Phytoextraction of heavy metals and risk associated with vegetables grown from soil irrigated with refinery wastewater

Abstract

With the increase in anthropogenic activities, Heavy metal contamination of vegetables is inevitable as such it has become a course for concern due to food safety issues and potential health risk. This research is aimed at evaluating the phytoextraction efficiency of some vegetables and the potential health risk resulting from the consumption of vegetables that are grown in agricultural soil irrigated with Refinery wastewater. Wastewater was collected from the effluent point of Kaduna Refining and Petrochemical Company from October 2016 to February 2018 and analyzed for the presence of heavy metals (Cd+2, Hg+2, Ag+2 and Pb+2, Cr+3) before use for irrigation. Soil samples were collected from a farm located in Rigasa, Igabi Local Government of Kaduna State. The soil samples were digested and analyzed for heavy metal (Cd+2, Hg+2, Ag+2 and Pb+2, Cr+3) and physicochemical parameter before and after the wastewater is the used for irrigation and treatment process. The seeds of the vegetables were planted in the botanical garden of the Biological Sciences Department of Kaduna State University and were constantly irrigated by a refinery wastewater throughout the period of the research. After germination the plants were harvested and separated into root/rhiziome and shoot, digested and analyzed heavy metals using Atomic Absorption Spectrometer. Bioconcentration factor, Biotranslocation factor, Daily intake of metal (DIM) and Health risk index (HRI) were calculated. The result obtained showed high accumulation trend in the vegetable for Cd and Hg in Solanum melongena, Cucumis sativa, Phasaelus vulgaris, Spinacia Oleracea, Allium cepa, Lactuca sativa, Daucas carota, Lycopersican esculentum, Pipper nigrum above recommended standard. The high DIM and HRI value by all the vegetables that are above FAO/WHO recommended a limit for the heavy metals. These researches thereby discourage the use of refinery wastewater in irrigation farming of vegetables. It also recommends the need to stop all vegetable farming activities within the bank of Romi stream since refinery wastewater is constantly been released into the stream.