Potential toxic elements distribution and phytoextraction status of Avicennia marina in eastern coast of Sri Lanka

Abstract

This research sought to evaluate the phytoextraction capability of Avicennia marina plants for potentially toxic elements (Cr, Ni, Co, Cu, As, Cd and Pb) in Batticaloa and Uppar lagoons along the east coast of Sri Lanka, thereby investigating its potential application in ecological restoration and coastal management. An experiment was conducted to identify the elemental concentration in roots above and below water level, stem and leaves of well grown Aicennia marina plants and sediment samples obtained along a transect from the plant to the deeper levels of the lagoon in six selected locations. The grain size distribution of sediments and organic geochemical proxies of sediments and plants were correlated with elemental distributions to identify their effect on the mobility. The average clay and silt contents of these lagoons are <1.03% with high contents of fine to medium size sands (about 66%). The pollution load indices (PLI) for both lagoons are low to moderate, however, Ni concentration exceeds Effect Range-median limit for some locations. The ecological risk indices and toxicity response of the sediments are in low risk levels may be due to the low development state of the region and sedimentary distributions. The elemental concentration in roots are high for Cr, Ni, Co, Cu and As compared to the stem and leaves of Avicennia marina whereas, Cd and Pb shows high values in stem parts regardless of the C/S and C/N ratios. The average bio concentration factor for Cr, As, Co, Ni, Cu, Pb and Cd are 31.77, 19.98, 17.33, 15.38, 4.57, 3.53 and 2.77 respectively indicating significant values compared to the most other studies which might be controlled by the climate.