Article
Musculoskeletal problems and fluoride exposure: A cross-sectional study among metal smelting workers
Toxicology and Industrial Health 1–8 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0748233714568477 tih.sagepub.com
A Saha1, AK Mukherjee1 and B Ravichandran2 Abstract Frequent and repetitive activities in job and awkward postures are shown as major contributors of musculoskeletal problems in most of the occupational health studies; however, efforts to explore newer risk factor are important to plan interventional measures. In this backdrop, this study examined contribution of fluoride exposure to musculoskeletal complaints. A cross-sectional interviewer-administered questionnaire survey was conducted involving 180 randomly selected subjects from a metal smelting industry. Clinical examination of the subjects was also performed to assess their health status and morbidity details. Assessment of personal exposure to particulate and gaseous fluoride at workplace was conducted. Urinary fluoride level was also examined in post-shift samples collected from study subjects. The mean age of the study subjects was 39.1 (+6.7) years. Majority of the workers (42.5%) were engaged in pot room. About 54% workers were suffering from backache and 66% subjects had joint pain. Exposure of workers to both particulate and gaseous fluoride and post-working shift urinary fluoride level was significantly higher in pot-room workers in comparison with all other workers. It was observed that age (odds ratio (OR): 1.62; 95% confidence interval (CI): 1.18–2.34), drinking untreated water (OR: 1.51; 95% CI: 1.03–2.76), working in pot room (OR: 1.44; 95% CI: 1.13–1.91) and urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) had significant effects on musculoskeletal complaints. This study concludes that along with other predictors such as nature of work, posture at work and age of worker, exposure to fluoride also has significant role in the occurrence of musculoskeletal morbidity. Keywords Musculoskeletal problems, exposure to fluoride
Introduction Work-related musculoskeletal problems are a group of painful conditions that mostly occur following either activities in awkward postures or frequent and repetitive activities. Musculoskeletal problems are a principal cause of occupational man-day loss and disability. Economic burden of these complaints has an impact on industry and society. Studies have shown that musculoskeletal problems are a major concern in most of the industrial operations and unorganized occupations like construction activity (Pandey et al., 2012), garment manufacturing (Lombardo et al., 2012), jute industries (Sett and Sahu, 2012), sugar manufacturing (Choobineh et al., 2009), rubber industry (Choobineh et al., 2007b), aircraft manufacturing (Menegon and Fischer, 2012), supermarket workers (Forcier et al., 2008), furniture industry (Nicoletti et al., 2008), semiconductor industry (Chandrasakaran et al., 2003), call
centre workers (Halford and Cohen, 2003) and petrochemical industries (Choobineh et al., 2012). Although frequent and repetitive activities in job and awkward postures are said to be the main causative factors in most of the occupational health studies, some studies have explored other risk factors (Aghilinejad et al., 2012; Choobineh et al., 2007, 2009) also. Such efforts are of immense importance because of
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Regional Occupational Health Centre (Eastern), Indian Council of Medical Research, Salt Lake, Kolkata, West Bengal, India 2 Regional Occupational Health Centre (Southern), Indian Council of Medical Research, Bengaluru, Karnataka, India Corresponding author: A Saha, Regional Occupational Health Centre (Eastern), Indian Council of Medical Research, Sector V, Block DP, Salt Lake, Kolkata 700091, West Bengal, India. Email: [email protected]
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the fact that finding and assessing newer risk factors can be an appropriate basis for planning interventional measures for alleviating the magnitude of the problem in the workplace. Metal smelting activity exposes its workers to respirable dusts, fluorides and other pollutants (Mukherjee et al., 2008). A study found ‘possible fluorosis’ or ‘initial fluorosis’ in 4.81% of the aluminium smelting workers (Martinotti et al., 2012). Study on the effects of chronic occupational exposure to aluminium on nervous system found headache, increased emotional irritability, concentration difficulty, insomnia and mood lability as predominating functional disorders (Sin´czuk-Walczak et al., 2003). Higher risk of respiratory problems such as bronchial asthma in workers engaged into aluminium production through electrolysis is also observed (Chashchin and Kuz’min, 2001). One study addressing musculoskeletal complaints in such industries showed that 65.5% of workers in past week and 77.5% of workers in past year had claimed one of the musculoskeletal complaints in their workplaces. Lumbar region, knee(s) and upper back had suffered most musculoskeletal complaints in participants (Aghilinejad et al., 2012). Fluorine is the most abundant element in nature, and about 96% of fluoride in the human body is found in bones and teeth. The principal sources of fluorine are drinking water and food such as sea fish, cheese and tea. Apart from this, industrial emissions are also potential sources of exposure. The available data suggest that 15 states in India are endemic for both dental and skeletal fluorosis (Arlappa et al., 2013). Endemic skeletal fluorosis is a chronic metabolic bone and joint disease caused by ingesting large amounts of fluoride either through water or rarely from foods of endemic areas. Fluoride is a cumulative toxin that can alter accretion and resorption of bone tissue. It also affects the homeostasis of bone and mineral metabolism. The total quantity of ingested fluoride is the single most important factor that determines the clinical course of the disease, which is characterized by immobilization of joints of the axial skeleton and of the major joints of the extremities. A combination of osteosclerosis, osteomalacia and osteoporosis of varying degrees as well as exostosis formation characterizes the bone lesions. In a proportion of cases, secondary hyperparathyroidism is observed with associated characteristic bone changes. Contrary to earlier thinking, severe crippling forms of skeletal fluorosis are seen in the paediatric age group too. Increased metabolic turnover of the bone, impaired
bone collagen synthesis and increased avidity for calcium are features in fluoride toxicity. Osteosclerotic picture is evident when small doses of fluoride are ingested over a long period of time during which calcium intakes are apparently normal, while osteoporotic forms are common in the paediatric age group and with higher body load of the element. Alterations in hormones concerned with bone and mineral metabolism are seen in fluorosis. Kidney is the primary organ of excretion for fluorides. Age, sex, calcium intake in the diet, dose and duration of fluoride intake and renal efficiency in fluoride handling are the factors that influence the outcome. Serum parameters rarely help in the diagnosis. Elevated urinary fluoride and increased bone fluoride content are indicators of fluoride toxicity (Krishnamachari, 1986). Fluoride is a major pollutant in aluminium smelting industries. Fluoride can have adverse effects on musculoskeletal system also. Musculoskeletal complaints (principally as backache and joint pain) are observed frequently in aluminium smelting operations. However, scientific efforts to explore any relationship between fluoride exposure and musculoskeletal complaints in such industries are scanty. In this backdrop, this study was initiated to examine association, if any, between musculoskeletal complaints and fluoride exposure. This study also aimed to assess the risk of such workers suffering from musculoskeletal complaints due to their occupational exposure.
