Distribution of U-Th nuclides in the riverine and coastal environments of the tropical southwest coast of India

A reconnaissance study has been made on the distribution of U-238, U-234, T h-232 and Tb-230 in soils, water, suspended particulate matter (SPM) and bo ttom sediments in the Kali river basin around Kaiga, its estuarine region a nd the adjacent Arabian Sea to obtain the baseline data of U-Th series nucl ides in view of the commissioning of nuclear power reactors at Kaiga, near Karwar, on the southwest coast of India. Drainage basin soils developed ove r greywackes (the dominant litho-unit upstream) are lower in U-238/Al and T h-232/Al ratios by factors of 3-5 in comparison with those developed over t onalitic gneisses (the dominant litho-unit downstream). The dominance of th e former type of soils is reflected in the composition of river-bottom sedi ments derived from the upstream drainage basin during the monsoon. The Th-2 32 in bottom sediments tends to increase towards the estuarine and coastal areas, presumably due to deposition of heavy minerals and onshore transport of coastal sediments into the estuary. The dissolved U in the Kali river i s low (0.001-0.02 mug/1) when compared to the major Indian rivers as the Ka li river flows through U-poor greywackes. Thus, the input of dissolved U to the Kali estuary is dominated by sea water. Although there is some evidenc e for the removal of dissolved U at low salinity during estuarine mixing, i ts behaviour is conservative in the lower estuary (at higher salinities). T he removal rate of dissolved U from the Kali river basin is similar to that reported from other tropical river basins. The U flux from all the west-fl owing rivers of Peninsular India is estimated at 26.3 x 10(6) g/yr to the A rabian Sea which is about 2% of the flux from the Himalayan rivers to the B ay of Bengal. (C) 2001 Elsevier Science Ltd. All rights reserved.