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Source Identification and Health Risks Assessment of Toxic Metals in Rainwater and Groundwater in Eket and Esit Eket, Nigeria

Imaobong Inyang Udousoro, Victor Matthew Udoh

Abstract


Eket and Esit Eket in South-South Nigeria are oil producing local government areas. Oil exploration activities with the attendant gas flares and recurrent oil spillages have degraded the environment including water sources. To determine the safety of rainwater and groundwater potability, the levels of metals (Ni, Cd, Pb, Cu, Fe, Mn and Zn using atomic absorption spectrophometer), non-carcinogenic and lifetime carcinogenic health risks in adults through two pathways (ingestion and dermal absorption) based on USEPA model were evaluated. The levels of Ni, Cd, Pb, Fe, and Mn in rainwater and groundwater at all sites exceeded the Nigerian and WHO’s quality guidelines while Cu and Zn were below. Esit Urua and Mkpok in Eket showed highest levels of metals in rainwater and groundwater, respectively. Multivariate analysis (correlation, cluster analysis and principal component analysis) identified the source of pollution as mixed anthropogenic (mainly oil and gas related activities, incineration of domestic and municipal wastes) and natural (lithogenic and entrained dust). Non-carcinogenic health quotients (HQ) and the combined hazard index (HI) were higher in groundwater than in rainwater via ingestion. The relative abundance of metals (for HQ and HI) followed the order: Zn<Fe<Ni<Cu<Mn<Pb<Cd (rainwater) and Zn<Ni<Fe<Cu<Cd<Mn<Pb (groundwater). The results indicated potential health hazards of rainwater and groundwater through ingestion; and Ni, Cd and Pb the main contributors to potential lifetime carcinogenic risks. Lifetime carcinogenic risks of metals increased in the order: Mn< Ni<Cd<Pb (both rainwater and groundwater) with values higher in rainwater, and revealed that rainwater through ingestion may pose much more lifetime carcinogenic risks than groundwater. Non-carcinogenic and lifetime carcinogenic risks of metals were not associated with rainwater and groundwater through dermal contacts for individual metals, at all sites.

This study is essential for alerting government on the danger posed by consumption of rainwater and groundwater in Eket and Esit Eket, and the need for establishing suitable remediation method for the water sources for potable use.


Keywords


Exposure route; Groundwater; Rainwater; Risk assessment; Toxic metal pollution

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