Scott Clark

Airborne Bacteria, Endotoxin and Fungi in Dust in Poultry and Swine Confinement Buildings

Airborne dust in swine and poultry confinements was analyzed to determine concentrations of total and gram-negative bacteria, total fungi, Aspergillus fumigatus and endotoxin. Airborne concentrations of total and gram-negative bacteria in swine and confinement units have been found to be as high as, or higher, than those found in other environments, such as wastewater treatment plants and cotton card rooms, where microbiologically contaminated organic dusts were present. Airborne endotoxin concentrations in the swine units (average 0.12 micrograms/m3) and poultry units (average 0.31 micrograms/m3) were in the range where clinical effects have occurred in other populations. Therefore, health studies of poultry and swine confinement workers with concurrent estimation of the individual daily exposure dose are warranted.

Imputation of Data Values That are Less Than a Detection Limit

Results of the analyses of occupational and environmental samples are frequently reported as “less than a specified value,” a practice followed by many analytical laboratories. A left-censored distribution occurs when analytical laboratories do not report results that fall below their limits of detection or quantification. Approximately 37% of the household interior dust lead loadings collected in a large-scale, multisite, longitudinal study of lead-based paint hazard controls were reported to be below the “method detection limit.” These unreported values are unusable in any statistical analysis of the data and must be replaced by a valid dust lead loading estimate, a process called data imputation. This investigation tested how well data imputed using a newly formulated procedure for estimating the data below the method detection limit were correlated with dust lead loadings reported by the participating laboratories after special request. These results were also compared with those obtained by imputing the minimum detectable level by the square root of 2. Imputation of the low lead loadings was accomplished by substituting the value associated with the median percentile below each laboratorys method detection limit. A correlation of r = 0.50 was calculated between the predicted and reported dust lead loadings, with only slight bias (2.9%) in the predicted values. An alternative imputation procedure that used the predicted value from structural equation models fit to the noncensored dust lead loadings performed about as well, although the predictions had to be “centered” to correspond to the censored data. An estimator that combined both of these imputation procedures only slightly improved the correlation between the predicted and laboratory values (r = 0.51). These results support the use of the new procedure rather than the commonly used imputed values of the method detection limit divided by 2 or by the square root of 2. Imputing values based on either of these common approaches may result in much more biased predictions for the censored data; in the case of these data, the dust lead loadings were overestimated by 348%. The results also suggest that analytical laboratories should provide a numerical result for all analyzed samples, with a “flag” of those values below their detection limit, since these results may be more accurate than any imputed value, particularly those provided by the commonly used method of dividing the minimum detection limit by the square root of 2.

Urban Lead Exposures of Children in Cincinnati, Ohio

AbstractEnvironmental dust lead and other lead measures were highly intercorrelated for the wide range of housing in the Cincinnati prospective study. The causal pathway revealed by the data (soil ...

The Cincinnati prospective study of low-level lead exposure and its effects on child development: Protocol and status report☆

This project attempts to integrate information on exposure history, cognitive and behavioral development, and health and social functioning in order to delineate the association between chronic, low-level lead exposure and behavioral development. A dose-response analysis will be made seeking to relate the frequency with which effects occur to degree of lead exposure.

The Influence of Exterior Dust and Soil Lead on Interior Dust Lead Levels in Housing That Had Undergone Lead-Based Paint Hazard Control

To aid in understanding the contribution of exterior dust/soil lead to postintervention interior dust lead, a subset of housing from the HUD Lead-Based Paint Hazard Control Grant Program Evaluation was selected for study. Housing from 12 state and local governments was included. Exterior entry and street dust samples were obtained by a vacuum method, and soil samples were building perimeter core composites. Interior dust wipe lead data (μg/ft2) and paint lead data (mg/cm2) were also available for each of the dwelling units and included in the modeling. Results from 541 dwelling units revealed a wide range of exterior dust and soil lead levels, within and between grantees. Minimum and maximum geometric mean lead levels, by grantee, were 126 and 14,400 μg/ft2 for exterior entry dust; 325 and 4,610 μg/ft2 for street dust; and, for soil concentration, 383 and 2640 ppm. Geometric mean exterior entry dust lead concentration (1641 ppm) was almost four times as high as street dust lead concentration (431 ppm), suggesting that lead dust near housing was often a source of street dust lead. Geometric mean exterior entry dust lead loading was more than four times as high as window trough dust lead loading and more than an order of magnitude higher than interior entry dust lead loading. Statistical modeling revealed pathways from exterior entry dust lead loading to loadings on interior entryway floors, other interior floors, and windowsills. Paint lead was found to influence exterior entry dust lead. Results of this study show that housing where soil lead hazard control activities had been performed had lower postintervention exterior entry, interior entry floor, windowsills, and other floor dust loading levels. Soil was not present for almost half the buildings. Statistical analysis revealed that exterior strategy influenced soil lead concentration, and soil lead concentration influenced street dust lead loading. This study represents one of the few where an impact of soil treatments on dust lead levels within the housing has been documented and may represent the first where an impact on exterior entry dust lead has been found. The inclusion of measures to mitigate the role of exterior sources in lead hazard control programs needs consideration.