Methods This study was conducted involving the workers of an aluminium smelting industry. This cross-sectional survey was undertaken among the workers working in different sections of the smelter. In India there are a number of such units that employ considerable number of workers. The principal sections of this type of industry are pot rooms, cast house and carbon area. These industries are organized industries and usually employ both direct and contract workers for different activities. Apart from workers employed in the main sections, some workers are also employed for different supporting and maintenance activities. In an aluminium smelter, smelting of alumina takes place by electrolysis and the pot room is the heart of the process. After this, the molten metal is transferred to the cast house for casting and moulded into different forms. The carbon area deals with the process of anode preparation necessary for the electrolysis
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process. This study was conducted in one such aluminium smelting industry encompassing all the workers of the above sections. The musculoskeletal problems and their associated factors were addressed in this study. Here, backache and joint pain constituted musculoskeletal problems for the purpose of this study. In this study, the subjects suffering from backache/joint pain at the study period for at least last 6 months or had suffered such problems in service period for at least 6 months were considered as having musculoskeletal problems. This was done to exclude the nonspecific temporary musculoskeletal problems. Apart from this, subjects with known causes of musculoskeletal problems (e.g. accidental) were not included in this study. The industry had about 3200 workers, of which subjects were selected for this study. The sample size was calculated on the principles of a prevalence survey. The prevalence of musculoskeletal problems was predicted as 20% in such population; we calculated the sample size for prevalence study using an acceptable range of 14%–26%. Here musculoskeletal problems in general were considered, as the intention was to consider all cases of musculoskeletal problems and examine the contribution of fluoride exposure in the occurrence of musculoskeletal problems. Thus, the minimum sample size for a 5% level of significance was calculated as 162. We set our target as 200 employees to take care of non-response. The workers were selected randomly from a list of workers. Of the 200 workers approached for study, 180 subjects participated in this study. All of them were interviewed with the help of an interviewer-administered questionnaire to collect information regarding their personal, occupational and work-related morbidity details. Clinical examination of the subjects was also performed to assess their health status and morbidity details. Workplace sampling and assessment of personal exposure to particulate and gaseous fluoride were conducted. Urinary fluoride level was also examined in post-shift samples collected from the study subjects. Necessary approval for this study was obtained from the institutional ethical committee as well as the scientific advisory committee of National Institute of Occupational Health, India. Initially, a descriptive analysis of the collected data was undertaken to understand the distribution of personal, occupational and morbidity characteristics among the subjects. Afterwards, a univariate analysis was done to know the distribution of musculoskeletal problems among the workers and contribution of worker characteristics towards the problem. Finally,
multivariate analysis was done using Statistical Package for the Social Sciences software to obtain the contribution of different factors to musculoskeletal problems. In multivariate analysis, the logistic regression method was used to obtain the contribution of individual factors like age (years), experience in this job/duration of employment (years), tobacco/alcohol use, education level (primary and secondary vs. college and university), drinking water quality, nature of job (pot room vs. others) and urinary fluoride level on musculoskeletal problems irrespective of the effect of the other factors. Whilst entering the variables in the logistic regression model, tobacco/alcohol use, education level (primary and secondary vs. college and university), drinking water quality and nature of job were taken as categorical variables. Other variables like age, experience in job and urinary fluoride level were taken as continuous variables. All variables were analysed simultaneously in the model in order to estimate the effect of every individual variable adjusting for the effect of other variables.
