G. B. Morgan and E. W. Bretthauer Environmental Monitoring and Support Laboratory U.S. Environmental Protection Agency Las Vegas, Nev. 89114
METAL
BIOENVIRONMENTAL SYSTEMS Public concern for the protection and enhancement of health and welfare has grown steadily over the past two decades. There is every indication that this concern will persist and that the public will increase its demand for correction of the problems arising from toxic pollutants as the pollutants transcend the environmental media— air, land, water, and food. The chronic exposure of man to increasing amounts of environmental trace metals is one of the problems of immediate concern and poses the following questions: • What is the limiting burden? • Can the increased exposure to abnormal amounts of trace metal pollutants continue without measurable alteration of the normal biochemical functions of man and the rest of the ecological system? • Are adverse subtle effects already beginning to appear? To answer these questions it is convenient to develop a model (providing adequate biological input information is available), relating the effects or biochemical changes to long-term, low-level exposure to both trace and ultratrace levels of toxic metals. To obtain such input information, it is necessary to look at the total exposure from all pathways, including air, food, water, and dust. We must determine the total absorption and residual concentration in the various parts of the body and then determine the biochemical reactions taking place in the body at the potential binding sites, i.e., metalloenzymes and nucleic acids. A pollutant-oriented integrated
monitoring system is the only way that definitive data can be obtained to determine the total exposure to the critical receptor from the various sources and to determine the chemical and physical forms of the pollutants reaching the receptor from each pathway. This system defines the complex relationship between sources, pollutants, and pathways. To provide the needed experimental and environmental data associated with the above requirements, the chemist is required to measure trace elements at extremely low concentrations—nanogram or subnanogram levels. In other words, he must be able to measure the low levels likely to be encountered in the environment, in biological organisms, and even their accumulation in a single cell. A great deal of data on long-term, low-level exposure to trace levels of metallic and metalloid elements in the environment is needed before the effects on humans can be definitively established. We presently lack such information even on the more toxic metallic and metalloid pollutants present in trace concentrations, let alone the information for those metals present in the ultratrace concentrations. To date, environmental surveillance with reference to trace metallic and metalloid pollutants has been largely after the fact. For before-the-fact surveillance for epidemiological, studies, analytical data must be available virtually on a real-time basis. Accurate measurements of trace metals as they move through the environment are useful for determining the exposure/
1210 A • ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
dose of the critical receptor. To obtain accurate measurements, many questions must be asked relative to the source and transport of the pollutants, exposure/dose relationships, and the biological effects. Some of these questions are as follows: What is the objective or the goal of the measurement program? What pollutants are of primary importance? Who or what is the critical receptor? What are the pathways of the pollutant through the environment and what physical and chemical changes will occur as it passes through the various media? How is a representative and accurate measurement of the pollutant obtained? How is the measurement of the exposure related to the dose? What are the observed or expected effects? The analytical chemist has a primary responsibility to assist in developing answers to all of these questions. Many of the past epidemiological studies have been planned and carried out without the participation of the analytical chemist, and such action has resulted in some of the problems that we now face. On the other hand, many chemists in the past were not particularly comfortable in assisting in the development of these answers, but preferred sitting back and analyzing samples delivered to the laboratory. The chemist's input into the program design should include providing detailed recommendations
Report
Exposure of man to increasing amounts of trace and ultratrace metals and metalloid pollutants is a problem of immediate concern. An integrated multimedia monitoring system is necessary to determine accurately the sources and pathways of these pollutants as well as total exposure to the receptor. The analytical chemist's input into such a system includes recommendations on sampling procedures and methods of analysis. Sensitivity, accuracy, selectivity, and cost-effectiveness of the various available methods must be considered. Interpretation of the data and adequate quality assurance are prime responsibilities of the analytical chemist:
on the type and size of sample to be obtained, methods of sample preservation and preparation, and the method of analysis. In recommending the method of analysis, he must consider the various available methods in terms of sensitivity, accuracy, selectivity, and cost effectiveness. Finally, it is the prime responsibility of the analytical chemist to interpret the analytical data, provide qualifications with certain data if necessary, and to implement a quality assurance program to assess the validity of the data being provided. Pollutant Pathways Studies Studies of pollutant flows through the environment are essential to the development of advanced monitoring systems in a number of ways. For example, the inter- and intramovements of a pollutant are necessary for the design of a pollutant-oriented integrated monitoring system for the determination of pollutant levels in the various environmental compartments as well as for the determination of the total exposure of the critical receptor. Through such studies, pollutant levels at any given point in the environment can be estimated. Based on these estimated levels, the optimum sampling site or sites for making definitive measurements can be identified. These studies are also extremely useful in determining or estimating the effects of industrial or urban areas on surrounding regions. This is of particular importance for land use or water use planning. Another use of these studies is to determine the fate of toxic metal-
