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At least 19 recordsLinked to original sources

PubMed1992

A rationale and framework for establishing the quality of human exposure assessments.

Exposure assessments, performed as input to an evaluation of potential human health risk, are an element of risk assessment. Risk assessment results feed governmental and corporate risk management decisions, which seek to balance the estimated potential human health risks with other factors. Risk managers presume that the risk information provided to them is scientifically valid and accurate. Government agencies have begun to apply a system known as good laboratory practices (GLP) to ensure adequate data quality on animal studies, which are often the first step in the health-effects evaluation of risk assessment. This paper explores a rationale and framework for establishing the quality of human exposure assessments and proposes a set of good exposure assessment practices (GEAP). The components of the proposed GEAP include the writing of a study protocol before conducting the study, consideration of available resources, specification of an exposure model, a study design (including sampling and analytical methods and data analysis), quality assurance, archiving, communications, and a statement of overall uncertainty in exposure estimates. The GEAP concept is offered as a starting point for developing a consensus among the community of exposure assessors regarding a minimum standard for good practices. If a consensus on GEAP can be reached and applied, exposure assessments would have improved scientific bases, interpretability, and utility.

Environmental Monitoring↗

PubMed1992

Exposure assessment of risk factors for disorders of the back in occupational epidemiology.

This review describes methods for assessing exposure to postural load of the back in occupational epidemiologic studies. Eighty-one original articles were selected that presented information on the prevalence of back disorders in occupational groups. In 47 (58%) of these studies no data on exposure to risk factors were given. In the remaining 34 studies (42%) exposure assessment was performed by questionnaire (33%), observation (9%), and direct measurement (5%). Measures of exposure were predominantly presented at the nominal and ordinal levels. It is argued that in most epidemiologic studies on disorders of the back in occupational groups the quality of exposure data is poor. Quantitative measurement methods need to be developed for application in occupational epidemiology.

Back Pain↗

PubMed1992

Do quantitative exposure assessments improve risk estimates in occupational studies of cancer?

Quantitative assessment of exposure intensity is a difficult process, particularly for jobs held long ago. Despite difficulties, the use of this approach is growing in occupational epidemiology because it is hoped that the estimates will more closely approximate delivered dose than more traditional measures such as duration of exposure. If this assumption is correct, development and use of quantitative exposure estimates should reduce nondifferential exposure misclassification, sharpen exposure-response gradients, and enhance interpretation of study results. In this report, we used two methods to assess the value of quantitative exposure assessments in cancer epidemiology. In one, we surveyed the literature for investigations on occupational cancer that included assessments of both duration and intensity of exposure. The results of this survey indicated that exposure measures based on some measure of intensity of exposure yielded monotonically increasing exposure-response gradients and larger relative risks more often than those based on duration of exposure. Duration of exposure, however, occasionally provided the larger relative risks. In another approach, we found that different measures of exposure to formaldehyde classified subjects quite differently. For example, duration of exposure was unrelated to average exposure and was only weakly associated with exposure intensity or peak exposure. Because different measures of exposure may classify subjects quite differently and because quantitative estimates usually, but not always, yield larger relative risks and sharper exposure-response gradients than other measures of exposure, we believe that the prudent approach in epidemiologic investigations would be to develop quantitative estimates of exposure and to conduct analyses using several different measures of exposure, or combinations such as duration by intensity. Multiple comparisons would, however, increase chance findings. The value of such an approach is twofold. When a true association exists, use of several different measures decreases the chances of an unfortunate selection of an exposure measure that is poorly related to delivered dose, which would tend to produce negative results, and increases the chances of uncovering sharper exposure-response gradients. Use of several exposure measures in investigations that fail to exhibit an association between exposure and disease would be of value because such an approach would provide greater confidence that negative findings were not simply due to exposure misclassification.

Formaldehyde↗

PubMedDate not supplied

Total exposure assessment in occupational epidemiology for risk management.

