Introduction:
Furniture industry is one of the largest industries in the world that contributes to the economic growth for many countries in which woods have been used for this purpose (1). Malaysia is a resource rich country with a variety of valuable wood species such as Dark Red Meranti (Shorea spp.), Meranti Bakau (Shorea uliginosa), Nyatoh (Sapotaceae spp.), Bintangor (Calophyllum spp.), Balau (Shorea spp.), Chengal (Neobalanocarpus heimii), Merbau (Intsia palembanica) and Rubber wood (Hevea brasiliensis) (2). The most common timber used in furniture making is the rubber wood (Hevea brasiliensis) due to the abundance of rubber plantations for producing natural-latex. In addition, the characteristics of the rubber wood such as its structure, color, lightness, easy drying and long lasting nature make it suitable for use in the furniture production (3). In 2008, almost 68,000 workers had been employed in the furniture industry in Malaysia (4).
Wood dust is produced during the process of the wood-furniture making which involves sanding, sawing and drilling either manually or with machines. The workers tend to inhale the wood-dust during the processes especially if there is no good ventilation and filtering system. The exposure of natural latex of rubber wood is well-known as potential sensitizer to health care workers (5). Besides that, not many studies have been done on the health effects of rubber wood. Therefore, a study was conducted to assess the level of wood dust and the prevalence of respiratory effects among workers exposed to the rubber wood dust in the furniture factory.
Rubber wood is in the group of hardwood. Literature reveals a spectrum of health effects due to hardwood exposure. Non-malignant respiratory diseases among woodworkers can occur at concentrations of hardwood or softwood dust exposure between 0.5 and 1 mg/m3 (6). Studies have shown that western red cedar is related to asthma among other species (7,8). Many studies found that wood dust increased the risk of developing upper and lower respiratory health symptoms especially in the furniture manufacturing sector (9,10).
Some wood dust, especially from the species of Beech and Oak, have been classified as class A1 carcinogen; and Birch, Mahogany, Teak and Walnut are classified as class A2 carcinogen (11). There are studies suggesting that wood dust exposure in the workplace will increase the risk of developing lung cancer (12), laryngeal cancer (13), and nasal cancer (14). Some studies also reported that wood dust exposure could lead to occupational skin symptoms (15,16). Previous studies also found a reduction of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and FEF25-75 among exposed workers (9,10). Thus, this study aims to assess the association between rubber wood dust exposures with workers’ respiratory and skin health effects.
Methodology
This was a cross-sectional study in which all workers in furniture factory were randomly selected. The sample size required for this study was calculated by using two proportions formula. The expected proportions were considered based on previous studies (17,18). After considering a = 0.05 (i.e. 5%) and ß = 0.20 (i.e. 20%) and additional 20% non-response, the final sample size was 271. It was found that sample size calculation based on respiratory symptoms provided the largest sample size, so these symptoms were used as the basis for sample size calculation in this study. Potentially all workers exposed to the rubber wood dust in the selected furniture factory were included in the study, whereas workers who had past history respiratory illness such as asthma and tuberculosis and skin allergy were excluded from the study. Data was collected using a validated questionnaire from the respiratory system questionnaire adapted from British Medical Research Council (MRC), 1984 (19,20). The information gathered were on personal characteristics, working information, past work history, past medical history, tobacco smoke, respiratory, nasal, eyes and skin symptoms. The information from the questionnaire was obtained within the same day of working to ensure that the responses were reliably assessed.
The portable type of SpirolabII (Medical International Research) was used to measure FVC, FEV1, and FEV1/FVC% for the lung function test. All tests were analyzed by applying six quality criteria (quality control), following the American Thoracic Society (ATS) recommendation (21). In addition, the reproducibility of the FEV1, FVC, FEV1% and FVC% parameters were also calculated. The respondents were guided on the correct technique to perform spirometry by the researcher prior to the test. Each of the respondents was given detailed explanation prior to the test so that they understood well on the procedures given.
The portable area dust sampling was used to collect the airborne wood dust sample exposed in the work area. The device used was the Dust Track Aerosol Monitor (Model 8520: USA). The Dust Track was positioned in the furniture factory areas with the height of 100 cm from the floor level or breathing zone level. The airborne wood dust concentration was measured continuously for eight hours.
