Assessment of heavy metal contamination in the surface sediments of Neyyar River- Kerala, South India

Neyyar River (Latitude 8 o 16' to 8 o 40' N and Longitude 77 o 5' to 77 o 16' E) with 56 Km length originating from the Agasthyamala, flows through the midland, low land and joins with the Lakshadweep Sea at Poovar Pozhi.Neyyar is the primary source of drinking water supply to entire Neyyattinkara taluk of Thiruvananthapuram district, Kerala.Study focused on the analyses of heavy metals in the surface sediments of Neyyar River and samples were collected from 10 previously identified station locations of the River for a period of one year and subjected for different heavy metal analysis.The study sites were categorized into fresh water zone (stations 1-8) and estuarine (9-10) zone depending on saline influence.Dried and powdered sediment samples are extracted using acid digestion method with concentrated nitric acid and perchloric acid (4:1 ratio).Analyses of various heavy metals such as copper, zinc, cadmium, chromium and lead were done using Atomic Absorption Spectrophotometer.Decrease in concentrations was observed in the estuarine zone for all five metals analyzed.Among them cadmium and lead showed comparatively higher concentration than internationally accepted standard values indicating the contaminative nature of the river sediments with respect to cadmium and lead.However, copper, zinc and chromium reported remained within the accepted standard values for particular metals.Spatial and temporal variations remained significant for all metals except copper where only monthwise variations were significant.Sediment contamination was assessed by enrichment factor and geo-accumulation index, and observed that sediments in Neyyar River are moderately contaminated.