Exposure assessment is an integral and essential component of occupational epidemiology necessary for risk assessment, risk management as well as for diagnostic and intervention efforts. It is a multidisciplinary approach that usually requires the combined expertise of environmental and industrial hygienists, toxicologists, epidemiologists, physicians, social scientists and statisticians. Exposure-assessment methodology employs various direct and indirect techniques, including environmental measurements, personal monitoring, biological markers, questionnaires, and mathematical modelling. Exposure assessments for occupational environment must be considered in the framework of potential contributions from other media and adding the incremental exposure from other media when necessary. Furthermore, to achieve effective risk assessment, all media and routes of exposure must be assessed for the relative magnitude of their contributions before an assessment of one medium is conducted. In the paper the concept of total human exposure assessment is introduced and measurement approaches have been discussed focusing attention on environmental research surveys.

Humans↗

PubMedDate not supplied

Human exposure assessment. I: Understanding the uncertainties.

Exposure estimates produced using predictive exposure assessment methods are associated with a number of uncertainties that relate to the inherent variability of the values for a given input parameter (e.g., body weight, ingestion rate, inhalation rate) and to unknowns concerning the representativeness of the assumptions and methods used. Despite recent or ongoing consensus-building efforts that have made significant strides forward in promoting consistency in methodologies and parameter default values, the potential variability in the output exposure estimates has not been adequately addressed from a quantitative aspect. This is exemplified by remaining tendencies within federal and state agencies to use worst-case approaches for exposure assessment. In this study, range-sensitivity and Monte Carlo analyses were performed on several different exposure scenarios in order to illustrate the impact of the variability in input parameters on the total variability of the exposure output. The results of this study indicate that the variability associated with the example scenarios range up to more than four orders of magnitude when just some of the parameters are allowed to vary. Comparison of exposure estimates obtained using Monte Carlo simulations (in which selected parameters were allowed to vary over their observed ranges) to exposure estimates obtained using standard parameter default assumptions demonstrate that a default value approach can produce an exposure estimate that exceeds the 95th percentile exposure in an exposed population.

Child, Preschool↗

PubMed1992

Comparison of exposure assessment guidelines for pesticides.

The field of exposure assessment of pesticides has become well established in the past decade. Consequently, government agencies and industry groups have identified the need for guidelines for conducting studies that assess mixer/loader/applicator exposure to pesticides, as well as the exposure of individuals to residues. This paper reviews guidelines on mixer/loader/applicator exposure studies issued by the International Group of National Associations of Manufacturers of Agrochemical Products, the National Agricultural Chemicals Association, the U.S. EPA, and the World Health Organization. Mention is also made of Canadian exposure guidelines in preparation. Also reviewed are two guidelines for conducting indoor occupant exposure studies, one by the National Agricultural Chemicals Association and one by Health and Welfare Canada. The only available guideline (EPA) on assessing pesticide exposure to workers upon reentry into treated fields is also reviewed. These guidelines are reviewed and compared as to criteria for requirements of exposure studies, methodologies recommended for dermal, inhalation, and biological monitoring, quality assurance and quality control, the use of surrogate data, data reporting, and exposure calculations. From this comparison, it is evident that there has been little significant progress in the area of methodologies used for dermal exposure monitoring. The use of patches as suggested by Durham and Wolfe (1962) is still accepted and widely used, despite its limitations. However, relatively recent research in this area has shown that the fluorescent tracer technique (Fenske et al. 1986a,b) and use of full-body dosimeters may help in overcoming some of these limitations. The tracer technique is mentioned in the EPA guidelines and full-body dosimeters are addressed by EPA, WHO, and NACA. Biological monitoring can also overcome many of the limitations of passive dosimetry, but all guidelines stress the need for extensive knowledge of the pharmacokinetics and metabolism of the pesticide before this approach can be used. Rapid advancement has been made in quality assurance/quality control and analytical techniques. This has increased the level of confidence placed in exposure estimates and is evidenced by the detailed requirements of quality assurance and quality control in most of the guidelines reviewed. Guidelines on conducting indoor occupant exposure studies deal extensively with methodologies for collecting residue samples, but do not make concrete recommendations for estimating human exposure based on these residues. More research is required before the subject can be adequately dealt with in guidelines. It is encouraging that this research is being coordinated among industry, academia, and government. Further research is also needed in determining exposure to pesticides during reentry into treated areas in order to develop further guidelines.(ABSTRACT TRUNCATED AT 400 WORDS)

Air Pollution, Indoor↗

PubMed1987

The TEAM (Total Exposure Assessment Methodology) Study: personal exposures to toxic substances in air, drinking water, and breath of 400 residents of New Jersey, North Carolina, and North Dakota.

