Biomedical subjects

Noah S Seixas

Publications and source records attributed to Noah S Seixas.

14 recordsLinked to original sources

PubMed2006

Modeling, estimation and validation of cotton dust and endotoxin exposures in Chinese textile operations.

In support of an epidemiological study of cancer incidence among cotton textile workers in Shanghai, PRC, historical estimates of exposure to cotton dust and endotoxin were developed for subjects drawn from a cohort of 267,400 female textile workers. A large dataset of historical cotton dust measurements were available from 56 of the study factories. Using these data, a series of models were developed to estimate cotton dust exposure by year, factory and process. Model estimates were validated by comparing with independently collected measurements gathered over a 15 year period and indicated a low relative bias (< 2%) and relative accuracy (+/- 61%). Endotoxin exposures were estimated using the endotoxin content of cotton dust by major processes obtained in five separate surveys in these factories. The validated exposures were assigned to the 7,242 jobs held by the 3,812 study subjects. Among the exposed workers, the mean cumulative exposure levels were 113.8 mg m(-3)*years for cotton dust and 6,707.7 EU m(-3)*years for endotoxin, respectively. The overall correlation among cotton dust and endotoxin exposures for these subjects was r = 0.58. Using an unusually rich set of historical cotton dust measurements, along with independently collected exposure measurements for validation and conversion to endotoxin levels, validated estimates of cumulative exposure were constructed for this large case-cohort study in the textile industry.

China↗

PubMed2006

Occupational risk factors for esophageal and stomach cancers among female textile workers in Shanghai, China.

The authors evaluated associations between occupational exposures in the textile industry and the risks of esophageal cancer and stomach cancer. The authors conducted a case-cohort study nested in a cohort of female textile workers in Shanghai, China. One hundred and two workers with incident esophageal cancer and 646 workers with incident stomach cancer diagnosed between 1989 and 1998 were compared with an age-stratified reference subcohort (n = 3,188). Work histories were ascertained for all study subjects from factory personnel records or interviews. Exposures were reconstructed for chemicals and dusts by linking work history data with a job-exposure matrix developed for the Shanghai textile industry. Hazard ratios and 95 percent confidence intervals were calculated with Cox proportional hazards modeling adapted for the case-cohort design. Risk of esophageal cancer was associated with long-term (> or = 10 years) exposure to silica dust (hazard ratio = 15.8, 95% confidence interval: 3.5, 70.6) and metals (hazard ratio = 3.7, 95% confidence interval: 1.9, 7.1). Cumulative exposure to endotoxin, a contaminant of cotton dust, was inversely related to risks of both esophageal cancer (p-trend = 0.01) and stomach cancer (p-trend < 0.001) when exposures were lagged 20 years. Endotoxin has not been previously reported to be a protective factor for either stomach cancer or esophageal cancer and therefore warrants further study.

Aged↗

PubMed2006

Noise exposures aboard catcher/processor fishing vessels.

BACKGROUND: Commercial fishing workers have extended work shifts and potential for 24 hr exposures to high noise. However, exposures in this industry have not been adequately characterized. METHODS: Noise exposures aboard two catcher/processors (C/P) were assessed using dosimetry, sound-level mapping, and self-reported activities and hearing protection device (HPD) use. These data were combined to estimate work shift, non-work, and 24 hr overall exposure levels using several metrics. The length of time during which HPDs were worn was also used to calculate the effective protection received by crew members. RESULTS: Nearly all workers had work shift and 24 hr noise levels that exceeded the relevant limits. After HPD use was accounted for, half of the 24 hr exposures remained above relevant limits. Non-work-shift noise contributed nothing to 24 hr exposure levels. HPDs reduced the average exposure by about 10 dBA, but not all workers wore them consistently. CONCLUSIONS: The primary risk of hearing loss aboard the monitored vessels comes from work shift noise. Smaller vessels or vessels with different layouts may present more risk of hearing damage from non-work periods. Additional efforts are needed to increase use of HPDs or implement noise controls.

Cross-Sectional Studies↗

PubMed2006

Risks of biliary tract cancer and occupational exposures among Shanghai women textile workers: a case-cohort study.

