U.S. Geological Survey researchers are investigating the use of a simple microbiological test as an aid in mineral exploration. Preliminary studies have shown that the dormant spores of a common species of soil bacteria, Bacillus cereus, are present in elevated numbers in soils over several types of mineral deposits, including vein-type and disseminated gold deposits, tested so far. During the last decade, environmental studies indicated that different heavy metals somehow create a selective pressure for various antibiotic resistances in bacteria living in metal-polluted sediments. In other words, bacteria resistant to metals and antibiotics may be indicative of metal-containing environments. However, studies of bacterial antibiotic resistance had never been conducted in naturally metalliferous soils associated with ore deposits.

When Geological Survey researchers tested the penicillin resistance of a normally penicillin-sensitive group of bacteria (the aerobic, spore-forming genus Bacillus) in soils near a porphyry copper deposit, they found a much larger percentage of the bacteria of this genus resistant to penicillin in the metalrich soils directly over the deposit than in more normal soils adjacent to the deposit (fig. 1). Significant correlations were found between the detailed distri

bution pattern of many different heavy metals in these soils and the pattern of penicillin resistance in Bacillus species.

Further investigation showed that the numbers of one particular organism, Bacillus cereus, the most penicillinresistant member of the genus, statistically explained the penicillin-resistance data. In fact, the distribution of this species correlated better with the distribution of heavy metals than did the penicillin-resistance pattern. The more laborious penicillin-resistance test, therefore, was dropped and replaced by a rapid assay method for Bacillus cereus. Tests now underway are providing some clues as to why this species colonizes soils over certain ore deposits.

In soils at a current "test" deposit, a weathering, 50-million-year-old copper deposit, the most representative type of microfungus is a Penicillium mold that produces penicillin and other antibiotics. This variety of mold has long been recognized as a problem in metalelectroplating vats and in laboratory jars of Fehling's solution (17 percent copper sulfate). These molds, which are among the most metal-tolerant organisms on Earth, may owe this special trait in part to the extraordinary metalbinding properties of penicillamine, a principal breakdown product of penicil

lin. Other fungal antibiotics, such as kojic acid, also form strong complexes with heavy metals. The ore deposit apparently provides conditions in which microorganisms that produce strong metal-binding agents, such as penicillin, have an advantage over other microorganisms.

Pure strains of Bacillus cereus were isolated from soils over and adjacent to the test deposit. These pure strains then were tested for their resistance to 32 different antibiotics and the salts of 21 metals. A pattern of elevated multipleantibiotic resistance in these isolates coincided well with the area over the ore deposit. Surprisingly, the metalresistance pattern showed a much poorer correlation with the deposit than the antibiotic-resistance pattern. Apparently, multiple antibiotic resistance is a far more important survival characteristic for Bacillus cereus in polymetallic soils than is metal resistance. In addition, the isolates from the deposit area were significantly more resistant to penicillin than isolates from adjacent areas, a finding which strongly suggests that penicillin is an important selective agent for bacteria over the

deposit at the genus and the species levels.

These different findings correlated very strongly with results of other experiments that showed that highly penicillin resistant Bacillus cereus isolates from the deposit area could grow in ultrapure water with no other nutrient than bits of colonies of the representative penicillin-producing mold. Penicillin resistance is apparently a kind of "meal ticket" for this bacterium. Thus, Bacillus cereus is better suited than other Bacillus species to obtain nutrients in a polymetallic soil.

After finding that Bacillus cereus populations are concentrated over veintype gold deposits, Geological Survey scientists are trying to learn if distributions of the spores can help locate the current number-one mineral target-large-tonnage, disseminated gold deposits. Encouraged by these recent results, these scientists have begun investigations to determine the details of the ecology and the indicator potential of this organism in soils overlying a wide variety of economic mineral deposit types.

