Brick manufacturing, particularly by hand molding, dates back thousands of years in Nepal, and continues to be a major industry in the Kathmandu valley and other areas throughout the country [1–3]. Currently and historically, bricks have been one the most common structural building materials used in the Kathmandu valley [3–5]. Furthermore, the Kathmandu valley has experienced significant population growth since the 1950s, creating a demand for more bricks and brick kilns [6]. As of 2000, there were over 100 kilns in operation in the valley, employing an estimated 30,000 seasonal workers [3, 7, 8].

Brick manufacturing has been identified as a major source of ambient air pollution in the Kathmandu valley. Current manufacturing processes include construction of buildings, construction of roads, and brick kilning. Operation time lasts from November until the middle of May when the brick kilns are in full production. In each case, bio-fuels, coal, and used tires are used as fuel sources in brick kilns [9]. Accordingly, several studies show positive associations between ambient air pollution levels and seasonal operation of brick kilns in Kathmandu valley [2, 10–12]. Similar findings have been reported in Budgam, India, and in Bangladesh [13–15]. Fatima [13] reported ambient air pollution concentrations of total suspended particulates (TSP) and respirable suspended particulates (RSP) as ³12.0 and 123.0 μg/m³ and 25.0 and 194 μg/m³, during the operational and non- operational seasons of brick kiln, respectively in Budgam, India. A study in Bangladesh revealed that brick kiln emissions contributed 7 to 99 μg/m³ to urban air pollution levels during brick kiln operation [15]. A study carried out during pre-operation, operation and post-operation phases in India uncovered that the RSP levels were 0.216, 0.241 and 0.214 mg/m³, respectively [16]. In Kathmandu valley, differences in ambient TSP between the operating and non-operating brick kiln seasons were 56.0 and 33.0 μg/m³, respectively, and for PM₁₀ were 50 and 29 μg/m³, respectively [11]. Similarly, in another study, the average TSP during the off-season was 0.265 mg/m3 whereas it reached to 0.634 mg/m³ during operation time [12]. Another study in Nepal shows, the PM₁₀ concentration in an area with brick kilns was found to be 0.569 mg/m³, while it was only 0.158 mg/m³ in an area without brick kilns [12]. Among sources, the brick industry contributes one third of all the dust pollution in the Kathmandu Valley [12, 17].

Although several studies have evaluated ambient air pollution associated with brick kilns, few studies report results of occupational exposures among brick kiln workers. Brick kiln workers are closer to pollution sources and likely experience higher exposures than the general public. Using direct-reading area sampling, Raza et al. [18] found PM₁₀ concentrations in Pakistani brick kilns were 888, 1830, and 861 μg/m³ for molding and loading, firing, and unloading sections, respectively, while PM_2.5 concentrations were 301, 307, and 628 μg/m³ for modulation and loading, burning, and unloading sections, respectively. Myers et al. [19] reported mean total and respirable dust levels of 15.16 and 2.22 mg/m³, respectively, among South African brick workers. Breathing zone dust levels varied considerably by job category; however, traditional brick kilns used in the Kathmandu valley may have significantly different exposure profiles. Occupational exposures in brick kilns may be one or more orders of magnitude greater than ambient levels, suggesting brick kiln workers are at greater risk of respiratory-related diseases.

Studies clearly show that brickfield workers and people in the surrounding community are more likely to suffer from illnesses caused by the kilns’ pollution [11, 20]. In addition, workers engaged in different work tasks inside brick kilns suffered variety of respiratory illnesses [2, 21–23]. In a study comparing brickfield workers to non-brickfield workers, 42% of brickfield workers had respiratory illnesses compared to just 9.3% for the referent group of workers [21]. A later study showed that illnesses such as chronic cough and phlegm, chest tightness were significantly higher among brickfield workers compared to referent workers [22, 23]. Respiratory illnesses reported in previous studies are thought to result from a variety of particulate exposures encountered in brick manufacturing. However, there has been little attention given to differential particulate exposures based on similar exposure groups (SEGs).

