Quantitative Radiological Risk Assessment for a Site-Specific Population: Defining the Lifetime Cancer Risk Associated with ²²⁶ Ra in Phosphate Plant Waste

This study addresses a critical gap in regulatory assessments for sites contaminated with naturally occurring radioactive materials (NORM) by defining the site-specific radiological risk profile associated with industrial phosphate waste and its long-term health impacts on permanent residents. While extensive research has focused on radionuclide behavior in deep geological systems or far-field environmental dispersion, the direct, quantifiable health impact on communities living in the immediate vicinity of NORM-enhanced industrial sites remains significantly undercharacterized. Although phosphate processing is known to concentrate radionuclides like 226 Ra into phosphogypsum waste, most studies rely on basic screening tools that often fail to capture the complete public health risk, particularly from internal exposure pathways such as radon gas inhalation. To quantify these risks, in this study, high-purity germanium gamma-ray spectrometry and passive CR-39 track detectors were utilized to measure natural radionuclides in soil and indoor air surrounding a major fertilizer processing plant. A soil analysis established a distinct industrial radiological signature, with a mean 226 Ra concentration of 283.87 Bq/kg (eight times the global average), contrasting with low 232 Th (16.15 Bq/kg) and 40 K (146.36 Bq/kg) levels. Although key dose metrics like the mean radium equivalent activity (Ra eq ) of 318 Bq/kg remained below regulatory screening limits, the total annual effective dose (AED Total ) was calculated as 3.54 mSv/year, significantly exceeding the International Commission on Radiological Protection public exposure limit of 1.0 mSv/year. This dose was overwhelmingly driven by internal radon exposure (almost equal to 95% of AED Total ), resulting from a mean indoor concentration of 118 Bq/m 3 . The calculated excess lifetime cancer risk was 1.39 × 10 −2 , two orders of magnitude greater than the internationally accepted risk threshold (1.0 × 10 −4 ) for residual contamination. These findings demonstrate that current environmental profiles pose an unacceptable chronic public health risk not adequately reflected by simple hazard indices, validating the necessity for immediate regulatory intervention and focused risk-based remediation strategies.