Assessment of Naturally Occurring Radioactive Materials and Trace Elements in Playgrounds of Selected Basic Schools in the Ga East Municipal District, Accra, Ghana

Abstract

The 235U, 232Th series and natural 40K are the main source of natural radioactivity in soil and have long half-lives up to 1010 years. Therefore their presence in soils and rocks is simply considered as permanent. Also due to rapid urbanization, most of Basic School playgrounds in Accra are built close to major roads or industrial areas for which they are subject to many potential pollution sources, including vehicle exhaust and industrial emissions.. A study has been carried out on playgrounds of basic schools in the Ga East municipal district in order to determine the exposure of the school children to naturally occurring radioactive materials (238U, 232Th and 40K) and trace elements [aluminum (Al), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), mercury (Hg), potassium (K), lanthanum (La), manganese (Mn), sodium (Na), nickel (Ni), lead (Pb), titanium (Ti), vanadium (V), zinc (Zn)]. The activity concentrations were determined using high‐purity germanium (HPGe) detector. The average activity concentrations of 238U, 232Th and 40K determined were 19.8 ± 8.7, 29.1 ± 16.3 and 119.4 ± 97.9 Bq.kg-1 respectively. The average annual effective dose was 0.039 ± 0.021 mSv and it is below the dose limit of 1 mSv/year recommended by International Commission on Radiological Protection (ICRP) for public exposure control. Radiological hazard assessments arising from the natural radionuclides were carried out. The average concentration of 222Rn and exhalation rate were estimated to be 32.13 kBq.m-3 and 0.016 Bq.m-2.s-1 respectively, which compared well with the world average values [78 kBq.m-3 and 0.033 Bq.m-2.s-1 reported by (UNSCEAR, 2000)]. Soil samples were also analyzed for trace elements by Instrumental Neutron Activation Analysis and Atomic Absorption Spectrometry in order to assess the potential adverse health effects of the exposure of children to trace elements during their games at school. Doses incurred via ingestion and inhalation and the dose absorbed through the skin were calculated using the United States Environmental Protection Agency’s hourly exposure parameters for children. The toxicity values considered in this study were adapted from the Risk Assessment Information System (RAIS) compilation of United States Department of Energy (USoDE). The results of the risk assessment showed that the highest risk pathway of exposure was associated with ingestion of soil particles. It was found that the trace element of concern was As and its estimated cancer risk was found to be 3.48E-06. This can be considered insignificant since it is below the recommended trivial cancer risk value of 1.00E-05. The total hazard index was found to be 0.17, below the threshold value of 1.0. The concentrations of trace elements were also used to evaluate the level of contamination. Soil pollution evaluation was carried out by enrichment factor (EF), geo-accumulation index (Igeo) and contamination factor. The enrichment factor (EF) for the trace elements (As, Cd, Cr, Mn, Ni, Pb, Ti and Zn) show that the soils in the study area are uncontaminated to moderately contaminated (Zn). This indicates that some of these elements are derived from both natural and anthropogenic sources. The overall Igeo values have revealed that the playground soils are practically uncontaminated to moderately contaminated, whilst contamination factors indicate that the study areas are none to medium polluted. Multivariate Statistical Analyses, Principal Component and Cluster Analyses, suggest that Al, K, La, Mn and Ti are derived from crustal origin, As, Hg and Ni which are identified as a result of atmospheric pollution, Cd, Co and Na which previously identified as a result of particulate matters emitted from the geologic media. Cr, Fe and Zn are derived from both natural sources (Cu, Fe) and traffic sources (Cr, Zn) since some of the playgrounds were found to be close to the road. Whilst Chromium (Cr) and Zinc (Zn) may have resulted from emissions of chromium-based automotive catalytic converters, cement and high Zn content in the soils may also come from traffic sources, particularly vehicle tyres.