EPA's TEAM Study has measured exposures to 20 volatile organic compounds in personal air, outdoor air, drinking water, and breath of approximately 400 residents of New Jersey, North Carolina, and North Dakota. All residents were selected by a probability sampling scheme to represent 128,000 inhabitants of Elizabeth and Bayonne, New Jersey, 131,000 residents of Greensboro, North Carolina, and 7000 residents of Devils Lake, North Dakota. Participants carried a personal monitor to collect two 12-hr air samples and gave a breath sample at the end of the day. Two consecutive 12-hr outdoor air samples were also collected on identical Tenax cartridges in the backyards of some of the participants. About 5000 samples were collected, of which 1500 were quality control samples. Ten compounds were often present in personal air and breath samples at all locations. Personal exposures were consistently higher than outdoor concentrations for these chemicals and were sometimes 10 times the outdoor concentrations. Indoor sources appeared to be responsible for much of the difference. Breath concentrations also often exceeded outdoor concentrations and correlated more strongly with personal exposures than with outdoor concentrations. Some activities (smoking, visiting dry cleaners or service stations) and occupations (chemical, paint, and plastics plants) were associated with significantly elevated exposures and breath levels for certain toxic chemicals. Homes with smokers had significantly increased benzene and styrene levels in indoor air. Residence near major point sources did not affect exposure.

Air Pollutants, Occupational↗

PubMed1987

Exposure assessment for occupational epidemiology.

Exposure evaluation for epidemiology has special requirements, which can be derived from the pharmacological processes that determine the exposure-effect relationship. Since environmental concentrations of toxic agents typically are highly variable over time, the tissue concentrations they produce will vary over time, and consequently the level of effects will also vary over time. A general, six-step approach is proposed for developing an exposure assessment for an epidemiologic study. This approach uses pharmacologic models to guide the choice of exposure measurement parameters and to guide the epidemiologic data analysis. The approach is illustrated for evaluations of reversible airway effects of ozone and irreversible pulmonary effects of a mixed silica dust. Effect indices are introduced as a means of quantifying the temporal interrelationships of the exposure profiles and the pharmacologic models. These indices have advantages over both dose indices and simple dose-outcome models.

Dose-Response Relationship, Drug↗

PubMedDate not supplied

Exposure assessment for electric and magnetic fields.

Exposure assessment for extremely low frequency (ELF) electric and magnetic fields (EMF) is discussed. It is suggested that such assessments can be designed by attempting to mimic the receptor's experience of interest. Present efforts are, however, hampered by the lack of clearly defined human health effects, or even important interaction mechanisms, which might be used to define the appropriate exposure measure, the experience of interest. The state of the art of ELF EMF exposure assessment is described, including the use of surrogates, models, and available instrumentation. Data indicate that magnetic field levels in the home are of the order of 0.1 microT and that nonoccupational total exposures may best be predicted by levels in the bedroom. Occupational exposures may be orders of magnitude higher where high currents are present.

Carbon Monoxide↗

PubMed1990

Methodologic issues in exposure assessment for case-control studies of cancer and herbicides.

Epidemiologic studies of cancer and exposure to herbicides have shown puzzling inconsistencies. Exposure-response gradients have been reported for non-Hodgkin's lymphoma in Sweden and Kansas, but no significant associations were seen in New Zealand or Washington State. Subjects in these studies were categorized by exposure using information obtained primarily by interview. A number of questions can be raised regarding the reliability and validity of such an exposure assessment. We examined procedures used to assess pesticide exposures in case-control studies of cancer to evaluate their limitations and their probable effects on risk estimates. Except for case recall bias, problems of misclassification in these studies would tend to bias risk estimates toward the null and dilute exposure-response gradients. These problems are, therefore, unlikely explanations for the positive associations between cancer and herbicide use noted in some investigations. A tendency for false-negative findings, however, is not reassuring, and improvements in exposure assessment are needed if epidemiologic investigations are to continue to provide reliable information on the relationships of cancer and pesticide exposure.

Bias↗

PubMedDate not supplied

Human exposure assessment. II: Quantifying and reducing the uncertainties.