Results The mean age of the study subjects was 39.1 (+6.7) years. The mean income was 17,925 (+8889) Indian rupees per month. One hundred and fifty-four (85.6%) workers were 30–49 years old, and 13 (7.2%) workers each were in up to 29 years and 50 years or above age group. Thirty-four and half percent subjects were either smokers or ex-smokers. About 67% of the subjects had a primary- or secondary-level education, whilst 45% were college- or university-level educated. The majority of the workers (42.5%) were engaged in pot room, whilst 18.8%, 20.4% and 18.3% were engaged in the cast house, carbon area and other supporting activity, respectively (Table 1). About 92% workers were married and 21.1% subjects were drinking untreated well water. The mean job duration of the subjects was 13.2 + 4.7 years for pot-room workers, 6.6 + 5.3 years for cast-house workers and 11.4 + 4.5 years and 9.8 + 5.8 years for carbon area workers and other supporting activity workers, respectively. So far as musculoskeletal morbidity is concerned, 54.4% and 66.6% workers were suffering from backache and joint pain, respectively. Personal exposure of study subjects to fluoride was measured by collecting workplace samples through personal monitoring equipments attached to workers at work and analysing the collected samples. The
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Table 1. Personal and occupational characteristics of the study subjects. Characteristics Age group Up to 29 years 30–49 years 50 years and above Marital status Married Unmarried Education Primary level Secondary level University level Drinking water Treated water Untreated well water Smoking Ever smoker Never smoker Alcohol use Ever alcoholic Never alcoholic Tobacco chewing Ever chewer Never chewer Nature of job Pot line Cast house Carbon area Others
Frequency (%; N ¼ 180) 13 (7.2) 154 (85.6) 13 (7.2) 166 (92.2) 14 (7.8) 17 (9.5) 103 (57.5) 60 (33.0) 142 (78.9) 38 (21.1) 62 (34.5) 118 (65.6) 72 (40.0) 108 (60.0) 56 (30.9) 124 (68.5) 76 (42.5) 34 (18.8) 37 (20.4) 33 (18.3)
post-shift urinary fluoride level was also assessed. Exposure of workers to both particulate and gaseous fluoride was significantly higher in pot-room workers in comparison with all other workers. Similarly postworking shift urinary fluoride level also was significantly higher in pot-room workers in comparison with all other workers (Table 2). In the univariate analysis, it was found that worker characteristics like age of 50 years and more (odds ratio (OR): 8.8; 95% confidence interval (CI): 1.1–93.3), drinking untreated well water (OR: 3.4; 95% CI: 1.4– 8.4) and working in pot room (OR: 6.1; 95% CI: 2.3–16.6) showed a significant effect on backache. In case of joint pain, working in pot room (OR: 5.2; 95% CI: 1.9–14.3) was the only worker characteristics that showed significant impact (Table 3). When multivariate analysis was performed using a logistic regression model entering all the variables simultaneously to understand the effect of different worker characteristics on musculoskeletal morbidity
(backache or joint pain or both), it was observed that age (regression coefficient 0.53; p value 0.035; OR: 1.62; 95% CI: 1.18–2.34), drinking untreated water (OR: 1.51; 95% CI: 1.03–2.76), working in pot room (OR: 1.44; 95% CI: 1.13–1.91) and urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) showed significant effects on musculoskeletal complaints (Table 4).
Discussion Systematic search and validation of newer factors of musculoskeletal morbidity is the key to the prevention of major cause of workplace disability, man-day loss and resulting loss of productivity. Efforts made in this direction have mostly highlighted ergonomic risk factors, faulty work area design, awkward posture and repetitive nature of work (Bhattacharyya and Chakrabarti, 2012). Some studies have identified other variables such as shift work, extended work time, type of employment, second job and job unit, job type as well as work perceptions as factors significantly associated with musculoskeletal complaints Parkes, 1999; Choobineh et al., 2012). Factors like increasing age, female gender and smoking have also been named as significant predictors (Dahlberg et al., 2004; Werner et al., 2011). One study found that apart from work in awkward posture, the role of psychosocial factors, such as sleeping problems and hurrying without reason were associated with musculoskeletal morbidity (Engholm and Holmstro¨m, 2005). Although few, studies are there that mentioned the role of work environment as a predictor of musculoskeletal problems (Parkes, 1999). So far as the aluminium smelting process is concerned, a study conducted in Iran addressing factors of musculoskeletal morbidity not only found job duration and age as contributing factors but also observed the necessity of ergonomic interventions for elimination of environmental hazards (Aghilinejad et al., 2012). As far as fluoride exposure and musculoskeletal problems are concerned, some studies have associated different morbidities with exposure to fluoride. A study reported significant relationship of exposure to fluoride with the frequency of back and neck surgery, fractures, symptoms of musculoskeletal disease and past history of diseases of bones and joints in the absence of the typical findings of skeletal fluorosis (Carnow and Conibear, 1981). A higher frequency of ossification of ligament, tendon and muscle attachments was observed among the fluoride-exposed subjects and these changes increased with the bone
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Table 2. Personal exposure of study subjects to fluoride at work and their urinary fluoride level.a Fluoride exposure (mg/m3); mean + SD (range) Process area
Particulate
Gaseous
Urinary fluoride (mg/dl); mean + SD (range)
Other areas
0.09 + 0.06 (0.05 – 0.16) 0.23 + 0.09 (0.08 – 0.28) p < 0.001
0.036 + 0.027 (0.014 – 0.067) 0.1128 + 0.110 (0.043 – 0.310) p < 0.01
0.090 + 0.068 (0.007 – 0.223) 0.190 + 0.139 (0.025 – 0.587) p < 0.001
Pot line Significance by t test (p value) a
Fluoride exposure (mg/m3) in 20 samples in each category.
