Dwight W. Underhill

Exposure from the Chernobyl accident had adverse effects on erythrocytes, leukocytes, and, platelets in children in the Narodichesky region, Ukraine: A 6-year follow-up study

BackgroundAfter the Chernobyl nuclear accident on April 26, 1986, all children in the contaminated territory of the Narodichesky region, Zhitomir Oblast, Ukraine, were obliged to participate in a yearly medical examination. We present the results from these examinations for the years 1993 to 1998. Since the hematopoietic system is an important target, we investigated the association between residential soil density of 137Caesium (137Cs) and hemoglobin concentration, and erythrocyte, platelet, and leukocyte counts in 1,251 children, using 4,989 repeated measurements taken from 1993 to 1998.MethodsSoil contamination measurements from 38 settlements were used as exposures. Blood counts were conducted using the same auto-analyzer in all investigations for all years. We used linear mixed models to compensate for the repeated measurements of each child over the six year period. We estimated the adjusted means for all markers, controlling for potential confounders.ResultsData show a statistically significant reduction in red and white blood cell counts, platelet counts and hemoglobin with increasing residential 137Cs soil contamination. Over the six-year observation period, hematologic markers did improve. In children with the higher exposure who were born before the accident, this improvement was more pronounced for platelet counts, and less for red blood cells and hemoglobin. There was no exposure×time interaction for white blood cell counts and not in 702 children who were born after the accident. The initial exposure gradient persisted in this sub-sample of children.ConclusionThe study is the first longitudinal analysis from a large cohort of children after the Chernobyl accident. The findings suggest persistent adverse hematological effects associated with residential 137Cs exposure.

Estimating the Contribution of Individual Work Tasks to Room Concentration: Method Applied to Embalming

A new approach for estimating emission rates from continuous concentration data was developed and applied to formaldehyde measurements collected during 25 embalmings. The instantaneous emission rate was estimated from the contaminant mass balance, which set the rate of emission equal to the sum of the rate of buildup in the room and the rate of removal in the exhaust flow. The generation rate of each specific work task was modeled using an equation that considered both the buildup and decay of the generation rate. Each term of the full modeling equation corresponded to a work task or event that occurred during the embalmings. The expected formaldehyde contribution of individual work tasks or events was then estimated by integrating each term using the gamma function. The work tasks or events with the largest formaldehyde contributions were aspiration of viscera after treatment with cavity fluid, embalming fluid spill, application of osmotic gel, and trocar cavity infusion. This analysis showed the relativ...

Effect of relative humidity on the adsorption of selected water-miscible organic vapors by activated carbon.

The adsorptive capacity of activated charcoal was determined experimentally for the vapors of 2-ethoxyethanol, pyridine, acetic acid, and piperidine from dry air and from air saturated with water vapor. Vapor concentrations ranged from 100 mg/m3 to at least 1000 mg/m3; the temperature was kept constant at 25 degrees C. The reduction in the adsorptive capacity of the activated charcoal by the relative humidity over the entire range of experimental conditions was accounted for by the Hansen-Fackler modification of the Dubinin-Radushkevich equation. This procedure allows the use of the activity coefficients, which are basic thermodynamic factors often available in the literature, to estimate the effect of adsorbed moisture on the adsorption of these organic compounds from a humidified atmosphere.

Convective transport in diffusive samplers.

Convective transport in diffusive samplers was determined by the loss of a dilute dye solution from these samplers while held in a water bath. The water flow in the bath was adjusted to give the same Reynolds number had the diffusive sampler been exposed to an airborne analyte at a predetermined flow velocity. By numerical analysis, estimates were made of the degree of interference of convection on sampler performance. The results indicate an enormous difference between commercial diffusive samplers with respect to the effect of convection on the transport of analyte into the sampler.