lic and metalloid pollutants, particularly those conserved in the environment. The California Institute of Technology (Cal Tech), through work partially sponsored by EPA, has developed a method for constructing mass balances for pollutants that move in a connected manner through the air, land, food, and water in an urban industrial region (7). The principle upon which this method is based is a conservation of mass for a given chemical element. The method employs chemical element balances for flow diagrams depicting the movement of pollutants through the environment; rates of flow and accumulation for a particular metal can be estimated and then measured for the separate environmental compartments. This method has been tested for lead, zinc, cadmium, and arsenic. Three basic types of information are needed to construct a mass balance. The development of a mass balance should be initiated by developing a flow diagram for each species of interest. The data necessary to prepare such a diagram are divided into three categories: source or input data, receptor site data, and regional or area output data. The output data refer to the flow of pollutants from an urban or industrial area into the outlying regions. The primary criterion of success for constructing a mass balance is that the sum of the input flows should equal the sum of the output flows plus the pollutant or metal conserved in the area. One problem that has been encountered is obtaining accurate source
emission rates. The lack of an accurate emission inventory may result in the failure to identify an important environmental pathway. The most accurate trace metal mass balance constructed to date has been for lead, which is emitted primarily from automotive exhaust. Not only has lead been measured as a pollutant itself, but it has also been correlated to carbon monoxide, which is emitted from the same source. By measuring carbon monoxide at selected sites, verification of the predicted lead level at a given point has been achieved. The Cal Tech scientists have developed a method to verify the relationship between airborne concentration and deposition of trace metals from the atmosphere. These researchers have shown that for the Los Angeles basin, the airborne size distributions of lead, zinc, and cadmium are bimodal with the upper mode occurring at greater than 10 ixm equivalent diameter. Sedimentation of large particles dominates mass deposition near the source. However, this is not the case far from sources. Once the larger particles have settled out, the small particles may remain airborne for considerable periods of time and may be transported over long distances. Most probably these smaller particles are deposited by diffusional deposition. Deposition velocities on rough natural surfaces are likely to be large. In the Los Angeles basin study, estimates were made of the daily emissions of lead from automobiles (Figure 1) and from lead smelters to the atmosphere. These emissions were then re-
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977 • 1211 A
Input 23.7 Metric Tons Lead per Day
Removal by Wind 25%
Evaporation 1 %
^ZIEZX
Vapor 4 % Aerosol 70%
Retained in Car 25%
40%
Near Deposition Street 8%
Land 32%
Far Deposition Land
Runoff 2%
Removed by Street Cleaning 6%
Coastal Waters
Sewage 0.64 Metric Tons/Day
Figure 1 . Fate of lead contributed f r o m automotive fleet
lated to the amounts deposited on lands and roadways, and the quantity advected from the basin. Some 24 metric tons of lead as a gasoline additive are consumed each day in the basin. Of this, approximately 18 tons per day are emitted from the exhaust to the atmosphere, and some 6 tons per day are retained in the automobile exhaust system. Of the lead emitted into the atmosphere, approximately two-thirds is deposited in the Los Angeles basin with the remainder advected out of the basin. The one-third advected out of the Los Angeles basin is a major source of atmospheric lead for regions downwind. In addition, more than half of the anthropogenetic lead in the Los Angeles coastal waters comes from automobile exhaust. The pollutant balance-flow pathway approach is general and can be applied to all environmental pollutants. Although the method does not reveal the details of pollutant dispersion in the environment, the requirements of the mass balance demand that all important environmental pathways, chemical and physical transformations, and sinks be identified and quantified. This is potentially a very powerful method in assessing the environmental impact of a pollutant. There are problems, however, in that
large uncertainties exist for both input and output terms for most pollutant species due to a very meager data base. Refinement of this method will require much more detail, better source characterizations, and a better theoretical and experimental understanding of the pollutant pathways and removal processes in the environment, from the source to the receptor. Some of the pathways that must be quantitated are shown in Figure 2. The integrated monitoring systems approach takes into account not only the pathways of pollutants through the environment to the critical receptor, but the pathways of the pollutant within the critical receptor so that some measurement can be obtained concerning the dose. It is important to realize that effects are based upon dose, not exposure. Figure 3 shows the possible pathways of trace metals in a critical receptor and also the tissues of the body, such as blood, soft tissue, and bone, where the pollutant may be monitored. Information of this type can indicate the dose of the pollutant to the receptor and also indicate some of the changes in biochemical functions that may take place. For many toxic trace metals, the blood level is presently the most important factor in determining effects.