Table 3. Distribution of musculoskeletal problems among the workers and contribution of worker characteristics towards the problem (univariate analysis). Worker characteristics
Backache frequency (%)
OR (95% CI)
Joint pain frequency (%)
OR (95% CI)
5 (38.5) 82 (53.3) 11 (84.6)
1 1.8 (0.5–6.8) 8.8 (1.1–93.3)
7 (53.8) 103 (66.9) 10 (76.9)
1 1.73 (0.98–6.1) 2.86 (0.4–22.0)
69 (48.6) 29 (76.3)
1 3.4 (1.4–8.4)
90 (63.3) 30 (78.9)
1 2.17 (0.8–5.57)
56 (72.7) 15 (44.1) 17 (45.9) 10 (30.3)
6.1 (2.3–16.6) 1.8 (0.6–5.6) 1.9 (0.6–5.9) 1
64 19 21 16
71 (59.2) 27 (45.0)
1.7 (0.9–3.4) 1
85 (70.8) 35 (58.3)
1.7 (0.8–3.4) 1
67 (55.8) 31 (51.7)
1.1 (0.6–2.3) 1
82 (68.3) 38 (63.3)
1.2 (0.6–2.5)
Age Up to 29 years 30–49 years 50 years and above Drinking water Treated water Untreated well water Nature of job Pot line Cast house Carbon area Others Education Primary/secondary level University level Tobacco/alcohol use Ever user Never user
(83.1) (55.9) (56.8) (48.5)
5.2 (1.9–14.3) 1.3 (0.4–3.9) 1.4 (0.5–4.0) 1
OR: odds ratio; CI: confidence interval.
Table 4. Effect of worker characteristics on occurrence of musculoskeletal problems (backache/joint pain/both; multivariate analysis). 95% CI Variable Age Job duration Tobacco/alcohol use Education Drinking untreated water Working in pot line versus other job Urinary fluoride level
Regression coefficient
Significance
OR
Lower limit
Upper limit
0.530 0.016 0.025 0.062 0.439 0.382 0.708
0.035 0.212 0.131 0.09 0.044 0.047 0.024
1.62 0.82 0.97 0.97 1.51 1.44 2.71
1.18 0.49 0.77 0.33 1.03 1.13 1.81
2.34 1.21 1.39 1.61 2.76 1.91 3.75
OR: odds ratio; CI: confidence interval.
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fluoride content (Boillat et al., 1980). A study observed that in light cases of fluorosis, the bone changes were often associated with non-specific joint and muscle pains, but the disease was entirely asymptomatic (Grandjean, 1982). Another study on aluminium smelter workers found that the total complaints reported by study groups were significantly higher than the control groups. Smelter workers had a significantly higher urinary and serum fluoride level than non-smelter workers; the nail fluoride content was also higher in smelter workers than non-smelter workers (Susheela et al., 2013). On the other hand, there are studies that found different observations. One such study found some changes of early skeletal fluorosis on pelvic X-rays like increased density, calcification of ligaments and periosteal changes in a few workers who were employed on the pot lines for more than 10 years. There was, however, poor agreement in the findings of the two radiologists who read the X-rays. This study commented that the entity ‘musculoskeletal fluorosis’ did not exist in the smelter where the pot-room workers were exposed to total fluoride levels below the threshold limit value of 2.5 mg/m3 (Chan-Yeung et al., 1983). However, for exposure of the general population to fluoride, reference exposure levels have been derived by applying a ‘benchmark dose’ approach to a variety of animal and human exposure studies. One-hour reference exposure level to protect against any respiratory irritation is about 0.6 mg/m3, and the level to protect against severe irritation from a once in a lifetime release is about 1.6 mg/m3. Data from various sources indicate that prolonged exposure of humans (workers and children) to fluoride concentrations between 0.1 mg/m3 and 0.5 mg/m3 leads to impairment of pulmonary function and skeletal fluorosis. It has been recognized that fluoride levels in ambient air should be less than 1 mg/m3 to prevent effects on livestock and plants. These concentrations will also protect human health sufficiently (World Health Organization, 2000). Knowledge of workplace and individual risk factors of musculoskeletal problems is far from complete. Studies are needed so that workplace-contributing factors for the development of musculoskeletal morbidity is properly validated and can be separated from factors resulting from it (Garg and Moore, 1992). Identification of jobs at risk and the associated factors should assist prevention; however, the extent to which these factors are causal or aggravating other contributing factors will further be
necessary for a successful intervention approach (Chen et al., 2006). This study made an effort to not only identify possible predictors of musculoskeletal complaints associated with metal smelting operations but also explore the role of occupational fluoride exposure on musculoskeletal complaints. This study observed that age of worker, drinking untreated water and working in pot room had significant impact on musculoskeletal problems. Post-shift urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) also showed significant contribution to musculoskeletal complaints. The area where the study was conducted was an endemic zone for fluoriderelated morbidity because of the fluoride content in underground water (Mahapatra, 2007). Hence, the finding of association between morbidity and drinking untreated water may also be due to fluoride exposure. Analysis of posture and ergonomic assessment of job details might have provided more information on the contribution of different factors to musculoskeletal morbidities. This was a limitation of this study. Inclusion of more variables during analysis in the logistic regression model could not be undertaken and separate analysis for backache and joint pain was not attempted in view of its sample size (calculated sample size was for a prevalence study only). This might have been another limitation of the study. The crosssectional design of the study also restricts analysis of the temporal relationship between predictors and musculoskeletal morbidity. Moreover, selection of subjects from more similar industries could have made the findings of this study more generalizable. This study concludes that along with other predictors such as nature of work, posture at work, and age of worker, exposure to fluoride also has significant role in the occurrence of musculoskeletal morbidity. However, a prospective study with a larger sample size taking care of the confounders may establish the fact in a more concerted manner. Acknowledgements We acknowledge the help of the subjects who participated in this study and also the support of the industry where the study was conducted. We are thankful to the Director, National Institute of Occupational Health and Indian Council of Medical Research authorities for their support.
