In Iran, expansion of iron ore mining is underway to meet the needs of a flourishing construction industry driven by the growing population and escalation of urbanization ensuing upturn in a number of quarry workers [1]. The Iranian government is encouraging mineral exploration to discover future deposits and is supporting plans towards the expansion of existing iron-ore mines [2]. Hence, there is a need for an increased workforce in mining, however, this occupation has inherent safety and health risks. Extraction of iron ore products during mining involves several processes that can produce dust crushing, screening, loading and transport of large quantities of rock. Therefore, mining environments expose workers over time to high concentrations of inhalable mineral dust that can potentially jeopardize their health [3].

Since the recent increase in mining, current estimates are unavailable for the number of mine workers in Iran. However, past estimates claim that in Iran, more than 8000 workers are exposed to mineral and silica dust [1]; while in the United States, 1.7 million are exposed to crystalline silica [4, 5]. The American Conference of Governmental Industrial Hygienists (ACGIH) and the Occupational Health Committee of Iran have both declared 10 mg/m³ and 3 mg/m³ as threshold limits for an 8-hour workday exposure to total dust and respirable dust, respectively [6]. However, growing concern for the occupational health of workers in the United States is causing a disputing among these existing levels for more conservative guidelines. In this study conducted, Naghizadeh et al. measured the exposure range of total dust and crystalline silica levels in iron ore open-pit mines of eastern Iran as 8.28-800.00 mg/m³ and 0.012-26.11 mg/m³ respectively; whereas the respirable dust and silica were reportedly between 5.26-66.14 mg/m³ and 0.01-1.48 mg/m³, respectively [7].

Constituents of dust generated by iron ore mining in Iran can vary based on the deposit. Currently, no cohesive literature is available encompassing asbestos contamination in mineral quarries of Iran, nevertheless, the presence of sulfur along with iron in the rock has been reported [8-10]. Various mines contain varied levels of silica-dust as well [11-13], instigating occupational complications like silicosis, bronchitis, renal and pulmonary lesions, oxidative stress and DNA damage [11, 13, 14]. Exposure may even cause tuberculosis, in the absence of silicosis [15, 16]. Such health hazards are often proportionate with the concentration of silica dust, percentage of crystalline silica in the dust, and duration of exposure (acute versus chronic). There are substantial public health concerns shared by the developing and developed nations alike in regard to mine workers' health [17]. The literature validates aggravating respiratory symptoms and attenuating pulmonary functions among mineral-dust exposed workers [18, 19]; including data pertaining to workers exposed to cement dust [20], and results from analyzing mine personnel with long-term exposure to mineral dust [11, 21]. Developing countries, especially Iran, lack formal data about the subject in question and safety of workers [13]. Mineral miners in Iran are non-compliant and fail to follow minimal personal protective measures including using their Personal Protective Equipment (PPE) There are grim and obstinate inadequacies in awareness and education regarding health and safety measures [22-24].

There remains a paucity of data about the respiratory health effects from exposure to iron ore dust generated by mining. The aim of this novel study was to examine respiratory abnormalities and impairments in lung functioning associated with exposure to dust from iron ore mining in Iran. The following research question was posed: “Is there a significant association between exposure to iron-ore dust and increased self-reported respiratory symptoms and decreases in pulmonary functioning?"

Out of 267 participants, 174 were mineral-dust-exposed. Table 1 illustrates demographic characteristics. Independent samples t-test did not reveal any significant difference between independent variables of the two groups (P>0.05). Mean exposure levels of inhalable and respirable dust among the exposed group were 15.09±2.34 and 3.45±2.57 mg/m³, respectively. Table 2 highlights that all PFT parameters (FVC, FEV1, FEV1/FVC and PEF) were significantly lower among exposed than others (P<0.05).

Table 3 depicts that the frequency of respiratory symptoms was higher among exposed than non-exposed respondents: cough (20.7% vs. 10.8%), phlegm (11.5% vs. 9.7%), wheezing (11.5% vs. 3.2%) and shortness of breath (21.3% vs. 10.8%), P-values for cough, wheezing and dyspnea being 0.041, 0.032 and 0.035 respectively.

Associations of independent variables (age, BMI, smoking) and length of exposure to respirable dust with various pulmonary parameters were analyzed by multiple linear regression analysis (Table 4). Findings after adjusting for vital confounders were as follows; a significant decrease in FVC(p<0.001), FEV1(p-0.002) and PEF(p-0.012) with an increase in dust exposure, with age and working years, a reduction in FVC(p-0.027 & 0.002 respectively) and FEV1/FVC (p<0.001 & 0.001 respectively), while cigarette consumption attenuated FVC(p-0.049), FEV1(p0.049) and PEF(p0.047). BMI did not cast any significant impact on any of the pulmonary parameters.

