Bioaccumulation of Toxic Heavy Metals in Tilapia Fish Species Oreochromis niloticus in River Riana Kisii County Kenya

Aquatic pollution with toxic heavy metals is currently a global threat to the survival of humanity. These metals may be bioaccumulated and biomagnified in aquatic food chains and food webs and eventually become toxic to human beings via consumption of aquatic resources such as fish. This study was carried out on the biological analysis of heavy metals in Tilapia Oreochromis niloticus from the Riana River. The fish samples were collected monthly using plastic nets from three sampling sites in the River. The fish samples were dissected in the laboratory using plastic knives to obtain gills and intestines. The fish organs were digested for heavy metal analysis using HNO3 according to the method used by Meche et al (2010). Toxic heavy metal analysis was done using the inductively coupled plasma optical emission spectroscopy (ICP-OES-Shimadzu ICPE 9000). The data collected was analyzed using t-tests and one-way ANOVA where significant differences were accepted at p<0.05. Turkey's HSD post hoc tests were used to separate means where ANOVA exposed significant differences. The average metal levels in gills and intestines in dry weight (mg/kg). The toxic metal levels in tilapia fish gills: Pb (.256±0.135), Ni (.279±0.143), Cr (.255±0.131), Mn (1.211±0.986), for Cu (1.265±0.723) and Zn (2.051±0.868). Equally, the levels in the tilapia intestines were: Pb (.235±0.089), Ni (.162±.058), Cr (.250±.102), Mn (.172±0.138), Cu (.343±0.142) and Zn (.395±0.175). The heavy metals in tilapia fish under study met the recommended WHO/FAO threshold limits except for Cr. The elevated Cr level was attributed to industrial pollution and agricultural application of Cr containing chemicals. Enhanced ecosystem management approaches were recommended for sustainable biodiversity conservation and protection of human health.