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Musculoskeletal problems and fluoride exposure: A cross-sectional study among metal smelting workers
Toxicology and Industrial Health 1–8 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0748233714568477 tih.sagepub.com
A Saha1, AK Mukherjee1 and B Ravichandran2 Abstract Frequent and repetitive activities in job and awkward postures are shown as major contributors of musculoskeletal problems in most of the occupational health studies; however, efforts to explore newer risk factor are important to plan interventional measures. In this backdrop, this study examined contribution of fluoride exposure to musculoskeletal complaints. A cross-sectional interviewer-administered questionnaire survey was conducted involving 180 randomly selected subjects from a metal smelting industry. Clinical examination of the subjects was also performed to assess their health status and morbidity details. Assessment of personal exposure to particulate and gaseous fluoride at workplace was conducted. Urinary fluoride level was also examined in post-shift samples collected from study subjects. The mean age of the study subjects was 39.1 (+6.7) years. Majority of the workers (42.5%) were engaged in pot room. About 54% workers were suffering from backache and 66% subjects had joint pain. Exposure of workers to both particulate and gaseous fluoride and post-working shift urinary fluoride level was significantly higher in pot-room workers in comparison with all other workers. It was observed that age (odds ratio (OR): 1.62; 95% confidence interval (CI): 1.18–2.34), drinking untreated water (OR: 1.51; 95% CI: 1.03–2.76), working in pot room (OR: 1.44; 95% CI: 1.13–1.91) and urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) had significant effects on musculoskeletal complaints. This study concludes that along with other predictors such as nature of work, posture at work and age of worker, exposure to fluoride also has significant role in the occurrence of musculoskeletal morbidity. Keywords Musculoskeletal problems, exposure to fluoride
Introduction Work-related musculoskeletal problems are a group of painful conditions that mostly occur following either activities in awkward postures or frequent and repetitive activities. Musculoskeletal problems are a principal cause of occupational man-day loss and disability. Economic burden of these complaints has an impact on industry and society. Studies have shown that musculoskeletal problems are a major concern in most of the industrial operations and unorganized occupations like construction activity (Pandey et al., 2012), garment manufacturing (Lombardo et al., 2012), jute industries (Sett and Sahu, 2012), sugar manufacturing (Choobineh et al., 2009), rubber industry (Choobineh et al., 2007b), aircraft manufacturing (Menegon and Fischer, 2012), supermarket workers (Forcier et al., 2008), furniture industry (Nicoletti et al., 2008), semiconductor industry (Chandrasakaran et al., 2003), call
centre workers (Halford and Cohen, 2003) and petrochemical industries (Choobineh et al., 2012). Although frequent and repetitive activities in job and awkward postures are said to be the main causative factors in most of the occupational health studies, some studies have explored other risk factors (Aghilinejad et al., 2012; Choobineh et al., 2007, 2009) also. Such efforts are of immense importance because of
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Regional Occupational Health Centre (Eastern), Indian Council of Medical Research, Salt Lake, Kolkata, West Bengal, India 2 Regional Occupational Health Centre (Southern), Indian Council of Medical Research, Bengaluru, Karnataka, India Corresponding author: A Saha, Regional Occupational Health Centre (Eastern), Indian Council of Medical Research, Sector V, Block DP, Salt Lake, Kolkata 700091, West Bengal, India. Email: [email protected]
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the fact that finding and assessing newer risk factors can be an appropriate basis for planning interventional measures for alleviating the magnitude of the problem in the workplace. Metal smelting activity exposes its workers to respirable dusts, fluorides and other pollutants (Mukherjee et al., 2008). A study found ‘possible fluorosis’ or ‘initial fluorosis’ in 4.81% of the aluminium smelting workers (Martinotti et al., 2012). Study on the effects of chronic occupational exposure to aluminium on nervous system found headache, increased emotional irritability, concentration difficulty, insomnia and mood lability as predominating functional disorders (Sin´czuk-Walczak et al., 2003). Higher risk of respiratory problems such as bronchial asthma in workers engaged into aluminium production through electrolysis is also observed (Chashchin and Kuz’min, 2001). One study addressing musculoskeletal complaints in such industries showed that 65.5% of workers in past week and 77.5% of workers in past year had claimed one of the musculoskeletal complaints in their workplaces. Lumbar region, knee(s) and upper back had suffered most musculoskeletal complaints in participants (Aghilinejad et al., 2012). Fluorine is the most abundant element in nature, and about 96% of fluoride in the human body is found in bones and teeth. The principal sources of fluorine are drinking water and food such as sea fish, cheese and tea. Apart from this, industrial emissions are also potential sources of exposure. The available data suggest that 15 states in India are endemic for both dental and skeletal fluorosis (Arlappa et al., 2013). Endemic skeletal fluorosis is a chronic metabolic bone and joint disease caused by ingesting large amounts of fluoride either through water or rarely from foods of endemic areas. Fluoride is a cumulative toxin that can alter accretion and resorption of bone tissue. It also affects the homeostasis of bone and mineral metabolism. The total quantity of ingested fluoride is the single most important factor that determines the clinical course of the disease, which is characterized by immobilization of joints of the axial skeleton and of the major joints of the extremities. A combination of osteosclerosis, osteomalacia and osteoporosis of varying degrees as well as exostosis formation characterizes the bone lesions. In a proportion of cases, secondary hyperparathyroidism is observed with associated characteristic bone changes. Contrary to earlier thinking, severe crippling forms of skeletal fluorosis are seen in the paediatric age group too. Increased metabolic turnover of the bone, impaired
bone collagen synthesis and increased avidity for calcium are features in fluoride toxicity. Osteosclerotic picture is evident when small doses of fluoride are ingested over a long period of time during which calcium intakes are apparently normal, while osteoporotic forms are common in the paediatric age group and with higher body load of the element. Alterations in hormones concerned with bone and mineral metabolism are seen in fluorosis. Kidney is the primary organ of excretion for fluorides. Age, sex, calcium intake in the diet, dose and duration of fluoride intake and renal efficiency in fluoride handling are the factors that influence the outcome. Serum parameters rarely help in the diagnosis. Elevated urinary fluoride and increased bone fluoride content are indicators of fluoride toxicity (Krishnamachari, 1986). Fluoride is a major pollutant in aluminium smelting industries. Fluoride can have adverse effects on musculoskeletal system also. Musculoskeletal complaints (principally as backache and joint pain) are observed frequently in aluminium smelting operations. However, scientific efforts to explore any relationship between fluoride exposure and musculoskeletal complaints in such industries are scanty. In this backdrop, this study was initiated to examine association, if any, between musculoskeletal complaints and fluoride exposure. This study also aimed to assess the risk of such workers suffering from musculoskeletal complaints due to their occupational exposure.
