Assay of Heavy Metals in Water Hyacinth (Eichhornia crassipes) Growing in River Benue, Nigeria and Its Safety as Food

Laboratory tests have established that some aquatic plants are heavy metal hyper-accumulators. To estimate the extent of this phenomenon on the field, an assessment of heavy metals (Fe, Mn, Zn, Cu, Cd, Cr, and Pb) content of water hyacinth (Eichhornia crassipes) freely growing in river Benue at Makurdi, Central Nigeria, was done using atomic absorption spectrophotometry (AAS). Heavy metal loading of the river water was also analyzed. The result showed the mean concentration of heavy metals in E. crassipes samples as: Fe, 103±95.7 mg/kg, Mn, 28.5±19.7 mg/kg, Zn, 34.0±21.0 mg/kg, Cu, 3.94±3.4 mg/kg, Cd 1.00±0.3 mg/kg, Cr 3.78±0.2 mg/kg and Pb 42.9±24.8 mg/kg. The load of heavy metals in water hyacinth leaves samples increased in the order Cd<Cr<Cu<Mn<Zn<Pb<Fe, this is similar to the order observed for the water samples (Cd<Cr<Cu<Pb<Zn< Mn<Fe). The concentrations of Fe, Mn, Zn and Cu were below permissible limits while Cd, Cr and Pb exceeded their permissible limits for vegetable samples set by Codex Alimentarius Commission. Considering the possible utilization of water hyacinth in nutrition (as table vegetable and animal feed) and industry, there is need to exercise caution in this regard and continuously monitor the heavy metal content of this plant growing in river Benue.