Although cement is the most widely used essential construction material, there are many hazardous environmental pollutants such as particulate matter, various oxides, and heavy metals, which are released in its production process. Most of the Portland cement plants in Korea have been in operation since the 1970s by the national policy to accelerate industrialization. The residents who have lived near the cement plants have always been complaining because of the inevitable dust created at plants when they were carrying limestone from the mine to the plant. However, because the protest movements from the residents have continued, epidemiological surveys have been conducted by the Ministry of Environment (National Institute of Environmental Research) since 2007 [1]. This survey was carried out in 2013, as one of a series of epidemiological investigations about the relationship between environmental particulates derived from a cement plant and pulmonary functions of the residents in Jeollanam-do Jangseong-gun.

Portland cement is composed of a mixture of materials. It is mostly made of calcium oxide (CaO, 62-67%) and silica glass (SiO₂,17-25%) with a lesser amount of aluminum trioxide(Al₂O₃ 3-8%), iron oxide(Fe₂O₃ 0-5%), magnesium oxide (MgO, 1-2%), and other heavy metals such as hexavalent chromium (Cr⁶⁺), nickel, etc. [2,3]. The cement manufacturing is done in three simplified steps. First, the raw material and fuel supply preparation (mining and/or outsourcing, crushing, storage, and preblending), second the pyroprocessing to make clinker, grinding of clinker and gypsum in the finishing mill to make cement, and finally the storage, packaging, and loading for the finished products [2]. Cement is made from the intermediate product of finely ground clinker formed through a high-temperature burning of limestone and other materials in a kiln (pyroprocessing). The emissions created by the combustion such as particulates, carbon dioxide (CO₂), nitrogen oxides, sulfur oxides, and heavy metals are discharged in the process [4]. There is additional dust generated from the mining and transportation. Various types of particulate emissions and dust are continually created by the comminution circuits when crushing and grinding the raw materials and clinker, from the pyroprocessing or kiln line, intermittently and diffusely from quarrying activities as well as through limestone transportation.

In general, fugitive emissions from coarse particulates (particularly of particle diameters >10 μm) are considered to be the reason for repeated protests by the residents near the cement plant. This is believed to be due to the visible accumulation rather than the health hazards. However, fine particulates, <10 μm (PM₁₀) and <2.5 μm (PM_2.5), can cause health problems, if one experiences prolonged exposure for 30 to 40 years, because of their respirable nature, and because they may contain potentially harmful concentrates of toxic metals and compounds. Cement dust can cause lung function impairment, pneumoconiosis [5], carcinoma of the lungs and larynx [6,7], and may cause inflammatory changes in the skin, and often leads to skin diseases or autoimmune diseases [8-10].

Many studies for cement factory workers on the adverse respiratory effects of cement dust exposure have been focusing on pulmonary function and symptoms, or their relationships [11-17]. But, few have researched the health effects of cement dust and asbestos [18,19], or heavy metals [20,21] derived from cement plants, thus a study on the relevance of dust and lung diseases of residents who live around these plants was rare. It is difficult to explain the relationship between environmental cement dust exposure and occurrence of a pulmonary disease due to the variety of other factors involved such as age, sex and smoking. Therefore, we are going to report about the difference in ventilation impairment between the more exposed group of residents and less exposed group of residents living around the cement plants or limestone mines in the region using the results of a health survey.

The residents who live around the cement plant have always complained about suffering in their daily lives because of dust originating from the plant. These complaints included respiratory symptoms such as chronic cough or phlegm as well as itching sensations from the body surface and prickly feeling eyes. While the residents refer to the irritant as ‘cement dust' it should be noted that ‘particulate' is the more scientific term. A particulate is anything solid or liquid suspended in the air [28]. It not only includes primary particles coming from limestone powder or directly out of the exhaust from a kiln during preprocessing, but also can include secondary particles, such as sulfates and nitrates, which are formed during the condensation of vaporized materials or from the by-products of the oxidation of gases in the atmosphere. Among these particles, particulates (<10 μm, PM₁₀) and fine particulates (<2.5 μm, PM_2.5) that were derived intermittently and diffusely from raw materials and other manufactured products appear to be more of a health hazard because of their respirable nature and because they may contain potentially harmful concentrations of toxic metals and compounds [4,29]. Various gases are generated directly from clinker manufacturing, according to a recent study on the health effects of fine particulates and how they affect mortality [30].

