Exposure to Airborne Contaminants and Respiratory Health Among Lithium Mine Workers in Western Australia

Abstract

Background: Lithium is an essential commodity; however, its mining and processing can expose miners to airborne contaminants such as inhalable dust, respirable dust and respirable crystalline silica. These exposures may adversely affect respiratory health. To protect the health of miners, exposure assessment and control activities are required, followed by respiratory health monitoring to assess the effect of exposure on respiratory health. This study aimed to investigate the relationship between workgroup exposure to airborne contaminants and respiratory health. To determine group exposure levels, exposure data was collected at the group level, which limits individual-level inference, followed by health monitoring. Methods: Industry health monitoring data were collected from miners in three surface lithium mines in Western Australia for the period between October 2023 and October 2024. Miners from Management Administration & Technical, Crusher/Dry/Wet Plant, and Laboratory Operations participated in a pulmonary function test, completed a health and exposure questionnaire and underwent a low dose high-resolution computed tomography. Multivariable linear and logistic regression models were fitted to identify factors associated with lung function and respiratory symptoms. Results: Older age, smoking and pre-existing respiratory conditions were correlated with poor respiratory airflow. The odds of having a respiratory obstruction or restriction were significantly higher by 3.942 and 2.165 times respectively, for miners who were 40 years old or above, and those who had existing diagnosed respiratory medical conditions. The risk of coughing among current smokers was more than four times higher compared to non-smokers. In addition, working in Crushing and Processing was significantly associated with the risk of experiencing respiratory symptoms compared to working in Management Administration & Technical and Laboratory Operations. Conclusions: The study demonstrated that respiratory health was influenced by non-work-related risk factors. Based on these results, it is recommended that health promotion programs be developed and implemented to empower miners to cease smoking and to manage non-work-related respiratory conditions.

1. Introduction

Lithium is a crucial commodity used to produce batteries for electric vehicles, consumer electronics, applications for energy storage, and medical purposes. In the healthcare industry, it is used for treating acute and chronic depression [1], bipolar disorders and associated mood disorders [2]. In addition to its therapeutic benefits, lithium-containing products and materials are essential in industrial products and processes including glass and glass ceramics, high-end lithium greases, air conditioning, the production of synthetic rubber, rubber vulcanisation, aluminium electrolysis, and brazing fluxes [3].

Electric Vehicles (EVs), which are powered by a compact rechargeable battery pack consisting of thousands of lithium-ion batteries (LIBs) [4], make lithium a critical commodity for EV production.

Consequently, a rapid surge in the demand for lithium is expected in the coming years for powering EVs [5,6], with a predicted annual global growth of lithium batteries at a compounding rate of approximately 30% per year [7].

Lithium mining follows conventional open-pit mining methods described in more detail in a previous study [8]. Drill and blast techniques are used to fragment the ore and waste material, followed by hydraulic excavators to load the haulage trucks, which transport the ore to the Run of Mine (ROM) for crushing and processing. The crushed ore is fed to parallel ball mills to produce a ground product, where milling of the ore is required for metallurgical processing. Following processing, the final product is referred to as the spodumene concentrate, with a by-product known as tantalum concentrate.

Whilst lithium is critical for the storage of electricity, its mining and processing are associated with exposure to hazards such as dust (inhalable and respirable fractions), respirable crystalline silica (RCS), noise, heat stress, solar ultraviolet, whole body and hand-arm vibration and manual handling [9]. The potential harm from these exposures is documented in our previous paper [10].

Dust is a prevalent exposure in the workplace in most industries, such as mining, foundries, chemical and food industries, stone working and woodwork [11]. When inhaled, the aerodynamic diameter of the dust particles determines the various regions of the respiratory tract they can reach [11]. The inhalation of particulates triggers the lungs in the respiratory system to react in different ways, which include airway irritation, asthma exacerbation, inflammatory reactions and fibrosis [12]. While short-term exposure to dust causes immediate and severe adverse respiratory impacts, chronic and persistent exposure can cause permanent respiratory diseases such as chronic obstructive pulmonary disease (COPD) [12]. Consequently, it is indisputable that exposure to dust reduces pulmonary function [12]. The exposure of lithium miners to airborne contaminants is documented in detail in previous papers [8,10].

Inhalable dust (INH) refers to dust with a particle size of less than 100 μm, which can be breathed into the nose or mouth and is usually trapped in the upper respiratory tract [13]. Respirable dust (RES) has a particle size of less than 10 microns [14]. It refers to very fine dust capable of reaching the secondary bronchioles and alveolar regions of the lungs through inhalation exposure [15]. The accumulation of RES in the secondary bronchioles and alveolar region over time may cause respiratory diseases such as pneumoconiosis, COPD, and interstitial pulmonary fibrosis [15]. RCS on the other hand, is a fibrogenic particulate material found in nature, exposure to which can cause interstitial pulmonary fibrosis known as silicosis [16]. RCS particles are respirable when they are less than 5 microns in diameter and when inhaled, are capable of reaching the distal airways and alveoli and causing scarring of the lungs [17,18]. Exposure to RCS has also been associated with COPD, lung cancer, airway obstruction and renal disease [19].

COPD is a lung disease characterised by a reduction in airflow related to increased resistance caused by the narrowing of the airway [20]. This occurrence of persistent airflow limitation is a defining attribute of COPD [21]. Chronic respiratory diseases are part of the leading causes of global mortality and morbidity, with COPD being one of the most prevalent. It ranked eighth on the 2015 disability-adjusted life years (DALYs) among the top 20 conditions causing disability globally [22]. In the United States, it is the third leading cause of death, with its incidence and mortality being higher in women than men in recent years [12].

Silicosis is a preventable respiratory disease caused by exposure to RCS, and thousands of workers in various industries are at risk of developing this condition due to exposure to RCS [23]. Crystalline silica particles are known to be more toxic than amorphous silica, and the most toxic form of crystalline silica is alpha quartz. The toxicity of the silica particles is determined by physiochemical properties such as size morphology, polymorphism, porosity and surface [17].

