Assessment of 226Ra and 228Ra activity concentrations in drinking water sources along Ghana’s coastal communities

This study reports a screening-level radiological assessment of drinking water sources – sachet water, tap water, borehole water and river water – across the Greater Accra, Central and Western Regions of Ghana. Activity concentrations of 226 Ra and 228 Ra were measured by high-purity germanium (HPGe) gamma spectrometry in 244 samples collected over one dry and one wet season, and screening-level committed effective doses were estimated for adult consumers. All sachet and tap water samples returned activity concentrations below the minimum detectable activity (MDA) of the method (0.12 Bq L − 1 for 226 Ra and 0.14 Bq L − 1 for 228 Ra) and are reported as < MDA. Because the 228 Ra MDA (0.14 Bq L − 1 ) is above the WHO guidance level for 228 Ra (0.1 Bq L − 1 ), compliance of these samples with the 228 Ra guidance level could not be demonstrated by the method used; a non-detect establishes only that the activity was below 0.14 Bq L − 1 . Treating both MDAs as upper bounds gives an upper-bound screening dose of 0.095 mSv y − 1 , which is just below – not well below – the WHO individual dose criterion of 0.1 mSv y − 1 . Borehole water showed elevated activity concentrations ( 226 Ra: 5.03–5.16 Bq L − 1 ; 228 Ra: 5.06–5.34 Bq L − 1 ) and river water the highest ( 226 Ra: 27.02–28.39 Bq L − 1 ; 228 Ra: 29.01–30.09 Bq L − 1 ), exceeding the WHO guidance levels of 1.0 Bq L − 1 for 226 Ra and 0.1 Bq L − 1 for 228 Ra by factors of about 5 and 51–53 (borehole) and 27–28 and 290–301 (river). Corresponding screening-level committed effective doses, calculated on the conservative assumption that an adult drinks 2 L d − 1 exclusively from a single source for a full year, were 3.58–3.73 mSv y − 1 for borehole water and 20.14–20.96 mSv y − 1 for river water. Wet-season activities were higher than dry-season activities for the untreated sources, significantly so for borehole 228 Ra and for river 226 Ra and 228 Ra. Differences among the three regions in river water were negligible and not statistically significant. The elevated activities in untreated sources are consistent with weathering of uranium- and thorium-bearing accessory minerals in the Precambrian basement, although the present dataset does not by itself establish a geogenic origin. Because WHO guidance levels are conservative operational screening criteria, these exceedances indicate a need for confirmatory sampling, source-specific investigation and consideration of treatment for borehole- and river-dependent communities, rather than a demonstrated health detriment.