Seasonal variations of bioaccumulation of heavy metals in a freshwater fish (Erpetoichthys calabaricus) from Ogba River, Benin City, Nigeria

Abstract

This investigation assessed and monitored accumulation levels of Cu, Mn, Zn, Cd, Ni and Pb in a freshwater fish (Erpetoichthys calabaricus) from Ogba River during the dry and rainy seasons of a hydrologic year (November, 2005 – October, 2006). The same metals were also examined in the water of the river over the period. The results showed that the accumulation levels in fish exceeded the levels of the metals in water and indicated bioaccumulation in fish. The dry and rainy season levels in fish as well as in water at each of the sampling stations varied, but the differences were not significant. However, among the stations, the differences in the seasonal levels for most of the metals were significant. A correlation between seasonal levels in water and fish as well as the lack of uniformity in the distribution of the metals in the river were established. The finding also that both dry and rainy season mean levels of Cu, Mn and Ni in fish exceeded WHO recommended limits in food, suggested that the fishes of the river are not suitable for human consumption. Consequently, close monitoring of metal pollution of Ogba River is strongly advocated, in view of possible risks to health of consumers of the fishes of the river.