When silica is inhaled, its recognition and internalisation by the alveolar macrophages in the lungs constitute the first step in initiating lung inflammation, which is regulated by macrophage scavenger receptions (SRs) [17]. In a recent study, SR-B1-mediated recognition of silica was found to be associated with caspase-1-mediated inflammatory response in mouse macrophages and human peripheral blood monocytes [17]. Toll-like receptors (TLRs) have also been identified as critical mediators of pulmonary inflammation and fibrosis, with evidence indicating that the inhalation of silica particles activates TLR4 and receptor activator of nuclear factor kappa-B ligand (RANKL). This signals pathways in lung macrophages, which induces lung inflammation and osteoclasts in the lungs and bones, with evidence suggesting that silica-induced lung inflammation may disrupt the functions of extrapulmonary organs in rats with long-term exposure to silica [17].

Over 500,000 Australians are exposed to RCS in the workplace [24] and there has been a recent surge in silicosis cases in Australia, consequent to the growth in the engineered stone industry [23]. Currently, there is no published literature on occupational exposures to RCS and silicosis cases in lithium mining. The industries currently known for occupational exposure to RCS include manufactured engineered stone, stone masons, coal mining, denim blasting, dental technicians and other various trades [23]. In response to the exposures to RCS in the engineered stone industry, Commonwealth, State and Territory Workplace Relations and Work Health and Safety (WHS) Ministers met on 13 December 2023 and unanimously agreed to prohibit the use, supply and manufacture of engineered stone commencing 1 July 2024 [25].

This paper aimed to (1) examine the difference in workgroup exposures to airborne contaminants (INH, RES and RCS) during the study period, and (2) investigate the relationship between workgroup exposure to airborne contaminants and respiratory health among lithium miners in Western Australia (WA). The study’s findings will offer valuable insights and drive advancements in controlling airborne contaminant exposure in the workplace while improving risk management strategies to protect the respiratory health of lithium miners.

2. Materials and Methods

2.1. Settings

This study used industry occupational health monitoring data from three lithium mines collected for the period between October 2023 and October 2024. The three lithium mines, where the study was conducted, are located in different geographical areas in WA. Although Mine A and Mine C are located in the Southern region and Mine B is located in the Northern region of WA, they are similar in relation to mining and processing operations. The process of lithium mining and the exposure assessment to airborne contaminants (including INH, RES, RCS and radiation) for the three lithium mines are documented in our previous papers [8,10].

2.2. Study Population

It is a requirement of the WA Work Health and Safety (Mines) Regulations 2022 that miners with exposures to RCS above the Exposure Standard (ES) undertake health monitoring [26]. Lithium miners with such RCS exposures represent the study population. Miners with similar roles, activities, and work areas were grouped into eleven workgroups including Management Administration & Technical (MAT), Cleaning and Utilities Staff (CUS), Blast Crew (BC), Geologists & Surveyor (GS), Drill Operators (DO), Mine Truck Operators (MTO), Earthmoving Equipment Operators (EMO), Crusher/Dry/Wet Plant Personnel (CDWPP), Laboratory Operations Personnel (LOP), Maintenance–Workshop & Infrastructure (MWI) and Workshop Boilermakers (WB). The volunteers for this study included males and females within the age range of 18–65 years. No miners were excluded from the exposure monitoring program, but only miners in three workgroups, namely, MAT, CDWPP, and LOP were selected for the health monitoring program (

Table 1. Workgroups for health monitoring [8].

Workgroup	Occupations in Workgroup	Activities
MAT	Manager Mining Engineer Metallurgist Site Administrator Health & Safety Advisor Environment Advisor Occupational Hygienist Compliance Trainer Emergency Services Officer Medic Maintenance planner Facilities Technician Service Personnel Warehouse personnel	Safe and efficient operation of surface and process plant operations. Ensuring compliance with mining regulations. Overseeing scheduling, planning and budgeting. Planning, design and overseeing mining operations. Processing grade control. Management of health and safety, and environment. Emergency preparedness and response. Training and compliance tracking. Medical treatment. Maintenance planning. Facilities maintenance and management. Management of warehouse.
CDWPP	Fitter Electrician Process operator Boilermaker Mobile machine operator Maintenance personnel Control room operator Supervisor	Monitoring and adjusting the day-to-day operation of the plant. Undertaking inspections of the plant and carrying out maintenance. Clearing blockages from the crushing circuit. Conducting continuous monitoring of conveyors. Completing daily shift log. Completing general housekeeping duties.
LOP	Laboratory Technician Laboratory supervisor	Preparing samples. Weighing samples in balance room. Operating jaw crusher, pulverisers, shakers and riffle splitters. Sampling, reagent preparation and analysis. Quality control of data and reporting.

). MAT and CDWPP were selected for health monitoring due to their exposure to RCS above the ES, as reported in our previous study [8]. The LOP miners were selected for health monitoring due to their proximity to crushing plants.

The available dataset used in this study consisted of health monitoring data among the three workgroups of lithium miners who were involved in surface mining activities (categorised into three workgroups) and group average exposure concentrations of INH, RES and RCS for the study period. The study subjects provided their written informed consent to participate which included personal monitoring for the exposures to the three airborne contaminants and health monitoring.

2.3. Exposure Assessment

Workplace group level exposure assessment was undertaken for INH, RES and RCS and findings were reported in our previous papers [8,10]. Exposure assessment was not undertaken at the individual level, and this is acknowledged as a limitation. The exposures were compared to the national Australian ES for each airborne contaminant. The Time Weighted Average (TWA) ES for INH is 10 mg/m³ [26]. The ES was adjusted to 7.1 mg/m³ for work shifts and rosters outside of the 8-h working shift for 40 h a week, using the formula in the legislation [26]. The TWA ES for RES and RCS are 3 mg/m³ and 0.05 mg/m³ [26]. These were also adjusted to 2.1 mg/m³ and 0.035 mg/m³ respectively, for work shifts and rosters outside of the 8-h working shift for 40 h a week, using the formula in the legislation [26].

In the United States, the Occupational Safety and Health Administration (OSHA) stipulates Permissible Exposure Limits of 15 mg/m³ for INH (Particulates Not Otherwise Regulated, Total Dust), and 5 mg/m³ for RES (Particulates Not Otherwise Regulated, Respirable Fraction) [27]. In comparison, the exposure standards for INH and RES in Australia are significantly lower than the permissible exposure limits in the United States.

