Heavy metal accumulation in soil and their transfer to lettuce (Lactuca sativa) irrigated with industrial effluent contaminated water

Heavy metal pollution is a major environmental problem especially in industrial areas adjacent cities centers were industrial effluent laden with heavy metals are channel to rivers and streams use by residence for domestic purposes. This study was conducted to evaluate heavy metals status of soil and their uptake by lettuce irrigated with effluent discharged from industries in Kaduna, Nigeria. Research plots were establish along effluent discharge points about 10 m away from the bank of river Kaduna. The effluent originated from the manufacturing activities of three major industries (Kaduna Petrochemical Refining Company site (KPRC), Nigeria Breweries Limited (NBL), United Nigeria Textile Limited (UNTL) and a control located at the Kaduna North Water Works (KNWW). Upon establishment of the field trials, soil and plant samples were collected at harvest respectively to assess the concentration of Fe, Pb, Cu, Zn, Cr, Ni and Cd, and their likely relationship in soil and plant system using AAS machine. Results showed that, soil heavy metal concentration varied with locations. Irrespective of locations, the magnitude of differences followed the sequence: Fe>Cr>Zn>Cu>Cd>Ni. Nevertheless, Fe and Zn were highly absorbed by lettuce in all the sites and the control. Higher concentration of each of the heavy metals was reported in the root and stem; whereas Pb was relatively high in lettuce leaf at KRPC. However, result of the test of toxicity indicated that all the heavy metals except Cr in lettuce were below the FAO/WHO permissible limit across the selected industrial sites and the control, and thus considered safe for consumption. Similarly, results of soil to plant transfer of heavy metals in lettuce revealed that KRPC and UNTL are possible risk areas for lettuce cultivation due to the high accumulation of most of the heavy metal species