The objective of this study, therefore, was to evaluate the prevalence of respiratory symptoms and illnesses, and to estimate the magnitude of particulate exposures according to SEGs among brickfield workers.

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) + (C_n × T_n]/8 h; where C = concentration for T_n (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.

The questionnaire was completed by 800 participants [exposed: 400 (50%); referent: 400 (50%)]. Almost 20.0% of exposed workers were less than 19 years of age whereas only three percent of referent were included in this age group. The mean ± SD age of exposed was 31.74 ± 12.97 years with range of 12 to 73 years and for referent was 33.33 ± 9.03 years with range of 14 to 68 years. Among those, 63.0% of brick workers achieved only primary education whereas almost 95% of grocery workers attained secondary and university education. Almost 40.0% among exposed and 35.0% among referent were ever smokers whereas 84.0% of exposed and 85.7% of referent were current smokers (Table 1). Among workers, 20.0% workers were from GBM and GBS/S each, 21.0% were from RBL/C, 18.8% were from CP, and 20.2% of them were FM zones (Fig. 1).

Socio-economic variables	Response groups
	Exposed		Referent
	Frequency	%	Frequency	%
Age group of the respondents
≤ 19 years	81	20.2	12	3.0
20–29 years	119	29.8	129	32.2
30–39 years	84	21.0	166	41.5
40–49 years	68	17.0	72	18.0
50–59 years	33	8.2	16	4.0
60–69 years	11	2.8	5	1.2
≥ 70 years	4	1.0	0	0
Total	400	100.0	400	100.0
Exposed: mean age = 31.74 years, SD of age = 12.97 years, range of age = 12 to 73 years Control: mean age = 33.33 years, SD of age = 9.03 years, range of age = 14 to 68 years
Gender
Female	102	25.5	130	32.5
Male	298	74.5	270	67.5
Total	400	100.0	400	100.0
Attainment of formal education
No	238	59.5	30	7.5
Yes	162	40.5	370	92.5
Total	400	100.0	400	100.0
Levels of education
Primary	102	63.0	16	4.3
Lower secondary	43	26.5	76	20.5
Secondary and higher secondary	14	8.6	203	54.9
University	3	1.9	75	20.3
Total	162	100.0	370	100.0
Duration of work in years
≤ 5 years	265	66.2	237	59.2
6–10 years	63	15.8	113	28.2
11–15 years	30	7.5	28	7.0
16–20 years	23	5.8	19	4.8
≥ 21 years	19	4.8	3	0.8
Total	400	100.0	400	100.0
Ever smoker
No	238	59.5	260	65.0
Yes	162	40.5	140	35.0
Total	400	100.0	400	100.0
Current smoker
No	26	16.0	20	14.3
Yes	136	84.0	120	85.7
Total	162	100.0	140	100.0

The relationship of the extent of PM concentration was assessed among SEGs using ANOVA. For RSP the relationship was significant with F value of 6.632 (P < 0.001) and for TSP, the relationship was significant with F value of 10.184 (p < 0.000). When performed multiple comparisons applying Tukey’s test to assess the extent of RSP among SEGs, the relationship was significant for GBM and RBL/C (p: 0.007). Likewise, RBL/C and CP (p: 0.012) and FM (p: <0.001) also showed high significance for the extent of RSP. Similarly, the TSP concentrations among SEGs for GBM and RBL/C (p: 0.002) had significant association. Alike, the red brick loading zone had a significant relationship and GBS/C (p: 0.018), CP (p: 0.010) and FM (p: <0.001). Also, fire masters zone was significant with green brick stacking (p: 0.002).

