Respirable dust (RD) generated during stone processing is an important occupational hazard because fine particles can penetrate to the alveolar region and, when containing crystalline silica, contribute to pulmonary fibrosis and other respiratory diseases. This study aimed to evaluate probabilistic lifetime cancer risk associated with RD exposure among informal stone workers in Sikhio District, Nakhon Ratchasima, Thailand. The analysis focused on estimating the Incremental Lifetime Cancer Risk (ILCR) using average daily dose (ADD)/lifetime average daily dose (LADD) and Monte Carlo simulation per U.S. EPA guidance. Non-cancer effects were not quantified using reference doses because no EPA RfD/RfC for crystalline silica was available for the authors’ quantitative assessment.
The field study was conducted in Sikhio District, an area with extensive sandstone deposits used for local stone production and carving. Work activities were grouped into five occupational categories by task: mining, cutting, splitting, knocking, and stone carving. Stone carving was identified as the process with the greatest potential for prolonged fine dust exposure due to continuous grinding and shaping.
A cross-sectional design enrolled 243 eligible informal workers aged 18–60 years who had been engaged in stone processing for at least one year. The sample size was calculated for the finite population of approximately 310 informal stone workers in the area using established sampling formulas and prior prevalence estimates. Participants provided demographic, occupational, and health-related information via a validated questionnaire administered by face-to-face interview.
Workplace RD concentrations were measured using personal air sampling consistent with the NIOSH 7601 method. Sampling employed SKC personal pumps with 10-mm nylon cyclones and 0.8 μm mixed cellulose ester filters, calibrated at a flow rate of 1.7 L/min. Sampling duration followed the study protocol to derive time-weighted average (TWA) concentrations representative of the Similar Exposure Groups (SEGs). A total of 83 personal air samples were collected across the five occupational categories to represent workers with comparable exposure patterns rather than sampling every individual.
ILCR was estimated using Monte Carlo simulation with 10,000 iterations to capture variability and uncertainty in exposure inputs and dose calculations. The modelling combined measured RD concentrations with exposure-related parameters from the questionnaire data and applied established cancer slope factors (in accordance with U.S. EPA methodology) to translate lifetime inhalation exposure into ILCR. The study used ADD or LADD as the dose metric for ILCR calculation under a linear no-threshold assumption. The analysis intentionally focused on cancer risk (ILCR) and did not attempt to quantify non-carcinogenic endpoints due to the absence of standardized RfD/RfC values for crystalline silica by the EPA.
Measured mean RD concentrations in all five occupational categories were below Thailand’s permissible 8-hour TWA occupational exposure limit (5 mg/m3) and did not exceed common TLVs. The highest mean RD concentration was recorded among stone carvers at 0.051 mg/m3.
Probabilistic ILCR estimates for all occupational groups fell below the commonly used acceptable risk threshold of 1.00 × 10−6. The stone carving group produced the highest mean ILCR, 3.325 × 10−7, while other groups yielded lower mean ILCRs (specific group-level ILCR distributions and percentiles were generated by the simulation but are not detailed here beyond the reported means and threshold comparisons).
Although both measured RD concentrations and ILCRs were within regulatory and commonly accepted risk limits, the authors note that measurable exposure and non-zero cancer risk remain, particularly for tasks with higher dust generation such as stone carving.
The use of Monte Carlo simulation allowed the study to incorporate variability and uncertainty in exposure inputs and to present probabilistic risk estimates rather than single deterministic values. This approach supports identification of high-risk tasks and sensitivity analysis of influential input parameters.
Limitations acknowledged in the source include reliance on the quality and representativeness of input data, which influence model accuracy, and the fact that only carcinogenic outcomes were quantified due to the lack of EPA RfD/RfC for non-cancer effects of crystalline silica. The Monte Carlo method can be computationally intensive and requires appropriate selection of input distributions; where empirical data are limited, assumptions may influence results.
Based on the findings, the authors recommend strengthened regulatory enforcement and implementation of comprehensive control measures in stone-processing settings. Suggested interventions include engineering controls to reduce dust generation and dispersion, appropriate respiratory protection programs, administrative controls to limit exposure duration, worker training and targeted health education, and ongoing health surveillance (symptom checks, pulmonary function testing, and radiography as indicated by exposure history).
Study data are archived under the stewardship of the Human Research Ethics Committee of Thammasat University (No. 3); external data requests can be made to the committee as specified in the source. The research was funded by the Thai Health Promotion Foundation (ThaiHealth) under a specified grant; funders did not influence study design, data collection, analysis, or publication. The authors declared no competing interests.
This probabilistic assessment found that mean RD exposures among informal stone workers in the study area were below national OELs and that estimated ILCRs were below the 1.00 × 10−6 benchmark. Nonetheless, the highest exposures and ILCRs occurred in the stone carving group, supporting the need for targeted exposure controls and surveillance to prevent silica-related disease in this high-risk occupational population.