Table 5 demonstrates associations between exposure to respirable dust and prevalence of respiratory symptoms using Logistic linear regression analysis. Age, BMI, work experience, smoking habits, and exposure to respirable-dust unmasked a substantial connection between respirable-dust exposure and respiratory symptoms (cough, wheezing and shortness of breath). Cigarette consumption aggravated cough (p<0.001) and phlegm (p<0.001), while wheezing and dyspnea exacerbated with age (p-0.016) and respiratory dust, respectively (p-0.049).

Mineral dust is a pervasive chemical hazard encountered in mines, which may cultivate respiratory problems after certain levels of exposure. Air-monitoring is imperative in industrial health to appraise workplace contaminants, apply and comply with control-measures and preclude enhanced levels of occupational exposure. In this study, the exposed mine workers and the unexposed reference workers were evaluated for differences in the prevalence of respiratory symptoms and impairments in lung functioning. Results of air testing in the exposed miner’s environments revealed that exposure rate of inhalable and respirable dust was higher than the Occupational Exposure Limits (OEL) recommended by the Technical Committee of Health Professionals of Iran and occupational exposure standard of the ACGIH [6].

Spirometry is an important, easily accessible and cost-effective para-clinical instrument, which detects pulmonary defects; therefore, it is extensively used to screen industrial lung diseases. This study inferred that pulmonary functions were lower among the exposed mine workers than their unexposed reference counterparts group. Literature validates that occupational-dust exposure impedes lung functions and capacities [29-32], as pronounced by Mahmood et al. and Zeleke et al. about people exposed to silica-containing dust [33, 34], and Isara et al. regarding stoneworkers [19]. This data also publicized that FVC, FEV1 and PEF were significantly reduced among exposed than counter-parts, while the least difference observed in FEV1/FVC. Similar results have been concurred by other authors [33]. FEV1 reduction indicates obstructive impairment, which may also depict dust-induced mechanical stimulation [35]. Contrarily, FVC alone cannot justify a change in lung functions as it may be slightly impaired in healthy subjects or in patients with the minimal obstructive pulmonary disease [36]. According to Gomes et al. among casting workers, FEV1, FEV1/FVC, FEF25-75 and PEF were less while FVC and Vital Capacity (VC) did not condense significantly in exposed than others [37].

As there was no significant difference between this study’s participant’s demographic variables, therefore, the reduction in FVC, FEV1 and PEF among dust-exposed mine workers could be attributed to occupational dust workplace, which was further diminished among dust-exposed cigarette smokers. Hochgatterer and et al. concurred that duration of dust-exposure and cigarette smoking cast cumulative effects to deteriorate lung functions [12].

Cigarette smoking imparts plummeting and perpetual hazards on the respiratory system, which in combination with dust-inhalation further casts resonating health perils on victims [38]; especially coal-mine workers [39]. Similar inferences were documented from Iran [40], Tanzania [41] and Ethiopia [42]; although researchers from Brazil defied such subtext [43]. Kuempel et al. reported that emphysema was more severe amid coal miners than non-miners among ever and never smokers; while cumulative exposure to respirable coal-mine dust was a considerable predictor of emphysema severity once accounted for cigarette smoking, age at death, and race [44].

Symptoms like cough, wheezing and dyspnea significantly differed among the two study groups. This finding is consistent with the results of Kakooei et al. [20] and Isara et al. [21] encircling cement and quarry workers respectively, which could be attributed to non-usage PPE. In the study of Mamuya et al., development workers who had more cumulative exposure to coal dust, had a significantly higher prevalence of acute and chronic respiratory symptoms than other workers [41]. In the study by Hamatui et al., exposure to respirable charcoal dust levels was higher than the occupational recommended limit in most units and participants had exposure-related adverse respiratory symptoms such as cough, phlegm and shortness of breath [45]. Ayaaba et al,. investigated respiratory disorders among gold miners in Ghana, in which cough was the most observed respiratory symptom [46]. The varying severity of respiratory symptoms in different studies can depend on the type of dust and the amount of exposure. In addition, the use of respiratory PPE along with higher educational levels was a protective factor for silicosis in mine workers [47].

This research recognizes several limitations. Although subject groups were consistent in terms of age, weight, and height, nevertheless, gender-bias and interview bias could not be ruled out. Added investigations like blood tests, chest X-ray and other radiological screenings could yield superior outcomes. None of the respondents provided detailed information about the proper usage of PPE; therefore, its effects on health outcomes of two groups could not be compared. Nonetheless, this study was the first survey of its type from a pertinent area and industry and may provide a way-forward for similar local, national or international surveys. It presented novel first-hand, genuine and useful data; and vetted the posed research question. These findings may lead to the formation of basic strategies to attenuate industrial dust-levels and promote protective measures among mine workers. Smoking should be more vividly discouraged among those already at risk to develop pulmonary disorders due to occupational dust exposure in mining environments.

The hazardous effects of mineral dust on exposed personnel should never be overlooked. Regular assessments of environmental dust in every industry, passable ventilation and adherence to protective measures including availability and use of high-quality PPE must be reinforced at all echelons. Health promotion, occupational exposure assessments and smoking cessation programs are strongly recommended for mine workers.