BACKGROUND: Biliary tract cancer (BTC) is a relatively rare malignancy worldwide. Little is known about potential etiologic contributions of occupational exposures. METHODS: The associations between occupational exposures to textile dusts and chemicals and BTC are investigated in a cohort of 267,400 women textile workers in Shanghai, China. A nested case-cohort analysis of 162 BTC cases diagnosed during 1989-1998 was conducted with a reference subcohort of 3,188 workers. Exposures to workplace dusts and chemicals were reconstructed by linking complete work history data with a job-exposure matrix (JEM). Hazard ratios (HR) and dose-response trends were estimated by Cox proportional hazards modeling modified for case-cohort design. RESULTS: An elevated risk of > or = 1-year employment in maintenance jobs (HR 2.92, 95% CI: 1.48, 5.73) with a significant trend by duration is observed. Excess risk was also found for > or = 20 years exposure to metals (HR 2.50, 95% CI: 1.09, 5.72). CONCLUSIONS: Long-term exposure to maintenance work and metals in the textile industry may have increased BTC risk in this population.

Adult↗

PubMed2006

Development of a job exposure matrix (JEM) for the textile industry in Shanghai, China.

We developed a job exposure matrix (JEM) for the Shanghai textile industry constructed along three axes: industry sector, textile process, and hazardous agent. We assessed 35 different categories of dust, chemical, and physical agents for 149 textile processes within nine industry sectors: cotton, cotton/synthetic, cotton/other (nonsynthetic), wool, silk, synthetic, mineral, other mixed (e.g., wool and synthetic), and nonproduction. The JEM was constructed from two components: a priori assessment of the textile process by a team of U.S. industrial hygienists, and the prevalence of exposures reported by Chinese industrial hygienists in specific textile processes within the factory. The JEM was applied to an ongoing case-cohort study of cancer in women textile workers. The JEM assessed only dichotomous exposure (ever/never), and could be coupled with cumulative exposure by years of employment. The most common exposures in cotton mills were cotton dust and solvent exposures. Dyeing processes had the highest frequency of exposures, including solvents, acids, bases and caustics, bleaching agents, dyes, dye chemicals and intermediates, and formaldehyde. Only two processes were identified with formaldehyde exposure, beck dyeing and resin finishing. The most prevalent exposures among the subcohort, occurring in more than 60% of the women, were electromagnetic fields, lubricants, and cotton dust. More than one-third of subcohort subjects were also exposed to synthetic fiber dust, and slightly less than one-third of women were exposed to endotoxin. This JEM could be applicable for epidemiologic research in other textile industries.

Aged↗

PubMed2006

Modeling distortion product otoacoustic emission input/output functions using segmented regression.

Distortion product otoacoustic emissions (DPOAEs) are low-level acoustic signals, the detection of which involves extraction from a background of noise. Boege and Janssen [J. Acoust. Soc. Am. 111, 1810-1818 (2002)] described a method for modeling the presence and growth of these responses. While improving growth function parameter estimation, this technique excludes a significant fraction of the data (especially low-level responses), and relies on ad hoc model fit acceptance criteria. The statistical difficulties associated with these limitations are described, and a weighted segmented linear regression model that avoids them is proposed. A simple test is presented for the presence of DPOAE growth. This technique is compared to that of Boege and Janssen in a dataset of 9 556 input/output (I/O) functions collected over 4 years on 866 ears from 379 construction apprentices and 63 age-matched controls. Comparisons are made on the entire dataset and within audiometric hearing loss categories. Segmented regression avoids the statistical pitfalls of the previous method, allows estimation of the threshold and slope of auditory response on a far greater number of I/O functions, and improves estimation of these parameters in this dataset. The potential for this method to yield more sensitive metrics of hearing function and compromise is discussed.

Acoustic Impedance Tests↗

PubMed2005

Occupational exposures and risks of liver cancer among Shanghai female textile workers--a case-cohort study.

BACKGROUND: Liver cancer is the fifth most frequent malignancy worldwide. Viral hepatitis B and C, alcohol, and aflatoxin are the major established risk factors. Little is known about the aetiological contributions of occupational exposures, as previous occupational epidemiological studies of liver cancer suggest few agent-specific associations. We investigated associations of occupational exposures to dusts and chemicals in a cohort of female textile workers. METHODS: Cancer incidence was determined among 267,400 female textile workers in Shanghai, China, who had been enrolled in an intervention trial of breast self-exam efficacy during 1989-98. Subjects were interviewed at baseline regarding basic demographics, smoking habits, alcohol consumption, and contraceptive practices. A case-cohort study of 360 liver cancer cases and 3,186 age-stratified randomly chosen subcohort subjects was conducted within this cohort. Exposures to workplace dusts and chemicals were reconstructed from complete work history data, historical exposure monitoring data for selected agents, and a specially designed job-exposure matrix for the textile industry. Relative risks and dose-response trends were estimated by Cox proportional hazards modelling, adapted for the case-cohort design. Latency analyses with different lag years were also applied. RESULTS: 2,095,904 person-years were contributed by this female cohort. The results of the case-cohort analysis revealed a protective effect of cotton fibre exposure years [adjusted hazards ratio (HR) = 0.64; 95% confidence interval (95% CI) 0.44-0.92] or endotoxin exposure (adjusted HR = 0.60; 95% CI 0.41-0.88) for the fourth quartile with significant trends for 20 year exposure lags. CONCLUSIONS: This study suggests that chronic exposure to endotoxin or some other component of cotton dust exposure may have reduced liver cancer risk in this population.

