Can Pongamia pinnata be an effective phytoremediation tool for tailings in the Copperbelt of Zambia?

Abstract

Mining in Zambia has left a legacy of degraded land that is unsuitable for most forms of agriculture, and contaminated land surrounds numerous mining towns in the Copperbelt. As mining activities decline, communities are left heavily impacted by the negative environmental and social conditions surrounding them. The challenge is to understand and promote an effective revegetation approach that is economically productive, providing environmental benefits, employment, and diversification. Pongamia pinnata (L.) Pierre, a tree member of the Fabaceae family, has generated interest as a potentially sustainable biofuel feedstock. It produces seeds with high oil content and Pongamia reforestation systems can potentially provide a perennial climate change resilient, drought tolerant, carbon negative alternative to annual oilseed crops for the provision of oil and biomass products capable of providing fuel and food protein products. Additionally, Pongamia can be cultivated in degraded and/or marginal land and, given its phytoremediation potential, it is an ideal candidate for the regeneration of the Copperbelt area. Our study aimed to gain a broader understanding of the potential of P. Pinnata as a phytoremediation tool in the Copperbelt. We have carried out bioassays to assess the toxicity of copper (Cu) in the tailings and measured copper concentrations in both the tailings and the organic amendment around the trees, and in Pongamia roots and leaves growing in a large-scale field trial. Results show high survival rates (98.95%) at relatively high levels of Cu in the tailings (2,997.42 mg.kg -1 on average), with Pongamia trees exhibiting normal development 4 months after being transplanted. Our results suggest that elite Pongamia trees have the potential to be a viable option as a phytoremediation tool in the Copperbelt of Zambia.