Almost 55% of exposed and 29% of referent reported coughing. among those who complained of cough, 29.5% of exposed and 12.8% of referent usually cough as much as 4 to 6 times a day, 4 or more days out of the week. Thus, the prevalence of chronic cough was 14.3% (9.91 to 18.69%) for exposed and 6.8% (2.92 to 10.68%) for referent populations. Nearly 42% of exposed and 11% of referent produced phlegm; among total participants 8.0% exposed and 3.0% referent usually produced phlegm as much as 4 to 6 times a day, 4 or more days out of the week. Consequently, the prevalence of chronic phlegm was 16.6% (10.99 to 22.21%) for exposed and 5.8% (0.86 to 10.74%) for referents. Approximately 25% of exposed and 16.0% of referents had episodes of cough and phlegm; amongst workers expectorating cough and phlegm, 19.0% (15.16 to 22.84%) of exposed and 10.8% (7.76 to 13.84%) of referent endured chronic bronchitis. Correspondingly, 11.3% of exposed and just two percent of referent were ill with wheezing and almost six percent of exposed and two percent of referent reported having asthma (Table 3). The prevalence of chronic cough, chronic phlegm, chronic bronchitis, wheezing and asthma among SEGs were as follow: GBM: 22.9%, 34.6, 15.0%, 13.8% and 7.5%; GBS/C: 13.5%, 15.8, 10.0%, 8.8% and 7.5%; RBL/C: 11.1, 17.1, 27.4, 19.0 and 11.9%; FM: 18.4%, 12.5%, 28.4%, 4.9% and nil; CP: 4.9, 6.33, 13.3, 9.3 and 4.0% (Fig. 2).

Respiratory illnesses	Exposed		Referent
	Frequency	%	Frequency	%
Cough
Absent	179	44.8	285	71.2
Present	221	55.2	115	28.8
Total	400	100.0	400	100.0
Usually cough as much as 4 to 6 times a day, 4 or more days out of the week
Absent	103	25.8	64	16.0
Present	118	29.5	51	12.8
Does not apply	179	44.8	285	71.3
Total	400	100.0	400	100.0
Chronic cough
Absent	209	85.7	151	93.2
Present	35	14.3 (9.91–18.69)	11	6.8 (2.92–10.68)
Total	244	100.0	162	100.0
Phlegm
Absent	231	57.8	355	88.8
Present	169	42.2	45	11.2
Total	400	100.0	400	100.0
Usually bring up phlegm as much as 4 to 6 times a day, 4 or more days out of the week
Absent	137	34.3	74	18.5
Present	32	8.0	12	3.0
Does not apply	231	57.8	314	78.5
Total	400	100.0	400	100.0
Chronic phlegm
Absent	141	83.4	81	94.2
Present	28	16.6 (10.99–22.21)	5	5.8 (0.86–10.74)
Total	169	100.0	86	100.0
Episodes of cough and phlegm
Absent	302	75.5	336	84.0
Present	98	24.5	64	16.0
Total	400	100.0	400	100.0
Chronic episodes of cough and phlegm
Absent	324	81.0	357	89.3
Present	76	19.0 (15.16–22.84)	43	10.8 (7.76–13.84)
Total	400	100.0	400	100.0
Wheezing on most days or nights
Absent	355	88.8	392	98.0
Present	45	11.3	8	2.0
Total	400	100.0	400	100.0
Attack of wheezing cause shortness of breath (asthma)
Absent	375	93.8	393	98.3
Present	25	6.3	7	1.8
Total	400	100.0	400	100.0

Logistic regression analysis was carried out to compare association between participants’ groups and chronic respiratory symptoms adjusted with age, duration of work and smoking practices. Brick industry workers were about two times more likely to have chronic cough (OR: 2.30; 95% CI: 1.13–4.67; p: 0.021) compared with grocery workers. The adjusted OR slightly increased and was significant (OR: 2.35; 95% CI: 1.14–4.85; p: 0.021). Age of participants and duration of work were significant predictors (P < 0.001 each) for chronic cough. Similarly, brick workers were almost three times more likely to suffer chronic phlegm (OR: 3.22; 95% CI: 1.20–8.66; p: 0.021) in comparison to referent participants. When adjusted it was still almost three times more likely (AOR: 2.98; 1.07–8.24; p: 0.036). Duration of work was a significant predictor (p < 0.001) for chronic phlegm. Likewise, brick industry workers were approximately two times more likely to have chronic bronchitis (OR: 1.95; 95% CI: 1.30–2.91; p: 0.001) when compared with grocery workers. Adjusted OR was also more or less the same (OR: 1.91; 95% CI: 1.26–2.90; p: 0.002) indicating age and smoking practice of workers were significant predictors (p < 0.001 each) of chronic bronchitis. In the same way, brick workers were six times more likely to have chronic wheezing (OR: 6.21; 95% CI: 2.89–13.36; p < 0.001) in comparison to grocery workers when adjusted the AOR remain more or less same (OR: 6.00; 95% CI: 2.78–12.94, p < 0.001). Smoking habits of the participants were a significant predictor (p < 0.001) for chronic wheezing. Also, exposed participants were about four times more likely to experience asthma (OR: 3.74; 95% CI: 1.60–8.76; p: 0.002) compared with referents. On adjustment, AOR slightly decreased but remained significant (OR: 3.18; 95% CI: 1.34–7.58; p: 0.009).