All statistical analyses were performed by using software package SPSS version 19.0. Descriptive data was analyzed to determine the prevalence and mean. The chi-square test was used to determine if two categorical variables are related. The student t-test wasused for testing the difference between means of two groups. Multivariate logistic regression models adjusted for sex, age, education, and smoking as potential confounders was used to analyze the effect of exposure level on respiratory symptoms.
Multiple linear regression analysis was used to identify the factors which had relationship with lung function parameters (FEV1, FVC, FEV1 % predicted, and FVC % predicted). Lung function parameters were adjusted for sex, age, education and smoking except that FEV1 % predicted, and FVC % predicted were already controlled for sex, age and height in the prediction equations.
Results
Out of 271 respondents, 241 eligible subjects participated in this study which gave a response rate of 88.9%. Material supply area denoted the highest concentration of inhalable dust, 1.1 mg/m3 followed by machinery area which was 1.01 mg/m3. These two workstation areas exceeded the permissible exposure limit of 1 mg/m3. Other workstation areas such as store, spray and sanding were below the permissible exposure limit (PEL) of 1 mg/m3 and within the range of 0.501 to 0.94 mg/m3.
The general characteristics of study population are presented in Table 1. High exposure denoted with the wood dust concentration level exceeded the PEL of 1 mg/m3 and vice versa for low exposure. Majority of the workers were males in both low (80.8%) and high (98.3%) exposure group. The mean age (± standard deviation) among the high exposure group was 30.9 ± 7.5 years and 34.9 ± 10.9 years for low exposure group. Most of the exposed workers were married and in the group of low educational status. The mean of the length of employment in this furniture factory were 1.1 ± 0.3 years and 1.0 ± 0.2 years for low and high exposure group respectively. Most of the workers were not smoking.
| Table 1: General characteristic of study population in furniture factory |
| Characteristics |
Low exposure group
(n=182) |
High exposure group
(n=59) |
p value |
Sex, n (%) |
Male |
147 (80.8%) |
58 (98.3%) |
0.001* |
Female |
35 (19.2%) |
1 (1.7%) |
Age (years), mean (SD) |
34.9 (10.9) |
30.9 (7.5) |
0.002* |
Educational group, n (%) |
Lower (none to secondary) |
135 (74.2%) |
46 (78.0%) |
0.558 |
High (high to degree) |
47 (25.8%) |
13 (22.0%) |
Marital status, n (%) |
Never married |
65 (35.7%) |
25 (42.4%) |
0.358 |
Married |
117 (64.3%) |
34 (57.6%) |
Length of employment, mean (SD) |
1.1 (0.3) |
1.0 (0.2) |
0.147 |
Face mask usage, n (%) |
Yes |
67 (36.8%) |
28 (47.5%) |
0.146 |
No |
115 (63.2%) |
31 (52.5%) |
Smoking status, n (%) |
Non-smoker |
126 (69.2%) |
34 (57.6%) |
0.101 |
Smoker |
56 (30.8%) |
25 (42.4%) |
*p<0.05 considered as significant |
As indicated in Table 2, the high prevalence of health symptoms among exposed workers were self-reported eyes symptoms (51.9%), nasal symptoms (50.6%), skin symptoms (23.2%) and cough (19.5%) in which higher percentage was among high exposure group. Eyes symptoms described as dryness, itchiness, irritation, watering and redness eyes; and nasal symptoms defined as repeated sneezing, runny and blocked nose were experienced by workers in the factory. Skin symptoms were described as redness, dry skin with scaling/flaking, fissures or cracks, weeping or crusts, tiny water blisters (vesicles), papules, rapidly appearing itchy wheals/welts (urticaria), itching, burning, prickling, or stinging, aching or pain.
| Table 2: Prevalence of respiratory, nasal, eyes and skin symptoms |
| Health symptoms |
High exposure (n=59) |
Low exposure (n=182) |
Total |
Cough |
14 (23.7%) |
33 (18.1%) |
47 (19.5%) |
Chest tightness |
8 (13.6%) |
27 (14.8%) |
35 (14.5%) |
Phlegm |
6 (10.2%) |
15 (8.2%) |
21 (8.7%) |
Breathlessness |
4 (6.8%) |
16 (8.8%) |
20 (8.3%) |
Wheezing |
3 (5.1%) |
6 (3.3%) |
9 (3.7%) |
Nasal symptoms |
43 (72.9%) |
79 (43.4%) |
122 (50.6%) |
Eyes symptoms |
39 (66.1%) |
86 (47.3%) |
125 (51.9%) |
Skin symptoms |
17 (28.8%) |
39 (21.4%) |
56 (23.2%) |
Table 3 describes the influence of rubber wood dust level on the workers’ complaint on respiratory and skin symptoms. There was significant difference between high exposure group and lower exposure group with regard to the nasal symptoms (adjusted POR=3.89, 95% CI=2.03 to 7.49) and eyes symptoms (adjusted POR=2.63, 95% CI=1.41 to 4.91). This explained that high exposed group had higher risk to experience nasal and eyes symptoms. The workers who worked for ten years or more in the furniture factory were having statistically significant higher prevalence of phlegm, chest tightness, breathlessness, and eyes symptoms (Table 4).
