Assessment of heavy metal concentrations and radiation exposure due to naturally occuring radioactve materials in the limestone deposits of kitui south district - Kenya.

Abstract

The heavy metals contents of Cu, Zn and Pb have been measured using Energy Dispersive XRay Fluorescence (EDXRF) and their pollution indexes calculated. The radiation background exposure at 1 m above the ground was measured using a survey meter and the annual effective doses and the absorbed dose rates calculated. The radioactivity levels of the limestone samples were also determined from the measurements done using a gamma ray spectrometry that consists of hyper pure germanium detector system. The results of measurements obtained indicated that heavy metal content in soils and limestone samples were generally below the soil metal limits given by U.S EPA with pollution indexes <1. The measured Annual effective dose rates averages of 0.768 mSv/yr, 0.907 mSv/yr and 0.743 mSv/yr, for Utekilawa- Kituvwi hills, Kamaluu- Mwanyani Hills and Ndulukuni Hills respectively which was below the recommended dose rate for the public (ImSv/yr) and the corresponding absorbed dose rates were 125.3 nGy/h, 147.82 nGy/h and 121.2 nGy/h which were about 2 times the average global absorbed dose rates. The area was therefore considered to be high background radiation area. The activity concentration mesurements showed that 238U was the highest contributor to the background with a mean activity concentration of 28.34 BqlKg, 47.4 BqlKg and 32.24 BqlKg for Utekilawa- Kituvwi hills, Kamaluu-Mwanyani Hills and Ndulukuni Hills respectively while 40K had activity concentrations 95.58 Bq/Kg, 142.63 BqlKg and 87.35 Bq/Kg for samples from Utekilawa- Kituvwi hills, Kamaluu-Mwanyani Hills and Ndulukuni Hills respectively but 232Th was below detection limits for all the samples anlysed. The contribution for the effective doses as a result of radionuclides in limestone were 0.047 mSv/yr (6%), 0.088 mSv/yr (10%) and 0.064 mSv/yr (9%) Utekilawa- Kituvwi hills, Kamaluu-Mwanyani Hills and Ndulukuni Hills respectively which was considered insignificant in the use of building materials made from the limestone.