Pollution indices and health risk assessment of heavy metals in floodplain of urban catchment of Asa drainage systems, southwestern Nigeria

Abstract

Urbanization and industrialization have significantly caused deterioration of surface waters. Since there is close association between river quality and its associated floodplain, the later could therefore provide a quality index of the former. This study examines heavy metal concentrations in floodplain sediment of urban catchment of Asa River and assessed associated risks. Samples were collected at 10 points but at interval of 5cm in vertical profile to a depth of 15cm. Atomic Absorption Spectrophotometer (AAS) analyses were done for Pb, Ni, Zn, Fe, Cu and Al. The following computational models were employed for risk analysis; Depth Ratio (DR), Contamination Factor (CF), Degree of Contamination (Cdeg), Geoaccumulation Index (Igeo), Pollution Load Index (PLI), Hazard Quotient (HQ), Hazard Index (HI) and Cancer Risk Index (CRI). Considerable degree of metal contamination was observed with various pollution levels from non-pollution with Ni, through moderate pollution with Pb, to a moderately strong pollution with Zn, Fe, Cu and Al. PLI revealed a baseline pollution level (PL ≈ 1) but contamination factor for each of Zn, Fe and Cu was considerable and may pose ecological threats and by extension, human health. Metal association reveals a positive correlation among all the metals evaluated (p < 0.05) which is suggestive of similar source. HQ via ingestion and dermal routes calculated were > 1 for both children and adult but< 1via inhalation. CRI for lead shows that children arepredisposed to cancer risks than adults. Hence, industrial activities in the urban catchment of Asa River must be monitored for environmental compliance.