| Table 3: Association between exposure status and health symptoms |
| Health symptoms |
Rubber wood dust exposure, n (%) |
Crude OR (95% CI) |
Adjusted OR# (95% CI) |
High exposure group (n=59) |
Low exposure group (n=182) |
Cough |
14 (23.7) |
33 (18.1) |
1.41 (0.69 to 2.85) |
1.95 (0.91 to 4.19) |
Phlegm |
6 (10.2) |
15 (8.20 |
1.26 (0.47 to 3.41) |
1.52 (0.53 to 4.36) |
Chest tightness |
8 (13.6) |
27 (14.8) |
0.90 (0.39 to 2.11) |
0.91 (0.38 to 2.18) |
Breathlessness |
4 (6.8) |
16 (8.8) |
0.76 (0.24 to 2.35) |
0.96 (0.29 to 3.15) |
Wheezing |
3 (5.1) |
6 (3.3) |
1.57 (0.38 to 6.49) |
1.04 (0.26 to 4.12) |
Nasal symptoms |
43 (72.9) |
79 (27.1) |
3.50 (1.84 to 6.68) |
3.89 (2.03 to 7.49)* |
Eyes symptoms |
39 (66.1) |
86 (47.3) |
2.18 (1.18 to 4.02) |
2.63 (1.41 to 4.91)* |
Skin symptoms |
17 (28.8) |
39 (21.4) |
1.48 (0.76 to 2.89) |
1.89 (0.93 to 3.82) |
#adjusted for sex, age, education and smoking; *significant (p<0.05) |
| Table 4: Association between length of employment and health symptoms |
| Health symptoms |
Length of employment, n (%) |
Crude OR (95% CI) |
Adjusted OR# (95% CI) |
10 years or more (n=22) |
Less than 10 years (n=219) |
Cough |
8 (36.4) |
39 (17.8) |
2.64 (1.04 to 6.72) |
1.59 (0.49 to 5.05) |
Phlegm |
6 (27.3) |
15 (6.8) |
5.10 (1.74 to 14.94) |
4.59 (1.25 to 16.86)* |
Chest tightness |
9 (40.9) |
26 (11.9) |
5.14 (2.00 to 13.20) |
6.33 (2.16 to 18.53)* |
Breathlessness |
8 (36.4) |
12 (5.5) |
9.86 (3.47 to 28.04) |
9.84 (2.75 to 35.26)* |
Wheezing |
2 (9.1) |
7 (3.2) |
3.03 (0.59 to 15.57) |
3.23 (0.50 to 20.86) |
Nasal symptoms |
15 (68.2) |
107 (48.9) |
2.24 (0.88 to 5.72) |
2.06 (0.77 to 5.49) |
Eyes symptoms |
17 (77.3) |
108 (49.3) |
3.49 (1.25 to 9.81) |
3.67 (1.24 to 10.89)* |
Skin symptoms |
6 (27.3) |
50 (22.8) |
1.27 (0.47 to 3.41) |
1.14 (0.38 to 3.38) |
#adjusted for sex, age, education and smoking; *significant (p<0.05) |
The result in Table 5 suggests that the high exposure group had reduced FEV1, FVC, FEV1% predicted and FVC% predicted as compared to low exposure group. These effects of lung function reached statistical significance. Those workers who worked for ten years and more in the furniture factory had reduced lung function, however, the results showed no significant difference with those who worked less than ten years (data not shown).
