Application of aqueous extracts of Alternanthera brasiliana, Chromolaena odorata and Tridax procumbens plants in remediating lead contaminated soils

Abstract

Soil washing is an effective method of removing lead from contaminated soils. However, great limitations abound in the choice of washing solution that is ecologically sustainable for agricultural soils. In this study, applications of plant soluble extracts in remediating of Pb contaminated soils for ecological sustainability were carried out. Batch laboratory experiments were done using aqueous extracts of Alternanthera brasiliana, Chromolaena odorata, Tridax procumbens and water as control at varying soil-pulp-densities (SPD) of 3, 6, 9, 12, 15%, and washing time of 1, 3, 6, 12 h. For contaminated soil, percentage removal efficiency followed the order: Alternanthera brasiliana (38.1±0.28%) > Chromolaena odorata (21.8±0.12%) > Tridax procumbens (21.3±0.18%). The most appropriate ratio for contaminated soil was 3% SPD at 12 h washing time. Removal efficiency was found to be substantially depended on geochemical phase of Pb (exchangeable-4.04%) in contaminated soil and washing solution pH (5.68). Lead removal efficiency was observed to increased proportionally with increasing washing time, but decreased with increasing SPD. Spike soil with high exchangeable Pb-78.9% recorded significant Pb removal of 63.4±0.24% with Alternanthera brasiliana, 47.8±0.22% with Chromolaena odorata, 38.3±0.38% with Tridax procumbens and 52.0±0.26% with water. Analysis of variance at p=0.05 indicated a significant difference in
percentage Pb removal efficiency across all the four washing solutions. However, the statistical T-test indicated no significant difference at p=0.05 in percentage Pb removal efficiency between both soils. Also, moderately positive correlations were observed between contaminated and spiked soils for Alternanthera brasiliana (0.676), Chromolaena odorata (0.570) and Tridax procumbens (0.517) while negative correlation observed for water (0.485) which served as the control. The three plant extracts exhibited good potential characteristics as washing solutions for the treatment of Pb contaminated soils. Chemical modifications are recommended to enhance and improve their efficiencies when considering the geochemical phase of Pb in soil.