In order to determine the health effects of particulates, pulmonary function tests have been used for quite a long time. Ventilation impairments in cement plant workers is already well documented [3,11-15]. According to relatively consistent reports, the FVC and FEV1 of such workers is significantly decreased when compared to their matched control groups. These were also meaningfully decreased based on the length employment [3]. However, the foundation of these studies is different than the situation affecting the health of the residents. These studies reported that the concentration of respirable dust in the workplace for 8 h/day shift ranged from 3.7 mg/m³ (kilns) to 23 mg/m³ (ore crushing area) [8]. It was the highest for the crusher at 27.49 mg/m³, 16.90 mg/m³ around the packing areas and 1.55 mg/m³ in administration offices throughout the production process [14,15,17].

However, it seems that there is a significant difference found in health effects between the studies examining ambient pollution and in studies about ventilation impairment among cement plant laborers. This is likely to be due to the concentration of dust within the plant being much higher than the outside of the plant. How is it possible to confirm that the health effects are the result of prolonged exposure to particulate arising from a cement plant? It's a question of whether the respiratory health effects of residents with ventilation impairments found using PFT can be proved to be due to the low concentration long-term exposure to particulates from the cement plant. This study used the data of particulate concentrations collected in a total of 21 days in June, August and October. Data was collected every seven days. The mean PM₁₀ concentration in the atmosphere was 45.5 μg/m³ (95% CI 37.8 ~ 53.3) beside the cement plant, higher than 38.5 μg/m³ (95% CI 32.3 ~ 44.7) in a 5 km away point from the cement plant. Also, the mean PM_2.5 concentration was 25.5 μg/m³ (95% CI 18.7 ~ 32.3), higher than 19.3 μg/m³ (95% CI 14.1 ~ 24.6), respectively (Figure 2). Of course, this does not measure the level of exposure of the past and may only reflects the current situation. However, it can be assumed that residents who live close to the cement plant were exposed to higher levels of particulate before dust collection facilities had been implemented in mid-1980s. When the plant location is used as the central location on the map (Figure 3), the LEG lived more than 5 km away in the northwest and the MEG lived within 1 km in the southwest. The wind direction is a northwester during the three seasons in the fall, winter and spring, and is a southwester during summer. The LEG habitats were in an independent wind direction while the MEG was right on the side of the plant, where the northwestern wind blows during three seasons, having the plant in the southwest of the area. It was confirmed that the particulate concentration in cement plant area (MEG region) was higher than that in the control area (LEG region) as well as continuously being exposed to more particulates due to the wind direction. Even so, the concentration around cement plant area would still be lower than the inside of the cement plant.

This study had obvious limitations that included the very small number of surveyed population as well as being a cross-sectional study. Moreover, the pulmonary function test performs a fundamental role in clinical setting, but its result varies with sex, age, height, and ethnicity. Furthermore, ventilation impairment degrees are greatly affected by smoking, occupational exposure (including organic or inorganic dusts), chemical agents and fumes [26], and the use of firewood as cooking or heating fuel in poorly ventilated kitchens. The smoking rates in Korean men were close to 80% in the 1980 ~ 90s [31]. Firewood has been used for a long time including recently as both a cooking and heating fuel source in the rural regions of Korea. Also, the target population in this study was residents who lived near the cement plant, and because many of them are current farmers or had farmed, they were always exposed to dust in the soil and to chemical substances like agriculture chemicals. In spite of these limitations, we were trying to assess pulmonary function status of the MEG who lived near the cement plant compared with the LEG who was living under similar economic living conditions and in sociocultural environments, for example, the use of firewood as cooking or heating fuel, similar types of occupations and smoking rates.

Everyone who was over the age of 40 living in these areas was to receive the pulmonary function test and we also encouraged them to participate actively. As a result, about 50% of the expected target population was examined. In validation checks on pre and post bronchodilator test, 26.2% of the participants were eliminated because the test reproducibility did not meet criteria [25] when matched with three acceptable curves or due to early termination of expiration. Therefore, approximately 40% of the target population was analyzed. The proportion of valid PTF readings in the MEG was 70.2%, but it was 84.2% in the LEG. Despite the PFT tests being carried out under the same conditions in a stable hospital room, there was difference in invalid test proportions between the two groups (Table 1). Unfortunately, the authors also could not find out why there was a significant difference in valid PFT proportions between the two groups. However, if the proportion of valid PFT proportions between the two groups had been similar, then it would mean that there would be a higher obstructive and restrictive ventilation impairment in the MEG while it would be lower in the LEG.

