Elevated radiological hazards in a legacy coal mining area: unveiling hidden cancer risks from natural radionuclides in Enugu Iva Valley, Southeast Nigeria.

The Okpara (Iva Valley) coal mine in Enugu State, Nigeria, represents an unmanaged legacy site where uranium- and thorium-enriched Enugu Shale waste releases radionuclides into a densely populated agricultural community through acid mine drainage (AMD) and aeolian dispersal. Certified gamma spectrometric analysis of 40K, 226Ra, and 232Th was conducted on 24 environmental samples (Activation Analysis Lab (Actlabs), Ancaster, Canada and Centre for Energy Research and Training (CERT) , Ahmadu Bello University). Eight hazard indices, compliant with UNSCEAR and ICRP frameworks, were derived alongside dietary ingestion dose estimates based on cassava consumption. Spatial distribution patterns were resolved using cubic interpolation (SciPy griddata, method='cubic'). Mean activity concentrations of 226Ra (51.23 ± 11.79 Bq/kg) and 232Th (68.86 ± 16.45 Bq/kg) exceeded global averages by factors of 1.46 and 2.30, respectively. The mean outdoor gamma dose rate (75.64 nGy/h) exceeded the world average in 87.5% of samples. Notably, the mean annual dietary ingestion dose (2.43 mSv/yr) exceeded the ICRP public exposure limit across all samples, with 226Ra contributing 68.8% of the total dose. Statistical analysis identified 232Th as the highest fractional contributor to calculated outdoor dose (55% of ODRA), while 226Ra contributes more to the ingestion dose (68.8% of AED_ing) due to its higher ingestion dose conversion factor. The representative level index (Iγ > 1.0) classified 75% of samples as unsuitable for unrestricted construction, while the mean excess lifetime cancer risk (3.25 × 10-4) exceeded global benchmarks in 66.7% of cases. Statistical analysis identified 232Th as the dominant contributor to outdoor dose (R2 = 0.804, p < 0.0001). Spatial mapping revealed peak contamination along the AMD drainage axis in the central-eastern sector. These results identify Iva Valley as one of the highest documented doses of dietary radionuclide ingestion found at a coal mining legacy site in West Africa, according to the comparative data available at the time of writing, potentially affecting ~ 50,000 residents. Immediate interventions are required, including AMD treatment, spoil containment, agricultural restrictions, and systematic NORM monitoring aligned with international safety standards.