Use of expert judgment in exposure assessment. Part I. Characterization of personal exposure to benzene.

This paper presents the results of the first phase of a study, conducted as an element of the National Human Exposure Assessment Survey (NHEXAS), to demonstrate the use of expert subjective judgment elicitation techniques to characterize the magnitude of and uncertainty in environmental exposure to benzene. In decisions about the value of exposure research or of regulatory controls, the characterization of uncertainty can play an influential role. Classical methods for characterizing uncertainty may be sufficient when adequate amounts of relevant data are available. Frequently, however, data are neither abundant nor directly relevant, making it necessary to rely to varying degrees on subjective judgment. Since the 1950s, methods to elicit and quantify subjective judgments have been explored but have rarely been applied to the field of environmental exposure assessment. In this phase of the project, seven experts in benzene exposure assessment were selected through a peer nomination process, participated in a 2-day workshop, and were interviewed individually to elicit their judgments about the distributions of residential ambient, residential indoor, and personal air benzene concentrations (6-day integrated average) experienced by both the non-smoking, non-occupationally exposed target and study populations of the US EPA Region V pilot study. Specifically, each expert was asked to characterize, in probabilistic form, the arithmetic means and the 90th percentiles of these distributions. This paper presents the experts' judgments about the concentrations of benzene encountered by the target population. The experts' judgments about levels of benzene in personal air were demonstrative of patterns observed in the judgments about the other distributions. They were in closest agreement about their predictions of the mean; with one exception, their best estimates of the mean fell within 7-11 microg/m(3) although they exhibited striking differences in the degree of uncertainty expressed. Their estimates of the 90th percentile were more varied with the best estimates ranging from 12 to 26 microg/m(3) for all but one expert. However, their predictions of the 90th percentile were far more uncertain. The paper demonstrates that coherent subjective judgments can be elicited from exposure assessment scientists and critically examines the challenges and potential benefits of a subjective judgment approach. The results of the second phase of the project, in which measurements from the NHEXAS field study in Region V are used to calibrate the experts' judgments about the benzene exposures in the study population, will be presented in a second paper.

Assessment of the risk of introducing foot-and-mouth disease into Panama via a ferry operating between Cartagena, Colombia and Colon, Panama.

It should be emphasized that the proposed ferry hazard categorizations do not represent absolute risks for introducing FMD into Panama, but instead provide a systematic method for comparing and estimating risks in the absence of quantitative data. A hazard rating of high may not necessarily represent a high quantitative risk for the introduction of FMD, but is high when compared to other scenarios. A low hazard rating may estimate a low quantitative risk of importing FMD, but economic consequences of a potential outbreak should also be considered. When further data become available, a more complete assessment of the risks of the Crucero Express compared to airplanes, cargo boats, and small boats can be performed. At present, the risk of the Crucero Express is at least as low as the other transport modes described above. Since vehicles are not presently allowed transport from Colombia to Panama, they present no risk to Panama, but with proper cleaning and disinfection procedures, vehicles can be permitted with low risk. However, the Crucero Express can carry 125 vehicles, and thorough cleaning and disinfection of this many cars will require modern and efficient facilities not yet present at either port.

Macroepidemiological contributions to quantitative risk assessment.

Macroepidemiology is the study of all inputs into national patterns and determinants of disease, including economic, social, and political factors. Macroepidemiology complements and enhances the usefulness of quantitative risk assessment by increasing risk communication and understanding among policy-makers and the affected public. Macroepidemiological applications include qualitative risk assessment, mapping of relative risk within a country and assessment of surveillance systems.

Role of exposure databases in risk assessment.

Risk assessments have assumed an increasingly important role in the management of risks in this country. The determination of which pollutants or public health issues are to be regulated, the degree and extent of regulation, and the priority assigned to particular problems are all areas of risk assessment that influence the country's $100 billion annual investment in environmental protection. Recent trends in public policy have brought the practice of risk assessment under greater scrutiny. As policy makers increasingly insist that specific numerical risk levels (so-called bright lines) be incorporated into regulatory decisions, the stakes for good risk assessment practice, already high, are raised even further. Enhancing the scientific basis of risk assessments was a major goal of the Workshop on Exposure Databases. In this article, we present the Risk Assessment Work Group's evaluation of the use of exposurerelated databases in risk assessment and the group's recommendations for improvement. The work group's discussion focused on the availability, suitability, and quality of data that underly exposure assessments, a critical component of risk assessment. The work group established a framework for evaluation, based on exposure scenarios typically used in regulatory decisions. The scenarios included examples from Superfund, the Clean Air Act, the Toxic Substances Control Act, and other regulatory programs. These scenarios were used to illustrate current use of exposure data, to highlight gaps in existing data sources, and to discuss how improved exposure information can improve risk assessments. The work group concluded that many of the databases available are designed for purposes that do not meet exposure and risk assessment needs. Substantial gaps exist in measurements of actual human exposure and in the data necessary to model exposures, to characterize distributions of exposure, to identify high-risk groups, and to identify possible environmental inequities in exposure. The work group, on the basis of its findings, made both short-term and longer-term recommendations for improving the collection of exposure data in the future.