An ES of 0.05 mg/m³ for RCS was recommended by the United States National Institute of Occupational Safety and Health (NIOSH) in 1974, while the American Conference of Governmental Industrial Hygienists (ACGIH) adopted a threshold limit value (TLV) of 0.025 mg/m³ in 2006 [8]. In Alberta Canada, an ES of 0.025 mg/m³ was adopted in 2009 for RCS [8]. The current ES for RCS (0.05 mg/m³) in Australia is twice the ES recommended by the ACGIH and adopted in Alberta.

The exposure data were provided in a collective and deidentified format for analyses, and the group arithmetic mean was representative of the individual exposures of the workgroup members. Where the exposures of the workgroup were at least 50% of the ES, health monitoring was undertaken for all members of each workgroup.

Results presented in our previous papers on lithium mining [8,10] indicated that the exposures to RCS for MAT (concentration) and CDWPP (concentration) were above the ES (as indicated by the AM), while the mean concentrations of RES were below the ES for all the workgroups. All mean concentrations of INH were also below the ES. During the health monitoring, undertaken between October 2023 and October 2024, exposures of the three workgroups to INH, RES and RCS were also assessed (Figure 1). The results showed that miners in the LOP group were exposed to significantly higher RES and RCS dust compared to the other two groups.

2.4. Health Monitoring for the Determination of Health Effects

Most jurisdictions in Australia have a Deemed Diseases List, which consists of diseases that are deemed to be work-related [28]. The existence of a probable causal link between disease and occupational exposure, the diagnosis of the disease, and the prevalence of the disease in the overall population or a subset of the population were used as the criteria to develop the Deemed Diseases List [28]. A miner who develops a disease listed in the Deemed Diseases List, with the relevant established workplace exposure, is assumed to have developed the disease due to workplace exposure unless there is strong evidence to prove the contrary [28].

In this study, miners in workgroups with any exposure to INH, RES and RCS between 50–100%, or greater than 100% of the ES were invited for health monitoring. In principle, if miners’ exposures are below the ES, their health condition should not be impacted. However, due to their proximity to crushing plants, health monitoring was undertaken for LOP miners among the workgroups only when exposures were less than 50% of the ES.

The health monitoring program, undertaken between October 2023 and October 2024, followed the DEMIRS Health Monitoring Guide for Registered Medical Practitioners: Silica (Respirable Crystalline) [29] and the Standards for the delivery of spirometry for Coal Mine Workers [30]. It consisted of low-dose high-resolution computed tomography (LDCT), pulmonary function test (spirometry), and health and exposure questionnaire [23]. NIOSH outlined the use of a questionnaire, radiography, spirometry, and biomarkers for respiratory surveillance. The health monitoring program in this study was aligned with these requirements, except for the use of biomarkers [23].

LDCT replaced chest X-rays following legislative changes announced on 15 January 2021 by the then WA Minister for Mines and Petroleum; Energy; Corrective Services; Industrial Relations [31]. Its high sensitivity makes it suitable for the early diagnosis of silicosis [32]. Trained medical professionals conducted LDCT in accordance with Schedule 14—Requirements for health monitoring (hazardous chemical, Crystalline silica) of the WA Work Health and Safety (Mines) Regulations 2022 [26], and the International Classification of low-dose HRCT for Occupational and Environmental Respiratory Diseases (ICOERD). The GE HealthCare CT scanners (GE Health Care, Chicago IL, United States), calibrated twice a year, were used for the LDCT scan. Each LDCT scan health monitoring appointment took approximately 10 min. During the LDCT scan, miners were required to lie on a procedural bed that moved in and out of a doughnut-shaped machine containing the X-ray tube and detectors. LDCT was less than 1 millisievert equivalent dose for the entire study. The study imaged the whole of each lung on inspiration at 1.5 mm slice thickness or less, without an interslice gap, and included expiratory imaging. The images were of adequate quality to detect subtle abnormalities, including ground glass opacities and small nodules [26].

Following the LDCT scan, a specialist radiologist reviewed the LDCT imaging data and provided the report to the referring doctor. In the event of adverse medical findings for a miner, the referring doctor reviewed the results to determine appropriate management actions.

Spirometry was undertaken by trained nurses using Medikro Primo spirometers (Medikro, Kuopio, Finland), calibrated daily and following the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines. Each miner was required to conduct the test in a sitting position after being trained on how to blow into the equipment. The test was carried out three times for each miner, and the maximum value of the conservative tests was recorded as their result. FEV1, FVC, FEV1/FVC results were documented, and reviewed by a medical doctor in occupational health. Referrals for additional respiratory function tests, where required, were directed by the occupational physician.

2.5. Statistical Analysis

The main outcome variable for this paper was respiratory health status, measured by lung function (FVC1, FVC, FEV1/FVC, spirometry test) and respiratory symptoms (cough, phlegm, wheezing and shortness of breath).

Explanatory/independent variables were social-demographic variables (age, employment duration, gender, smoking status), individual existing medical condition, working respiratory protection (respiratory protection fit testing provided, respiratory protection provided) and training (trained in airborne contaminants, trained in respiratory protection use), and miner’s workgroups (defined by similar exposure groups).

We conducted three levels of analyses, namely univariate, bivariate and multivariable analysis, to achieve our research objectives.

In the univariate analysis, descriptive statistics were produced to summarise the sample population characteristics. Mean ± standard deviation (median (interquartile range) for skewed data) was used for reporting continuous variables whereas frequency (n) and percentage (%) in relevant categories were used for describing categorical variables.

In the bivariate analysis, a two-sample t-test and one-way analysis of variance (ANOVA) (Mann-Whitney U test or Kruskal-Wallis test for skewed data) were used to compare the lung function, whilst the chi-square test (or Fisher’s exact test) was applied to compare the prevalence of respiratory symptoms, between groups. Simple linear and logistic regression analyses were performed to examine the unadjusted association between each explanatory variable and respiratory health status (lung function and respiratory symptoms), respectively.

In our multivariable analysis, multivariable linear and logistic regression models were fitted to identify factors associated with lung function, and respiratory symptoms, respectively, adjusting for the effect of other explanatory variables. Only explanatory variables having a p value of 0.05 or less in the bivariate analyses were eligible to be included in the multivariable regression models. Adjusted regression coefficient (Adj-Beta) obtained from the multiple linear regression models, adjusted odds ratios (Adj-OR) obtained from the multiple logistic regression models, and their corresponding 95%CI and p-values were reported as the regression findings.

