Radioactivity concentrations of nuclides of the ²³²Th and ²³⁸U radioactive chains and ⁴⁰K, ⁹⁰Sr, ¹³⁷Cs, and ^239+240Pu were surveyed for raw and cooked food of the population in the Red River delta region, Vietnam, using α-, γ-spectrometry, and liquid scintillation counting techniques. The concentration of ⁴⁰K in the cooked food was the highest compared to those of other radionuclides ranging from (23 ± 5) (rice) to (347 ± 50) Bq kg⁻¹ dw (tofu). The ²¹⁰Po concentration in the cooked food ranged from its limit of detection (LOD) of 5 mBq kg⁻¹ dw (rice) to (4.0 ± 1.6) Bq kg⁻¹ dw (marine bivalves). The concentrations of other nuclides of the ²³²Th and ²³⁸U chains in the food were low, ranging from LOD of 0.02 Bq kg⁻¹ dw to (1.1 ± 0.3) Bq kg⁻¹ dw. The activity concentrations of ⁹⁰Sr, ¹³⁷Cs, and ^239+240Pu in the food were minor compared to that of the natural radionuclides. The average annual committed effective dose to adults in the study region was estimated and it ranged from 0.24 to 0.42 mSv a⁻¹ with an average of 0.32 mSv a⁻¹, out of which rice, leafy vegetable, and tofu contributed up to 16.2%, 24.4%, and 21.3%, respectively. The committed effective doses to adults due to ingestion of regular diet in the Red River delta region, Vietnam are within the range determined in other countries worldwide. This finding suggests that Vietnamese food is safe for human consumption with respect to radiation exposure.

Groundwater in the Red River’s delta plain, North Vietnam, was found in Holocene, Pleistocene, Neogene and Triassic aquifers in fresh, brackish and saline types with a total dissolved solids (TDS) content ranging from less than 1 g L⁻¹ to higher than 3 g L⁻¹. Saline water exists inHolocene aquifer, but fresh and brackish water exist in Pleistocene, Neogene and Triassic aquifers. This study aims at the investigation into genesis and processes controlling quality of water resources in the region. For this isotopic, combined with geochemical techniques were applied. The techniques include: (i) measurement of water’s isotopic compositions (δ²H, δ¹⁸O) in water; (ii) determination of water’s age by the ³H- and ¹⁴C-dating method, and (iii) chemical analyses for main cations and anions in water. Results obtained revealed that saline water in Holocene aquifer was affected by seawater intrusion, fresh water in deeper aquifers originated from meteoric water but with old ages, up to 10,000–14,000 yr. The recharge area of fresh water is from the northwest highland at an altitude of 140–160m above sea level. The recharge water flows northwesterly towards southeasterly to the seacoast at a rate of 2.5m y⁻¹. Chemistry of water resources in the study region is controlled by ferric, sulfate and nitrate reduction with organic matters as well as dissolution of inorganic carbonate minerals present in the sediment deposits. Results of isotopic signatures in water from Neogene, Triassic and Pleistocene aquifers suggested the three aquifers are connected to each other due to the existence of faults and fissures in Mesozoic basement across the delta region in combination with high rate of groundwater mining. Moreover, the high rate of freshwater abstraction from Pleistocene aquifer currently causes sea water to flow backwards to production well field located in the center of the region.