Hydrochemistry and heavy metals concentrations in sediment of Woji creek and Bonny estuary, Niger Delta, Nigeria

Abstract Physicochemical characteristics of the surface water and heavy metals levels in sediment of Woji creek and upper reaches of the Bonny estuary, Niger Delta, Nigeria were investigated between October, 2012 and September, 2014. Ten sampling stations were established along the main creek course based on accessibility and proximity gradient from expected pollution sources. Water and sediment samples were collected monthly at each sampling station for twenty four months, using Hydrobios Water Sampler and Van-veen grab respectively. Water samples were analysed in the laboratory following standard procedures. Heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb) levels in sediment were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The surface water temperature showed seasonal changes, pH (6.68 ± 0.7) showed spatio-temporal uniformity throughout the study period and Total Organic Carbon (TOC) was generally low (0.23 ± 0.06). There was no seasonal variation in Biochemical oxygen demand (BOD 5 ). Salinity showed a positive correlation with pH and conductivity but negative correlation with temperature. Physicochemical properties of the water body were however, within Federal Ministry of Environment set limits for coastal water. The levels of heavy metals in sediments were in the order: Fe > Mn > Cu > Ni > Co > Zn > As > Cr > Pb > Cd. Sediments were found to have low levels enrichment of heavy metals from anthropogenic sources. This could be as a result of high tidal flushing in the study area. Pollution load index (PLI) and the degree of contamination (C d ) evaluated showed that sediment of the study area has low level of contamination from heavy metals and can be said to be relatively unpolluted.