| Table 5: Lung function effect between high exposure group and low exposure group# |
Lung function parameters |
Rubber wood dust exposure, mean ± S.D |
Crude B coefficient (95% CI) |
Adjusted B coefficient (95% CI) |
High exposure group (n=59) |
Low exposure group (n=182) |
FEV1 (l)a |
2.16 ± 0.58 |
2.48 ± 0.72 |
-0.31 (-0.52 to -0.11) |
-0.51 (-0.69 to -0.34)* |
FVC (l)a |
2.79 ± 0.72 |
2.96 ± 0.85 |
-0.17 (-0.41 to 0.08) |
-0.39 (-0.61 to -0.19)* |
FEV1% predicted b |
59.61 ± 13.04 |
73.73 ± 15.19 |
-14.12 (-18.46 to -9.78) |
-14.62 (-18.98 to -10.27)* |
FVC % predicted b |
65.76 ± 13.35 |
74.76 ± 15.58 |
-8.99 (-13.44 to -4.55) |
-9.67 (-14.13 to -5.22)* |
#Multiple linear regression; a Effect estimate adjusted for sex, age, height, education and smoking; b Effect estimate adjusted for education and smoking; *significant (p<0.05). |
Discussion
Based on the results on the inhalable dust concentration in different workstation areas, the level measured in the material supply and machinery area showed the concentration level of rubber wood dust exceeded the permissible exposure limit of 1 mg/m3 under Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health (USECHH)) regulations (2000) (22). Previous studies also reported that the highest wood dust concentration level was generated from the process which involved machining such as sawing (10,23,24).
The most common symptoms among workers exposed to rubber wood dust were ocular and nasal symptoms. Other studies have also reported that ocular and nasal symptoms were among the common complaints in exposed factory workers (10,25). When comparing between the high exposure group and low exposure group exposed to rubber wood dust, there was a significant difference on complaints of eyes and nasal symptoms. This explains that furniture factory workers exposed to rubber wood dust exceeding 1 mg/m3 showed significant health effects.
It was reported that the health effects were evident at levels between approximately 1 and 5 mg/m3 inhalable particulate mass (11). Exposure to rubber wood dust more than 1 mg/m3 can cause an increased risk of ocular and nasal symptoms (10). Those who worked for ten years or more showed frequent complaints of phlegm, chest tightness, breathlessness, and ocular symptoms. Osman and Pala (2009) also reported that working for ten years or more led to was more frequent complaints of ocular and nasal symptoms.
There were significant differences between high exposure group and low exposure group regarding effects on lung function due to exposure to rubber wood dust in the furniture factory. The high exposure group had reduced lung function as compared to low exposure group. Several studies had also shown the impairment of lung function among occupationally exposed workers to wood dust (10,25–27). The length of employment status among workers exposed to rubber wood dust in the furniture factory showed evidence that lung function was decreased especially for those workers who worked for ten years or more. However, the results were not statistically significant. Other studies have also reported that longer exposure to the wood dust can significantly reduce the lung function parameters (9,28). It can be deduced that length of employment in the dusty workplace, especially for those exposed to wood dust, can potentially lead to symptoms involving respiratory, nasal, ocular and skin organs and lead to reduced lung function.
It has to be emphasized that this research study employed a cross-sectional design that may present a number of limitations. One of the limitations is recall bias due to the fact that most of the information was obtained from the questionnaire. Another limitation is that the exposure assessment in this study only reflects on measurements of inhalable dust in different workstation areas through area sampling but not on personal sampling. Even area sampling may misrepresent the individual’s average daily exposure as compared to personal monitoring but it can give general average of daily exposure that focus on groups at different workstation areas.
There is a probability of exposure to rubber wood dust alone or in combination with other chemicals, especially in spraying and assembly areas, which may influence the respiratory and skin effects among furniture’s workers. Thus, it is recommended that future studies must verify this matter by measuring the concentration level of chemicals used in the furniture factory particularly in spraying and assembly areas.
Conclusion
Material supply and machinery areas had dust levels exceededing the PEL. More than half of the workers showed higher prevalence of nasal and eye symptoms. High level of dust exposure may reduce the lung function of the workers. In addition, long service workers have higher prevalence of respiratory symptoms. Thus, it is suggested that appropriate and immediate control measures should be implemented, especially by providing suitable personal protective equipment and proper maintenance of local exhaust ventilation.
Acknowledgement
The authors would like to acknowledge Malaysian Timber Industry Board and all the workers who participated in this study.
Ethical consideration and consent to participate
This study was approved by the Research and Ethics Committees Universiti Kebangsaan Malaysia (FF-072-2011). Informed consent was obtained from each participant.
Conflict of interest
The authors declare that they have no conflict of interest
Funding
The authors would like to acknowledge the funding support of this work by IIUM internal grant (RIGS16-116-0280).
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