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Monitoring Human Tissues for Toxic Substances Appendix C Summary of Workshop The workshop conducted by Committee on National Monitoring of Human Tissues was held on January 24–25, 1989, and had several objectives: (1) to gather specific information about EPA’s National Human Monitoring Program and specifically, the National Human Adipose Tissue Survey (NHATS), (2) to gather general information about other types of monitoring programs, and (3) to consider the needs for monitoring of human tissues on a national scale. The workshop was organized to enable committee members to hear presentations from individuals who have used NHATS data or tissues, as well as from individuals who might be likely to use NHATS data (e.g., those involved in public health, regulatory branches of the government, and research organizations). The committee also invited Dr. Robert Lewis, from the Federal Republic of Germany, to provide a general overview of monitoring and specimen banking from an international perspective (as he is involved with monitoring/ banking programs in Europe, Japan, and the United States). Individuals representing various U.S. government agencies were asked to present national monitoring objectives and to comment on NHATS from their agencies’ perspectives (Dr. Vernon Houk, Centers for Disease Control (CDC); Dr. Barry Johnson, Agency for Toxic Substances and Disease Registry (ATSDR); Dr. Fred Shank, Food and Drug Administration (FDA); and Dr. George Lucier, National Institute of Environmental Health Science (NIEHS)). Several individuals were invited to discuss monitoring objectives with regard to specialized program needs. Others were asked to address specific technical areas that are directly applicable to the NHATS program, including tissue collection, storage and archiving, data management, etc. In addition, several presentations were made about alternative types of monitoring programs
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Monitoring Human Tissues for Toxic Substances narrowly focussed or broadly conceived; these presentations were invaluable to the committee as they defined monitoring and banking objectives, described various methodologies, discussed areas of success and failure, and described budgetary requirements. MAJOR THEMES Several themes were repeated during the workshop of both a general and a specific nature. General Themes Human tissue monitoring is valuable and necessary and should be expanded. Specimen banking should be an integral part of monitoring programs. The goals of monitoring must be clearly defined. Monitoring programs are expensive, long term, and often without immediate results; however, funding must be made available as well as institutional commitment. Interagency cooperation would increase usefulness of the program and lessen the cost burden to any one agency. Specific Themes The current collection method needs improvement: a close relationship with cooperators should be encouraged; more frequent contact with cooperators is necessary; sterile or clean autopsies should be standard; sterile, insulated containers should be provided for transport to the archive; and proper conditions for storage (before storage in the archive) should be emphasized. The storage conditions (at the archive or bank) need to be improved: lower temperatures are necessary (-80°F, or the temperatures of liquid nitrogen); proper storage containers and proper labelling are needed; correct orientation of samples in storage must be maintained. The samples should not be compromised. A chain-of-custody record for the specimens is needed with respect to storage conditions at initial collection site, during transportation and at the archive. The management of data and their availability need improvement. The initiatives taken in improvement of the analytic techniques and in
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Monitoring Human Tissues for Toxic Substances broadening the range of chemical analyses should continue and be repeated with future samples. Quality control of specimens, analytic techniques, and sample stability is necessary, and quality assurance of the data needs to be ensured. The statistical design of the program needs to be improved: rural areas need to be represented; samples need to be “representative” of the general U.S. population; more information is needed about the sample in addition to age, sex, and general geographic location, e.g., occupation, area of residence, and diet; a determination of the effects of compositing samples is necessary, as is the development of a standard error around the mean values. A number of samples (representative of the population) should be banked specifically for long-term archiving. A sufficient amount of material should be banked for future multiple analyses or multiple assays. Procedures for sample collection should be standardized, and individuals should be trained in these procedures. SUMMARY The workshop began with an overview of the NHMP presented by Dr. Joseph Breen of EPA’s Office of Toxic Substances. The NHMP comprises the National Human Adipose Tissue Survey (NHATS), which has collected approximately 20,000 specimens since 1967; the National Blood Network (NBN) which has been funded but not implemented; and the special ad hoc studies that involve human tissue monitoring, e.g., the Veteran’s Administration study of Vietnam veterans’ exposure to “Agent Orange.” Dr. Han Kang, director of the Office of Environmental Epidemiology described the joint study between the VA and EPA (an NHMP special study). The VA analyzed the adipose tissues of Vietnam veterans collected and archived between 1965 and 1971 by the NHATS program. Dr. Kang found the archive very useful for the analysis of “Agent Orange,” which is a mixture of two commercial herbicides, and for the analysis of other chemicals, including dioxin and dibenzofurans. During the general discussion period, Dr. Vernon Houk criticized the VA study. He commented that the President’s Agent Orange Working Council’s Science Panel specifically recommended against the use of these adipose tissue specimens for analysis of dioxins. Dr. Lynn Goldman, chief of the Environmental Epidemiology and Toxicology Section at the California Department of Health Services, had several general comments on human monitoring for contaminants in tissues, as well as
