TOXICOLOGY EVALUATION OF LEAD SIMULATION IN SOIL AND MITIGATION BY TITHONIA DIVERSIFOLIA BIOCHAR (TITHOCHAR)

Lead (Pb) is classified as a major pollutant in the environment arising from its natural occurrence aggravated by weathering process, exhaust from automobiles, battery waste, industrialization and agrochemical use. It is also most reported heavy metal in the food chain. Intensive and indiscriminate use of agrochemicals (chemical fertilizers and pesticides) among local farmers therefore calls for an investigation into the fate of soil impacted by Pb. The objectives of this study are to assess the concentrations of selected heavy metal in Pb simulated soil, evaluate the toxicity of Pb simulation on leachate quality, earthworm and okra performance, and determine the heavy metal mitigation potentials of two Tithochar types in Pb impacted soil pretreated by these biochar types Soil samples were collected from the Teaching and Research Farm, LAUTECH, Ogbomoso, preparation involved filling leaching columns with 2.5 kg of soil, A factorial combination of two biochar types (STD and TDBM) was applied at two rates of 2.5 and 5.0 t/ha under two heavy metal conditions non-heavy metal (NHM) and with heavy metal (WHM) arranged in a completely randomized design (CRD) with three replications, totaling 30 experimental units and moistened to field capacity with 530 ml tap water. And 0.73 g portion of Lead(II) acetate trihydrate (CH3COO)2Pb.3H2O) was dissolved in distilled water to create an 800 ppm Pb stock solution, which was applied at 20 ml/column alongside a basal NPK 15:15:15 application for 2 weeks of incubation. followed by a one-time leaching simulation with 200 ml of water and the sowing of okra for 3 weeks. Three earthworms were collected and introduced into each column, with initial weights recorded; the setup was kept moist and covered for three weeks, after which final weights were taken. Soil data collected included pH, electrical conductivity (EC), Pb, cadmium (Cd), available phosphorus (P), and organic carbon. Water data included pH, EC, Pb, and Cd contents, while plant data comprised fresh biomass weight, Pb, and Cd contents. Earthworm data included initial and final weights, percentage weight loss/gain, and mortality counts, with all data analyzed using two-way ANOVA in Genstat at p < 0.05.