Logistic regression analysis compared the association between chronic respiratory symptoms/illnesses and type of work performed by the brick industry workers. Green brick molders were nearly six times more likely to experience chronic cough (OR: 5.80; 95% CI: 1.20–27.93; p: 0.028) when compared with workers involved in coal crushing/carrying work. Age and duration of work were significant predictors for chronic cough (p: 0.001 each). There was no association between chronic phlegm and other work types (green brick stacking/carrying, red brick loading/carrying and firing) when compared with coal crushing/carrying work. Upon adjustment the association did not exist.

Green brick molders were about eight times more likely to develop chronic phlegm (OR: 7.94; 1.54–41.10; p: 0.013) compared to workers involved in coal crushing/carrying work. The association could not persevere up on adjustment. Duration of work of the participants was a significant predictor (p < 0.001) for developing chronic phlegm. There was no association between chronic phlegm and other work types (green brick stacking/carrying, red brick loading/carrying and firing) when compared with coal crushing/carrying work. There was no association when adjusted with the predictors.

This study involved 800 participants (400 exposed and 400 referent populations). Socio-demographic results of this study reveal significant differences between these two industries. Specifically, compared with grocery stores, brick kilns were more likely to employ children under the age of 18 and older workers above the age of 60. There are fewer females working in the brick kilns which may be due to the greater hazard found in the kilns. Workers in brick kilns have less education but tend to stay working in the brick kiln for a longer duration. Additionally, smoking was more prevalent among workers in the brick kilns.

While several prior studies show significantly greater respiratory symptoms/illnesses among brick kiln workers compared to referent groups, there is little data on the influence that job category has on exposure or respiratory symptoms/illness. Based on our findings, workers engaged in red brick loading and green brick stacking tasks experienced higher particulate exposures compared with workers in other job categories. Red brick loaders suffered disproportionately from wheezing, asthma and chronic bronchitis compared to other SEGs. These results suggest protective measures are needed, particularly among work groups with higher exposures or higher prevalence of respiratory symptoms/illness. In addition, these results suggest future research is needed to identify particulate matter constituents and how they vary by job classification. For instance, green brick molders were among the lowest RSP and TSP exposures, but they experienced the highest prevalence of chronic cough and phlegm.

There is a resounding need for improved evaluation of the hazards within the kilns in the Valley and the risks posed to the workers and the community. Control areas of focus in the brick kilns include: improve the quality fuel used in the kilns; update kiln technology; crackdown on illegal kilns in the Valley; decrease the long hours on the job leading to greater risk of overexposure; and provide personal protective equipment (PPE) to the workers. No governmental standards on occupational exposure have been promulgated yet. A reactive legislation approach to control is falling behind, with occupational safety and health standards unenforced; nevertheless, priorities geared towards the health of the community and the workers in the brick kilns are increasingly pertinent with the rise in industry.

Voluntary organizational efforts to promote and educate the workers in the kilns, their employers and the general public on the necessity of industrial hygiene practice should be considered. These measures to investigate further into the industrial hazards of the brick kilns in Kathmandu Valley, Nepal and mitigation strategies will help promulgate the need for greater intervention. All workers deserve a workplace environment free from extreme health hazards and unsafe conditions.