Contamination profile and potential human health risks of radon in groundwater of southwest region of Punjab, India.

Radon (Rn) is a naturally occurring radioactive gas produced by the decay of uranium-bearing minerals in rocks and soils. Long-term exposure to elevated radon levels in drinking water is associated with an increased risk of stomach and lung cancers. This study aims to assess the concentration of radon in groundwater and evaluate its potential health risks in six cancer-affected districts, i.e., Bathinda, Mansa, Ferozepur, Faridkot, Fazilka, and Sri Muktsar Sahib, of southwest Punjab, India. A total of 186 samples were collected from deep and shallow borewells using a 10 × 10 km grid-based sampling strategy, and Rn concentrations were measured onsite. Detectable levels of Rn were observed in 100% of the samples, ranging from 0.841 to 11.80 Bq/L, with an average of 3.63 ± 1.50 Bq/L. Most values were below the USEPA limit of 11.1 Bq/L (≈300 pCi/L). The annual effective dose from ingestion and inhalation was within the WHO-recommended safe reference dose level of 100 µSv/year across all age groups. However, the estimated excess lifetime cancer risk ranged from 0.29 × 10 to 8.37 × 10, with an average value of 2.57 × 10, indicating that a majority of samples exceeded the USEPA unacceptable risk level of ≤ 1.00 × 10⁻. While current Rn levels may not pose immediate health threats, the potential for long-term risks, particularly lung/stomach cancer and leukemia, remains. The study highlights the need for regular groundwater quality monitoring and the implementation of mitigation strategies in vulnerable regions.