Adult↗

PubMed2004

Peak exposures in aluminium potrooms: instrument development and field calibration.

Aluminium smelter potrooms are unique in that workplace exposures to hydrogen fluoride (HF), sulfur dioxide (SO2), and particulate matter occur simultaneously for some tasks. The peak exposures to these contaminants are of increasing interest in discovering the etiology of respiratory health effects. While a variety of direct-reading instruments are available for sulfur dioxide and particulate matter, only a few exist for hydrogen fluoride. The sensors in these HF instruments have a cross-sensitivity to sulfur dioxide making it difficult to monitor HF in an environment that also contains SO2. To overcome this problem, we assessed the simultaneous use of two electrochemical instruments: one with a SO2 sensor that does not respond to HF and the second with a hydrogen fluoride sensor that responds to both HF and SO2 in a 1 : 1 ratio, termed 'total acid gas'. The difference in the response between the two instruments should indicate the HF concentration: [HF + SO2] minus SO2 equals HF. The performance characteristics of this sampling train were evaluated in the laboratory through the generation of both HF and SO2 with permeation tubes. The response and recovery times for the SO2 only instrument were acceptable (6 and 15 s, respectively), but the "total acid gas" instrument exhibited both slow response and slow recovery approaching three and six min. The association between the traditional integrated filter sampling method and the direct-reading instrument for SO2 is 0.80 (Spearman's rho). The use of the digital filter strengthens the association between the HF direct-reading instrument and the integrated samples from 0.41 to 0.68.

Air Pollutants, Occupational↗

PubMed2004

The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding.

This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Surface grinding was conducted at six commercial building construction sites in Seattle, WA, by cement masons. Time-integrated filter samples and direct reading respirable dust concentrations were collected using a cyclone in line with a direct reading respirable dust monitor. Personal exposure levels were determined with and without LEV, one sample directly after the other. A total of 28 paired samples were collected in which three different dust collection shroud configurations were tested. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and was subsequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m(3), a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22 and 26% of the samples collected while LEV was being used were greater than the 8 h time-weighted average permissible exposure limit (Occupational Safety and Health Administration) and threshold limit value (American Congress of Governmental Industrial Hygienists) for respirable crystalline silica, respectively.

Construction Materials↗

PubMed2002

Noise exposure and hearing conservation practices in an industry with high incidence of workers' compensation claims for hearing loss.

BACKGROUND: Washington State has experienced a striking increase in workers' compensation claims for hearing loss. METHODS: This cross-sectional study examined noise exposures and hearing conservation practices in one industry with a high rate of hearing loss claims. We evaluated 10 representative foundries with personal noise dosimetry, management interviews, employee interviews, and existing audiometry. RESULTS: Noise levels routinely exceeded 85 dBA. All companies were out of compliance with hearing conservation regulations. Most employees with important findings on audiograms were not aware of their findings. There was a significant positive correlation between management-interview scores and worksite-average employee-interview scores (r = 0.70, P = 0.02). CONCLUSIONS: Companies where more effort is put into hearing conservation program activities can achieve a greater positive impact on employee awareness. However, there were broad deficiencies even in the better programs in this sample, suggesting that workers in this industry probably face a continuing substantial risk of occupational hearing loss.

Adult↗

PubMed2002

Effect of sampling time on the culturability of airborne fungi and bacteria sampled by filtration.

