Asbestos exposure during renovation and demolition of asbestos-cement clad buildings

External asbestos cement (AC) claddings become weathered after many years by the gradual loss of cement from exposed surfaces; as a result, loosely bound layers enriched with asbestos fibers are formed. This effect usually appears pronounced with roof cladding but slight with wall cladding. Asbestos fibers on such weathered surfaces may be mixtures of chrysotile with amosite or crocidolite. Renovation and demolition of old AC clad buildings could cause asbestos fiber emission, but this has not been investigated in the past. The exposure of workers to asbestos dust during these operations and precautions to minimize exposure now have been investigated at several building sites. Asbestos dust concentrations during water jet cleaning or painting of weathered AC roofing were approximately 0.1 to 0.2 fibers per milliliter (f/ml.). Limited results suggest that concentrations may be reduced substantially by avoiding abrasion of surfaces. Concentrations during AC roof replacement averaged approximately 0.1 f/mL and were reduced markedly by employing more careful work procedures (e.g., by careful handling of sheets or by wet stacking of sheets). Asbestos dust concentrations during demolition by removal of whole sheets averaged 0.3 to 0.6 f/mL for roofs and less than 0.1 f/mL for walls, reflecting the significant differences in extent of weathering between these elements. Suppression of asbestos emissions from roof sheets by wetting or sealing of weathered surfaces was not predictable because of the occurrence of asbestos fibers in dust trapped under sheet laps. Precautions such as respiratory protection and clothing decontamination are considered to be essential for the demolition of roofing containing amosite or crocidolite by the procedures investigated.     

Control of industrial exposure to tetrachloroethylene by measuring alveolar concentrations: theoretical approach using a mathematical model

Guberan, E. and Fernandez, J. (1974).British Journal of Industrial Medicine,31, 159-167. Control of industrial exposure to tetrachloroethylene by measuring alveolar concentrations: theoretical approach using a mathematical model. The uptake, distribution, and elimination of tetrachloroethylene were studied using a mathematical model, and predicted alveolar concentrations were compared with experimental data. Because of its high fat solubility the solvent accumulated in adipose tissue with a predicted biological half-life of 71·5 hours. The relation between the alveolar concentrations and the level or duration of exposure was discussed. The alveolar concentrations of tetrachloroethylene during and after similar exposure were predicted in subjects who differed in age, body weight, height, and body fat content, both at rest and during physical effort. Predictions were made of the alveolar concentrations following exposures to steady and variable concentrations in ambient air, and following exposures of several weeks of the type occuring in industry. It was concluded that measurement of the postexposure alveolar concentrations could be used to estimate the mean exposure to tetrachloroethylene in most industrial situations.     

Human environmental exposure to trichloro- and tetrachloroethylene from water and air in Milan,Italy

Annual consumption of trichloro- (TRI) and tetrachloroethylene (PER) in the Milan city area is estimated to be between 1,500 and 2,000 tons. Improper use and disposal of TRI and PER for many years have led to a serious pollution of groundwater, which is used untreated by 1,750,000 inhabitants through the municipal aqueduct. Two separate sub-areas of the city were considered, namely zone A (TRI and PER concentrations: 80 and 20μg/L, respectively) and zone B (12 and 4μg/L). Trento, a 70,000 inhabitants town of northern Italy, supplied with drinking water not contaminated with TRI and PER, was chosen as a control (zone C). Atmospheric levels of TRI and PER were also measured: TRI concentrations were similar in zones A and B (7.6 and 7.1 mg/m³), but higher levels of PER were found in zone A (14.8vs 9.5μg/m³), where many dry-cleaning laundries are located. In human subjects from the three zones, the total exposure to TRI and PER was biologically evaluated by measuring the plasmatic level of their metabolite trichloroacetic acid (TCA). Median plasmatic TCA levels were 38.2μg/L in zone A, 19.0 in zone B and only 7.5 in the control zone. The observed differences were highly significant, and unrelated to sex, age, body weight, residence, and the amount of water consumption.     

An empirical model for estimating census unit population exposure in areas lacking air quality monitoring

This study presents the methods and results of part of the HAPiNZ (Health and Air Pollution in New Zealand) study. A part of this project was to produce accurate measures of pollution exposure for the entire population of New Zealand living in urban areas. Suitable data are limited in most parts of New Zealand with some areas having no monitoring at all. As a result, this project has developed an empirical model to estimate annual exposure values for the whole country down to the census area unit level. This uses surrogate emission indicators and meteorological variables. Data sources used include census data on domestic heating, industrial emissions estimates, vehicle kilometres travelled and meteorological measurements. These were used to calculate annual exposure estimates and were then compared to monitored data for the areas where monitoring data were available. Results show a good association between the model estimates and the monitored data, enabling advanced health effects assessments for the country's entire urban population.     

