Ecological risk assessment of selected heavy metals in the surface sediments of three estuaries in the southeastern coast of India

Distribution and ecological risk assessment of heavy metals in surface sediments of Vellar, Coleroon and Tirumalairajan estuaries were investigated. Fifteen sediment samples from five locations in each estuary were collected during March 2010, and organic matter, grain size and metal contents (Al, Fe, Mn, Zn, Cu and Pb) were characterized. Mean metal levels in three estuaries were followed in a descending order as Al > Fe > Zn > Mn > Cu > Pb (Vellar and Coleroon) and as Al > Fe > Zn > Cu > Mn > Pb in Tirumalairajan estuary sediments. Concentration pattern revealed that the mean values of Vellar estuary are enriched with Al (20,528 μg/g), Fe (16,368 μg/g), Zn (102.7 μg/g), Mn (63.5 μg/g), Cu (47.6 μg/g) and Pb (7.9 μg/g). Coleroon and Tirumalairajan surface sediments concentration suggested Al (4813 μg/g), Fe (2734 μg/g), Zn (47.6 μg/g), Mn (34.2 μg/g), Cu (23 μg/g) and Pb (9.2 μg/g) and Al (5348 μg/g), Fe (2257 μg/g), Zn (36 μg/g), Cu (23.5 μg/g), Mn (21.9 μg/g) and Pb (3.7 μg/g), respectively. Correlation analysis and two-way joining cluster analysis clearly exhibited the good relationship of grain size and organic matter with metals. Geo-accumulation index (I_geo) revealed that the values of Zn (2) and Cu (1) were slightly higher in Vellar estuary when compared to the other two estuaries. The enrichment factor (EF) and pollution load index values showed that the Vellar estuary was more contaminated by Zn, Pb and Cu than the Coleroon and Tirumalairajan estuaries. This study suggested that heavy metal input to the Vellar estuary should be regulated in the near future, particularly with regard to Zn, Cu and Pb on the basis of threshold effect level and effects range low benchmarks when compared to the other two estuaries. Comparative results with three estuaries suggested anthropogenic input rather than a natural process as a contamination source. This study will help in developing the effective strategies of pollution control and sediment remediation of the estuarine and marine environments.