Multicollinearity occurs when the explanatory/independent variables included in a multiple regression model are highly correlated to each other and it can distort the regression outcomes or lead to incorrect conclusions. In our multiple linear and logistic regression models, multicollinearity was assessed by checking the variance inflation factor (VIF), which measures the degree of multicollinearity and indicates the presence of multicollinearity when its value is greater than 5 to 10 [33]. In all the multiple linear and logistic regression models, VIF showed that there was no concern about multicollinearity for the data (mean VIF = 1.05).

Only two missing values were found for “smoking status (2/430 = 0.465% of the total observations”, whereas no missing values were found in other variables. Due to this small proportion of missing values in only one variable, we did not conduct a missing value analysis or sensitivity analysis. We conducted a complete-case multivariable regression analysis following Stata default listwise deletion for handling these two missing values.

All analyses were carried out by using Stata Release 18 [34]. All tests were two-sided with a p value < 0.05 considered as statistically significant.

3. Results

3.1. Exposure Assessment

In this paper, the miner’s individual exposures were not available, and the exposure levels to each of the contaminants (INH, RES, and RCS) were measured only at the group level (Figure 1), indicating all miners in one workgroup had the same exposure level.

Regarding RES and RCS, the group mean exposure levels follow an identical pattern across the 3 workgroups given below: MAT group had the lowest mean exposure, CDWPP had a medium mean exposure, and LOP had the highest exposure on average, respectively (Figure 1). For INH, the MAT group still had the lowest mean exposure, while the LOP group had a medium mean exposure, and CDWPP had a slightly higher exposure than their laboratory colleagues on average, respectively.

3.2. Sample Population Characteristics

The average age of lithium miners in this study was 41.41 years of age (with a standard deviation of 10.59 years) (

Table 2. Health monitoring sample population characteristics.

Sample Characteristics	Total (n = 430)	CDWPP (n = 377)	LOP (n = 10)	MAT (n = 43)
Age in years, mean ± SD	41.41 ± 10.59	41.05 ± 10.63	49.90 ± 10.46	42.56 ± 9.51
Age in years, n (%)
<40	202 (46.98)	180 (47.75)	2 (20.00)	20 (46.51)
≥40	228 (53.02)	197 (52.25)	8 (80.00)	23 (53.49)
Gender, n (%)
Female	32 (7.44)	17 (4.51)	5 (50.00)	10 (23.26)
Male	398 (92.56)	360 (95.49)	5 (50.00)	33 (76.74)
Employment duration in years, median (IQR)	2.40 (2.53)	2.40 (2.45)	6.10 (4.23)	2.30 (2.90)
Employment duration in years, n (%)
<10	418 (97.21)	366 (97.08)	10 (100.00)	42 (97.67)
≥10	12 (2.79)	11 (2.92)	0 (0.00)	1 (2.33)
* Smoking, n (%)
Current smoker	95 (22.09)	82 (21.75)	3 (30.00)	10 (23.26)
Ex smoker	129 (30.00)	116 (30.77)	5 (50.00)	8 (18.60)
Never smoked	204 (47.44)	177 (46.95)	2 (20.00)	25 (58.14)
* Existing respiratory condition, n (%)
Yes	144 (33.49)	125 (33.16)	9 (90.00)	18 (41.86)
No	286 (66.51)	252 (66.84)	1 (10.00)	25 (58.14)
* Training and respiratory protection, n (%)
Trained in airborne contaminants (yes)	290 (67.44)	254 (67.37)	8 (80.00)	28 (65.12)
Trained in respiratory protection use (yes)	299 (69.53)	261 (69.23)	9 (90.00)	29 (67.44)
Respiratory protection fit testing provided (yes)	220 (51.16)	195 (51.72)	9 (90.00)	16 (37.21)
Respiratory protection provided (yes)	365 (84.88)	324 (85.94)	9 (90.00)	32 (74.42)

n = number of miners. Categorical data were presented as frequency (percentage); continuous data were presented as mean ± standard deviation (SD), or median (interquartile range (IQR)). * Data with missing values.

). The majority of the lithium miners were male (n = 398, 92.56%), while only 7.44% were females. CDWPP represented the largest group (n = 377) among the three workgroups. Approximately 47.44% of the workforce reported to have never smoked, while 22.09% were current smokers and 30.00% were ex-smokers. It was also revealed that about 33.49% of the study population had pre-existing respiratory conditions, compared to 66.51% who did not have any pre-existing respiratory medical conditions (Table 2). Gender was taken into account for spirometry and results were normalised accordingly.

3.3. Lung Function and Respiratory Symptoms

The ratio of FEV1/FVC of less than 0.70 is considered the key indicator of airway obstruction [21]. Miners who were 40 years old or older had a lower mean FEV1/FVC ratio compared to miners under 40 years of age. There was also a noticeable difference in the mean FEV1/FVC ratio for the smoking status and pre-existing respiratory conditions (

Table 3. Lung function and respiratory symptoms according to miners’ characteristics.

