Chapter 4 – Employment
2. Non fraternisation policy
Exposure to both organic and inorganic dust has been associated with a negative impact on respiratory health. The effect of exposure to cement dust on cement loaders was explored in this study.
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5.1.1 RESPIRATORY SYMPTOMS
This study showed a high prevalence of respiratory symptoms among cement loaders. The crude prevalence of respiratory symptoms in the subjects was 55.5%. This finding was not unexpected because level of dust exposure has been recognized to significantly impact on the prevalence of respiratory symptoms.8, 10-12
Some studies have reported higher prevalence values for respiratory symptoms than that obtained in this study. Urom et al74 reported a prevalence of 71% among workers exposed to dust generated from crushing granite rocks in Calabar, Eastern Nigeria. Also in Rio de Janerio, Lemle and colleagues75 reported a 65% prevalence of respiratory symptoms among quarry workers. Although these studies did not estimate quantity of dust exposure, Ali et al 52 in Saudi Arabia found dust levels exceeding the acceptable limit of 5 mg/m3 in all parts of a cement factory studied. They also noted that highest dust levels were present in the quarry.
Whereas dust levels at the cement depots visited in Jos ranged between 0.4-12mg/m3, Oleru UG16 found dust levels as high as 30.81mg/m3 in his study and also noted that people more highly exposed to
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cement dust had a higher prevalence of respiratory symptoms. In Norway, Mwaiselage55 et al observed that prevalence of cough, phlegm, breathlessness and COPD correlated with a cumulative dust level of >
100.0 versus < 20.0 mg/m3-year.
Prevalence of respiratory symptoms among the subjects of this study were: cough (27.8%), phlegm (16.7%), breathlessness (10%), wheeze (13.3%) and chest tightness (20%). In the United Arab Emirates, Al Neami and co-workers17 recorded a similar prevalence of respiratory symptoms among workers at a Portland cement plant; cough (30%), phlegm (25%), wheeze (8%), dyspnea (21%) and shortness of breadth (8%). Other investigators have reported similar symptoms following exposure to cement dust.17, 53, 54, 55
Cement is alkaline and hence irritant. It also contains chromate which has been found to act as an allergen stimulating IgE production which may result in irritant induced asthma. 76, 77 This sensitization is however ameliorated by the addition of Iron during the cement manufacturing process.77 The addition of Iron, paradoxically portends a health risk for workers in the cement manufacturing plants.
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In Western Nigeria, Akinlolu and co-workers 78 analysed dust samples obtained from the air and soil around the Sagamu cement factory.
The found very high levels of heavy metals in the samples analysed. They also went through medical records at the Obafemi Awolowo Teaching Hospital located in the town and noticed an increasing prevalence of diseases linked to heavy metal toxicity in the environment, especially those related to dust generation.
Respiratory symptoms in cigarette smokers
Cigarette smoke is an established cause/contributor to respiratory disease globally. Cigarette smoking alters both structure and function of central and peripheral airways, alveoli and capillaries, and the immune system of the lungs.
In the studied population there were 28 current smokers with a mean pack year of 5.49 ± 6.18 (Range 0.2 to 30 years). There were no ex-smokers. The smokers had similar demographic characteristics as their non-smoking colleagues. The prevalence of respiratory symptoms was however higher among cement loaders who smoked. Prevalence of symptoms among the cement loaders who smoked were; cough (53.6%),
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breathlessness (21.4%), chest tightness (57.1%), and wheeze (26.6%).
Among the non-smoking cement loaders the prevalence were; 16.1, 4.8, 3.2 and 6.5% respectively. Sputum production was found in 28.6% of the current smokers compared to 11.3% of non- smoking cement loaders.
Femi Pearse in the study of the relationship of respiratory symptoms and dusty occupations found that chronic cough and phlegm production were significantly higher among smokers than non-smokers.58 It was concluded that the effect of cigarette smoking was additive to that of dust exposure. Higher prevalence rates of respiratory symptoms among smokers have been reported in literature.
Active smoking has been recognized as the most important modifiable risk factor for the development of chronic obstructive pulmonary disease (COPD). Buist et al 79, in the BOLD study, identified age and cigarette smoking as important determinants of the varying prevalence of COPD among the studied populations.