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Monitoring Human Tissues for Toxic Substances several specific suggestions relating to the NHATS program. Dr. Goldman stressed the importance of having data on background levels of contaminants in human tissues and suggested that these data are generally lacking for most xenobiotics other than lead and heavy metals. She found the data collected by EPA’s NHMP useful because they were the only data available on background levels of pentachlor, phenol, and dioxin at a time when the California Department of Health Services was conducting studies at Superfund sites contaminated with these compounds. Dr. Goldman stressed the difficulties that arise when state health department officials are asked to investigate allegations of toxicant exposure of the general public. In most cases, very little reference information is available on toxicant background levels or metabolism. State health department officials, therefore, find it difficult if not impossible, to interpret their findings. Furthermore, the lack of a comparison population often leaves citizens open to anxiety over the findings. Several suggestions were discussed by Dr. Goldman as methods to improve the NHATS program and to increase its general usefulness: Specific studies aimed at contaminant levels and pharmacokinetics in populations that are considered vulnerable, e.g., children and pregnant women. The collection of data on background levels and other information that would be useful for assessing the introduction of new technologies. A ranking of activities and exposure assessments that are related to environmental clean up and regulation. The development of a more complete picture of substances to which the population is being exposed, e.g., broad-scan analysis of chemicals to determine real exposures. Screening techniques or bioassays that are less specific but highlight toxicologic end points might make the examination of the population more efficient than the current process. An expansion of the exposure data to include rural and urban residences, occupational history, and diet, in addition to age, sex, and geography. An increased emphasis on data-base management and encouragement of outside collaboration to ensure inclusion of the data in the scientific literature. A closer working relationship with established medical and public-health networks, especially in participating MSAs, and more frequent contact with collectors to encourage a better response rate. Dr. Goldman concluded her statements by reiterating the need for data on background levels of contaminants of the U.S. population for conducting
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Monitoring Human Tissues for Toxic Substances epidemiological studies, interpretation of findings from epidemiologic studies, planning environmental abatement programs, and exposure assessment. Dr. Robert A.Lewis, currently working in the Federal Republic of Germany (FRG), gave a broad overview of monitoring and remarked on the status of environmental specimen banking in relation to health and environmental assessment. Dr. Lewis stated that environmental protection should be anticipatory in nature. To translate the principle of anticipatory action into practical policy, a corresponding scientific infrastructure is needed, as well as a comprehensive database to determine the actual status of the environment. The latter requires continuous monitoring of the environment and archiving or specimen banking as a necessary complement to monitoring. The archive can then provide the basis for future retrospective studies. A panel discussion on national monitoring objectives was held with several individuals from federal agencies, including: Dr. Vernon Houk, director of the Center from Environmental Health and Injury Control at CDC; Dr. Barry Johnson, associate administrator of ATSDR; Dr. George Lucier, chief of the Laboratory of Biochemical Risk Analysis, NIEHS; and Dr. Fred Shank, acting deputy director for the Center for Food Safety and Applied Nutrition at FDA. Dr. Houk described monitoring objectives and techniques currently employed at CDC and specifically addressed EPA’s NHATS. One area of concern at CDC is the analysis of compounds on the ATSDR/EPA list of 200 priority toxicants. Monitoring these compounds to determine exposures is being emphasized, as is the development of methods for analysis of these compounds. A priority toxicant reference range study is being conducted at CDC and coupled to NHANES III (National Health and Nutrition Examination Survey) in collaboration with ATSDR and the National Center for Health Statistics (NCHS). The focus of this study is to determine background levels of 50 priority toxicants, primarily volatiles, and phenols in 1,000 people with no known excessive exposures. Individuals are being selected by age, sex, and geographic region, a strategy similar to that used in NHATS. Unlike NHATS, however, urban/rural status and individual analysis of samples will be considered. There will be no compositing of samples in NHANES III. Another similar study currently planned with NCHS and coupled to NHANES III will examine other priority toxicants. In its various exposure/monitoring studies, CDC uses direct measurements of toxicants to assess exposures. According to its collection and storage procedures, a pedigree of the specimen is made, which provides the documentation necessary for future use of the samples. Dr. Houk stated that -70° Fahrenheit or the temperatures of liquid nitrogen are necessary for long-term storage.