Methods This study was conducted involving the workers of an aluminium smelting industry. This cross-sectional survey was undertaken among the workers working in different sections of the smelter. In India there are a number of such units that employ considerable number of workers. The principal sections of this type of industry are pot rooms, cast house and carbon area. These industries are organized industries and usually employ both direct and contract workers for different activities. Apart from workers employed in the main sections, some workers are also employed for different supporting and maintenance activities. In an aluminium smelter, smelting of alumina takes place by electrolysis and the pot room is the heart of the process. After this, the molten metal is transferred to the cast house for casting and moulded into different forms. The carbon area deals with the process of anode preparation necessary for the electrolysis
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process. This study was conducted in one such aluminium smelting industry encompassing all the workers of the above sections. The musculoskeletal problems and their associated factors were addressed in this study. Here, backache and joint pain constituted musculoskeletal problems for the purpose of this study. In this study, the subjects suffering from backache/joint pain at the study period for at least last 6 months or had suffered such problems in service period for at least 6 months were considered as having musculoskeletal problems. This was done to exclude the nonspecific temporary musculoskeletal problems. Apart from this, subjects with known causes of musculoskeletal problems (e.g. accidental) were not included in this study. The industry had about 3200 workers, of which subjects were selected for this study. The sample size was calculated on the principles of a prevalence survey. The prevalence of musculoskeletal problems was predicted as 20% in such population; we calculated the sample size for prevalence study using an acceptable range of 14%–26%. Here musculoskeletal problems in general were considered, as the intention was to consider all cases of musculoskeletal problems and examine the contribution of fluoride exposure in the occurrence of musculoskeletal problems. Thus, the minimum sample size for a 5% level of significance was calculated as 162. We set our target as 200 employees to take care of non-response. The workers were selected randomly from a list of workers. Of the 200 workers approached for study, 180 subjects participated in this study. All of them were interviewed with the help of an interviewer-administered questionnaire to collect information regarding their personal, occupational and work-related morbidity details. Clinical examination of the subjects was also performed to assess their health status and morbidity details. Workplace sampling and assessment of personal exposure to particulate and gaseous fluoride were conducted. Urinary fluoride level was also examined in post-shift samples collected from the study subjects. Necessary approval for this study was obtained from the institutional ethical committee as well as the scientific advisory committee of National Institute of Occupational Health, India. Initially, a descriptive analysis of the collected data was undertaken to understand the distribution of personal, occupational and morbidity characteristics among the subjects. Afterwards, a univariate analysis was done to know the distribution of musculoskeletal problems among the workers and contribution of worker characteristics towards the problem. Finally,
multivariate analysis was done using Statistical Package for the Social Sciences software to obtain the contribution of different factors to musculoskeletal problems. In multivariate analysis, the logistic regression method was used to obtain the contribution of individual factors like age (years), experience in this job/duration of employment (years), tobacco/alcohol use, education level (primary and secondary vs. college and university), drinking water quality, nature of job (pot room vs. others) and urinary fluoride level on musculoskeletal problems irrespective of the effect of the other factors. Whilst entering the variables in the logistic regression model, tobacco/alcohol use, education level (primary and secondary vs. college and university), drinking water quality and nature of job were taken as categorical variables. Other variables like age, experience in job and urinary fluoride level were taken as continuous variables. All variables were analysed simultaneously in the model in order to estimate the effect of every individual variable adjusting for the effect of other variables.