On-site monitoring of personal exposure to tetrachloroethylene at dry cleaning establishments

Methods for monitoring personal exposure to tetrachloroethylene vapour in the dry cleaning industry have been investigated. A Draeger diffusive colorimetric gas detector tube and the Delta vapour detection system manufactured by Sabre Gas Detection were both shown to be suitable for preliminary on-site monitoring. A range of short-term pumped colorimetric tubes were also shown to perform well under a range of environmental conditions. Data on laboratory evaluations and field trials are presented.     

An approach for estimating exposure to ambient concentrations

The degree of certainty in epidemiological studies is probably limited more by estimates of exposure than by any other component. We present a methodology for computing daily pollutant concentration fields that reduces exposure uncertainty and bias by taking account of spatial variation in air quality. This approach, using elliptical influence functions, involves the optimum blending of observations from a monitoring network with gridded pollution fields predicted by the complex air quality model TAPM. Such fields allow more information to be incorporated in the exposure fields used in epidemiological studies, rather than having to assume that ambient exposure is the same across a whole city and/or that individuals remain at the one location for the duration of a study.     

Urinary excretion of tetrachloroethylene (perchloroethylene) in experimental and occupational exposure

Fifteen human volunteers were exposed to tetrachloroethylene (perchloroethylene, tetrachloroethene) vapor at 3.6-316 mg/m3 for 2-4 hr at rest (10 cases) and during light physical exercise (5 cases). Subsequently, 55 workers who were occupationally exposed to tetrachloroethylene in eight commercial dry cleaning facilities were studied (median value, 66 mg/m3; geometric standard deviation, 3.15 mg/m3). In both the experimentally exposed subjects and occupationally exposed workers the urinary concentration of tetrachloroethylene showed a linear relationship to the corresponding environmental time-weighted average concentration. The findings indicate that the urinary concentration of tetrachloroethylene can be used as an appropriate biological exposure indicator. In occupationally exposed subjects performing moderate work, the urinary tetrachloroethylene concentration corresponding to the time-weighted average of the threshold limit value proved to be 120 mcg/L and its 95% lower confidence limit (biological threshold) 100 mcg/L. The effects of workload on the tetrachloroethylene urinary elimination are also accounted for.     

log-binomial模型估计的患病比及其应用

[导读]探讨有和无连续协变量时的log-binomial模型估计患病比的统计方法及其应用.文中使用禁烟立法态度与吸烟关联的研究实例,比较log-binomial模型估计的现患比(PR)与logistic回归模型估计的优势比(OR).当模型中无连续协变量时,采用最大似然估计拟合log-binomial模型;当因含有连续协变量导致模型不收敛时,则采用COPY方法估计PR.分别估计男、女禁烟立法态度与吸烟的关联.由于女性吸烟率低,用PR与OR所估计的关联结果相似.而男性吸烟率较高,OR值明显大于PR.当年龄作为连续协变量纳入模型时,导致log-binomial模型不收敛,采用COPY方法解决此问题.所有分析均在SAS软件中实现.结论:当患病率较高时,PR比OR更好地测量了暴露与疾病的关联.文中给出log-binomial回归模型和COPY方法估计PR的SAS程序.     

A retrospective job exposure matrix for estimating exposure to 2,3,7, 8-tetrachlorodibenzo-p-dioxin

BACKGROUND: A job exposure matrix was developed to estimate the 2,3, 7,8-tetrachlorodibenzo-p-dioxin exposure of 3,538 workers who produced 2,4,5-trichlorophenol and its derivatives. METHODS: Daily TCDD exposure scores that were plant, process, and period specific were estimated for each job title as the product of 1) the concentration of TCDD (microg/g); 2) a qualitative factor to account for the extent of worker contact and 3) time exposed to TCDD contamination. Daily scores were summed to compute individual cumulative TCDD exposure scores. RESULTS: Daily TCDD exposure scores ranged from 0.001 to 1,250. Cumulative TCDD scores ranged from 0.002 to 1,559,430. The 393 workers with records of chloracne in the TCDD exposure cohort (11%) had markedly higher cumulative scores than those with no record of chloracne (a median score of 11,546 vs. 77). CONCLUSIONS: The cumulative TCDD exposure scores incorporate both duration and level of exposure, and permit the relative ranking of worker exposures for the evaluation of exposure-response relationships between TCDD exposure and mortality in an updated cohort study analysis. Copyright Published 2000 Wiley-Liss, Inc.     