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Monitoring Human Tissues for Toxic Substances Dr. Houk made several comments that were specific to the NHATS: The NHATS is useful in detecting trends in levels of toxicants over time. It does not, however, provide population-based data. The program complements CDC’s efforts in identifying and measuring toxicants that are present in humans at concentrations of concern. The design of NHATS and NBN are constrained by practical limitations on sample availability. The data resulting from NHATS reflect substantial numbers of persons but do not allow U.S. population percentile estimates to be made. Compositing of samples restricts their usefulness for determining background ranges, i.e., the measured value of a composite sample is the same as the mean of the samples that make up the composite. Thus, the distribution of the results of the composites is a distribution of means rather than a distribution of individual values. Dr. Houk encouraged EPA to continue its activities, but with added emphasis on population-based estimates of measured toxicants. He further encouraged information exchanges with CDC and EPA laboratories with regard to methods used for chemical analyses of samples. He stressed the need for close attention to accuracy, precision, limit of detection, and quality assurance in test methods. His concluding statement, “[I]f a program is worth doing, it’s worth doing right,” was echoed many times during the workshop. Dr. Barry Johnson briefly described ATSDR’s mandate and monitoring objectives. He also addressed specific comments to the NHMP/NHATS and made several recommendations for increasing the utility of this program. Dr. Johnson explained that ATSDR was mandated by Congress to implement health-related sections of three laws (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) 1980, amendments to the Resource Conservation and Recovery Act (RCRA) of 1984, and the Superfund Amendments and Reauthorization Act (SARA) of 1986) that are designed to protect the public from adverse health effects caused by hazardous substances. The agency has developed ten program areas to aid in the implementation of congressional mandates. Three of the program areas involve evaluation of adverse human health effects and diminished quality of life resulting from exposure to hazardous substances in the environment: health assessments and health studies, toxicological profiles, and exposure and disease registries. Dr. Johnson commented on each of these three areas and explained their relevance to exposure monitoring data. He stated that the presence of population-based exposure monitoring data could be a very useful source of informa-
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Monitoring Human Tissues for Toxic Substances tion to ATSDR. He stressed, however, that the agency does not believe that such a national data base of population-based data is available to ATSDR at this time. Dr. Johnson described specific criteria that ATSDR would consider minimum criteria for any national monitoring/exposure data: The data and information must fit the needs of ATSDR (i.e., data must be relevant to ATSDR’s charge). The data sources must be credible (it should be evident that sound scientific methodology was used to generate those data). The data should be readily available, easily interpreted and current. Dr. Johnson stated that a national chemical exposure monitoring program would likely be used by ATSDR and other agencies if consideration were given to the following objectives: The data should reflect the entire U.S. population. The program should provide sufficient depth of data to permit subdivisions into key demographic groups. The program should provide quality control of its data and quality assurance of its laboratory analyses. The program and data should meet the expectations and conditions of scientific peer review. Dr. Lucier presented a perspective on monitoring objectives that reflect the fact that NIEHS is not a regulatory agency. He stated that NIEHS’s primary interest in monitoring programs is in the development and validation of biomarkers. Dr. Lucier also suggested that a national monitoring program should be developed that involves several agencies. The multi-agency approach would enable several organizations with varied expertise to address issues such as funding, sample collection, storage and distribution, priorities for sample access, and ethical issues. Dr. Lucier also concluded with the comment that a program worth doing is worth doing well. He expressed the opinion that well-designed and -conducted national human monitoring program will require more funds than are currently being directed toward the NHMP. Dr. Shank gave a brief overview of FDA’s monitoring programs, including programs that monitor for pesticide residues and toxic elements, including heavy metals, and industrial contaminants. The objectives of the programs vary, but enforcement of pesticide tolerances (established by EPA), and determination of incidence and level of residues in foods are of primary concern.
