Bioavailable trace metals in micro-tidal Thambraparani estuary, Gulf of Mannar, SE coast of India

Thirty surface sediment samples from two different seasons pre-monsoon (PRM), post-monsoon (POM) were analyzed for texture, carbonates, organic matter (OM) and leachable trace metals (LTMs) (Fe, Mn, Cr, Cu, Ni, Pb, Zn, Cd) from the micro-tidal estuary of Thambraparani river located in Gulf of Mannar, SE coast of India. Finer fractions (mud: 3–87%) and OM (2.6–8.0%) dominate the region and the concentration pattern of LTMs indicate that mostly all the metals are concentrated in the POM season than PRM. Correlation analysis indicates that LTMs are also bound with the OM, mud and are bound with Fe–Mn oxides. Pb concentration (14–103 μg g−1) exceeds the sediment quality guideline value indicating its anthropogenic origin. Low flow condition exists in the estuarine region due to the control over fresh water inflow in the upstream side and the higher concentration of metals [avg. (μg g−1) Cr 10; Cu 11; Zn 28] is due to the precipitation from estuarine water to the sediments and is also bioavailable to the marine biota in the region.