EVALUATION OF SEDIMENT PARTICLE SIZES OF HEAVY METAL CONTAMINATION IN THE LAGOS INLAND WATER SYSTEM.

Sediments are important in the geochemical cycles of marine and estuarine ecosystems with the ability to influence ecological processes and inhabiting biota. This study evaluated sediment particle sizes of the Lagos Harbour and inland water system with a view to determine their diversity and influence on heavy metal levels. Samples were collected using Van veen grabs, viz; dry season 2013 (DS-1), wet season 2013 (WS) and dry season 2014 (DS-2) for a period of 18 months in the Lagos Lagoon and inland water system. The sediments collected were analysed according to the British Standard (BS 1377-2, 1990) at the instrument Physical Geography Laboratory, University of Portsmouth. The mean clay, silt, course and sand were found to be 6.67± 4.51, 6.0 ± 3.0, 9.17± 3.25 and 0.37 ± 3.06 respectively. The particle size in relation with total metals/metalloids concentration in the sediment revealed positive correlation with significant differences (p<0.05) between clay and Fe (r = 0.391*), clay and Pb (r = 0.40*). While the particle size in relation and recoverable metals/metalloids concentration in the sediment revealed positive correlation with significant differences (p<0.05) between clay and Mn (r = 0.416*), silt and Mn (r = 0.414*). The particle size in relation with bioavailable metals/metalloids concentration in the sediment revealed positive correlation with were significant differences (p<0.05) between silt and Pb (r = 0.426*). This implies that the widespread dredging of the lagoon sediments and artisanal sand mining has had its toll on the structural integrity of the substratum. The strong correlation between the finer particle sizes with total, recoverable and bioavailable fractions of Fe-Mn-Pb in the sediment samples is notable and implies increased chances of retention of pollutants in the sediment matrix. Keywords: Evaluation Techniques, Inland-Lagoons, Sediment texture, Heavy metal/metalloid, Marine pollution.