Alternative methods of human exposure assessment that reduce and/or allow quantification of the uncertainties associated with exposure estimates are surveyed and illustrated. These alternative approaches include (1) use of more appropriate exposure parameter default values rather than values that result in extreme exposure estimates; (2) incorporation of time-activity data to better define appropriate exposure duration values; (3) the use of reasonable exposure scenarios rather than the traditional Maximally Exposed Individual (MEI) approach; (4) the use of stochastic approaches such as Monte Carlo-based and information analysis-based methods; (5) use of bivariate analysis to identify the extent to which interdependencies between different exposure parameters affect the distribution of exposure estimates; (6) use of less-than-lifetime exposure and risk assessment; and (7) incorporation of physiological considerations relevant to absorbed dose estimation, including route-specific impacts, use of improved absorption factors, and application of pharmacokinetic models. Other ways to improve the exposure assessment process, including assuring statistical equivalency in comparing different exposure estimates and incorporation of sensitive subpopulation considerations are also discussed, as are key research needs.

Child↗

PubMed1989

Toxicological evaluation of complex industrial wastes: implications for exposure assessment.

We evaluated a variety of short-term bioassays to construct a battery of tests that could be used for assessing the biological effects of potentially hazardous complex industrial wastes. Ten samples were studied for hepatotoxicity; these samples and an additional 5 were studied for mutagenicity. Although the data are limited to these samples, the results suggest that the Salmonella assay (strain TA98) or a prophage-induction assay (both in the presence of S9) in combination with determination of relative liver weight and levels of a set of serum enzymes in rats may provide a battery of tests suitable to characterize complex industrial wastes for mutagenic and hepatotoxic potential. The biological activities exhibited by the wastes were not readily predicted by the chemical profiles of the wastes, emphasizing the importance of characterizing potentially hazardous complex industrial wastes by both chemical and biological means. DNA from liver, lung and bladder of rats exposed to some of the wastes was analyzed by the 32P-postlabeling technique for the presence of DNA adducts. A waste that produced mutagenic urine produced a DNA adduct in bladder DNA. The implications of this approach for assessment of exposure to complex hazardous waste mixtures are discussed.

Animals↗

PubMed1992

The Workplace Exposure Assessment Expert System (WORKSPERT).

The fundamental principles of industrial hygiene are based upon the recognition, evaluation, and control of workplace hazards. Occupational safety and health professionals (e.g., industrial hygienists) perform this task by assessing numerous complex factors. In many situations industrial hygienists are not available; therefore, an expert system has been developed to assist the performance of workplace exposure assessments (WEAs). The Workplace Exposure Assessment Expert System (WORKSPERT) evaluates various hazardous substances, workplace conditions, and worker exposures for designated homogeneous exposure groups (HEGs). The three major components of WORKSPERT (i.e., substance, workplace, and exposure factors) are described by 27 multiple attribute variables. An air monitoring program (AMP) may be recommended for each HEG based upon the WEA. The AMP provides recommendations for an appropriate sampling strategy, sampling duration, multiple substance exposures, and number of samples to be obtained in the future. The use of WORKSPERT or other expert systems should never supersede the judgment of occupational safety and health professionals. However, WORKSPERT can be a valuable tool when used by knowledgeable, qualified technical professionals (e.g., safety and health specialists, chemists, engineers, and toxicologists) who understand the specific substance, workplace, and exposure factors for designated HEGs. WORKSPERT allows these people to benefit from the expertise of an industrial hygienist by performing systematic evaluations and obtaining recommendations for corrective actions or an AMP. The use of WORKSPERT to perform WEAs promotes the protection of workers from hazardous substances and assists compliance with occupational safety and health regulations. It also facilitates the communication of substance hazards, workplace controls, and worker exposures in a succinct manner.

Air Pollutants, Occupational↗

PubMedDate not supplied

Exposure assessment: input into risk assessment.

