Radiological assessment of radon concentration in drinking water from Lagos State University campus, Nigeria

Radon-222 is odorless and colorless and is highly soluble in water. Radon-222 cannot be detected by other means except measurements. When taken internally or inhaled through volatilization of water, it may lead to internal irradiation which targets the lungs and gastro-intestinal tract. The current study seeks to find out the radon-222 concentrations in 50 water samples collected from Lagos State University campus, Nigeria in November 14, 2024, using passive LR-115 Type II solid state nuclear track detectors. The results indicated concentrations in the range 3.7 ± 0.3 to 40.7 ± 8.3 Bq/L with an average concentration of 18.4 ± 3.5 Bq/L exceeding the NESREA recommended level of 11.1 Bq/L by 74%. Although the surface geology of the Ojo area is dominated by sedimentary formations of the Dahomey Basin, elevated radon concentrations can still occur due to upward migration of radon from deeper uranium-bearing basement rocks through fractures and faults, as well as from radium adsorbed on clay minerals and organic matter within the sedimentary sequence. The concentrations are up to 3.7 times the standard value. The average annual effective dose is 0.07 mSv/y for adults, 0.03 mSv/y for children and 0.02 mSv/y for infants, below WHO's 0.1 mSv/y standard value. The average lifetime excess cancer risk is 0.193 × 10^-3, which exceeds USEPA's risk limit of 10^-4 in 94% of the samples, signifying high risk of cancer. The risk categorization indicates 26% low risk (≤11.1 Bq/L), 50% medium risk (11.1-22.2 Bq/L) and 24% high-concentration sources (>22.2 Bq/L). It is below WHO's standard value of 100 Bq/L but exceeds the standard in some cases and thus has real health implication on consumers of untreated water in the university campus.