The Influence of Meteorological Parameters on Groundwater Radon Concentration in Oyo State, Southwestern Nigeria

Radon (²²²Rn) is a naturally occurring radioactive noble gas produced from the alpha decay of radium (²²⁶Ra) in the uranium (²³⁸U) decay series, with a half-life of about 3.82 days. Being chemically inert, radon can migrate easily through soil and rock pores via recoil, diffusion, and advective transport, eventually dissolving in groundwater (UNSCEAR, 2008). Radon in groundwater is of environmental and health concern because it contributes to radiation exposure through ingestion and inhalation when released into indoor air during domestic water use (WHO, 2017; Isinkaye et al., 2021). Prolonged exposure to elevated radon concentrations has been associated with increased risk of lung cancer (Darby et al., 2005; ICRP, 2014). Groundwater radon concentration varies widely depending on geological and hydrogeological conditions. Factors such as lithology, uranium content of rocks, aquifer depth, permeability, and water–rock interaction time significantly influence radon levels in groundwater (Appleton, 2007; Schubert et al., 2012). Areas underlain by granitic or metamorphic rocks generally show higher radon concentrations due to elevated uranium content, while structural features such as fractures and faults can enhance radon migration into aquifers (Przylibski, 2011). In Nigeria, studies have reported varying radon concentrations in groundwater across different geological settings. Relatively low concentrations within recommended limits have been reported in Lagos State (Abdulkareem & Ademola, 2019), whereas elevated levels exceeding guideline values have been observed in parts of Kwara State (Jimoh & Ademola, 2023). Similarly, investigations in Ogun State revealed generally moderate concentrations with localized exceedances (Fatoki & Ademola, 2021). Other studies have also confirmed that groundwater radon levels in southwestern Nigeria are largely controlled by geological composition and aquifer characteristics (Ademola & Olatunji, 2016; Isinkaye & Emelue, 2015). However, these studies mainly focus on spatial distribution and radiological risk, with limited consideration of atmospheric and climatic factors that may influence radon variability. Meteorological parameters such as atmospheric pressure, rainfall, temperature, wind speed, and relative humidity are known to influence radon transport and concentration in environmental systems (Fujiyoshi et al., 2002; Nazaroff & Nero, 1988). Variations in atmospheric pressure affect pressure gradients between the subsurface and the atmosphere, thereby influencing radon exhalation and migration (Schery & Gaeddert, 1984). Rainfall can also influence radon levels by mobilizing radon from soil pores into groundwater or by diluting concentrations during intense recharge events (Sundal et al., 2008; García-Tobar, 2013). Wind speed and relative humidity affect soil–atmosphere gas exchange processes, while temperature influences radon solubility and diffusion rates (Pinza-Molina et al., 2018; Spasić & Gulan, 2022; Huang et al., 2024). Although numerous studies worldwide have examined the relationship between meteorological conditions and radon variability, most of these investigations have been conducted in temperate regions (Zmazek et al., 2003; Chambers et al., 2015). In Nigeria, the combined influence of meteorological parameters on groundwater radon concentration remains largely unexplored. Therefore, this study investigates the influence of key meteorological parameters on groundwater radon concentration in Oyo State, southwestern Nigeria, using field measurements and statistical analysis to identify the dominant environmental controls on radon variability in tropical groundwater systems.

METHODOLOGY

The study was conducted in Oyo State, South-Western Nigeria, located within the Precambrian Basement Complex, which is characterized by uranium-bearing rocks that contribute to groundwater radon occurrence. Oyo State lies approximately between latitudes 7°00′N and 9°00′N and longitudes 2°30′E and 4°30′E, and is bounded by Kwara State to the north, Osun State to the east, Ogun State to the south, and the Republic of Benin to the west. The area experiences a tropical climate with distinct wet and dry seasons, which influence groundwater recharge and radon transport. Geologically, the region is predominantly underlain by crystalline basement complex rocks known to host uranium- and radium-bearing minerals, enhancing radon generation in groundwater. The spatial distribution of sampling locations in Oyo State is shown in Figure 1.