Spatial distribution and statistical analysis of radon concentration in water sources of District Karak, Khyber Pakhtunkhwa, Pakistan: implications for health risk assessment.

This study provides an extensive investigation of radon concentration (222Rn) in water resources of District Karak, Khyber Pakhtunkhwa, Pakistan, a geologically complex area with sedimentary rocks containing uranium and uranium-bearing lithologies. Eighty-four water samples were taken from various water sources such as hand pump, bore well, open well and springs in different localities. The radon detected using RAD7, in the concentration measurement ranged between 1.12 Bq/L and 25.10 Bq/L, with a mean of 9.38 Bq/L and a standard deviation of 3.79 Bq/L. To characterize the data distribution and spatial autocorrelation, statistical analyses were performed such as histogram distribution, normal Q-Q plots and geostatistical semivariogram and covariance modelling. A map of the radon distribution throughout the district was created by spatial interpolation using ordinary kriging. The findings show that a significant proportion of the samples are above the lower Nordic/German and EU investigation thresholds of 0.1-1.0 Bq/L for radon in drinking water but are not exceeding the higher levels set by WHO (100 Bq/L) and USEPA (148 Bq/L), and hotspot zones have been identified in the eastern parts of study area (Shahedan, Shaheen Banda, Meta Khel) and some spring sources (Chashmai Spring, 25.10 Bq/L). The annual affective ingestion doses and excess lifetime cancer risk (ELCR) were calculated for each locality and for several sites, especially Chashmai Spring, Shahedan and Meta Khel, exceeds the excess lifetime cancer risk (ELCR) of 1 × 10-4, recommended by USEPA. Implications for human health, including ingestion dose, inhalation exposure from domestic water use, and lifetime excess cancer risk, are discussed in relation to the local geology and hydrogeology of the district.