Determination and Evaluation of Heavy Metal Concentration in Surface Water and Sediment from Orashi River in Rivers State, Nigeria

The research was intended to study the influence of human and industrial activities on the Orashi River. Three groups are observed to have impacted the environment – Oil/gas industries, tyre burning (smokes and ashes) released during roasting of slaughtered animals in abattoir, untreated human and animal waste from settlers and the abattoir. The study was carried out from September 2019 to August 2020. The mean concentrations of the parameters studied in some samples were close to or exceeded World Health Organization (WHO) and Nigerian Federal Ministry of Environment (FMEnv) recommended limits for drinking water and seafood. The results from this study have provided information on the heavy metals profile on the surface water and sediment of the river. Essential heavy metals detected in water were in the range of Cu (1-5.4mg/l), Zn (1-4.4mg/l) and Fe (0.1 – 1.8 mg/l) which were within the WHO (1989), USEPA (1986), FEPA (1999) permissible limit of 3mg/l. The non-essential metals investigated were Cd, Cr and Pb but only Cd was detected. Cd levels (0.1-0.8mg/l) were slightly high, above the permissible limit of 0.01mg/l. Heavy metals in sediment were higher than those in the water body, occurring in the sequence Zn>Cu>Fe >Cd. The ranges were Zn (1.4-5mg/kg), Cu (0.8-3mg/kg), Fe (0.4-4.9mg/kg) and Cd (0.5-1.8mg/kg). All relationship were statistically significant (p=0.05). With regards to seasonal variation, dry season recorded higher values than rainy season. Heavy metals in sediment were higher than those in the water body, occurring in the sequence Zn>Cu>Fe >Cd. The ranges were Zn (1.4-5mg/kg), Cu (0.8-3mg/kg), Fe (0.4-4.9mg/kg) and Cd (0.5-1.8mg/kg). Cd and Fe in water and sediment have higher concentration during the dry season while Cu and Zn are higher during the rainy season in both parameters during the study period. Increased level of pollutants in the Orashi River may have significant effect on the ecological balance of the River. Again, long term bioaccumulation through food chain is a major concern as this study had revealed that sediment act as sink of pollutant loads than the water samples.