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.