Study of seasonal variation of U-238 concentration in PM2.5 and associated health risks to inhabitants in cities of Bihar

Uranium, a chemically toxic and radioactive element, poses significant environmental and health risks from both natural and anthropogenic sources such as mining, fertilizers, and nuclear activities. This study quantified uranium-238 (23⁸U) concentrations in PM₂.₅ across all seven cities under study in Bihar, India: Aurangabad, Gaya, Muzaffarpur, Samastipur, Hajipur, Sonpur, and Patna. Samples were collected using a high-volume air sampler (Envirotech APM 550) at 1 m3/min over 24-h periods during summer and winter, followed by acid digestion and analysis via ICP-MS. The mean concentration of PM2.5 at all study sites was 120.72 ± 0.91 µg/m3 in the summer and 155.34 ± 1.04 µg/m3 in the winter season. The mean uranium concentration across all seven study cities was 5.38 ± 0.11 µg/m3 in the summer and 3.01 ± 0.07 µg/m3 in the winter. The global reference value for radioactivity concentration is 1.0 µBq/m3, whereas the measured airborne 23⁸U levels were below this threshold. The mean concentration was 0.01 ± 0.001 µBq/m3 in summer and 0.004 ± 0.0009 µBq/m3 in winter. Uranium in PM₂.₅ mainly originates from crustal dust and soil resuspension, influenced by meteorological conditions. Higher concentrations in hot, dry summers suggest enhanced resuspension and regional transport, while winter levels are reduced due to moisture and limited dust mobility. The estimated annual inhalation dose (0.62–4.40 nSv/year) remains far below the public exposure limit of 1 mSv/year. The total annual dose increases for the older age groups (from 3-month-old infants to 15-year-old adolescents and adults). The estimated lifetime cancer risks from uranium-containing PM₂.₅ were within safe exposure limits for all age groups, indicating no immediate radiological concern.