Heavy Metals Health Risk Index (HRI) in Human Consumption of Whole Fish and Water from Some Selected Dams in Katsina State Nigeria

This study was conducted in the year 2016 to determine the heavy metal concentrations in whole fish (Clarias gariepinus) samples and water obtained from some selected Dams (Ajiwa, Zobe and Dannakola) in Katsina state Nigeria. The objectives were mainly to detect the presence of heavy metals in whole fish and water from some selected Dams in the study area, compare the concentration of heavy metals in samples from the selected Dams concerning the permissible limits specified by WHO/FAO and USEPA Standards. Eight (8) water samples were collected at 8 random points within approximately 1000 meters on each extremity and median parts of the selected dams. Fish (Clarias gariepinus) was sampled using standard methods (AOAC, 1990). The fish and water samples were collected from Ajiwa, Zobe and Dannakola Dams of Katsina state Nigeria. Nine adult fish samples, three each from Ajiwa Dam, and Dannakola were procured from fishermen. Analysis of the concentration of these heavy metals; Cr, Cd, Fe, Ni, Mn, Pb and Zn was conducted by the use of AAS (by Atomic Absorption Spectrophotometry) method. The results showed wide mean concentrations of the heavy metals in the selected dams water; iron recorded the highest level (range 0.4596 μg / g - 2.9510 μg / g) and lead (range 0.0031 μg / g -0.0323 μg / g) recorded the lowest level, for the fish samples the mean concentrations of the same heavy metals showed iron recording the highest level (range 1.8847 μg / g -10.0474 μg / g) and cadmium (0.0130 μg / g -0.0138 μg / g) recording the lowest level. Results from this study indicate that with the exception of the heavy metals Cd, Fe and Pb (from Zobe dam sample) values of Mn, Pb (Ajiwa and Dannakola dams samples) and Zn in the water samples were generally lower than the USEPA, WHO/FAO maximum permissive limits while Ni was below the detection level (BDL) in all the samples. the results of this study showed that apart from Mn (PI range = 0.02-0.09), Zn (PI range = 0.01-0.03) and Pb for sampled water from Dannakola dam (PI= 0.77) which have no effect on the water quality, all the other heavy metals have pollution indices which suggest slightly, to moderate and strong effect on the selected dams water quality consideration for human and aquatic health. The metal indices also showed that all the heavy metals are at the threshold level (MI > 1) except for the heavy metals Mn and Zn in sampled waters from all the selected dams, Pb for water samples from Ajiwa and Dannakola dams and Cr for Zobe dam water sample. With the exception of the heavy metals Pb, Ni and Cr that were BDL in the fish samples the levels of the heavy metals all fall below the USEPA, WHO/FAO permissible limit for fish. The results from the present study suggests that the selected dams water quality is threatened by heavy metals pollution and may have adverse implication for drinking and aquatic health, in the fish samples the concentration levels of the heavy metals all fall below the USEPA, WHO/FAO permissible limit for fish. However, the fish’s bio-accumulation factors of the metals suggest that they have high potentials to bio-accumulate some of the heavy metals to high levels and this may have adverse implication for human consumption.