Effect of clay minerals on heavy metals distribution in mangrove sediments at the msimbazi creek

The effect of clay minerals in heavy metals distribution in mangrove sediments at Msimbazi creek has been assessed. Types of clay minerals determined are smectite and kaolinite. Clay mineral determination was done by XRD. The concentrations of heavy metals (Fe, Cd, Co, Cr, Ni Zn and Pb) were determined by using AAS, in sediments including the suspended fraction. The ranges of concentrations in ppm of heavy metals in sediments were as follows Fe (1000 - 27000), Cd (0.03 - 3.87), Co (4.09 -17.40), Cr (13.20 -71.20),Ni(6.91 - 24.00), Zn (16 -173) and Pb (3.13 -77.7). The heavy metals concentration in suspended sediments was determined before and during the rains. Concentrations of Zn and Pb were higher during the rains than before the rains. This is a good indicator of contamination fluxes from city runoffs. However, Fe concentrations were higher before the rains than during the rains indicating that there is dilution effect. The ranges of other factors affecting heavy metals distribution in the sediments were as follows, pH (6.0 - 7.6), EC (5.11 - 15.16 mS/cm), redox potential (-411 - 136), CEC (35.69 - 98.21 meq/100 g), % 0 M (0.839 - 9.391 %), sand (0.96 - 56.2 %), silt (11.67 - 47.8 %) and clay (15.78-85.04 %). A decreasing trend of heavy metal concentrations, CEC, clay content and redox potential with increase in depth from the surface was observed. Therefore, heavy metals distribution in mangrove sediments is affected by clay type and content. CEC, OM and redox potential have an influence on heavy metals distribution in mangrove sediments. It is recommended that industries should conduct treatment of industrial effluents before discharging to the river. This will help to reduce pollution at the Msimbazi creek.