Monitoring Human Tissues for Toxic Substances (1991) / Chapter Skim
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6. Chemical Assay of Specimens
6. Chemical Assay of Specimens
Pages 111-142
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From page 111... ...
and assay methods that have been validated for the sample type and concentration range of interest. A successful monitoring program maintains results over time for comparison and must therefore be technically adequate at the outset.
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From page 112... ...
Those opportunities and other efforts parallel to the monitoring tasks should support continuing development of the monitoring program itself. MAJOR FEATURES OF A PROGR~I FOR CHEMICAL ANALYSIS OF TISSUES FOR POPUI^TION-BASED SURVEILLANCE OF EXPOSURES Monitoring-Program Development One must first establish goals, specify target chemicals and quantities, and identify analytic methods.
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From page 113... ...
Selection Based on Analytic Expediency and Constraints In formulating a new monitoring program, one might choose analytic methods to maximize the likelihood of detection of key target chemicals. Multiagent analytic schemes that rely on gas chromatography and mass spectrometry (GC-MS)
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From page 114... ...
and the NIST Human Specimen Banking Reports (Wise and Zeisler, 1984~- not only are tools for locating candidate target chemicals that might conform to pre-existing analytic capabilities, but also might indicate a need for new analytic approaches to widen the range of chemicals detected. Selection Based on Indications of Health Relevance Testing programs conducted by NIH or by nongovernment researchers will continue to provide findings that increase or decrease health concerns related to possible exposures to individual agents.
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From page 115... ...
At a minimum, method development will include modification of existing protocols and methods developed for use in other applications or taken from the scientific literature, so that one can demonstrate adequate performance for the specific target chemicals, tissue sample type, and concentration range desired. Some of the steps (not necessarily in order)
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From page 116... ...
Several of those steps should be performed in replicates, so that assay variability can be assessed. More extensive method development will be required for analytic needs or target chemicals that do not conform closely to an existing protocol.
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From page 117... ...
Reference materials offer several advantages over blended samples: stability and homogeneity have been well established; reference values for certified contaminants are well established and documented; and a large community of users is sharing the same materials, so that evaluation of comparability of results is enhanced. The appropriateness of existing reference materials to the needs of any monitoring program will depend on the match between matrix type, analyte list, and concentration range in standard reference materials and monitoring-program samples and target chemicals.
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From page 118... ...
Pilot-Scale Monitoring Pilot-scale testing will identify and help to correct problems in the various elements of a monitoring program, including collection and transmission of samples, sample management before assay, chemical measurements, data management, and reporting. Each modification of the assay opens new possibilities for unforeseen technical problems.
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From page 119... ...
Exploratory activities within a monitoring program can provide an anticipatory approach to hazard recognition and provide for efficient application of new findings in the basic program. Incorporation of new agents into existing assay protocols and development of new protocols to address new monitoring goals can be planned as continuing activities.
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From page 120... ...
Mass spectrometry as a detection and quantitation method typically involves collection and storage of sequential mass spectra representing the entire detectable portion of the sample or solution analyzed. Computerized comparisons with massspectrum libraries can tentatively identify some proportion of "unknown" components, if the library of standards contains mass spectra similar to the unknown spectrum from the sample.
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From page 121... ...
Among those methods are new interface designs to permit high-performance liquid chromatography and mass spectrometry (LCMS) (Covey et al., 1986)
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From page 122... ...
Close coordination with environmental monitoring programs, as well as with bioassay and other toxicity-testing programs, is essential. Program design in this field will need to rely on scientific advisers who are familiar with the state of analysis and toxicology and who can realistically assess the probable benefit of a given exploratory program.
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From page 123... ...
, the loss of some information on joint exposure, and a loss of attention in the user community. Special Studies The characterization of particular exposure situations, such as a geographic region of high environmental contamination or those that focus on special subpopulations, is more efficiently addressed by special studies than by a nationwide survey.
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From page 124... ...
Although some basis for their selection can be inferred from the EPA literature supplied to the committee, the rationale is not clear. For example, the inclusion of brominated dibenzodioxins and dibenzofurans as target chemicals without method validation in the planned analysis of 1986 specimens was based not on prior detection in adipose tissue, but on "the potential for exposure to brominated analogues of dioxins and furans from specific brominated commercial products" (MRI, 1988~.
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From page 131... ...
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From page 132... ...
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From page 135... ...
Selection of analytic methods was generally based on methods already used and reported in published applications to analysis of adipose tissues (Macleod et al., 1982) , other tissues (Norstrom et al., 1986)
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From page 136... ...
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From page 137... ...
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From page 138... ...
No side-by-side comparison of results for each preparation method is shown, although such data were presumably generated. The consequences of that approach include the use of multiple methods of sample preparation when the method initially adopted was judged to be inadequate for some samples of target chemicals, lack of clarity about which methods produce which results, and uncertainty regarding comparability of results of the two methods.
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From page 139... ...
For example, the proposed inclusion of brominated analogues of PCDD and PCDFs as target chemicals without an explicit validation effort is a short cut that can lead to "mess/' and unsatisfactory results. Overall confidence in the results of the program would be strengthened if results of "try it and seer assays of study samples were more clearly distinguished from results of wellvalidated analyses.
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From page 140... ...
Formalization of the Planning Process Present reports do not address the larger issues underlying selection of project goals, nor do they provide insight into the information and alternatives considered in defining those goals. The result is an appearance of arbitrary program decisions; in some cases, decisions regarding the choice of analytic method seem to reflect a "shotgun" approach (e.g., elemental analysis of adipose tissue and possibly the volatile-chemicals projects)
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From page 141... ...
One limitation common to all the project reports produced in the 1980,s is that they report very little analysis of final results beyond analytic validity. Data sets are a prime product of a monitoring program, but interpretation of findings in relation to larger program goals (such as time trends, efficacy of interventions, relative importance of different environmental contaminants, and regional or demographic trends in exposures)
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From page 142... ...
142 O MONITORING HUMAN TISSUES years (3 years for the broad-scan pesticides, if the comparability study is included)
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