Results The mean age of the study subjects was 39.1 (+6.7) years. The mean income was 17,925 (+8889) Indian rupees per month. One hundred and fifty-four (85.6%) workers were 30–49 years old, and 13 (7.2%) workers each were in up to 29 years and 50 years or above age group. Thirty-four and half percent subjects were either smokers or ex-smokers. About 67% of the subjects had a primary- or secondary-level education, whilst 45% were college- or university-level educated. The majority of the workers (42.5%) were engaged in pot room, whilst 18.8%, 20.4% and 18.3% were engaged in the cast house, carbon area and other supporting activity, respectively (Table 1). About 92% workers were married and 21.1% subjects were drinking untreated well water. The mean job duration of the subjects was 13.2 + 4.7 years for pot-room workers, 6.6 + 5.3 years for cast-house workers and 11.4 + 4.5 years and 9.8 + 5.8 years for carbon area workers and other supporting activity workers, respectively. So far as musculoskeletal morbidity is concerned, 54.4% and 66.6% workers were suffering from backache and joint pain, respectively. Personal exposure of study subjects to fluoride was measured by collecting workplace samples through personal monitoring equipments attached to workers at work and analysing the collected samples. The
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Table 1. Personal and occupational characteristics of the study subjects. Characteristics Age group Up to 29 years 30–49 years 50 years and above Marital status Married Unmarried Education Primary level Secondary level University level Drinking water Treated water Untreated well water Smoking Ever smoker Never smoker Alcohol use Ever alcoholic Never alcoholic Tobacco chewing Ever chewer Never chewer Nature of job Pot line Cast house Carbon area Others
Frequency (%; N ¼ 180) 13 (7.2) 154 (85.6) 13 (7.2) 166 (92.2) 14 (7.8) 17 (9.5) 103 (57.5) 60 (33.0) 142 (78.9) 38 (21.1) 62 (34.5) 118 (65.6) 72 (40.0) 108 (60.0) 56 (30.9) 124 (68.5) 76 (42.5) 34 (18.8) 37 (20.4) 33 (18.3)
post-shift urinary fluoride level was also assessed. Exposure of workers to both particulate and gaseous fluoride was significantly higher in pot-room workers in comparison with all other workers. Similarly postworking shift urinary fluoride level also was significantly higher in pot-room workers in comparison with all other workers (Table 2). In the univariate analysis, it was found that worker characteristics like age of 50 years and more (odds ratio (OR): 8.8; 95% confidence interval (CI): 1.1–93.3), drinking untreated well water (OR: 3.4; 95% CI: 1.4– 8.4) and working in pot room (OR: 6.1; 95% CI: 2.3–16.6) showed a significant effect on backache. In case of joint pain, working in pot room (OR: 5.2; 95% CI: 1.9–14.3) was the only worker characteristics that showed significant impact (Table 3). When multivariate analysis was performed using a logistic regression model entering all the variables simultaneously to understand the effect of different worker characteristics on musculoskeletal morbidity
(backache or joint pain or both), it was observed that age (regression coefficient 0.53; p value 0.035; OR: 1.62; 95% CI: 1.18–2.34), drinking untreated water (OR: 1.51; 95% CI: 1.03–2.76), working in pot room (OR: 1.44; 95% CI: 1.13–1.91) and urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) showed significant effects on musculoskeletal complaints (Table 4).
Discussion Systematic search and validation of newer factors of musculoskeletal morbidity is the key to the prevention of major cause of workplace disability, man-day loss and resulting loss of productivity. Efforts made in this direction have mostly highlighted ergonomic risk factors, faulty work area design, awkward posture and repetitive nature of work (Bhattacharyya and Chakrabarti, 2012). Some studies have identified other variables such as shift work, extended work time, type of employment, second job and job unit, job type as well as work perceptions as factors significantly associated with musculoskeletal complaints Parkes, 1999; Choobineh et al., 2012). Factors like increasing age, female gender and smoking have also been named as significant predictors (Dahlberg et al., 2004; Werner et al., 2011). One study found that apart from work in awkward posture, the role of psychosocial factors, such as sleeping problems and hurrying without reason were associated with musculoskeletal morbidity (Engholm and Holmstro¨m, 2005). Although few, studies are there that mentioned the role of work environment as a predictor of musculoskeletal problems (Parkes, 1999). So far as the aluminium smelting process is concerned, a study conducted in Iran addressing factors of musculoskeletal morbidity not only found job duration and age as contributing factors but also observed the necessity of ergonomic interventions for elimination of environmental hazards (Aghilinejad et al., 2012). As far as fluoride exposure and musculoskeletal problems are concerned, some studies have associated different morbidities with exposure to fluoride. A study reported significant relationship of exposure to fluoride with the frequency of back and neck surgery, fractures, symptoms of musculoskeletal disease and past history of diseases of bones and joints in the absence of the typical findings of skeletal fluorosis (Carnow and Conibear, 1981). A higher frequency of ossification of ligament, tendon and muscle attachments was observed among the fluoride-exposed subjects and these changes increased with the bone
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Table 2. Personal exposure of study subjects to fluoride at work and their urinary fluoride level.a Fluoride exposure (mg/m3); mean + SD (range) Process area
Particulate
Gaseous
Urinary fluoride (mg/dl); mean + SD (range)
Other areas
0.09 + 0.06 (0.05 – 0.16) 0.23 + 0.09 (0.08 – 0.28) p < 0.001
0.036 + 0.027 (0.014 – 0.067) 0.1128 + 0.110 (0.043 – 0.310) p < 0.01
0.090 + 0.068 (0.007 – 0.223) 0.190 + 0.139 (0.025 – 0.587) p < 0.001
Pot line Significance by t test (p value) a
Fluoride exposure (mg/m3) in 20 samples in each category.
