Transport of Trace Metals by the Rainwater Runoff in the Urban Catchment of Guwahati, India

Rapid urbanization and the consequent changes to urban traffic characteristics such as increased volume and congestion affect pollutant build-up on road surfaces as well as the top layer of soil (Zhao et al. 2010). In such cases, surface runoff accounts for quite a considerable contribution to the total runoff from land, and carries with it various contaminants from the road surfaces, built-up areas and other settlements to the receiving waters. The runoff quality is also important in identifying the nature of biogeochemical weathering processes (Skidmore et al. 2004) and in characterizing the evolution of the drainage system (Tranter et al. 1996). This has necessitated the study of basic qualities and characteristics of organic or inorganic contaminants in the rainwater runoff all over the world (Monticelli et al. 2004; Wei et al. 2010). Metals in water and soil are involved in various sorption/desorption interactions, redox reactions and chemical complexation with inorganic and organic ligands (Li et al. 2000; Violante et al. 2010). The mobility and reactivity of metals in water and soil affect their bioavailability, toxicity and distribution in the environment (Xue and Yong 2007). The solubility during precipitation and the redistribution into water can alleviate their immobilisation by adsorption or complexing (Misra and Chaturvedi 2007).