Variable	FVC1		FVC		FEV1/FVC		Cough	Phlegm	Wheezing	Shortness of Breath
	Mean ± SD	Median (IQR)	Mean ± SD	Median (IQR)	Mean ± SD	Median (IQR)	n (%)	n (%)	n (%)	n (%)
Age group (in years)
<40	4.14 ± 0.67	4.15 (0.90)	5.10 ± 0.93	4.13 (1.23)	0.82 ± 0.07	0.81 (0.07)	30 (14.85)	28 (13.86)	16 (7.92)	17 (8.42)
≥40	3.45 ± 0.63	3.48 (0.92)	4.35 ± 0.84	4.29 (1.11)	0.80 ± 0.08	0.80 (0.07)	33 (14.47)	16 (7.02)	21 (9.21)	22 (9.65)
p	<0.001		<0.001		0.002		0.912	0.019	0.634	0.657
Employment duration (in years)
<10	3.78 ± 0.73	3.79 (1.05)	4.72 ± 0.96	4.70 (1.29)	0.81 ± 0.08	0.80 (0.07)	60 (14.35)	43 (10.29)	34 (8.13)	38 (9.09)
≥10	3.43 ± 0.76	3.51 (1.36)	4.16 ± 0.82	4.19 (1.55)	0.82 ± 0.07	0.83 (0.07)	3 (25.00)	1 (8.33)	3 (25.00)	1 (8.33)
p	0.100		0.047		0.180		0.396	1.000	0.040	1.000
Gender
Female	3.04 ± 0.57	2.94 (0.68)	3.73 ± 0.77	3.67 (0.63)	0.82 ± 0.08	0.81 (0.08)	3 (9.38)	3 (9.38)	2 (6.25)	5 (15.62)
Male	3.83 ± 0.72	3.83 (0.98)	4.78 ± 0.93	4.81 (1.24)	0.81 ± 0.08	0.80 (0.07)	60 (15.08)	41 (10.30)	35 (8.79)	34 (8.54)
p	<0.001		<0.001		0.308		0.602	1.000	1.000	0.194
* Smoking status
Current smoker	3.82 ± 0.70	3.71 (1.07)	4.78 ± 0.99	4.66 (1.22)	0.81 ± 0.10	0.80 (0.06)	30 (31.58)	19 (20.00)	10 (10.53)	9 (9.47)
Ex smoker	3.72 ± 0.77	3.85 (1.17)	4.71 ± 0.94	4.79 (1.38)	0.79 ± 0.08	0.79 (0.07)	12 (9.30)	7 (5.43)	13 (10.08)	14 (10.85)
Never smoked	3.79 ± 0.73	3.77 (1.11)	4.67 ± 0.96	4.67 (1.34)	0.82 ± 0.07	0.81 (0.06)	21 (10.29	18 (8.82)	14 (6.86)	16 (7.84)
p	0.560		0.644		<0.001		<0.001	0.001	0.454	0.643
Existing respiratory condition
Yes	3.82 ± 0.73	3.82 (1.14)	4.86 ± 0.98	4.89 (1.39)	0.79 ± 0.10	0.79 (0.07)	26 (18.06)	15 (10.42)	25 (17.36)	30 (14.85)
No	3.75 ± 0.74	3.75 (1.05)	4.63 ± 0.94	4.54(1.28)	0.81 ± 0.07	0.81 (0.07)	37 (12.94)	29 (10.14)	12 (4.20)	33 (14.47)
p	0.390		0.016		<0.001		0.157	0.929	<0.001

* Data with missing values. Continuous data are presented as mean ± standard deviation (s.d), and median (Interquartile range: IQR), Categorical data are presented as frequency n (percentage %). n, number of measurements; SD, standard deviation. p-values were based on a two-sample t-test, ANOVA (Mann-Whitney U test or Kruskal-Wallis test for skewed data) for continuous data, Differences between groups were assessed by chi-square test or Fisher’s exact test for categorical data.

). Ex-smokers had the lowest mean FEV1/FVC ratio, compared to current smokers and miners who had never smoked. There was no significant difference in the mean FEV1/FVC ratio between employment duration (<10 vs. ≥10 years) and gender (Female vs. Male). Miners who were older than 40 years, current smokers and miners with existing medical conditions reported a higher prevalence of respiratory symptoms compared to their counterparts (Table 3).

3.4. Prevalence of Respiratory Symptoms and Respiratory Health Determination

Figure 2 presents the prevalence of respiratory symptoms for the three workgroups. Miners in the CDWPP workgroup recorded the highest number of respiratory symptoms cases, followed by miners in the MAT workgroup. There were only 2 reported cases in the LOP workgroup.

Lung function results are presented in Figure 3. CDWPP recorded the highest mean FEV1 and FVC results. There was no significant difference in the lung function between the workgroups as indicated by the mean FEV1/FVC ratio.

3.5. Factors Associated with Miner’s Health Status Revealed by the Multivariable Linear and Logistic Regression Models

The multivariable linear and logistic regression models indicated that older age and being female were associated with reduced/weaker lung function (lower FEV1). Specifically, compared to miners younger than 40 years old, those who were 40 years old or above had an average FEV1 reduction of 0.713 litres. In addition, females had an average FEV1 that was 0.829 litres lower than males (

Table 4. Factors associated with miner’s health status revealed by the multivariable linear and logistic regression models.

Lung Functions
Social-Demographic Factors	FEV1		FVC		Abnormal Ratio of FEV1/FVC (≤0.7)		Abnormal Spirometry Result (Obstructive or Restrictive)
	Adj-Beta (95% CI)	* p Value	Adj-Beta (95% CI)	* p Value	Adj-OR (95% CI)	# p Value	Adj-OR (95% CI)	# p Value
Age (years)
≥40	−0.713 (−0.833, −0.593)	<0.001	−0.779 (−0.939, −0.618)	<0.001	5.167 (1.445, 18.483)	0.012	3.942 (1.932, 8.040)	<0.001
<40	ref				ref		ref
Employment duration (years)
≥10	−0.141 (−0.498, 0.2155)	0.437	−0.340 (−0.818, 0.137)	0.162	1.214 (0.133, 11.114)	0.864	1.575 (0.395, 6.274)	0.520
<10	ref				ref		ref
Gender
Female	−0.829 (−1.065, −0.593)	<0.001	−1.082 (−1.398, −0.767)	<0.001	0.642 (0.072, 5.723)	0.691	0.172 (0.020, 1.487)	0.110
Male	ref		ref		ref		ref
Smoking status
Current smoker	0.054 (−0.096, 0.204)	0.478	0.137 (−0.064, 0.338)	0.182	2.387 (0.602, 9.467)	0.216	1.728 (0.810, 3.688)	0.157
Ex-smoker	0.061 (−0.077, 0.199)	0.388	0.192 (0.007, 0.377)	0.042	4.112 (1.234, 13.704)	0.021	1.502 (0.747, 3.021)	0.254
Non-smoker	ref		ref		ref		ref
Existing medical condition
Yes	0.038 (−0.087, 0.162)	0.552	0.202 (0.036, 0.368)	0.017	5.427 (1.971, 14.945)	0.001	2.165 (1.177, 3.984)	0.013
No	ref		ref		ref		ref
Respiratory Symptoms
Social-Demographic Factors	Cough	Phlegm	Wheezing	Shortness of Breath
	Adj-OR (95% CI)	# p Value	Adj-OR (95% CI)	# p Value	Adj-OR (95% CI)	# p Value	Adj-OR (95% CI)	# p Value
Age (years)
≥40	0.997 (0.562, 1.767)	0.991	0.504 (0.257, 0.987)	0.046	0.998 (0.475, 2.098)	0.996	1.183 (0.595, 2.350)	0.632
<40	ref		ref		ref		ref
Employment duration (years)
≥10	2.264 (0.554, 9.250)	0.255	1.186 (0.142, 9.909)	0.875	4.376 (0.919, 20.846)	0.064	0.918 (0.112, 7.528)	0.936
<10	ref		ref		ref		ref
Gender
Female	0.832 (0.225, 3.070)	0.782	1.209 (0.324, 4.511)	0.777	0.389 (0.078, 1.940)	0.250	2.834 (0.924, 8.691)	0.068
Male	ref		ref		ref		ref
Smoking status
Current smoker	4.200 (2.229, 7.912)	<0.001	2.751 (1.354, 5.588)	0.005	1.624 (0.655, 4.028)	0.295	1.218 (0.511, 2.901)	0.656
Ex-smoker	0.898 (0.421, 1.913)	0.780	0.661 (0.265, 1.650)	0.375	1.724 (0.742, 4.009)	0.206	1.327 (0.613, 2.872)	0.473
Non-smoker	ref		ref		ref		ref
Existing medical condition
Yes	1.528 (0.541, 4.317)	0.423	0.994 (0.505, 1.955)	0.985	4.873 (2.311, 10.274)	<0.001	1.276(0.639, 2.550)	0.490
No	ref		ref		ref		ref