Table 3. Distribution of musculoskeletal problems among the workers and contribution of worker characteristics towards the problem (univariate analysis). Worker characteristics
Backache frequency (%)
OR (95% CI)
Joint pain frequency (%)
OR (95% CI)
5 (38.5) 82 (53.3) 11 (84.6)
1 1.8 (0.5–6.8) 8.8 (1.1–93.3)
7 (53.8) 103 (66.9) 10 (76.9)
1 1.73 (0.98–6.1) 2.86 (0.4–22.0)
69 (48.6) 29 (76.3)
1 3.4 (1.4–8.4)
90 (63.3) 30 (78.9)
1 2.17 (0.8–5.57)
56 (72.7) 15 (44.1) 17 (45.9) 10 (30.3)
6.1 (2.3–16.6) 1.8 (0.6–5.6) 1.9 (0.6–5.9) 1
64 19 21 16
71 (59.2) 27 (45.0)
1.7 (0.9–3.4) 1
85 (70.8) 35 (58.3)
1.7 (0.8–3.4) 1
67 (55.8) 31 (51.7)
1.1 (0.6–2.3) 1
82 (68.3) 38 (63.3)
1.2 (0.6–2.5)
Age Up to 29 years 30–49 years 50 years and above Drinking water Treated water Untreated well water Nature of job Pot line Cast house Carbon area Others Education Primary/secondary level University level Tobacco/alcohol use Ever user Never user
(83.1) (55.9) (56.8) (48.5)
5.2 (1.9–14.3) 1.3 (0.4–3.9) 1.4 (0.5–4.0) 1
OR: odds ratio; CI: confidence interval.
Table 4. Effect of worker characteristics on occurrence of musculoskeletal problems (backache/joint pain/both; multivariate analysis). 95% CI Variable Age Job duration Tobacco/alcohol use Education Drinking untreated water Working in pot line versus other job Urinary fluoride level
Regression coefficient
Significance
OR
Lower limit
Upper limit
0.530 0.016 0.025 0.062 0.439 0.382 0.708
0.035 0.212 0.131 0.09 0.044 0.047 0.024
1.62 0.82 0.97 0.97 1.51 1.44 2.71
1.18 0.49 0.77 0.33 1.03 1.13 1.81
2.34 1.21 1.39 1.61 2.76 1.91 3.75
OR: odds ratio; CI: confidence interval.
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fluoride content (Boillat et al., 1980). A study observed that in light cases of fluorosis, the bone changes were often associated with non-specific joint and muscle pains, but the disease was entirely asymptomatic (Grandjean, 1982). Another study on aluminium smelter workers found that the total complaints reported by study groups were significantly higher than the control groups. Smelter workers had a significantly higher urinary and serum fluoride level than non-smelter workers; the nail fluoride content was also higher in smelter workers than non-smelter workers (Susheela et al., 2013). On the other hand, there are studies that found different observations. One such study found some changes of early skeletal fluorosis on pelvic X-rays like increased density, calcification of ligaments and periosteal changes in a few workers who were employed on the pot lines for more than 10 years. There was, however, poor agreement in the findings of the two radiologists who read the X-rays. This study commented that the entity ‘musculoskeletal fluorosis’ did not exist in the smelter where the pot-room workers were exposed to total fluoride levels below the threshold limit value of 2.5 mg/m3 (Chan-Yeung et al., 1983). However, for exposure of the general population to fluoride, reference exposure levels have been derived by applying a ‘benchmark dose’ approach to a variety of animal and human exposure studies. One-hour reference exposure level to protect against any respiratory irritation is about 0.6 mg/m3, and the level to protect against severe irritation from a once in a lifetime release is about 1.6 mg/m3. Data from various sources indicate that prolonged exposure of humans (workers and children) to fluoride concentrations between 0.1 mg/m3 and 0.5 mg/m3 leads to impairment of pulmonary function and skeletal fluorosis. It has been recognized that fluoride levels in ambient air should be less than 1 mg/m3 to prevent effects on livestock and plants. These concentrations will also protect human health sufficiently (World Health Organization, 2000). Knowledge of workplace and individual risk factors of musculoskeletal problems is far from complete. Studies are needed so that workplace-contributing factors for the development of musculoskeletal morbidity is properly validated and can be separated from factors resulting from it (Garg and Moore, 1992). Identification of jobs at risk and the associated factors should assist prevention; however, the extent to which these factors are causal or aggravating other contributing factors will further be
necessary for a successful intervention approach (Chen et al., 2006). This study made an effort to not only identify possible predictors of musculoskeletal complaints associated with metal smelting operations but also explore the role of occupational fluoride exposure on musculoskeletal complaints. This study observed that age of worker, drinking untreated water and working in pot room had significant impact on musculoskeletal problems. Post-shift urinary fluoride level (OR: 2.71; 95% CI: 1.81–3.75) also showed significant contribution to musculoskeletal complaints. The area where the study was conducted was an endemic zone for fluoriderelated morbidity because of the fluoride content in underground water (Mahapatra, 2007). Hence, the finding of association between morbidity and drinking untreated water may also be due to fluoride exposure. Analysis of posture and ergonomic assessment of job details might have provided more information on the contribution of different factors to musculoskeletal morbidities. This was a limitation of this study. Inclusion of more variables during analysis in the logistic regression model could not be undertaken and separate analysis for backache and joint pain was not attempted in view of its sample size (calculated sample size was for a prevalence study only). This might have been another limitation of the study. The crosssectional design of the study also restricts analysis of the temporal relationship between predictors and musculoskeletal morbidity. Moreover, selection of subjects from more similar industries could have made the findings of this study more generalizable. This study concludes that along with other predictors such as nature of work, posture at work, and age of worker, exposure to fluoride also has significant role in the occurrence of musculoskeletal morbidity. However, a prospective study with a larger sample size taking care of the confounders may establish the fact in a more concerted manner. Acknowledgements We acknowledge the help of the subjects who participated in this study and also the support of the industry where the study was conducted. We are thankful to the Director, National Institute of Occupational Health and Indian Council of Medical Research authorities for their support.
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