Determination of tri-n-butyltin in oysters by reaction-gas chromatography of hydride derivatives.

A reaction-gas chromatography method for determining tri-n-butyltin (TBT) as the hydride derivative has been adapted to allow determination of TBT in oysters. The extraction method has been modified to prevent fouling of the hydride formation reactor and the gas chromatography has been made faster by employing a different column and temperature program. The detection limit is 3-6 ng/g in oyster tissue. Apparent recoveries of TBT from oyster tissue at 25 and 125 ng/g levels are 107 and 97%, respectively.

Selective determination of histamine by flow injection analysis.

A flow injection analysis (FIA) method for the determination of histamine is described. Control of reaction timing allows exploitation of a transient, chemical-kinetic increase in selectivity that occurs when o-phthalaldehyde reacts with histamine. The molar fluorescence ratio (selectivity) of histamine/histidine reaches a maximum value of 800 in 32 s, precluding the need for separation of histamine from histidine, spermidine, and other potential interferences in biological samples. On-line dilution prevents matrix effects and affords a linear response up to approximately 4.45 mM histamine, or 500 mg of histamine free base/100 g. Under these conditions the detection limit (3 times peak-to-peak baseline noise) is 5.5 pg (corresponding to 0.60 mg of histamine free base/100 g of sample) and throughput is 60 injections per hour. The high sensitivity and high selectivity of the method allow the rapid determination of histamine in fish with minimal sample conditioning and will find application in the determination of endogenous histamine as well, such as in blood plasma and brain tissue.

Erythema elevatum diutinum in a patient with Crohn's disease.

A possible association between erythema elevatum diutinum and Crohn's disease is described. To our knowledge, erythema elevation diutinum has never been reported in a patient with Crohn's disease, nor has the disorder been considered one of the cutaneous manifestations of inflammatory bowel disease. Erythema elevatum diutinum is believed to be mediated by the deposition of circulating immune complexes in the dermal perivascular spaces. Our patient showed clinical and histopathologic findings typical of both erythema elevatum diutinum and Crohn's disease. The patient also had a positive Raji cell assay, which demonstrates the presence of a circulating immune complex. Increased levels of circulating immune complexes have been found in patients with inflammatory bowel disease, and the gastrointestinal inflammation in Crohn's disease could lead to enhanced antigenic exposure and increased formation of immune complexes. We contend that inflammatory bowel disease may have contributed to the development of erythema elevatum diutinum in our patient.

Ultraviolet and blue light induced damage to the Drosophila retina: microspectrophotometry and electrophysiology.

Intense ultraviolet (UV) and blue stimulation decreases visual pigment concentration and increases long wavelength fluorescent emission in R1-6 photoreceptors in the white eyed fruit fly Drosophila melanogaster. We used microspectrophotometry to show that the threshold for visual pigment decrease is about 1 log unit lower for UV than for blue light (18.7 vs approximately 19.9 log quanta/cm2 respectively). UV and blue stimuli about 0.2 log units brighter had been shown to cause structural degeneration. Above the threshold for structural damage, visual pigment is decreased permanently while below this level, a recovery of visual pigment was achieved within several hours. Microspectrofluorometric data are partially consistent with the hypothesis that the visual pigment is converted into a fluorescent product which had been named M'. M' had been proposed to be a new form of metarhodopsin which absorbs chiefly in the yellow and which has a fluorescent emission in the red; long wavelength stimulation had been reported to regenerate the native visual pigment from M'. Our data suggest that the situation is significantly more complex than this simple model. For instance, we report that long wavelength stimulation regenerates only a small fraction of the visual pigment which had been decreased by UV or blue stimulation. Furthermore, several lines of evidence suggest that other fluorescent products are also created by intense UV and blue stimulation. We were particularly interested in the lower damage threshold for UV light because of the hypothesis that UV visual sensitivity is mediated by a sensitizing pigment which absorbs UV light and transfers its energy to the blue absorbing rhodopsin. Our data suggest that the UV light decreases the rhodopsin without preferentially decreasing the sensitizing pigment.