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Monitoring Human Tissues for Toxic Substances Continuous studies are directed toward these objectives, e.g., the Total Diet Study, commodity monitoring, and special surveys. Dr. Shank stressed the need for improved monitoring strategies for the food supply and the environment. He suggested that the nation pursue those programs that provide accurate data on issues most important to public health. Dr. Renata Kimbrough, director, Risk and Health Capabilities, EPA, raised many questions about the general usefulness of monitoring programs and problems associated with monitoring as well as the expense of monitoring. She raised issues about representative and statistical sampling and commented that it would be very expensive to produce either a representative or statistical sample of the population. Chlorinated hydrocarbon pesticide levels increase in individuals for various reasons (e.g., advanced age, weight loss, sex differences—levels are higher in men, occupation, diet and individual metabolism). Interpretation of data on pesticide levels, therefore, is very difficult. The problem may be further compounded by the reliability of the analytical methodology employed, the number of laboratories analyzing samples, and reproducibility of the results. Dr. Kimbrough stated that there are many reasons to continue monitoring programs, even with the difficulties discussed above. The objectives of monitoring should be focused on the development of baseline data, the analysis of trends to determine whether levels of targeted chemicals are decreasing once a regulatory action has been taken, and the development of biological markers as measures of indirect exposure. Dr. Donald E.Stevenson, chair of the Scientific Committee, American Industrial Health Council, and toxicology consultant to Shell Oil in Houston, contrasted the high priority and strong support of reliable exposure data in the United Kingdom with the type of support this activity has in the United States. Dr. Stevenson believes that, because of the interdisciplinary nature of such activity, there is no one group or agency that has taken “ownership” of all aspects of environmental exposures. Dr. Stevenson further noted the lack of interagency communication with respect to exposure measurements. Dr. Stevenson stated his bias as strongly in favor of exposure assessment playing a key role in identifying situations which require risk evaluation and in determining public health priorities. Dr. Stevenson stated that exposure assessment should be emphasized in the risk reduction process. In addition, he stated that NHATS has provided a truly unique source of data, and it would be unfortunate if EPA did not continue to analyze a sufficient number of samples to follow continuing trends over the next 5 to 10 years. He emphasized the usefulness of the FY 1982 NHATS study, which provided valuable baseline information. He urged EPA to continue this broader approach.
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Monitoring Human Tissues for Toxic Substances He stressed the usefulness of the broad-scan approach to determine subsequent sampling strategies and to detect the relatively small number of substances that require more detailed investigation. He also noted that a coordinated interagency strategy is necessary to ensure that all potentially important exposure sources are investigated. This strategy must also be integrated into the national priority strategy for health risk reduction. Several presentations dealt with specific aspects of the NHATS design. Dr. Roger Aamodt, program director for Cytology/Pathology, National Cancer Institute (NCI), discussed patient rights, quality of tissue, and equitable distribution of tissue as it relates to the NCI program. He stressed the importance of quality control of the tissues and stated that experienced pathologists are called upon to insure appropriate patient diagnosis. He discussed the protocols to collect and process tissue to ensure (1) rapid collection and transfer of tissue from the operating room in fresh condition; (2) accurate pathologic diagnosis by preserving appropriate samples; (3) availability of a pathologist at the time the tissue is collected to enable immediate examination; (4) sample sterility; and (5) important research specimens are not lost by preservation in formalin or in other ways that would destroy their value. Dr. Aamodt reiterated the importance of a close relationship between tissue procurement personnel and the operating room personnel. He also stressed the importance of sterility and freshness of the collected tissue: NCI provides iced, sterile containers for their collectors and instructs them on correct collection and storage procedures. Quality control is very important, and samples are packaged appropriately and shipped in insulated containers in wet or dry ice by overnight delivery service. The question of biohazard is an important one, i.e., the risk of infection to anyone handling the tissues. NCI will not knowingly collect any tissue from patients who have known transmissible bacterial or viral infections. Furthermore, to ensure the adequacy of investigative procedures, each investigator is required to inform and train all personnel in the dangers of and procedures for handling human tissues. NCI has developed a set of guidelines that provide extensive detailed information and procedures for handling human tissues and body fluids. Dr. Peter Mazur, a cryobiologist and corporate fellow, Oak Ridge National Laboratory, discussed the problems associated with the freezing of tissues. He stated that freezing is a viable option for storage of adipose tissues, but explained that freezing can either preserve cells or destroy them. Freezing under damaging conditions disrupts cell membranes and internal organelles. Cells that have been damaged by freezing will leak intracellular enzymes when thawed. However, storage temperatures of cells, regardless of freezing conditions, should be the temperature of liquid nitrogen (-196°F) or liquid nitrogen