The validity of a risk assessment can be no better than that of the exposure assessment upon which it is based. The general paucity of relevant exposure data, combined with the limited appreciation by most risk assessors of the critical dimensions and metrics of exposure, often leads to an overreliance on exposure models of questionable validity. The problems of identifying and interpreting relevant metrics of exposure for epidemiologic studies and risk assessments are illustrated through the presentation of three case studies. The first examines the effects of ozone on respiratory mechanical function and demonstrates that the appropriate averaging time is greater than or equal to 6 hr, rather than 1 hr, as is implied by the current ambient air quality standard. The second case study examines the effects of sulfur oxides and particulate matter in ambient air on morbidity and mortality. It indicates that the effects are most closely associated with the acidity of the aerosol, providing a basis for an index of exposure more relevant than those currently used, i.e., sulfur dioxide and nonspecific gravimetric mass concentration of particulate matter. The third case study examines the effects of lead on blood pressure. It shows that blood lead in concentrations below 35 micrograms/dL correlates with blood pressure in both humans and animals independently of other known causal factors for blood pressure elevation. It also examines the variable relations between levels of lead in blood and in environmental media to illustrate the potential problems which can arise from the use of biological markers, such as lead in blood, as indices of exposure.

Adolescent↗

PubMed1991

Conservatism in maximally exposed individual (MEI) predictive exposure assessments: a first-cut analysis.

The United States Environmental Protection Agency (USEPA) sometimes applies exposure assessment models based upon the concept of a hypothetical "maximally exposed individual" (MEI) as a means of dealing with uncertainty. This concept has been described in the benzene NESHAPS rule, the proposed RCRA Corrective Action Rule, and the Clean Air Act reauthorization debate. This paper describes a first-cut analysis of the level of conservatism of the current MEI approach relative to a central estimate of exposure of the most exposed population around a source. The inherent level of conservatism of the current MEI model, which appears to be at least one order of magnitude, is usually left unstated. The significance of this conservatism is described along with some proposals for future research.

Benzene↗

PubMed1991

Human exposure assessment: a graduate level course.

The course has been offered three times. The content and the approach to each lecture has evolved after each time it was given. This is not unexpected since the field has been undergoing major transformations, and new approaches to measurement and modeling are being applied to current problems. The most recent student evaluation, 1990, indicates a difficulty rating of "just right" (70%) to "difficult" (30%). Most felt the course stimulated their interest in the topic (72%) and the examinations were learning experiences as well as a grading exercise. The major need for the discipline is an adequate text book. The GRAPE program has excellent potential as an educational took, but it needs to make more interactions and allow introduction of activities and data. The major strengths of the course are the problems provided to the students for homework. These give the student quantitative perspective on the concepts, range in values, variables, and uncertainties necessary to complete an assessment. In addition, the development of the mathematical and conceptional continuum for placing exposure assessment in the context of toxicology, environmental science, epidemiology, and clinical intervention provides a basic framework for the discipline.

Air Pollutants↗

PubMed1990

Assessing exposures to environmental tobacco smoke.

The combustion of tobacco indoors results in the emission of a wide range of air contaminants that are associated with a variety of acute and chronic health and comfort effects. Exposures to environmental tobacco smoke (ETS) are assessed for epidemiologic studies and risk assessment and risk management applications. An individual's or population's exposure to ETS can be assessed by direct methods, which employ personal air monitoring and biomarkers, and indirect methods, which utilize various degrees of microenvironmental measurements of spaces, models, and questionnaires in combination with time-activity information. The major issues related to assessing exposures to ETS are summarized and discussed, including the physical-chemical nature of ETS air contaminants, use of proxy air contaminants to represent ETS, use of biomarkers, models for estimating ETS concentrations indoors, and the application of questionnaires.

Biomarkers↗

PubMedDate not supplied

Biological markers in chromium exposure assessment: confounding variables.

An estimated two million tons of chromate production waste pollution has caused a major environmental and public health concern in Hudson County, New Jersey. As part of an occupational exposure assessment, urinary and red blood cell (RBC) chromium measurements were performed on 52 state employees who worked either near a contaminated site or elsewhere. Samples were collected so as to minimize contamination, and they were analyzed using sensitive techniques. These workers also completed a questionnaire that addressed potentially important third variables. Individual analyses suggested that exercise, drinking beer, past employment in chromium-related occupations, and diabetic status had an important effect on urinary chromium levels. These variables were entered into a regression model and were all found to be significant predictors of urinary chromium level (p less than .10). Some variables were also examined for their influence on RBC chromium level, but none had a measurable effect.

Adult↗