In this study, 21.4% of cement loaders who smoked had symptoms suggestive of chronic bronchitis compared to 3.2% of the non-smoking cement loaders. Alakija et al8 also found a high prevalence of symptoms of
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chronic bronchitis among Okpella cement factory workers who smoked cigarette.
In addition to its effect on the respiratory system, cigarette smoking increases morbidity and mortality by increasing the risk of several diseases including ischemic heart disease, cerebrovascular disease, peripheral vascular disease, esophageal cancer and bladder cancer
5.1.2 PULMONARY FUNCTION TESTS
In this study the subjects had significantly lower mean peak expiratory flow rates (PEFR), forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) than control.
Decline in lung function parameters following exposure to cement dust has also been described within and outside Nigeria.8, 16, 17, 55 Decline in respiratory indices has likewise been reported following several occupational exposures including silica20, 72, flour 10 and wood dust 12.
Mwaiselage and co-workers55 in Tanzania found an exposure-response relationship between cumulative total dust exposure and reduction in FEV1, FVC and PEFR among Portland cement factory workers.
They observed that a cumulative total dust level of more than 300mg/m3 –
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year versus lower than 100mg/m3 was significantly associated with increased risk of developing airflow limitation (odds ratio= 9.9).
Following the recognition of the negative impact of asbestos exposure on lung function of workers in the cement industry and subsequent efforts to minimize such exposures, exposure to silica remains a potential cause of lung injury in cement workers. There is however scanty literature on the prevalence of silicosis following exposure to cement dust.
Most studies have however documented a reduction in lung volume in cement workers16,17,55, which was similarly noted in this study. Warrell and colleagues81 however investigated the prevalence of silicosis among stone cutters in Kano, Northern Nigeria. Stone cutters are similarly exposed to crystalline silica. Of the 126 stone cutters studied, 49 (38.8%) had radiological evidence of silicosis with 17 having progressive massive fibrosis.
Follow-up investigations on the participants of this study with chest x-rays and possibly more intense studies like the diffusion capacity of carbon monoxide may help elucidate these issues. Unfortunately this study lacks the necessary facilities for such investigations.
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In this study, the calculated mean ventilatory ratio (FEV1/FVC), although lower among cement loaders than controls, was not statistically significant. This is in keeping with findings from previous studies. 55, 72, 73
An interesting finding in this study was that despite the significantly lower forced vital capacity (FVC) among the cement loaders compared to the control group; mean FVC was 6.8% higher among cement loaders than predicted values for non-smoking male Nigerians.72 Mean forced vital capacity value for the control group was 28.1% higher than predicted value for male Nigerians.
Lawrence et al82 in a study among high altitude residents of European ancestry found that residents of La Paz, Bolivia (average altitude of 3,600 m above sea level) had significantly higher FEV1 and FVC than residents of the lowland. This was attributed to the enhanced lung volumes of the La Paz residents.
An enhanced lung volume has been recognised as an adaptive mechanism for persons staying at high altitudes to compensate for the fall in oxygen tension with increasing height.83
Jos, at an altitude of 1,250 m above sea level is one of the highest parts of Nigeria. Populations from which the predictive equations for
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Nigerians were derived were from the lowland dwellers.72,73 The absence of a variable for altitude in the predictive equation for normal lung indices limits the usefulness of these equations among high altitude dwellers, particularly in defining restrictive pattern of lung disease. In this study, the prevalence of restrictive pattern of lung disease was 3.3%. This may be lower than the true prevalence due to the limitation of the predictive equation for normal Nigerian used.
Respiratory function of smoking subjects
In this study, current smokers had significantly lower PEFR than non-smoking subjects. Ukoli et al 84 in Jos also found a significantly lower PEFR among smokers compared to matched non-smokers. FEV1 values in the present study were lower in the smokers compared to the non-smoking subjects but the difference was not statistically significant. Current smokers however had a steeper decline in FEV1% and PEFR with age, than non-smoking equally exposed subjects. In a 7 year prospective study in Norwegian men, fitness and FEV1 declined twice as much in smokers compared to non-smokers during the period of the study.85
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Similarly, mean FEV1/FVC% in the cement loaders was significantly lower among the smoking group (77.03 ±16.66) compared to the non-smoking subjects (83.20 ± 10.18) p< 0.05, with 17.9% of current smokers having an obstructive pattern of lung disease compared to 6.5% found in non-smoking subjects. This finding further supports the role of cigarette smoking in the pathogenesis of COPD. 41, 43, 44
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