ISODOSE MAPPING AND ITS RADIOLOGICAL IMPLICATIONS IN LAGOS STATE, NIGERIA

Abstract

In this research, the annual effective dose rate (AEDR) due to ionizing radiation in 20 Local Government Areas (LGA) and 37 Local Council Development Areas (LCDA) in Lagos State, Nigeria have been determined. Data acquisition was carried out with the use of a Geiger-Muller counter. A global positioning system (GPS) device was used to take readings of the coordinates and elevation of each data point. The isolevels of the AEDR in the study area was represented by using the kriging interpolation technique on ArcGIS 10.1 software. Duncan multiple range test was performed using Statistical Package for Social Sciences (SPSS) software so as to determine if there is any significant difference between the distributions of the annual effective doses in the study area. The result obtained shows that the values of the AEDR ranged from 0.19±0.01 mSv/y to 0.35±0.02 mSv/y with a mean value of 0.27±0.03 mSv/y. This value is lower than the maximum permissible limit of 1 mSv/y as recommended by ICRP. Comparing the geospatial map of the AEDR and that of the elevation map in the obtained result, the AEDR was higher in areas with high elevations and lower in areas with low elevations. The distribution of the AEDR to different organs (gonad, breast, red bone marrow, lung, thyroid, bone e.t.c) of the body, the excess lifetime cancer risk (ELCR), the collective effective dose equivalent (SE) and the collective health detriment (G) were calculated so as to assess the effects of ionizing radiation on the populace of the study area. The ELCR range from 0.0007 to 0.0012, with an average value of 0.0010. The average value of the excess lifetime cancer is close to the recommended permissible limit of 1 as recommended by ICRP. Hence, the populace of the study area are now so much at risk of developing cancer over a period of time. The total collective effective dose equivalent is 4839.49 person-Sv. This implies that approximately twenty-eight (28) in every one hundred thousand (100,000) people are at risk of suffering radiation-induced disease in the State.