A cross-sectional study was conducted in Kathmandu valley that includes three densely populated districts (Kathmandu, Lalitpur and Bhaktpur) targeting brick kiln workers. There were 106 operating brick kilns in Kathmandu Valley at the time of sampling and interviews. Among them, 62 brick kilns were in Bhaktpur, 26 brick kilns were in Lalitpur and 18 brick kilns were in Kathmandu district. First, all the brick kilns were visited and added as part of the potential sampling frame.
Multi-stage probability proportionate to size (PPS) sampling was applied to select brick kilns and brickfields workers [24]. In total, 9 kilns from Bhaktapur, 4 kilns from Lalitpur and 3 kilns from Kathmandu district were selected. A total of 800 participants, 400 brick workers as exposed and 400 grocery workers from Bhaktapur, Lalitpur, Kathmandu districts proportionately as referent group were recruited for the interviews. The aim of this study was to to find out the additional contribution of exposure to the brick kiln for the workers as there is already air pollution in the valley with significant contribution of respiratory health [25]. The groceries and grocery worker were taken as referent group. This group was chosen as the reference group because both the groups were from the similar socioeconomic background. Brick kilns workers who had been working for more than 1 year were included in the study. Workers who had been working for more than 1 year in small and middle groceries, excluding large shopping malls and roadside huts were interviewed. Field surveys were completed during February–March 2015 using structured interviews administered by trained health workers making unannounced visits to brick kilns.
A strategy has been developed based on grouping workers who have similar job duties within a production unit of a plant. This processing of grouping is called similar exposed groups (SEGs) [26, 27]. Brickfield SEGs are commonly classified as green brick molding (GBM), green brick stacking/carrying (GRS/C), red brick loading/carrying (RBL/C), coal preparation (CP) and fireman (FM) zones. It stands to reason that different job classifications may result in widely different exposures, both in concentration of contaminant, and in the constituents that make up the particles.
Socio-demographic characteristics and health data were assessed applying a Nepali version of the field pre-tested questionnaire. Monitoring and supervision of interviewers was done by the principal investigator frequently during interview time in the field.
Personal air samples were collected following NIOSH Method 0500 for TSP and NIOSH Method 0600 for RSP. During the course of the survey, 89 personal samples for TSP and 72 personal samples for RSP were obtained using SKC AirChek® 52 personal air sampling pumps pre-calibrated to a flow rate of 2.0 liters per minute for TSP and 2.5 liters per minute for RSP. Average sampling time was 120 min for TSP and 160 min for RSP. Pre- and post-calibration was completed to verify flow rates using a DryCal® Defender 510 primary volumetric flow standard. For TSP, particulate air samples were collected on pre-weighed 5.0 um PVC membrane filters (37 mm) placed in-line with pump air flow, and clipped to the collar within the employees’ breathing zone. For RSP, particulate air samples were collected on pre-weighed 5.0 um PVC membrane filters (37 mm) with aluminum cyclone all placed in-line with pump air flow, and clipped to the collar within the employees’ breathing zone. The samples, including field and laboratory blanks, were analyzed using gravimetric methods at ALS Laboratories in Salt Lake City, Utah, USA.
It was assumed that the exposure for the various workers would be the same for the entire workday of 8 h. Workers did not transfer to other jobs during the day. Thus, before interpreting the results all the values were converted to 8 h time weighted average (TWA) using the following formula: TWA = [(C1 × T1) + (C2 × T2) + (Cn × Tn]/8 h; where C = concentration for Tn (mg/m3), T = sampling time (hours).
Proportions, mean, median and range were calculated for socio-demographics (age, gender, marital status, schooling and duration of work) and particulate matter (TSP, RSP). The prevalence with 95% confidence intervals (CIs) for all respiratory symptoms and illnesses (chronic cough, chronic phlegm, chronic bronchitis, wheezing and asthma) within a year were estimated. One way ANOVA analysis was applied to compare the level of RSP and TSP among work zones (WZs) using log10 transferred PM values as the values were skewed. Bivariate and multivariate logistic regression analysis was carried out to evaluate associations between respiratory symptoms/illnesses and participant groups (exposed and referent) and SEGs among brickfield workers. CP zone workers were used as the reference group in the logistic regression analysis among SEGs because the exposure to coal dust was viewed as a much different hazard compared to the brick dust to which the other SEGs were exposed. For instance, coal dust exposure may be a greater risk to workers in coal crushing, while respirable silica may be the primary particulate exposure during brick molding. The level of significance was set at <0.05 level. Statistical analyses were performed using the IBM SPSS Statistics 21, Armonk, NY, USA. To calculate 95% CI of the prevalence, stat calculator online software was used.
Ethical approval for study was obtained from the institutional review committee of Kathmandu University School of Medical Sciences (IRC-KUSMS). Participation in the study was voluntary and written consent was obtained from the brick kiln owners before obtaining any data. Written consent (thumb print in case of illiterate interviewees) to publish the data was obtained from each interviewee before interviews.
Operational definitions of the study outcomes [22, 28]:
Chronic Cough: cough as much as 4–6 times per day occurring for most days of the week (≥5 days) for at least 3 months of the year and for at least two consecutive years.
Chronic Phlegm: sputum expectoration as much as twice a day for most days of the week (≥5 days) for at least 3 months of the year and for at least two consecutive years.
Chronic Bronchitis: cough and sputum expectoration occurring for most days of the week (≥5 days) for at least 3 months of the year and for at least two consecutive years.
Wheezing: chest ever sounds wheezy or whistling most days or nights in the past 2 months
Asthma: at least two or more attacks of shortness of breath with wheezing (whistling sound on expiration) in the past 2 months with normal breathing in between episodes of shortness of breath or diagnosed asthmatic by a physician.
Ever smoker: more than 20 packs of cigarettes in a lifetime or more than 1 cigarette a day for 1 year.
Never smoker: less than 20 packs of cigarettes in a lifetime or less than 1 cigarette a day in 1 year.