Metal accumulation and its spatio-temporal variation in Negombo and Rekawa lagoons of Sri Lanka

Abstract

Metal (Cr, Mn, Tl, Ni, Cu, Zn, As, Pb, U, Cd, Ba, Sr) concentrations in water, sediments and aquatic plants in two coastal lagoons o f Sri Lanka were determined by Inductively Coupled Plasma Spectroscopy (ICP-MS). The main sources o f heavy metals were observed as industrial effluents and agricultural runoff respectively fo r Negombo and Rekawa lagoons. There are 86 industries including metal use industries such as leather tanning, metal plating, manufacturing o f metal etc. in the Katunayake Export Processing Zone and treated, partially treated or untreated effluents are released to the Negombo lagoon. Concentrations o f most metal ions in water, sediments and aquatic plants were relatively higher in Negombo lagoon compared to Rekawa lagoon. The concentration ranges o f Cu, As, U, Cd and Sr in water o f Negombo lagoon were 0.37-1.89, 0.03-2.16, 0.03-0.29, 0.01-0.12 and 4.24-481 pg/l respectively and varied significantly (P<0.05) with the sampling occasions. It would be related to the seasonal variations o f rainfall and discharges o f effluents to the lagoon. Only the concentrations ofU , Ba and Sr in sediments (3-22, 16.5-257, 17-101 p.g/1 respectively) and Zn and U (21-152, 0.7-12 pg/l respectively) in aquatic plants o f Negombo lagoon varied significantly with the sampling occasions (P<0.05). The concentrations ofM n, Zn and Ba (193-1510, 31-88, 20-46 pg/l respectively) in sediments o f Rekawa lagoon varied significantly with the sampling occasions (P<0.05). Principal component analysis (PCA) was used to study distribution and accumulation o f metals in water, sediment and in algae. PCA shows that Cr, Tl, Pb and As accumulate more in sediments than in aquatic plants. Meanwhile Mn, Cd, Ba and Sr would concentrate more in aquatic plants than in sediments. Likewise metal accumulation in sediments and in algae depends on metal binding properties o f sediments and algae. However, concentrations o f metal ions in water were low and therefore their distribution was not shown on the selected axes o f PCA.