CI: confidence Interval. Ref: reference group. * p value: obtained from the multivariable linear regression model fitted to FEV1 and FEV, separately, where age, employment duration, gender, smoking status, and existing medical condition were included as covariates/confounders. Adj-Beta = adjusted regression coefficient, representing the mean difference in lung function FEV1 or FVC. # p value: obtained from the multivariable logistic regression model fitted to each respiratory symptom, separately, where age, employment duration, gender, smoking status, and existing medical condition were included as covariates/confounders. Adj-OR = adjusted odds ratio, representing the ratio of odds of having a respiratory symptom.

). For FVC, older age and being female were associated with weaker lung function (lower FVC), whereas having existing medical conditions and being an ex-smoker (compared to a non-smoker) were found to have a higher FVC. Particularly, miners aged 40 years old or above had an average FVC reduction of 0.779 litres compared to their younger colleagues. Females had an average FVC that was 1.082 litres lower than males.

Age, smoking status and existing medical conditions were significant factors associated with an abnormal ratio of FEV1/FVC. Especially, the age of 40 years old or above (compared to younger than 40 years), being an ex-smoker (compared to a non-smoker) and having existing medical conditions was significantly associated with a higher likelihood of having an abnormal ratio of FEV1/FVC (≤0.7) by 5.167, 4.112, 5.427 times, respectively. Age and existing medical conditions were also significantly associated with an abnormal spirometry report (Obstructive or Restrictive). The odds of having a respiratory obstruction or restriction were higher for miners aged 40 years or older, and those with existing diagnosed medical conditions, by 3.942 and 2.165 times, respectively (Table 4).

Smoking status was identified as a significant factor associated with coughing. The risk of coughing among current smokers was more than four times higher [adjOR = 4.200, 95%CI (2.229, 7.912)], compared to non-smokers. Current smokers also had significantly higher odds of having phlegm [adjOR = 2.715, 95%CI (1.338, 5.510)], compared to their non-smoking counterparts. The risk of wheezing among those who had existing medical conditions was nearly five times higher [adjOR = 4.873, 95%CI (2.311, 10.274)] (Table 4).

4. Discussion

Workplace exposure assessment undertaken during the health monitoring period (October 2023 to October 2024) indicated that the exposure levels to RCS for MAT and CDWPP workgroups had been reduced to levels below the ES, which were historically above the ES [8]. Exposures to RES and INH remained below the relevant ES.

The health monitoring data indicated that age, smoking status and pre-existing diagnosed respiratory conditions were factors that adversely impacted respiratory airflow. The study further revealed that smoking increased the risk of coughing and phlegm, and the odds of having a respiratory restriction or obstruction were increased from age 40 years.

A review of the respiratory symptoms and LDCT analyses indicated that the CDWPP miners had the highest prevalence of reported respiratory symptoms compared to the MAT and LOP groups.

4.1. Exposures, Respiratory Airflow Limitations and Respiratory Symptoms

Obstructive lung diseases are characterised by a reduction in airflow related to increased resistance caused by airway narrowing [20]. These obstructions cause respiratory symptoms such as dyspnoea, cough, sputum and wheezing, and may occur by either narrowing the airway lumen or by decreased elasticity of the parenchyma surrounding the airways [20]. Spirometry is a mandatory test to determine the persistent airflow limitations [21].

Using spirometry to define persistent airflow limitations, forced expiratory volume in 1 s (FEV1), and the ratio of FEV1 and forced vital capacity (FVC) values are the best indicators of airway obstruction [20]. The current study showed that the mean FEV1/FVC ratio was 0.80 for MAT, 0.81 for CDWPP, and 0.81 for LOP. MAT miners who recorded the highest mean RCS exposures in previous years (2017–2023) [8], had a slightly lower mean FEV1 and FEV ratio compared to the CDWPP and LOP miners.

These findings are consistent with a study undertaken among tunnel construction workers in the United States between 1991 and 1999, which aimed to determine exposures and lung function decline [35]. The study revealed that exposure to RES and RCS among underground heavy construction workers was the most important risk factor for airflow limitation [35]. During the eight-year study, exposures to dust and silica were measured, and health monitoring was undertaken using spirometry on the subjects; with findings indicating an established association between a decrease in FEV1 and cumulative exposure to RES (p < 0.001) and RCS (p < 0.02), after adjusting for age and smoking [35]. The mean RES and RCS exposures among the tunnel workers ranged between 1.2 to 3.6 mg/m³ and 0.019 to 0.044 mg/m³, respectively [35]. While the mean exposures among tunnel workers are inconsistent with our study findings in relation to RES, they are consistent with the RCS exposures.

