Comparative studies on trace metal geochemistry in Indian and Chinese rivers

The trace metal geochemistry in Indian and Chinese rivers in the Asian region was studied to understand its variation on a global scale in terms of climate, geological conditions and anthropogenic impact. The average particulate trace metal concentration of Indian rivers (∼300-1000 μg g^-1) is higher than that of Chinese rivers (∼150-300 μg g^-1) and the global average (∼170-350 μg g^-1). Molar ratios of alkaline and alkaline earth metals to Fe and Al (i.e. segregation factor, SF) were calculated in Indian bed sediment and in suspended matter of Chinese rivers to determine metal reactivity over the drainage basin. The segregation factors for bed sediments in Indian rivers were generally <1, except for the Tapti (∼1.7) and the Godavari (1.4) systems. Regional and watershed differences in segregation factors were observed, reflecting variable weathering rates due to differing mineralogy, preferential removal of alkaline and alkaline-earth metals relative to oxide-forming elements (Fe and Al), and a regional climatic shift north to south from temperate to sub-tropical conditions. Elevated levels of lead in Chinese rivers and of cobalt and zinc in Indian rivers indicated anthropogenic inputs of these heavy metals.