Evaluation of the recursive model approach for estimating particulate matter infiltration efficiencies using continuous light scattering data

Quantifying particulate matter (PM) infiltration efficiencies (F(inf)) in individual homes is an important part of PM exposure assessment because individuals spend the majority of time indoors. While F(inf) of fine PM has most commonly been estimated using tracer species such as sulfur, here we evaluate an alternative that does not require particle collection, weighing and compositional analysis, and can be applied in situations with indoor sources of sulfur, such as environmental tobacco smoke, gas pilot lights, and humidifier use. This alternative method involves applying a recursive mass balance model (recursive model, RM) to continuous indoor and outdoor concentration measurements (e.g., light scattering data from nephelometers). We show that the RM can reliably estimate F(inf), a crucial parameter for determining exposure to particles of outdoor origin. The RM F(inf) estimates showed good agreement with the conventional filter-based sulfur tracer approach. Our simulation results suggest that the RM F(inf) estimates are minimally impacted by measurement error. In addition, the average light scattering response per unit mass concentration was greater indoors than outdoors; after correcting for differences in light scattering response the median deviation from sulfur F(inf) was reduced from 15 to 11%. Thus, we have verified the RM applied to light scattering data. We show that the RM method is unable to provide satisfactory estimates of the individual components of F(inf) (penetration efficiency, air exchange rate, and deposition rate). However, this approach may allow F(inf) to be estimated in more residences, including those with indoor sources of sulfur. We show that individual homes vary in their infiltration efficiencies, thereby contributing to exposure misclassification in epidemiological studies that assign exposures using ambient monitoring data. This variation across homes indicates the need for home-specific estimation methods, such as the RM or sulfur tracer, instead of techniques that give average estimates of infiltration across homes.     

A comparative study of human levels of trichloroethylene and tetrachloroethylene after occupational exposure

The rate of trichloroethylene (TRI) and perchloroethylene (PER) absorption was investigated in workers who were (1) occupationally exposed to TRI in four dry-cleaning shops (Group 1, n = 10) and (2) occupationally exposed to PER in one dry-cleaning shop (Group 2, n = 18). Concentrations of TRI and PER in blood were analyzed, and concentrations of trichloroethanol (TCE) and trichloroacetic acid (TCA) in blood and urine were analyzed. Results varied widely: PER was found in the blood of workers in group 1, but TRI was not detected in blood from any worker in group 2; most blood samples from group 2 workers did not contain a detectable quantity of TCE, and urine TCE concentrations in this group were very low. During the work week, a significant difference was found in group 1 for TRI in blood and TCE in blood and urine. In group 2, however, the only significant difference during the work week was for PER in blood. Therefore, the most reliable biological indicators for TRI and PER exposure are TCE in blood and PER in blood, respectively.     

Evaluation of the predictive abilities of a qualitative exposure assessment model

Various qualitative exposure assessment models based on different underlying assumptions requiring distinct inputs and providing diverse outputs are used by occupational hygienists and risk managers to evaluate the magnitude of occupational exposures. Although a wide variety of exposure assessment models are available, most models have not been validated. This study compared the inhalation risk factor of a qualitative exposure assessment model with quantitative exposure data collected at a manufacturing facility for more than 9 years for 12 worker groups involving 24 chemical agents. A Spearman's rho correlation found no significant correlation between the model's risk factor and the maximum measured exposure (rs=0.119, p=0.496). A Fisher exact test found that the maximum measured exposure was independent of the model's inhalation risk factor (chi2=0.203, p=0.653). The model accurately classified measured exposures in 18 out of 35 cases (51%), 53% of the measured exposures classified as acceptable were correctly classified by the model (sensitivity), whereas 33% of the measured exposures classified as uncertain/unacceptable were correctly classified by the model (specificity). There was a 67% probability that the model would result in a false low classification and a 47% probability that the model would result in a false high classification. Although the model was simple to apply, the overall predictive ability for the low level exposures seen in the study were poor and inconsistent among worker groups compared.     

Kinetics of tetrachloroethylene in volunteers; influence of exposure concentration and work load

Summary Six male volunteers were exposed for 4 h to 72 ppm tetrachloroethylene (PERC) at rest, to 144 ppm PERC at rest, and to 142 ppm PERC at rest combined with work load (2 times 30 min, 100 W). Minute volume and concentrations in exhaled air were measured to estimate the uptake. Concentrations of PERC and trichloroacetic acid (TCA) were determined in blood. Exhaled air was analysed for PERC; urine for TCA.The uptake/min decreased in the course of the exposure to 60 % of the initial uptake. The total uptake was influenced more by (lean) body mass than by respiratory minute volume or adipose tissue. During work load the uptake and minute volume increased to 3 fold the value at rest. In the post exposure period the quotient of the bloodconcentrations and exhaled air concentrations of PERC remained nearly constant at 23. Following exposure about 80–100 % of the uptake was excreted unchanged by the lungs, whereas till 70 h after exposure the amount of TCA excreted in urine represented about 1 % of the uptake.