The study findings indicate that CDWPP had the highest reported cases for all the respiratory symptoms, 58 cases for cough, 41 cases for phlegm, 27 cases for wheezing, and 37 cases for shortness of breath, compared to MAT (5 cases for cough, 3 cases for phlegm, 9 cases for wheezing, and 1 case for shortness of breath). There were only 2 reported respiratory symptoms cases for LOP miners, 1 for wheezing and the other for shortness of breath. The high reported respiratory symptoms in CDWPP can be explained by their high exposure to INH and RCS. The maximum exposure to INH (10.00 mg/m³) was also recorded in this workgroup, which exceeded the ES. While all mean exposures for LOP were below the ES, this workgroup recorded the maximum exposure to RCS (0.160 mg/m³), exceeding the ES. LOP miners have the highest exposure to RCS and RES but there were no reported respiratory symptoms.

A similar study on exposure to dust and respiratory health was undertaken in Iran. This study was undertaken among street sweepers in the municipality of Zahedan, comparing the exposures to dust and the health impact between street sweepers (the exposed group) and office workers [12]. The results demonstrated that the mean of FEV1 for the street sweepers was significantly lower compared to the office workers, and it was also revealed that respiratory symptoms such as cough, phlegm, cough with phlegm, dyspnoea and wheeze were significantly more common among the street sweepers (the exposed group) than the office workers [12]. In addition, coughing and wheezing were five and six times more common, respectively, in the street sweepers than in the office workers [12]. Further analyses of the results from this study indicated that the chances of experiencing coughing and phlegm were 21.9 and 48.6 times higher in sweepers than in office workers, leading to the conclusion that street sweepers’ exposure to dust increased their chances of developing respiratory symptoms [12]. These findings are consistent with our findings on the adverse impact of exposure to INH, RES and RCS on respiratory airflow. Both studies examined exposure to dust, and the findings of both studies revealed a reduction in airflow.

4.2. Silicosis and Its Global Emergence

Silicosis is a progressive, irreversible pulmonary disease caused by the inhalation of RCS [36]. It can be categorised into acute silicosis, accelerated silicosis and chronic silicosis [23]. Acute silicosis develops after exposure to high concentrations of RCS from a few weeks to five years; its symptoms include dyspnoea, dry cough, fever, fatigue, and weight loss. Accelerated silicosis has similar features to chronic silicosis and it develops between five to ten years after exposure, while Chronic silicosis develops after exposure to a low concentration of RCS for ten or more years [23].

The findings of the exposure assessment reported in a previous related paper revealed that the exposure to RCS in lithium mining falls within the range associated with Chronic silicosis [8]. Also, according to the scientific literature, cumulative exposure to RCS increases the incidence of COPD [37]. However, the LDCT health monitoring results in this study did not indicate the presence of silicosis and COPD.

There is indisputable evidence available to demonstrate that exposure to RCS causes silicosis irrespective of the industry [23]. While silica concentration levels in the lithium mining and processing industry are at levels capable of causing silicosis, the findings from the health monitoring in this study indicate that there were no silicosis cases, which highlights the effectiveness of the existing controls identified at the lithium mines where this study was undertaken.

4.3. Training and Respiratory Protection Use in Lithium Mining

Health and safety precautions are critical to prevent workplace exposure to health hazards [38], part of which is the use of respiratory protection. Respiratory protection refers to a specific type of personal protective equipment (PPE) used to protect the user from the inhalation of harmful particulates, aerosols, and other airborne hazards [38]. The N-95 in the United States of America, the equivalent of a P2 mask in Australia, provides adequate protection against airborne contaminants such as dust and mould spores [39].

During the health monitoring in the current study, information was collected on training and respiratory protection availability and use. Approximately 67.44% of lithium miners reported to have received training on airborne contaminants, while 69.53% reported to have received training on the use of respiratory protection.

According to the data collected on respiratory protection, 84.88% of miners reported to have been provided with respiratory protection—P2 disposable dust masks and powered air-purifying respirators (PAPR), while about 51.16% of miners reported having been provided with respiratory protection fit testing. Respiratory protection fit testing is a validation process for the determination of the type and size of respiratory protection equipment that achieves an adequate seal on an individual’s face [40]. It is a critical process for the selection of appropriate respiratory protection, and data indicates that approximately half of the studied population went through this process. It must also be noted that not all respiratory protection equipment requires a fit testing assessment to verify the seals. Respiratory protection equipment such as the PAPR used by the LOP and CDWPP workgroups did not require a fit testing verification process.

Respiratory protection use was identified as a critical control intervention for the prevention of silicosis and COPD. Among the miners in the CDWPP and LOP groups, it was identified that miners were provided with PAPR for their individual use. The exposure levels in lithium mining, reported in our previous paper, indicated that they were in a range capable of causing chronic silicosis over a ten-year exposure duration [8]. It must be noted that about 97.21% of miners had been at the lithium mines for less than ten years, where this study was conducted, and this exposure duration could have been the reason for the absence of respiratory diseases associated with the known exposures.

Approximately 54.3% of the lithium miners reported wearing respiratory protection, compared to 45.7% who did not [8]. However, these figures were not broken down into distinct percentages for each workgroup. It must also be noted that respiratory protection was only required for access and work within crushing and processing, laboratory operations and the boilermaker workshop, based on the exposures to airborne contaminants. Respiratory protection was not required for all other workgroups, and this could explain why 45.7% of miners did not wear respiratory protection.

A study undertaken on respiratory protection revealed that the barriers to the effective use of respiratory protection can be categorised into organisational (the lack of provisions of respiratory protection for miners, and the lack of the incorporation of the control into existing work protocols), personal (the refusal of miners to use respiratory protection) and product (discomfort and difficulty in using the respiratory protection) [38]. As such, lithium mining companies could focus on interventions to remove barriers to the use of respiratory protection such as incorporating exposure controls in work procedures and processes, training and education, and the selection of respiratory protection, taking into consideration the comfort of the individual user.