1212 A • ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
Analytical Requirements for Assessment of Human Exposure Over the past two decades, analytical chemistry has been elevated to a sophisticated automated state. Unfortunately, however, there has been a lag in applying these more sophisticated methods to the routine measurement of environmental pollutants. This has been due to the high cost associated with automation as well as a lack of understanding the applications and the limitations of these more sophisticated methods. The lower limits of detection for a large number of trace metals are already adequate for situations where large or composite samples can be collected. Conversely, however, we do not have adequate methods, in most cases, for measuring trace and ultratrace levels of metals in cellular and subcellular components. In spite of the enormous amount of literature dealing with metallobiochemistry of living organisms, very few attempts have been made to understand the metabolism of trace and ultratrace metals at typical environmental levels. Again, the paucity of data is because of the lack of proper analytical techniques. Perhaps more use should be made of neutron and/or proton activation analysis for in vivo tracer studies of ultratrace metals as well as for the study and identification of metal biocomplexes in human tissue. As has been identified many times, the weakest link in pollution health effects studies is inadequate knowledge of individual exposure.
Stationary
Mobile
Nature
Pollutant Source
[ Air
:
j Soil fjm
Water
Surface Precipitation
l^fl^fl
Receptor
Figure 2 . Environmental pathways of pollutants from source to receptor
Grou
Analytical Requirements for Measurement of Trace and Ultratrace Metals There are no widely accepted definitions of trace and ultratrace elements. In the following discussion trace elements will be defined as those elements found at the parts per million (ppm) concentration, and ultratrace elements will be defined as elements occurring below the ppm level. Obviously, almost all of the radionuclides are determined at the ultratrace levels. The exceptions would be a few of the naturally occurring radionuclides such as uranium and thorium, which are determined at trace concentrations. Generally, the concentration determines whether an element is toxic, benign, or essential. Frequently, however, knowledge of the chemical species (ion or compound form) is equally important. This situation is further complicated by the synergistic effects of groups of elements in both metabolism and toxicity. Due to the considerable difference in the analytical techniques between stable and unstable elements, separate sections in this manuscript will be devoted to each of these elemental types. Stable Elements Existing analytical techniques are capable of detecting practically all stable elements of current and future interest. The analytical procedures that appear to have greatest capabilities for trace and ultratrace level stable elemental analysis at the present time are spark source mass spectrometry, neutron activation analysis, optical emission spectrometry, and, at the trace level, x-ray emission spectrometry. At ultratrace concentrations the methods may not be very accurate. However, a semiquantitative survey is frequently useful at these levels. Gas chromatography (GC), GCmass spectrometry (GC-MS), gas chromatography-microwave emission spectrometry (GC-MES), and infrared Fourier transform spectrometry are routinely used for metallo-organic compound speciation determination. Proper sampling procedures are of the utmost importance for trace and ultratrace analysis. For solid samples a homogeneous and representative sample must be obtained. Contamination of the sample must be prevented. In the case of soils, plant tissue, or animal tissue, this may not be an easy task. In the case of liquids, the samples must be adequately preserved to prevent precipitation, chemical transformation, and/or adsorption of the elements of interest. The sample container itself must not contribute to the analysis result. Since any sample han-
Inhalation
Soft Tissue
Upper Respiratory System
Bone
Lower Respiratory System
Hair Nails
Gl Tract
Brain
Ingestion
Urine Sweat Feces
Figure 3. Pathways of metals in critical receptor • Rates variable, depending on many factors
dling may easily introduce contaminants, methods that require minimal sample treatment should be employed. The arc or spark optical emission, neutron or proton activation, spark source mass spectrometry, and x-ray emission techniques meet this requirement for solids. Furthermore, all of these techniques are very sensitive and are rapid multielement procedures. For aqueous solutions the plasma excitation optical emission and the other techniques mentioned above may be used. In the case of spark source mass spectrometry and x-ray emission, the solutions that may introduce contaminants must be evaporated. Atomic absorption (AA) does not have the sensitivity for many of the elements required and is not a multielement technique. Furthermore, AA is most easily adapted to liquid solutions. A critical problem in analyzing samples at the trace and ultratrace levels is the calibration of the analytical instrumentation. Normally, highly diluted aqueous solutions are used to calibrate most instruments. At trace and ultratrace levels the calibration standards are not very stable and are easily contaminated. Therefore, it is very important to have independent accuracy standards that have certified values of a wide range of trace elements at low concentrations. At the present time the National Bureau of Standards has only a few Standard Reference Materials (SRM) available for plant, animal, or soil analysis.