The classification of ventilation impairment is based on a modified GOLD criterion for COPD definition [26,32]. Regardless of the presence of symptoms like chronic coughing or sputum, and dyspnea, the obstructive type was considered to be FEV1/FVC <0.7 in post-bronchodilator readings. If the FVC% predicted was less than 80%, it was considered the restrictive type, even if the FEV1/FVC was above of 0.7. Although the PFT tests showed about 15% difference in invalid test proportions between the two groups, it put us on the spot to compare the two groups for ventilation impairment. Whatever results came from the analysis, the most characteristic finding was a 10% difference in the restrictive type between two groups. There was less visible difference in obstructive type, 9.7% in the MEG and 8.5% in the LEG (Table 3). The relationship between particulates and COPD or increasing mortality rate in respiratory disease is well known [29,33]. The prevalence of COPD was 14.0% in those with the post-bronchodilator test, whereas the prevalence was 20.9% in those with a pre-bronchodilator test during 2007-2010, the National Health and Nutrition Examination Survey of Americans aged 40-79 years [34]. Similarly, the prevalence of COPD in post-bronchodilator tests ranged from 23.4% to 11.6% in 10,360 adults aged 40 years and older in 14 countries in North America, Europe, Africa and Asia who participated in the Burden of Obstructive Lung Disease study [35]. The prevalence rates in China and the Philippines, which belong to Asia like Korea, were the lowest at 11.6% and 12.7%, respectively. When compared with such reports, a prevalence of obstructive type of ventilation impairment in this study was presumed to be similar.

By the way, how can we say that restrictive ventilation impairment in the MEG is much higher than that of LEG? In the regression analysis, the OR of all ventilation impairment was higher in persons of older age and who are men. Smoking is known to be the biggest cause of COPD (chronic obstructive pulmonary disease) [26,36]. We have not separated the number of ex and current smokers in Table 2, because there was no significant difference in both groups. In men in MEG, 37.2% were ex-smokers and 39.5% were current smokers, whereas in men in LEG, 48.9% and 28.9%, respectively. In women, the percentages were very low. In women of MEG, 0.5% were ex-smokers and 2.6% were current smokers, whereas in LEG, 3.6% were ex-smokers and 3.6% were current smokers. Therefore, the reason the obstructive type OR of men against women in Table 4 is as high as 4.16 (95% CI 1.35 ~ 12.83) is because most of the ex and current smokers are men. In fact, the MEG and LEG are similar people living in the same rural area with similar economic and socio-cultural settings. The aim of this study is to determine whether the particles from the cement plant have an effect on ventilation impairment, so we did not need to subdivide the smoking history into more categories.

Restrictive impairment was unrelated to smoking history, while smoking history was a main risk factor of for obstructive impairment. Restrictive impairment may occur because of increased lung recoil caused by pulmonary fibrotic change or weakened respiratory systems due to old age, or both [37]. Particulates were in the lung parenchyma, blood vessel walls, airway, lymphoid follicles and alveolar macrophages [33]. Particulates can be sensed by the airway's epithelial cells, activate macrophages, dendritic cells and innate immune cells. They can then initiate responses in various populations of specific immune cells such as T helper cells, T cytotoxic cells and B cells. Initiation of inflammatory immune responses, activation of immune cells and release of many cytokines, chemokines and other inflammatory molecules, have variable pathologic effects like fibrotic change [38]. There is a limit which is that we could not confirm the total lung capacity (TLC) for restrictive type impairment by body plethysmography or DLco (diffusion capacity of lung for carbon monoxide) [39], in the few residents without a history of occupational dust-related who were diagnosed with pneumoconiosis.

The strength of this study is that at present a particulate (PM 10 and PM 2.5) concentration was measured to evaluate a level of dust exposure related a cement plant; the concentration of the particulate was higher in the area around the cement plant (MEG) than the other area (LEG). And we have compared the health effects by chronic particulate exposure according to GOLD's guideline (post-bronchodilator spirometry) [40]. The PFT was carried out in order to obtain a reliable value by the same examiner in comfortable and stable environment in the hospital. However, we need to take the limitations into account when interpreting the result. This is a cross-sectional study with not enough number of residents to find a significant difference in the ventilation impairment, especially in the obstructive type between the two groups. We have reviewed other data related to this epidemiologic survey such as population change, the lung cancer incidence and mortality due to respiratory diseases, 70% of the residents who were living in the area when the cement plant was first built (1973) have moved to larger cities (as of 2013). And there is also a possibility that the residents whose health had been compromised have already died of lower respiratory tract disorder or lung cancer. The residents who were too old to go through PFT or have been diagnosed with contraindicated diseases have been excluded from the study. In addition, there were significantly lower valid PFT proportions in MEG (70.2%) compared to those of LEG (84.3%). Therefore, it is possible that the health effects of chronic particulate exposure has are actually underestimated.

Although this study was a limited cross-section study with a small number of subjects, the ventilation impairment rate, particularly in restrictive not obstructive type, is higher in the MEG than the LEG even with a lower valid PFT proportion in MEG. There might be a possibility that it is due to long-term exposure to particulate dust generated from the cement plant.