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Monitoring Human Tissues for Toxic Substances vapor (-150°F); these temperatures will ensure that degradation during storage will not occur. There is strong evidence that at -196°F no thermally driven reactions can occur. In addition, if cell viability is not a matter of concern, then any freezing procedure that gets the tissues rapidly down to -196°F and keeps them at this temperature is acceptable. Dr. Robert Hay, Cell Culture Department of the American Type Culture Collection (ATCC), discussed storage of cells at the ATCC. This collection of cells is the largest of its kind in the world (2,000 new strains accessioned each year; 40,000 strains are maintained in an inventory of more than 1 million ampules; ATCC distributes 80,000–100,000 cultures a year). Cells at ATTC are stored in liquid nitrogen (-196°F) or in liquid nitrogen vapor, although animal viruses are stored at -70°. Each freezer unit (including alarm system) costs about $13,000. The yearly annual cost for liquid nitrogen is about $1,500/unit. The units are very reliable, and require repair or replacement only approximately every 15 years. Dr. Steven Wise, research chemist, National Institute of Standards and Technology (NIST), discussed environmental specimen banking and specimen archiving procedures at NIST. Specimens are archived as an alternative way of doing long-term trend monitoring. The advantages of banking specimens are obvious: as analytical techniques change and improve, banked specimens can be analyzed with new techniques. Furthermore, the opportunity exists for doing retrospective analyses on compounds that could not be measured at the time of collection. Dr. Wise presented a generic design for a tissue archival program based on NIST’s experience over the past 10 years. The following considerations were suggested as a necessary part of the specimen banking program: A specimen bank should be an integral part of a monitoring program. A representative number of specimens should be archived. A sufficient amount of materials should be archived for multiple analyses or multiple assays. Ample storage space should be available for archived specimens. Sample analysis should be based on individual samples rather than on composites, as individual specimens have more meaning than a composite. Samples should not be compromised, and procedures for collection and storage should be standardized and well documented. Procedures used by all collectors should be the same, and a formalized, detailed protocol for sample collection and storage should be encouraged. If deviations are made from protocols, these should be noted and accompany sample at all times. Samples should not be thawed to homogenize them for analyses. Cryo-
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Monitoring Human Tissues for Toxic Substances genie homogenization procedures (at liquid nitrogen vapor temperatures) are available to prevent thawing of the sample. Storage conditions should provide temperatures of at least -80°F, but liquid nitrogen vapor temperatures are preferable. Samples should be analyzed for stability, which provides an element of quality control. Finally, several presentations were made from individuals involved with alternate monitoring programs and program strategies. Dr. John Gannon, U.S. Fish and Wildlife Service (FWS), discussed monitoring and specimen banking in the Great Lakes Region. The program falls under an agreement between the United States and Canada, is administered by the International Joint Commission (IJC), and is funded by the United States and Canada jointly in an effort to monitor toxic chemicals in the Great Lakes. Dr. Gannon urged EPA and the Committee on National Monitoring of Human Tissues to consider the Canadian Wildlife Service Great lakes specimen banking program as a model. Its capability for retrospective study has been extremely successful. For example, herring gull egg tissue collection and source of dioxui contamination within the Great Lakes was easily determined from tissues banked since 1970. Dr. Gannon encouraged EPA and other federal agencies to establish human monitoring of tissues and to institutionalize specimen banking. He acknowledged, however, the difficulties with securing long-term funding for monitoring and banking programs in a climate of short-term budget cycles. Dr. Robert Murphy, director of the Division of Health Statistics, National Center for Health Statistics (NCHS), described the NHANES program, which is one of the major data collection systems of NCHS. Dr. Murphy stated that NHANES does have national reference distribution information and a national probability sample. NHANES is a representative sample; the measurements that are taken are those that may have health significance or are descriptive factors that can be useful in looking at health risk factors. NHANES is a very expensive monitoring program (NHANES III will cost $100 million, although in the OMB clearance package it is $115 million). NCHS encourages the involvement of other public and private agencies. It attempts to ensure continuity of resources with reference to personnel and equipment to run the program. Finally, the resources are available to the program for standardization, quality control, monitoring, criticism, and review of the data for the entire length of the program. Dr. Murphy urged federal agencies and the Committee on National Monitoring of Human Tissues to take into consideration the need for continuity, stability of staff, and collection methods when designing programs that monitor human tissues.
