Measurement of Radon concentration in water, soil and air in and around earthquake hit areas in N.W.F.P

Abstract

In this work measurements of radon concentration in water, soil and air in and around earthquake hit areas in N.W.F.P, Pakistan( new name is now Khyber Pakhtun-Khwa Province) were carried out keeping in view that there may be more radon concentrations because the area was hit by an earthquake of M L = 7.6 on October 8, 2005. High radon levels in soil and water may have contributed to the indoor radon concentration, subsequently a threat to the health of the people. The centre of the October 8, 2005 devastating earthquake was the northwest- striking Balakot–Bagh (B–B) fault, which had been mapped by the Geological Survey of Pakistan prior to the earthquake but had not been recognized as an active fault except for a 16 km section near Muzaffarabad. The area had not been surveyed previously for radon concentrations. The area has geological importance as well; because some of it lies on the active Balakot-Bagh fault line while other is located in its surroundings. This survey was conducted in three different media; water (from drinking sources), soil (sub-surface radon gas) and air (in the dwellings). The survey was carried out in the five districts of Hazara Division in general and in Balakot area in particular, being located at or around the Balakot-Bagh active fault, using two techniques: (i) the passive technique is based on tracks formation in CR  39 (trade name of diethylene glycol bis allyl carbonate) alpha track recorder used in the NRPB dosimeter with a known calibration and (ii) the active technique is based on the α activity measurements through spectral analysis in the instant air samples collected through the RAD 7 instrument of Durridge company. This technique is useful for getting average radon concentrations from the data integrated over certain time period. Doses were calculated from the indoor air and groundwater radon concentrations and the results obtained were then interpreted. The water samples were from drinking sources of the area near the fault line of Balakot especially and in the surroundings generally. The drinking sources include surface, spring and bore-hole water. Near the fault line at Balakot, the drinking source is the spring water so the spring water results of this area were compared with the spring water of the other parts of the study area. However, the sources of drinking water such as surface and bore-hole water in the Balakot area were also surveyed. xRadon concentration in the spring water near the B-B fault line were compared with the radon concentrations in the spring water in other part of study area away from the fault zone. Soil gas radon concentration in an area can be used not only to know about the radon related health hazards but also can be used as a useful tracer for locating active geological faults and for predicting any forthcoming earthquake within an area. The soil gas radon concentrations near the B-B fault line and other parts of study areas were measured. The results of B-B fault line were analyzed and compared with the other parts of the study area. Indoor radon survey was carried out in dwellings during four seasons of the year for one year and also on year basis to study the seasonal variation and to calculate the seasonal correction factor, respectively. The indoor radon concentrations were measured in the houses near the fault line and the surroundings. The results for the two regions were then compared. Indoor radon concentration levels of different seasons were compared with each other and with those taken on yearly basis. Comparison of radon levels in the indoor air of the houses made up of different materials and among the radon levels of the same houses on different stories were made. The groundwater radon concentration is higher in some part of the area than the US EPA recommended maximum contamination limit ( MCL ) of 11.0 kBq m  3 nevertheless within the range of limit adopted by European countries. Soil gas radon concentrations were found higher near the B-B fault line with an average value of 11.9 kBq m  3 as compared to other sites of the study area. The mean value of soil gas radon concentrations in the whole study area was found as 7.6 kBq m  3 . The indoor radon concentrations were found to be higher than the world average of 48 Bq m  3 but most of the values are below the Environmental Protection Agency’s US EPA recommended value of 148 Bq m  3 and the annual doses which the people of the area receive are within the safe limits of 3-10 mSv set by International Council of Radiological Protection  ICRP  65  . The indoor, soil gas and ground water radon concentrations were found to be higher near the fault line as compared to the areas away from the fault zone.