None of these has an adequate range of trace or ultratrace elements certified. Clearly, more SRM's are needed for trace and ultratrace elements in animal and soil samples. The existing plant SRM's should also have more trace and ultratrace elements certified. If ultratrace analyses of metals are to be performed accurately, the analytical laboratory must be extremely clean. This necessitates the use of a carefully filtered air supply. All reagents must be ultrapure, certified, and maintained in an ultrapure state. The deionized water supply must be carefully monitored to ensure that trace element contamination is absent. Careful attention must be given to the personal hygiene of all technicians because hair, skin, cosmetics, excretions, and exhaled air can possibly lead to contamination. In the case of trace and ultratrace analysis, very strict quality assurance procedures must be instituted and enforced. Only careful, experienced personnel are qualified to perform these types of analyses. Very close monitoring of reagent blanks, standards accuracy, and sample preservation must be maintained to perform analyses at these low concentration levels. Blank levels may easily obscure natural levels of trace or ultratrace elements. Radioactive Elements and Isotopes The area of radionuclide analysis offering the greatest challenge is the measurement of the naturally occur-
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977 • 1213 A
Hot BOX Tem-Pres Internally Heated Pressure Vessels
For subjecting samples to pure hydrostatic pressures up to 10 kilobars and temperatures up to 1400°C simultaneously. Tem-Pres offers a variety of pressure vessels with a furnace located inside the vessel housing. Easily replaceable, cartridgetype furnaces, with dual control zones, allow complete control of hot-zone location. The units operate horizontally or vertically, and open at either end for easy access to the furnace and sample-holding assembly.
specialists
in high pressure/high temperature research systems
contact R. M Shoff Leco Corporation Tem-Pres Division 1401 South Atherton Street State College. Pennsylvania 16601 Phone: 8 1 4 - 2 3 7 - 7 6 3 1
LECO®
ring alpha emitters and the artificially produced transuranium actinides. Procedures for these elements require time-consuming separations (precipitations, solvent extraction or extraction chromatography, ion-exchange chromatography, electrodeposition) and extremely long measurement times (hours to days). In this area of analysis many invalid results are now caused by processing high-level samples in moderate- or low-level laboratories or moderatelevel samples in low-level laboratories. The lack of knowledge of the appropriate activity of unknown samples is due primarily to the lack of techniques to adequately screen the samples prior to analysis. The erroneous results are caused by cross-contamination between samples, contamination of one or more of the many reagents used in the sample decomposition or analytical separations, mismatching the amount of tracer to the amount of activity actually in the sample, and contamination of counting systems. A large percentage of actinide analyses currently conducted in the United States is done by contract, under some form of contractual arrangement, where a certain number of analyses are performed for a given amount of money. This fact has probably contributed "directly" or "indirectly" to some of the more serious errors in assessments of actinides in the environment. It has been our experience over the past 10 years that there are many samples that are expected to be accommodated by a "routine" procedure but in reality are quite unusual or nonroutine. For example, soils collected in the same geographic areas may vary considerably, both in their ability to be completely solubilized in a given dissolution procedure, and in the types and levels of chemical interferences with the measurement process. Similar situations exist in the analysis of animal or plant tissue samples. Over the past few years we have recognized that as many as 40% of the samples encountered cannot be considered "routine" and that as much as 10 times the effort may be required to analyze these unusual sample types and produce results comparable to those obtained from the analysis of a "routine" sample. There is also an urgent requirement for additional standard reference materials containing the naturally occurring alpha emitters and the actinides. The most critical materials would include radium, polonium, thorium, uranium, and plutonium in soil, air filters, water, animal tissue and vegetation. At least two levels of these SRM's should be prepared. One level should be slightly above background levels, and the second SRM should
CIRCLE 126 O N READER SERVICE CARD
1214 A • ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
contain moderately higher levels. The only materials available at present are a National Bureau of Standards sediment sample certified for plutonium and several soil samples containing known levels of uranium and thorium produced by the International Atomic Energy Agency and the Energy Research and Development Administration. References
(1) S. K. Friedlander et al., W. M. Kick Laboratories, California Institution of Technology, "Mass Balances for Pollutants in Urban Regions", Special Report to U.S. Environmental Protection Agency, November 1976. (2) G. L. Fisher, Sci. Total Environ., 4, 373 (1975). (3) E. Sabbioni and F. Sirardi, ibid., 5,145 (1977). (4) E. Schuck and G. Morgan, "Design of Pollutant Oriented Integrated Monitoring System", International Conference on Environmental Sensing and Assessment, IEEE, September 1975. Presented at the Division of Analytical Chemistry, 174th Meeting, ACS, Chicago, 111., August 28-September 2, 1977.
George B. Morgan is director of the U.S. Environmental Protection Agency's Environmental Monitoring and Support Laboratory at Las Vegas, Nev. He directs a multidisciplinary staff of nearly 400 people in the development of systems and techniques to monitor environmental quality.
A
.
Erich W. Bretthauer is chief of the U.S. Environmental Protection Agency's Methods Development and Analytical Support Branch, Environmental Monitoring and Support Laboratory, Las Vegas, Nev. His interests include the development of analytical methods for the measurement of both radioactive and stable pollutants.