Clean-up of Lead in Household Carpet and Floor Dust

Methods to remove lead-containing dust were tested on carpets from homes of children with high blood lead and on new carpets artificially contaminated in the laboratory. The household carpets could not be cleaned effectively by repetitive vacuuming with HEPA-filtered cleaners. The lead concentration in the removed dust remained about the same from the initial cleaning (1 min/m2) to the final cleaning (total cleaning time of 10 min/m2). The lead loading on the surface of the carpets often increased during cleaning because vacuuming brought lead from deeper in the carpet to the surface. Over 95% of the total dust was removed from bare wooden floors by dry vacuuming (5 min/m2). For linoleum, more than 75% was removed by vacuuming for 5 min/m2. However, little was removed in vacuuming after the initial two minutes and about 20% was removed in a final wet-washing step. HEPA-vacuuming of the laboratory-contaminated carpets revealed that two of the commercially available vacuum cleaners tested were essentially equivalent and each removed significantly more dust than a third vacuum during a total cleaning time of 10 min/m2. Cleaning for 6 min/m2 was necessary to remove more than 70% of the embedded dust by the two more efficient vacuums. Cleaning efficiencies were about the same for short pile and sculptured carpets. It was concluded that it may be more practical to replace rather than clean carpets. HEPA-vacuum cleaning of carpets was shown to increase lead dust on the surface under some conditions.

Factors affecting microbiological colony count accuracy for bioaerosol sampling and analysis.

The effects of the following variables on the occurrence of colony masking (the indistinguishable merging or overlap of sufficiently close colonies) were evaluated experimentally using the bacterium Bacillus subtilis: spore density on a collection surface, concentration of nutrients in the culture medium, sample incubation time, and ability of an observation system to distinguish overlapped colonies. Increasing spore surface density and incubation time increased colony masking, whereas lowering nutrient concentration decreased colony diameter and, therefore, masking but also limited spore germination and growth. Overall, full-strength medium was best for accurate counting of early microcolonies examined with the aid of a microscope, whereas half- or quarter-strength medium was better for counting older readily observable macrocolonies. Masking bias was determined for varying spore surface densities and colony diameters and was applied to two widely used slit-to-agar bioaerosol impactors. Appropriate collection times have been determined for these samplers to minimize colony masking for expected bioaerosol concentrations. It was found, for example, that 6-min samples collected from an environment with an air concentration of 10(3) CFU m-3 would result in colony surface densities, for 3-mm colonies, of 1.5 and 3.9 microorganisms cm-2 for the two samplers with respective masking biases of < 10% and < 20%.

Midvale Community Lead Study

AbstractThe primary objective of this study was to ascertain whether children living in close proximity to mill tailings and a former lead smelter site were currently exhibiting elevated blood lead (PbB) concentrations. To address this issue, the mean PbB for community children and the relationship between PbB and the proximity of the childs residence to the site was estimated. A secondary objective was to identify and quantify accessible lead (Pb) and arsenic (As) in the environment (e.g. Pb in soil, dust, paint and water or As in soil and dust). A third objective was to test for association between specific sources of environmental Pb and PbB and to estimate the relative contribution of these proximate sources of lead to the childrens PbB. The data analytic methods allowed estimation of both direct and indirect impact of environmentally accessible Pb. The average PbB level of all children screened in Midvale was 5.2 μg dL−1. Three percent exceeded 15 μg dL−1; 12.7% exceeded 10 μg dL−1. Pb-based house ...

Particle Settling After Lead-Based Paint Abatement Work and Clearance Waiting Period

This study investigated the evolution of airborne particle concentration and size distribution following abatement work in a controlled environment utilizing direct real-time particle monitoring and used it to project potential lead loadings as those particles settle. An 860 ft3 environmental test chamber with sophisticated ventilation and air purifying systems was built. Wooden doors with lead-based paint were dry sanded or scraped to generate the highest feasible airborne lead concentrations. Size-fractional airborne particle concentrations decreased exponentially with time in all tests, even with no air exchange, consistent with the stirred model of constantly mixed air, which predicts longer settling than for tranquil settling. Very low levels of air mixing generated by temperature gradients and initial room air turbulence affected particle settling. About 90% of airborne lead mass settled within 1 hour after active abatement, before final cleaning began. During the second waiting period of 1 hour, which followed cleaning of the floor, additional dust settled so that the additional potential lead loading from remaining airborne lead was less than 20 microg/ft2. For this worst case scenario, the underestimate of the lead loading done by the clearance sampling did not exceed about 30%. For more realistic conditions, the underestimates are projected to be much lower than the new 40 microg/ft2 Housing and Urban Development (HUD) clearance standards for floor dust lead. These results were obtained for the first waiting period (between the end of active abatement and the beginning of cleaning) of 1 hour, as recommended by HUD guidelines. Thus, this study demonstrates no need to increase either the first or second waiting period.

The effectiveness of ice- and freon®-based personal cooling systems during work in fully encapsulating suits in the heat

The use of cooling garments in conjunction with fully encapsulating suits offers the potential for reducing the heat strain for workers at hazardous waste sites and chemical emergencies. This study examined the use of ice- and Freon-based cooling garments during exercise in the heat while wearing a U.S. Coast Guard chemical response suit (CRS), a fully encapsulating, Teflon-coated, Nomex suit. Responses of nine healthy men (mean age 28.8 yr) were measured during moderate exercise at 30% of their maximal oxygen consumption in an environmental chamber maintained at 33.9 degrees C (93 degrees F) and 82% relative humidity. The four randomly assigned experimental conditions were (1) the CONTROL, consisting of a self-contained breathing apparatus (SCBA) worn in conjunction with shorts, shirt, helmet, and shoes; (2) the CRS, consisting of the Coast Guard CRS worn with shorts, shirt, SCBA, helmet, gloves, and boots; (3) the ICE, which was identical to the CRS ensemble, with the addition of an ice and water cooling system; and (4) the FREON, which was also identical to the CRS ensemble, with the addition of a Freon-based cooling system. To the authors knowledge, this paper is the first to quantify and compare a Freon-based system with a circulating ice water system. The subjects performed repeated rest/work intervals for 45 min, followed by a 10-min recovery period. Measured physiological responses, including heart rate, skin, rectal, and axillary temperatures, were recorded at 1-min intervals during the tests.(ABSTRACT TRUNCATED AT 250 WORDS)