Evaluation of Radon (222Rn) Distribution and its Implications vis-a-vis Water Quality of Killiyar River, Kerala, India

Abstract

The discharge of tropical rivers is mainly contributed by the baseflow from groundwater especially during summer. Hence, in order to sustain the environmental flow of rivers, the conservation of locations where groundwater discharges into river is a better option than conventional practices viz., redesigning river channel structure and flow regime. Radon (222Rn), a colourless, odourless, inert and natural radioactive noble gas (t1/2= 3.8 days), can be used as a proxy to trace the groundwater discharge location/s in the river course. As 222Rn readily dissolves in groundwater, its content in groundwater is relatively higher than surface water. We report here the activity of 222Rn in the river water at ten locations from upstream to downstream of Killiyar river – KR (n= 6th, L= 24 km, A= 102 km2), the main tributary of Karamana river, Kerala, India. Surface water samples (n=10) were collected during pre- and post-monsoon of 2017. The radon activity was performed by RAD7, an electronic radon detector (Durridge Company Inc., USA). The activity of radon varied from 157 to 4588 Bq/m3 in pre-monsoon and 147 to 1740 Bq/m3 in post-monsoon. The spatial variability of 222Rn activity is observed, and the anomalous high activity location/s indicates groundwater potential in that area. Further, the factors controlling spatial variation of radon were also discussed. Moreover, physico-chemical parameters of river water were also studied. And all the parameters were found to be within the permissible limit of Bureau of Indian Standards (BIS) specifications for potable water (IS -10500: 2012). This is a case study of application of radon for prospecting groundwater potential zones in Killiyar river course, henceforth useful for the water resource management in this riverine environment and is first of its kind in the study region.