In 1973, the oil embargo emphasized to the United States its economic vulnerability to supplies of foreign energy resources. As a result, the Nation has begun to use more of its abundant coal resources. This substitution has not been without cost. The environmental impact of acid precipitation and toxic metals, the pollution of ground water by scrubber sludge, reduced boiler efficiency, and excess slagging problems caused by the use of a fuel other than the one for which systems were designed are but a few of the penalties to be paid for fuel switching. The discussions surrounding acid precipitation and other environmental impacts, substitution of western coal for eastern coal, boiler efficiency, and improved export markets are national and international concerns. In these discussions, the use of scientific knowledge and skills to mitigate or improve the situation must be addressed. Coal quality is the common denominator in all of these problems and, thus, is the principal avenue of research that will lead to their solution. The Clean Air Act, enacted in 1970, was intended to lower commercial boiler sulfur emissions into the atmosphere to no more than 1.2 pounds of sulfur dioxide per million British thermal units from any powerplant built or modified after August 17, 1971. Coal capable of meeting these requirements without flue-gas scrubbers has become known as compliance coal. Recent proposals to lower the compliance coal requirement to 0.6 pound sulfur dioxide per million. British thermal units do not address properly the availability of coal that can meet this standard or the economic impact it will have on the U.S. coal industry. The considerations in the compliance coal discussions are How much sulfur is there in U.S. coal? How much will meet various emission standards? What is its variability? Can sulfur and other contaminants be cleaned from coal? Can high-sulfur coal be blended with lower sulfur coal to meet various standards? Most available data are based on coal that has been or is being mined and not on coal to be mined. Thus, answers to these questions

are difficult to obtain because little reliable data on the sulfur content of unmined U.S. coal are available. However, decisions and regulations based on these inadequate data continue to be made.

The conversion of powerplants from eastern to western coal or from oil to coal is technically difficult. Most powerplants generally are built for a particular “design fuel." The plant boiler and attendant combustion processes are engineered around the physical and chemical properties of the "design fuel." Thus, such properties as British thermal units, sulfur and ash contents, volatile matter, and the content of many of the inorganic elements in the coal are critical elements in the plant design. Switching from a higher to lower British-thermalunit coal, which contains less sulfur, may appear, on the surface, to be an ideal solution to meeting the standards required by the Clean Air Act; however, other coal-quality characteristics for which the plant was not designed may cause problems. The amounts of such elements as silicon, aluminum, iron, sodium, potassium, magnesium, and calcium and of such minerals as quartz, clays, and sulfides in the coal will determine some of the chemical reactions in the combustion chamber. Some coal-quality problems which are critical to the environment are not confined to the combustion chamber but are more widely distributed. Volatile minor and trace elements such as mercury, selenium, and arsenic are emitted through the stack into the air either as gases or absorbed on particulates. Many of these elements also may be concentrated in the bottom ash or in the scrubber sludge and, upon disposal, can be released into the environment by weathering, leaching, and oxidation processes.

The Federal Government owns approximately 70 percent of the coal west of the Mississippi River, and many tracts of Federal coal have been leased for mining by the Department of the Interior. In the 1950's and 1960's, only the heat content and ash values were deemed important coal-quality prop

Figure 1. Distribution of coal samples collected from U.S. coal basins.

erties; more recently, toxic trace elements and sulfur contents of the coal, major and minor constituents of the ash, and ash-fusion temperatures and coking properties have become critical to the marketability and royalties paid for Federal coal. In recent years, coal quality also has become a critical component of the U.S. coal export market. Foreign buyers and investors are requiring coal-quality certification. Their quality requirements are focused on the content of sulfur, ash, phosphorus, fluorine, chlorine, mercury, arsenic, silicon, aluminum, calcium, potassium, sodium, and other elements. Reliable data on the chemical constituents have now become essential to making wise economic, technologic, and environmental decisions. Such data can be provided only by characterizing the quality of our Nation's coal and by developing predictive quality models in advance of leasing, development, and use of coal. The U.S. Geological Survey conducts research in the following coalquality topics to address these requirements:

COAL GEOCHEMISTRY

During the last 50 years, tens of thousands of U.S. coal samples have been analyzed. However, many of these analyses are useless because sample locations were known inadequately or correlated inadequately, samples were not collected or prepared properly, or samples were not analyzed according to standard methods. In addition, many analyses are part of the confidential records of coal companies and, thus, are not available to the public. To correct these inadequacies, the Geological Survey organized a cooperative collecting and testing program with the geological surveys of the States with coal deposits. This effort has resulted in the collection and the analysis of more than 8,000 carefully documented coal samples (fig. 1). This coal-quality data base contains data for ultimate and proximate analyses, coking properties, heat content, forms of sulfur, ash-fusion temperatures, and more than 50 inorganic elements for each sample. This data base is available and used by