4.4. Risk Factors for Respiratory Ill Health in Lithium Mining

The potential factors associated with lithium miners’ respiratory health were investigated in this study. A slight difference in the mean FEV1/FVC ratio was identified for miners under 40 years of age (0.82 ± 0.07), compared to miners who were 40 years old or over (0.80 ± 0.08) (p value of 0.002). It was also revealed that miners with pre-existing diagnosed respiratory conditions had a lower mean FEV1/FVC ratio (0.79 ± 0.10), compared to miners who did not have any pre-existing diagnosed respiratory conditions (0.81 ± 0.07). The reported pre-existing diagnosed respiratory conditions were asthma (childhood and adult-onset), bronchitis, hay fever, pleurisy, COPD and pneumonia. This difference in the FEV1/FVC ratio suggests that pre-existing diagnosed respiratory conditions have potential adverse health effects on the respiratory airway. Across the workgroups, the study showed a non-significant difference in lung function attributable to dust exposure.

A total of 430 spirometric lung function tests were undertaken, with 87.44% of the results indicating normal lung airway functionality, and 12.56% indicating either a restrictive or obstructive pattern. The abnormal results were attributed to non-work-related medical conditions and smoking. The study findings are consistent with those of previous studies, which indicated that mechanical processes such as sawing, crushing, drilling, polishing, cutting, or grinding of natural stone are dust-generating [23]. Although dust exposure can be associated with potential health risks among miners, the current study did not identify any respiratory occupational illnesses.

This study showed that the risk factors for respiratory health were non-work-related, including age, smoking status, and pre-existing respiratory conditions. It is therefore recommended that health promotion programs, inclusive of lung function assessment and LDCT, be developed and implemented to empower miners for smoking cessation. Lithium mining companies could also develop and implement chronic respiratory conditions management programs for non-work-related diagnosed respiratory conditions, to ensure miners are supported in managing these conditions during their employment with the mining companies.

4.5. The Impact of Smoking on Respiratory Health and Smoking Cessation

Smoking and ambient exposure to particulate matter have been reported to be the main risks for COPD, followed by air pollution in households, occupational exposures to particulates, ozone, and second-hand smoke [22]. In countries with higher socio-demographic index (SDI), smoking has been identified as the largest contributor to the COPD burden [22]. However, research indicates that smoking prevalence in men and women has decreased since the 1990s [22]. This is consistent with the findings of the current study with only 22.09% of lithium miners reporting current smoking, 30.00% were ex-smokers, while 47.44% had never smoked. Miners who never smoked had a slightly higher FEV1/FVC mean ratio, compared to current smokers and ex-smokers (0.82 ± 0.07, 0.81 ± 0.10, and 0.79 ± 0.08, respectively). Ex-smokers had a slightly lower FEV1/FVC mean ratio compared to current smokers.

Smoking cessation programs such as LDCT screening have proved to be effective public health interventions [41,42], for the prevention of respiratory diseases such as COPD. Research has indicated that LDCT screening reduces lung cancer mortality by 20–26%. A recent study undertaken in Australia indicated that participation in LDCT screening is associated with higher smoking cessation, 33% of smokers in the study quit smoking within 3 years [41]. In China, tobacco smoking accounts for about 75% and 18.4% of lung cancer deaths for men and women [42]. A study was undertaken between 2014 and 2019 among 2000 participants in China, to explore the relationship between LDCT and smoking cessation, it revealed a significant reduction in smoking prevalence after 5 rounds of LDCT screening, with findings indicating smoking cessation rates ranging from 7% to 23% [42]. Given the evidence on the impact of LDCT screening on smoking cessation and the relationship between smoking and COPD, the monitoring of this health risk factor and the development and implementation of health promotion programs should be considered by the lithium mining industry for supporting smoking cessation.

4.6. Study Limitations

The current study used group exposure to air contaminants and could not account for individual variations which is acknowledged by the authors as a limitation. Nonetheless, evaluating exposures at the group level is often more practical and efficient than individual assessments in occupational epidemiologic studies. Individual measurements require extensive data collection from all or most miners, which is rarely achievable [43].

Subjectively reported respiratory symptoms may be prone to misclassification and lack of consideration of other potential confounding factors, such as diet, lifestyles and comorbidities might have affected the results which is another study limitation.

It is also acknowledged that the study is a cross-sectional study and cannot infer causality.

The impact of heavy metals with the potential to induce oxidative stress [23], and the release of other compounds was not taken into account in determining the health effects. The authors acknowledge this as a study limitation.

Despite these limitations, this study provides comprehensive data on dust exposures among lithium miners in Western Australia in association with their respiratory health, and it is the first of this kind of study conducted in Australia.

5. Conclusions

The findings from the investigation of exposure to RES, RCS and INH in lithium mining and respiratory health indicate that these exposures exist mainly among miners in crushing and processing and laboratory operations. While these exposures are present, controls currently implemented include dust suppression techniques (using chemical binders where necessary), local exhaust ventilation for dry crushing, tunnels, and pulverising in sample preparation sheds and welding workshops, automation of sample preparation using the Autobatch technology, and the implementation of a robust respiratory protection program [8]. The above-mentioned techniques have proved to be effective in the prevention of occupational illnesses. While the authors also acknowledge that exposure to airborne contaminants such as silica and dust has the potential to cause respiratory illness [17], the control interventions in the lithium mines, where this study was undertaken, proved effective for the prevention of the associated respiratory illnesses.

The study identified age, smoking status and existing diagnosed respiratory health conditions as risk factors for respiratory health. This research and its findings are the first of their kind in the lithium industry, highlighting the exposures in lithium mining and the respiratory health of lithium miners in the industry.

Based on the study findings, it is recommended that lithium mining companies maintain the disciplined implementation of airborne contaminants controls, and verification practices for the protection of lithium miners’ health. While the authors acknowledge the provision of respiratory protection for miners, they would like to bring to the attention of the lithium mining industry that an improvement opportunity exists for the verification of respiratory protection use during the working shift of miners.

The authors present an opportunity for further research to investigate the dust composition and to examine the individual exposure of lithium miners to airborne contaminants and the long-term respiratory health effects. Additionally, there is an opportunity for future studies to undertake a cumulative risk assessment and determine environmental impacts.

In alignment with the findings of this research on the impact of smoking and pre-existing diagnosed respiratory health conditions on lung function, it is recommended that lithium mining companies develop and implement health promotion programs, inclusive of respiratory health assessment to empower miners for smoking cessation, and for the management of non-work-related respiratory conditions.