Environmental and Health Related Assessment of NORMs and Trace Elements from the Pozzolana Industry in Ghana

Abstract

The cement industry processes and uses raw materials with varying concentrations of Naturally Occurring Radioactive Materials (NORMs), some being of more radiological significance than others. Additionally, these raw materials may contain hazardous trace elements from which the workers and the public might be exposed to as a result of the various processes involved in the manufacture of cement. Therefore, it is important to establish the levels of the radionuclides in cement types for radiation protection purposes and also investigate the effect of cement industry activities on the surrounding environment. This study therefore, focused on estimating possible radiological health hazards associated with the manufacture and use of Crystal cement, a product of mixing clay Pozzolana with Ordinary Portland Cement as well as the investigation of the factory surroundings for possible pollution from trace elements and radionuclides. A total of one hundred cement samples representing four major brands of Ordinary Portland Cement used in Ghana were collected from various cement dealers. Additionally, samples of Palm Kernel Shells (PKS), raw clay and clay Pozzolana were collected from Pozzolana Ghana Limited while 62 soil samples were collected within and around the factory premises. All the samples were analyzed for the activity concentrations of Ra-226, Th-232 and K-40 using the High Purity Germanium Detector. Soil samples and clay Pozzolana were further analyzed for elemental concentrations of Pb, Cr, Cd, As and Hg using the Atomic Absorption Spectroscopy (AAS). Results showed that after mixing clay Pozzolana with Ordinary Portland cement, there was enhancement in the individual activity concentrations of Ra-226, Th-232 and K-40 in some mixed cement types while there was reduction in the activity concentrations of the same radionuclides in other mixed cement types. The resultant effect of alterations in activity concentrations on the indoor absorbed gamma dose rate was insignificant in CEM (CEMENT) IA (0.47% increase from CEM I) and CEM IIC (1.38% decrease from CEM III). However, these alterations were significant in CEM IIB and CEM IVD as there was an increase of 5.45% in indoor absorbed gamma dose rate from CEM II to CEM IIB and a 48.48% reduction in the indoor absorbed gamma dose rate from CEM IV to CEM IVD. Regardless of the enhancement or reduction in individual activity concentrations of the radionuclides, results revealed that the annual indoor effective dose from gamma radiation in Crystal cement ranged between 0.28±0.01 and 0.40±0.02 mSv, the maximum value in this range being lower than 1 mSv per year considered as the limit for public exposure. Similarly, estimation of internal exposure from the alpha activity in all Crystal cement types indicated that the maximum indoor radon concentration of 73.02 Bq/m3 was lower than 300Bq/m3 which is considered as the action level in dwellings and other buildings for members of the public. The natural radioactivity in soil samples around the factory indicated that the average annual outdoor effective dose was 0.03±0.01 mSv still lower than 1 mSv per year considered as the limit for public exposure. The range of calculated Pollution Index, ( ij P ), Ecological risk factor ( i r E ) and Geo-accumulation index ( geo I ) indicated the following: ij P : 0.06-0.49 <1; i r E : 0.14-14.70 <40; geo I :-5.98- -2.91≤ 0. The calculated value of improved comprehensive pollution index ij P was 0.54 indicating clean soils around the factory. Hence, both the single and integrated indices indicated no possible environmental pollution with trace elements. Therefore, the use of Crystal cement as a building material is considered safe and no soil pollution with radionuclides and trace elements from the factory activities was established by this study.