Assessment of The Levels Of Heavy Metals In Sediments, Water And Fish From The Weija Dam

ABSTRACT

This study was conducted to assess the levels of heavy metal contaminations within the Weija dam area of the Weija Lake. Sediments, water and fish samples were taken from ten different sites within the Weija dam in March, 2014 (dry season) and August, 2014 (wet season). The sediment, water and fish samples were analysed for Hg, Se, Fe, Cd, Mn and Pb using Atomic Absorption spectroscopy (AAS). Mercury was determined using a cold vapour technique with the AAS equipped with hydride generator (CV-ASS). Selenium was also determined by hydride generation atomic absorption spectrometry (HG-AAS). Water samples were analysed for pollution indicators using Standard Methods from the American Public Health Association (APHA) manual. Physicochemical parameters such as temperature, pH, conductivity, hardness and nutrients were all below WHO maximum permissible limits. The results of this study indicated that there were significant differences in concentrations of the physicochemical parameters between the two seasons. The Coefficients of Variation for physicochemical parameters were all below 50% for both seasons. Nutrient concentrations were also below the WHO maximum permissible limits. Total mercury (T-Hg) levels were below detection limit in sediments and water samples for the ten sites investigated, in both dry and wet seasons. However, all samples of the fish species studied showed mean T-Hg concentrations below the World Health Organization (WHO/FAO) limit of 0.5 mg/kg wet weight. The mean concentration of other heavy metals in the water were 0.155 mg/L (Fe), 0.021 mg/L (Cd), 0.031 mg/L (Mn) and 0.010 mg/L (Pb). Levels of all trace metals were below the WHO guideline values for drinking water. Apart from Hg and Se, the levels (mg/kg) of other metals in the sediment were higher than that of water and fish species. The results from this study therefore showed that the water in the Weija dam is relatively clean with regards to measured heavy metals.