Spatial Distribution of Heavy Metals in Sediments of the Negombo Lagoon, Sri Lanka

Heavy metals accumulate in the sediments of aquatic environments due to poor water solubility. Their toxic effect poses a significant threat to living organisms. Negombo Lagoon, a vital aquatic ecosystem in Sri Lanka, has become vulnerable to heavy metals mainly from urbanization-related anthropogenic activities. Previous research in this respect has sampling points restricted to the boundary area. Since the heavy metal concentration is a static parameter, continuous research needs to keep the data updated. This study aims to investigate the spatial distribution of several heavy metals (Cr, Ni, Co, Cu, As, Cd, and Pb) in the surficial sediment of the Negombo Lagoon. Fifteen grab sediment samples were collected from the lagoon and analyzed for heavy metal concentration and grain size. The range of concentrations of each metal in test samples were between (78.07 - 222.68 mg/kg) Cr, (376.7-1298.05 mg/kg) Ni, (15.875-43.74 mg/kg) Co, (32.45-112.79 mg/kg) Cu, (20.17-55.81 mg/kg) As, (0.30-1.4 mg/kg) Cd, and (16.57-70.97 mg/kg) Pb. Heavy metal concentrations and sediment grain sizes show significant spatial variation over the Negombo lagoon area. Heavy metals were highly concentrated in locations, where finer sediments are accumulated (i.e., towards the eastern and southern part of the lagoon). Heavy metal concentrations were found to be increased with the decreasing grain size. High heavy metal concentrations are also found at places where there is a river discharge. Among the sources which feed heavy metals into Negombo Lagoon anthropogenic activities such as municipal and industrial waste disposal, rapid urbanization, shipping, and naval activities etc. have a significant impact.