Assessment of Heavy Metals and Polycyclic Aromatic Hydrocarbons in Water, Fish and Sediments of Rivers Niger and Benue Confluence, In Lokoja, Kogi State, Central Nigeria.

Abstract

The concentration of six heavy metals and six of sixteen (16) US EPA priority polycyclic aromatic hydrocarbons (PAHs) in water, fish and sediment samples of the confluence of rivers Niger and Benue were investigated in triplicates using atomic absorption spectrophotometer (AAS) for the heavy metals determination and gas chromatography coupled with mass spectrometer detector for the PAHs after acid digestion of the samples for heavy metals,liquid-liquid and solid-liquid extraction for the PAHs samples. The heavy metals were profiled for dry and rainy seasons whereas, the PAHs concentration in the samples were profiled for only rainy season in five sample locations. The concentration of the metals in water across the locations ranged from Cd (0.038 to 0.089), Cr(0.106 to 0.240), Cu(0.092 to 0.0164), Fe(0.682 to 0.878), Pb(0.058 to 0.309) mg/L with distribution pattern of Zn>Fe>Pb>Cr>Cu>Cd for the dry season water samples and Cd(ND to 0.027), Cr(ND), Cu(ND to 0.021), Fe(2.236 to 13.634), Pb(0.119 to 0.205) and Zn(0.121to 0.216) mg/L with distribution patter of Fe>Zn>Pb>Cd>Cu>Cr during the rainy season.The sediments’ metals concentration across locations ranged from Cd(2.189 to 2.893), Cr(4.367 to 9.927), Cu(3.433 to 6.780), Fe(233.210 to 254.160), Pb(8.967 to 17.420) and Zn(6.027 to 20.380) mg/kg with distribution pattern of Fe>Zn>Pb>Cr>Cu>Cd during the dry season and Cd (0.321 to 1.024), Cr(0.456 to2.662), Cu(ND to 8.599), Fe(1.234 to 2.062), Pb(8.721 to 17.737) and Zn(12.350 to 66.343)mg/kg with distribution pattern of Zn>Pb>Cu>Cr>Fe>Cd for the rainy season samples.The mean concentration of the metals in Catfishduringthe dry and rainy seasons were Cd(3.367 and 0.666) Cr(- and 0.293), Cu(7.050 and 4.952), Fe(44.775 and 1.230), Pb(3.842 and 8.683) and Zn(63.625 and 85.266)mg/kg and the Tilapia mean concentration values for dry and rainy seasons were as follows Cd(4.850 and 0.453), Cr(- and 0.164), Cu(8.042 and 1.658), Fe(44.108 and 0.198), Pb(4.717 and 6.704), Zn(63.742 and 40.680) mg/kg.The concentrations of the PAHs in water across locations ranged from Nap(ND to 0.543), Ph(ND to 0.083) Ant (ND to 0.083), BbF(0.080 to 0.093), BkF(0,083 to 0.093) and BaP(0.083 to 0.113) mg/L with distribution pattern of Nap>BaP>BbF=BkF>Ant=Ph.The concentration of PAHs in sediment across the locations ranged as follows Nap(ND to 2.210), Ph(ND to 0.053), Ant(ND to 0.053), BbF(0.053 to 0.383), BkF(0.053 to 0.110) and BaP(ND to 0.053)mg/kg with distribution pattern of Nap>BbF>BkF>Ph=Ant=Bap.The mean concentration value of PAHs in Catfish and Tilapia were Nap(2.383 and 1.947), Ph(0.050 and 0.057), Ant(0.057 and 0.057), BbF(0.043 and ND), BkF(0.043 and ND) and BaP(0.050 and ND).The result of the heavy metals in water and fish samples were tested for non-carcinogenic and carcinogenic health risk using health risk assessment models such as hazard quotient (HQ), Total hazard index(THI) cancer risk(CR) and cancer risk index(CRI). The health risk assessment showed that Cd andPb are of great concern.The ecological risk factors for the concentration of heavy metal and PAHs in sediment were estimated using ecological risk models such as geo-accumulation index (I-geo), contamination factor (CF), single ecological risk factor(ER), ecological risk index (RI), pollution load index (PLI) and polycyclic aromatic hydrocarbons pollution index (PPI).The results showed that sediment pollution ranged from no heavy metals pollution, low risk and very high risk pollution.The heavy metals and PAHs data were subjected to ANOVA at probability values less than 0.05 (P<0.05) level of significance.The heavy metals concentration in sediment were significantly different but, HMsand PAHs were all not different significantly in the water and fish respectively. The data generated for HMS and PAHs were correlated for source identification and the correlation showed that the majority of the pollutants were from the same source