Assessment of Naturally Occurring Radionuclides in Domestic Water of Three Settlements in the Ketu South Municipality

Abstract

This study was carried out to determine the concentration of naturally occurring radionuclides (226Ra, 228Ra, 232Th and 40K) in water from hand dug wells and few mechanized boreholes used domestically by the people of Aflao, Denu and Agbozume -Klikor communities of Ketu South Municipality. The concentrations of radionuclides from these water sources were measured using gamma spectrometry. The annual effective dose they are exposed to as a result of the consumption was estimated for various age groups. The risk associated with the radionuclides as a result of usage was also estimated. The physico-chemical parameters such as pH, temperature, TDS , conductivity, Ca2+, Mg2+ alkalinity and Cl- were measured using portable water kits analyzer and titrimetric method to determine any possible influence on the radionuclide distributions. Water from three hand dug wells and three mechanized boreholes were sampled in each of the communities. The mean Activity concentrations of 226Ra, 228Ra 232Th and 40K recorded from the wells and boreholes water in the three communities were, Aflao: 226Ra 3.44±1.07 Bq/ℓ, 228Ra 1.59±0.5 Bq/ℓ, 232Th 1.17±0.11 Bq/ℓ, and 40K 17.98±1.78 Bq/ℓ, Denu: 226Ra 1.973±0.60 Bq/ℓ, 228Ra 1.065±0.38 Bq/ℓ, 232Th 2.16±0.36 Bq/ℓ, and 40K 6.38±1.20 Bq/ℓ and Agbozume obtained 226Ra 0.70±0.12 Bq/ℓ ,228Ra 0.12±0.03 Bq/ℓ, 232Th 0.65±0.10 Bq/ℓ and 40K 2.20±0.28 Bq/ℓ. Generally, almost all the radionuclides measured in both Wells and Boreholes water exceeded the maximum allowable world limits of 1 Bq/ℓ for 226Ra/228Ra and 232Th. Thorium isotopes are highly insoluble and therefore their contribution to radioactivity in water is negligible. 40K is also not considered in the radionuclide standards. Hence the radionuclide of concern is 226Ra, which has recorded relatively significant concentrations. Therefore, any possible radiological impact as a result of usage of water in these localities would likely come from radium. The estimated total equivalent doses for the various age groups for Aflao ranges from 1.64 to 5.50 mSv/a; Denu ranges from 1.62 to 5.45 mSv/a; and Agbozume ranges from 0.01 to 0.58 mSv/a. The WHO (2004) limit for quality water is 0.1 mSv/a. This limit therefore suggests that the water quality in the wells of Aflao Second Low-cost and Aflao Well 5 do not meet the WHO reference limit, however, Aflao Beat-9 generally seemed to be nearer to the reference limit but, not good for infants at the age < 1a. Similarly, the water from Aflao Boreholes does not generally meet the WHO standards. Denu Well 1 does not meet the WHO standards but water from Well 2 was found to be generally within the limit. The Denu Boreholes generally do not meet the WHO reference limit. The Agbozume- Klikor Wells on the average, recorded slightly higher doses than the allowable limits especially for infants at the age < 1a. Similarly, for Agbozume boreholes, the doses recorded are above the world limits. The estimated fatal cancer risk values for Aflao, Denu and Agbozume were 2.31×10-3, 1.22×10-3 and 0.46×10-3 respectively. The values obtained for Aflao is slightly higher than the world’s average value of 1.45×10-3. There is therefore the need for continuous monitoring of groundwater in these communities for early detection of any threat of radiological health hazards in the long term. The Wells in the Municipality have generally recorded doses lower than Boreholes. This difference may be due to the varying depths. The Wells are generally shallow compared to the Boreholes which are deeper. The Boreholes are possibly closer to the geological rocks than the Wells. Thus water from the Boreholes have higher chances of interaction with the rocks than the Wells. Interaction with these geological materials increases the possibility of leaching the radionuclides into the water. The electrical conductivity and TDS recorded significantly high values in water from Aflao and Denu compared to water from Agbozume-Klikor. This indicated that, the high salinity of the domestic water in these localities has contributed to enhancing the concentration of the radionuclides in the various Wells and Boreholes water in the Municipality. Temperature and pH do not seem to have any significant impact on the domestic water in all the various locations. The result obtained for the Chemical parameters showed that for Aflao; Wells ASLW1, AW3 and Boreholes ASLBH1, AWWBH3 seemed to contain more radium than Ca2+ and Mg2+, a possible indication of higher concentrations of CO3 2/HCO3  which seemed to have improved the dissolution of radium in the water. However, in Well B9-AW2 and Borehole ASLBH2 of Aflao, Ca2+ and Mg2+ contents recorded higher values than the radium, an indication that there was relatively greater immobilization of Ra on the sediments by co-precipitation with the sulphates. Similar trends were repeated in the Denu and Agbozume-Klikor Wells and Boreholes. The higher values of Cl- might be attributed to the proximity of the municipality to the sea and the Keta lagoon.