A Second Look at the Palmes’ Diffusive Sampler

Abstract The Palmes’ tube, the first diffusive sampler incorporating a fixed path length, has received wide usage for the sampling of a large number of gaseous pollutants. But despite numerous previous studies, questions remain regarding the accuracy of these inexpensive, simple-to-construct, open-ended samplers. Here the mass transfer resistance in a Palmes’ diffusive sampler was measured using the loss of cyclohexane from a Palmes’ tube containing liquid cyclohexane at its base. The average loss rates, at factorial combinations of five air incidence angles evenly spaced from 270° to 90°, and five air speeds from 0.5 m/sec to 2.5 m/sec ranged from 46% to 121% higher than rates calculated from the physical dimensions of the sampler, proving the need to calibrate these samplers rather than relying on a theoretical calculation. The mass transfer resistance was nearly constant when the airflow was perpendicular to the sampler and sufficiently high to avoid stagnation, a finding that may explain the widespread acceptance of the results obtained using this sampler.

Correlation of mass transfer rates for a diffusive sampler with air speed and incidence angle.

An accurate measurement of a gas concentration in air by diffusive sampling requires knowing the sampling rate. Both the boundary layer between turbulent ambient air and the sampler and the stagnant air layer inside the sampler impose resistance to the transport of analyte into the sampler. As the boundary layer mass transfer resistance is a function of the air speed and direction of the air movement, the sampling rate also depends on these variables. By the procedure developed here, the boundary layer mass transfer resistance was accurately measured as a function of wind speed and direction, and from these data a basic correlation with dimensionless parameters describing mass transfer was obtained. Deviation of air incidence angle and speed during sampling from the calibration conditions may produce a small positive bias, probably not in excess of 10%. Random variation of incidence angle and air speed while the sampler is in use may also contribute to the variability of this sampling method.

The Sampling Rates of Diffusive Samplers Measured in the Laboratory and in Simulated Use as Personal Samplers

This study investigated the effect of the speed and direction of air movement and the presence of the human body on sampling rate by changes in the boundary layer mass transfer resistance of samplers. The mass transfer resistance of a modified commercial diffusive sampler was measured mounted on a mannequin and compared with the mass transfer resistance of a sampler in an unobstructed airstream. The latter condition is the normal manner in which diffusive samplers are calibrated, while the former is more representative of field use. Results of the analysis are generalized in terms of dimensionless parameters. The presence of the mannequin produced boundary layer mass transfer resistances from 0.8 to 10 times that of samplers in unobstructed airflow for the range of air speeds and incidence angles studied. Illustrating the impact of the mannequins presence on sampling performance, the sampling rate for m-xylene at 25°C and 1 atm would range from 0.390 to 0.514 cm3/sec, or ± 13.7% of the midrange value. Th...

Optimal design of diffusive samplers

Some commercially available diffusive samplers use two layers of adsorbent placed in series. After sampling is completed, the time weighted average concentration of analyte is estimated from the weighted sum of the uptake of analyte on these two layers. It is known that such a division into layers can increase the permissible sampling time. Here the principles underlying this sampling procedure are analyzed through a fundamental application of the theory of diffusion. Using a trial and error procedure, the optimal division of adsorbent was calculated, and the increase in sampling time that such a division can give was confirmed theoretically. Also, should the uptake in the backup layer exceed a predetermined fraction of the total uptake, this will indicate misuse of the diffusive sampler.

Error bounds in diffusive sampling with reversible adsorption.

Diffusive samplers are commonly used in the work place for compliance monitoring of gases and vapors. Because the workplace concentrations of analyte are not constant, the usual procedure of calibration of a diffusive monitor by exposure to a known constant concentration of analyte may lead to an unacceptable error. By considering the maximum possible error in the time weighted average (TWA) concentration, with no restrictions regarding the concentration as a function of time, a permissible sampling time is defined that is consistent with any possible concentration fluctuation.

The Use of Reverse Diffusion to Validate the Performance of Diffusive Samplers

A number of different protocols have been put forth for measuring reverse diffusion from diffusive samplers. The basic concept is that reverse diffusion tests, depending as they do on basic laws of mass transfer, are not independent of one another, but may give general information about the limits to the possible change that can occur if the conditions to measure reverse diffusion are changed. Laboratory measurements of the reverse diffusion of vinyl chloride, using 3M and SKC diffusive samplers, following both the National Institute for Occupational Safety and Health (NIOSH) and the European Union test protocols, support the mathematical analysis developed in this article. An important conclusion is that if in following the NIOSH protocol a diffusive sampler loses 10% of its analyte over a period of 4 hours, then the maximum loss expected from a sampler allowed to back-diffuse for 8 hours is 19%.