibly other elements from ash piles and 

10 laqoons. This information is needed to quard aqainst unnecessary contamination of surface waters, qroundwaters, soils, and veqetation • • Better understandinq is needed of the factors influencinq the availability of molybdenum and selenium to crops qrown in ash- contaminated or ash-amended soils in relation to their chemical, physical, and bioloqical properties. Knowledqe of the fate of molybdenum and selenium in ash-amended soils over extended periods of time is also needed to evaluate adequately the possible accumulations of molybdenum and selenium in foraqe qrown on ash-amended soils to levels considered to be unsafe for livestock consumption. • Techniques are needed to quard aqainst excessive accumulations of salts and boron in reqions adjacent to coal-ash disposal or utilization locations. Total dissolved salts and boron in leachates from coal ash frequently reach levels that are toxic to plants • • The increased use of lime and/or limestone to remove S02 from flue qas will result in the production of larqe quantities of waste referred to as flue-qas desulfurization sludqe (FGD sludqe). Techniques are needed to use this sludqe or to dispose of it in a manner consistent with preservation of environmental quality, particularly with relation to its readily mobilized trace elements and soluble salts derived from coal. • Althouqh the percentaqe of coal ash emitted from stacks in a modern coal-fired power plant represents less than l percent of the total ash that is produced, the size of particles enterinq the atmosphere is of submicrometer size, and they are known to have abnormally hiqh concentrations of surface-adsorbed trace elements. Additional information is ne~ded on the possible impact of inhalation of these submicrometer particles on human health. • A uniform method of expressinq data for the chemical composition of coal and coal ash should be established. • Research is needed to hasten the reveqetation process of renovatinq lands disturbed by strip mininq. The use of fertilizers and irriqation to re-establish native veqetation should be investiqated more thorouqhly. • Research is needed to characterize more completely the chemical composition and to develop improved techniques for the safe disposal or recyclinq of the larqe volumes of coal-cleaninq liquid wastes that qenerally have abnormally hiqh concentrations of certain metallic trace elements. • Investiqations are needed to determine the condition under which coal ash can be used to remove phosphorus and other undesirable trace- element constituents from surface waters and wastewaters. • Continued efforts are required to identify reqions that are subject to mobilization of trace elements by acid mine drainaqe (AMD) and to take appropriate corrective action, even thouqh substantial proqress toward correctinq AMD has been made. • To extend coal-ash disposal studies and to enhance evaluations of the impact of coal residues on the quality of soils, veqetation, and surface and underqround waters, field-plot studies on aqricultural land with coal ash containinq notable amounts of possibly deleterious trace elements are needed. Such studies have been mainly limited to qreenhouse conditions.