Air sampling of bioaerosols by filtration may be preferable for many epidemiological studies because the methods can be used to collect personal samples for a full work-shift. There is some concern, however, that the viability of fungal spores and bacterial cells might be compromised by sampling for as long as a full shift. This study was designed to determine the effect of sampling up to 6 h on the viability (measured by culture) of airborne fungi and bacteria at composting facilities. Six side-by-side samples were collected in two locations at each of three composting facilities for 1 h at 2 l/m on polycarbonate filters. Two samples in each set were then capped while clean, HEPA-filtered air was drawn across two others for an additional 2 h and across the last two for an additional 5 h. Filters were washed and the samples were analyzed for culturable bacteria and fungi, and for total bacteria and fungi by microscopic counting. Concentrations ranged from 1.7 x 10(3) to 6.2 x 10(7) c.f.u./m3 of culturable fungi and 1.17 x 10(4) to 1.0 x 10(6) c.f.u./m3 of culturable bacteria. In linear models that included duration of sampling, location, and the interaction of location and sample duration, neither sample duration nor the interaction term were significant predictors of the logs of the concentrations of culturable fungi or bacteria or of the ratio of the logs of the culturable concentrations to total concentrations for fungi or bacteria. This suggests that increased sampling time does not affect the viability of the organisms commonly found in the air at composting facilities.

Air Microbiology↗

PubMedDate not supplied

The effect of local exhaust ventilation controls on dust exposures during concrete cutting and grinding activities.

This study assessed the effectiveness of commercially available local exhaust ventilation (LEV) systems for controlling respirable dust and crystalline silica exposures during concrete cutting and grinding activities. Work activities were performed by union-sponsored apprentices and included tuck-point grinding, surface grinding, paver block and brick cutting (masonry saw), and concrete block cutting (hand-held saw). In a randomized block design, implemented under controlled field conditions, three ventilation rates (0, 30, and 75 cfm) were tested for each tool. Each ventilation treatment was replicated three times in random order for a total of nine 15-min work sessions per study subject. With the exception of the hand-held saw, the use of LEV resulted in a significant (p < 0.05) reduction in respirable dust exposure. Mean exposure levels for the 75 cfm treatments were less than that of the 30 cfm treatments; however, differences between these two treatments were only significant for paver block cutting (p < 0.01). Although exposure reduction was significant (70-90% at the low ventilation rate and 80-95% reduction at the high ventilation rate), personal respirable dust [corrected] exposures remained very high: 1.4-2.8 x PEL (permissible exposure limit) at the low ventilation rate and 0.9-1.7 x PEL at the high ventilation rate. Exposure levels found under actual field conditions would likely be lower due to the intermittent nature of most job tasks. Despite incomplete control LEV has merit, as it would reduce the risk of workers developing disease, allow workers to use a lower level of respiratory protection, protect workers during short duration work episodes reduce exposure to nearby workers, and reduce clean-up associated dust exposures.

Air Pollutants, Occupational↗

PubMedDate not supplied

Development of a cancer research study in the Shanghai textile industry.

This article describes the development of a cancer study among Shanghai textile workers. Due to the organization of work between 1949 and the 1980s, and superior record-keeping practices, it is possible to track textile workers' job tasks and workplace exposures over virtually the entirety of their working lives. The authors' experiences utilized important relationships developed over more than ten years to access work exposures and cancer outcomes. Initial findings indicate a significantly increased risk for breast cancer for women employed in cotton, wool, mixed-fiber, and machine-maintenance sectors. This project is an example of the unique research opportunities to be found in China, and illustrates how these data sources may be lost due to ongoing changes in the Chinese economy.

Air Pollutants, Occupational↗

PubMedDate not supplied

Comparison of task-based estimates with full-shift measurements of noise exposure.

Using a large data set of noise exposure measurements on construction workers, task-based (TB) and full-shift (FS) exposure levels were compared and analyzed for the sources and magnitudes of the error associated with this methodology. Data-logging dosimeters recorded A-weighted sound pressure levels in decibels using Occupational Safety and Health Administration criteria for every minute of monitoring and were combined with information from task cards completed by subjects. Task-related information included trade, construction site type, location, activity, and tool. A total of 502 FS measurements were made, including 248,677 min of exposure on five construction trades. Six TB models of varying degrees of specificity were fit to the minute-level data and the results used to obtain TB estimates of the daily FS exposure levels. The TB estimates were derived using the predictions alone and also including subject and shift-specific residual means and variances. The predictions alone, which ignore within-task variability, produced a significant negative bias that was corrected by incorporation of the residual variance. This bias is only an issue in this setting in which the exposure of interest is noise, which follows a nonlinear averaging relationship. These estimates explained 10 to 60% of the variability in FS measures; adding the residual mean produced estimates that explained about 90% of the variability. In summary, TB estimates are important for exposure estimation when task time varies substantially. However, TB estimates include a substantial degree of error when there is large interindividual or intershift variability in exposure levels for a given task. Methods to improve the prediction of task-associated exposure, or adjusting for individual and shift differences, are needed.

Data Collection↗