Radiological, chemical, and microbiological risks in drinking water from the Brazilian semiarid: Public health...

This study presents a regional survey of treated and untreated water sources in the Seridó Ocidental region of Paraíba, Brazil. A single-sampling campaign was conducted to evaluate chemical, microbiological, and radiological parameters against national standards. High concentrations of sodium (up to 5000 mg L^-1), chloride (up to 1579 mg L^-1), calcium (up to 105 mg L^-1), and magnesium (up to 124 mg L^-1) were observed, exceeding recommended limits and affecting taste and hardness. Turbidity in untreated water reached up to 105 NTU, about 20 times the permissible limit. Nitrate levels reached 34 mg N-NO₃^- L^-1 (26% non-compliance), and lead concentrations up to 0.026 mg L^-1 were found, both exceeding regulatory limits. Activity concentrations of ²²⁶Ra (up to 1.28 Bq L^-1) and ²²⁸Ra (up to 1.20 Bq L^-1) in some untreated sources also exceeded standards, associated with local geochemical conditions such as uranium- and thorium-rich minerals and high salinity. Calculated annual effective doses for children aged 1 to 10 years exceeded the WHO reference value of 0.1 mSv in several cases, indicating a need for further assessment and management. These results highlight the need for continuous monitoring and targeted interventions to ensure safe water in vulnerable semi-arid regions.