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Monitoring Human Tissues for Toxic Substances Dr. Pat Lombardo described the U.S. Food and Drug Administration’s (FDA) Market Basket (Total Diet) Survey. Dr. Lombardo explained that EPA registers or approves the use of pesticides and established tolerances if use of a pesticide may lead to residues in food, and with the exception of meat and poultry, for which USDA is responsible, the FDA is charged with enforcing tolerances for food shipped via interstate commerce. FDA has carried out a large-scale monitoring program for pesticide residues since the early 1960s. The program has two principal approaches: commodity monitoring to measure residue levels in domestic and imported food to enforce tolerances and other regulatory limits, and the total diet study to measure intakes of pesticides in foods prepared for consumption. The FDA considers the analytical approach to be critical. Most analyses are carried out using one of five well-tested multi-residue methods that can determine a number of pesticides in a single analysis. Findings from the studies are made public. This program was started in the 1960s and the current version has been in place since 1982. Dr. Lombardo stressed the importance of public perception, and the importance of understandable and timely communication of monitoring data. Dr. Lance Wallace, environmental scientist, U.S. EPA, described the Total Exposure Assessment Methodology (TEAM) study. The main TEAM study measured the personal exposures of 600 people to toxic or carcinogenic chemicals in air and drinking water. Twenty target chemicals were selected on the basis of their toxicity, carcinogenicity, mutagenicity, production volume, presence in preliminary sampling and pilot studies, and amenability to collection on Tenax. The subjects were selected to represent a total population of 700,000 residents of cities in New Jersey, North Carolina, North Dakota, and California. Each participant carried a personal air sampler throughout a normal 24-hour day, collecting a 12-hour daytime sample and a 12-hour overnight sample. Identical samplers were set up near some participants’ homes to measure the ambient air. Each participant also collected two drinking water samples. At the end of the 24 hours, each participant contributed a sample of exhaled breath. All air, water, and breath samples were analyzed for the 20 target chemicals. Mr. Gunnar Lauenstein discussed the National Oceanic and Atmospheric Administration’s (NOAA) National Status and Trends Program (NS&T). This environmental monitoring program is very specific in nature and has well-defined goals, which are to quantify the spacial distribution and long-term temporal trends of contaminants in the marine environment. This goal is accomplished by annual collection of bivalves, bottom feeding fish and surficial sediments around the United States. The Mussel Watch collects specimens from 177 sites around the United States and the benthic surveillance program
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Monitoring Human Tissues for Toxic Substances collects specimens from 50 different sites. NIST is responsible for the organic quality assurance of the analyses; the trace element quality assurance is handled by the National Research Council of Canada. A specimen-banking component of the NS&T program is carried out with the cooperation of NIST. Dr. Steven Wise discussed the several specimen banking activities of NIST, including the ongoing cooperative efforts with NOAA. Approximately 10 years ago, NIST became involved in specimen banking with EPA to determine the feasibility of long—term storage of different environmental specimens. The EPA Offices of Research and Development, and Health Effects Research funded the pilot environmental specimen bank program. NIST’s approach was to gain experience in the various aspects of specimen banking, including collection, storage and analysis. Although the program was initially intended to focus on four areas—human, marine, food and air—funding constraints have limited the focus to human tissues with limited work on the marine sample (e.g., in cooperation with NOAA). The various programs in which NIST has been associated in cooperation with other agencies are the human liver project with EPA, two NOAA programs and the NS&T Program, two projects with NCI, and the Total Human Diet Program with FDA. The human liver project (collections and banking) was initiated in late 1979. More than 550 specimens have been collected, along with analytical data for trace elements, organic pesticides, and PCBs on about 100 of these samples. In addition, NIST has made a comparison of different storage conditions by storing aliquots of the same samples at varying conditions and evaluating their stability. Furthermore, protocols have been developed for sampling and storage procedures, control samples are banked for quality assurance. This summary represents the opinions of individual workshop participants. This workshop summary has not been formally reviewed, but has been cleared for transmittal to the sponsor by the NRC Report Review Committee. A formal review will be applied to the committee report to be delivered to EPA in September 1990.
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Representative terms from entire chapter: