Emission Model Limitations and Considerations

This study shows that quarry workers have high prevalence rate of respiratory symptoms when compared with control group. The prevalence of respiratory symptoms in male quarry workers was 70.5%

while that of control was 6.4%. This difference is statistically significant (P<0.001). The prevalence of respiratory symptoms in female was 85%

against 45% observed in control. This is also statistically significant. This result is similar to study published by Lemla et al ⁽⁸⁰⁾ where 65. 3% of quarry workers in Rio de Janerio had one or more respiratory symptoms.

This clearly confirms the injurious nature of silica dust on respiratory health.

As regards specific respiratory symptoms, this study showed a high prevalence rate of specific respiratory symptoms of cough, sneezing, nasal stuffiness, sputum production, breathlessness, chest pain, chest tightness and wheeze in both males and females. This is similar to previous studies ⁽⁸⁰,81, 82, 87, 99).

There is however slight variation among the various studies of the degree of increase of the prevalence of the various respiratory symptoms. In study published by Neaimi et al ⁽⁸⁶⁾, a high percentage of exposed workers reported recurrent cough {30%}, phlegm {25%}, wheeze {8%}, and nasal congestion {27%}. Among the control, the prevalence of symptoms were 10%, 5%, 3%, 5%, 4% respectively. Hilda et al ⁽⁹⁸⁾ in a study on respiratory health among quartz exposed slate workers found a higher prevalence of respiratory symptoms among slate workers than control. They had cough with sputum(38%), breathlessness (28.2%), Nasal stuffiness (31%) as against 17.5%, 11.5% and 18.4% for control respectively. Other study (84, 96,100, and 101) showed that exposed workers had a higher prevalence of respiratory symptoms compared with unexposed workers of similar age and ethnic group.

Ezeonu ⁽¹⁰²⁾ in a study on occupational health hazards among cement industry workers noted a high prevalence of chronic phlegm and wheezing in cement workers than control.

The high prevalence of respiratory symptoms in quarry workers compared to control in this and other studies show that silica in the dust is allergenic and may therefore irritate the respiratory tract leading to cough and other respiratory symptoms ⁽¹⁰³⁾.

The slight variation in the prevalence rates of the specific respiratory symptoms in the various studies may be attributed to the concentration

of silica dust in the various quarry sites and the occupational hygiene variable employed.

5.3 LUNG FUNCTIONS IN QUARRY WORKERS

The mean values of the four lung function tests employed in this study showed that the control subjects had higher mean values for FEV1, FVC and PEFR than the quarry workers. This difference is statistically significant [P< 0.05}. This is in line with previous works on lung functions in quarry workers (1, 7, 71, 81, 100). Neaimi et al ⁽⁸⁶⁾ noted a decrease lung function in workers in cement industry compared to unexposed control.

Similarly, Bahrami et al ⁽¹⁰³⁾ in a study on Iranian factory workers exposed to silica found that decreases in FEV1 , FVC and PERF were associated with increased concentration of respiratory dust in ambient air. Also, Ng et al ⁽⁹⁷⁾ in a study on lung function in silica exposed granite workers found that decreased lung function values were related to silica exposure. The lung function loss he attributed to fibrotic lung disease associated with silicosis, and exposure of total granite dust beyond respirable range.

Yang et al ⁽⁹⁶⁾ found a significantly lower FVC, FEV1, and PEFR in Portland cement workers compared to control. The annual average losses of FVC and FEV¹ he found were 0.0l8L and 0.030L respectively.

In his own study, Hilde et al ⁽⁹⁸⁾ found significantly lower PEFR among quartz exposed slate workers. The spriometric ^results did not show any statistical difference. Akahara ⁽¹⁰⁴⁾ and Oleu ⁽¹⁰⁵⁾ in separate studies on cement workers showed a decrease lung function in cement workers compared to control.

The impairment in lung function noticed in quarry workers is not unexpected as silica in the dust as stated earlier is allergenic and may therefore irritate the respiratory track ⁽¹⁰³⁾ causing inflammation of the lungs. Silica may also form silicotic nodules in the lung parenchyma. All these will impair lung functions. For the mean values of FEV1 / FVC%, this parameter though numerically higher in control subjects than quarry workers is not statistically significant. This is also in agreement with previous studied (80, 81).

Moreover, in this study, the mean lung function indices of quarry workers and control subjects were stratified into age groups. The reason for this is to find out if the younger age groups were spared from this lung function impairment. This study showed significant difference in the mean lung function value, between quarry workers and control subject in various age groups except for FEV, / FVC % which though higher in the control group than in quarry workers in all age groups did not attain statistical significance. FEV1, showed no significant difference between quarry workers and control subjects who are 55yeares and above. This may be because of the small number involved in this age group which might have given spurious values.

The female quarry workers have more lung function impairment than the males in this study.

This is due to the fact that the females are shorter, older, weighted less and have a longer duration of exposure.

Also, female generally have a lower lung function indices than men when anthropometric factors are considered (70,71,72,73).

Study published by femi-pearse and Elebute ⁽⁶⁶⁾ observed this difference in value for men and women. It is suggested that the size and shape of the rib large, muscle size and elasticity of the lungs may be responsible.

5.4 DURATION OF EXPOSURE AND LUNG FUNCTION

In this study, the duration of exposure was measured by the duration of employment.

The male and female quarry workers were divided into two groups: those that have been employed for up to 10years and below and those above 10years. The FEV1, FVC, PEFR showed decreased mean value in both male and female quarry workers with increased duration of exposure.

However FEV1 and FVC in female quarry workers were not statistically significant {P> 0.05}. In the work done by Lemle et al ⁽⁸⁰⁾, there was no statistically significant influence of higher dust exposure on lung functions. Bahrawn et al ⁽¹⁰³⁾ showed no significant difference in lung function in those with less than 20 years duration of exposure. In another study done by Urom et al ⁽⁸¹⁾, the duration of employment of male subjects in granite dust generating industries correlated negatively with lung functions indices. FEV1, FVC and PEFR showed a significant negative correlation {P< 0.01} with duration of service in males, while FEV1 /FVC% versus duration of employment was not significant. Among the females, only PEFR showed a significant negative correlation {P<0.01} with duration of employment.

Alakija et al ⁽¹⁰⁶⁾ in a study on ventilatory function of workers at Okpala cement factory in Nigeria noted that FEV1, FVC, PEFR decreased with duration of employment.

The worsening of lung function with duration of exposure is indicative of the importance of the duration of exposure as one of the major predisposing factors in the etiology of lung function impairment among silica dust exposed male and female workers studied. Other studies done by Humerfelt et al ⁽⁷³⁾ and Forastier et al ⁽⁷⁸⁾ showed an inverse relationship between duration of silica exposure and lung function.

Hertzberg et al ⁽⁷⁹⁾ calculated that there would be a decrease of 104.4ml for FEV1, 137.7ml for FVC and 1.49% for FEV1 / FVC% after 40 years exposure to silica at occupational safety and health association {OSHA}

exposure level of 0.1gm / m^3.

5.5 COMPARISM BETWEEN OBSERVED VALUES FOR