Abstract
Compost has been used to stabilise lead (Pb) in soil. However, compost contains a high level of dissolved organic matter (DOM) which may make Pb bioavailable in plant and thereby limiting its effectiveness and application. Addition of biochar to compost can reduce this effect. Rice husk (RH) and Cashew nut shell (CNS) biochars and compost-modified biochars were used in comparison to compost for stabilizing Pb in lead smelting slag (LSS)-contaminated soil (Pb = 18,300 mg/kg) in Nigeria. Efficiency of Pb stabilisation in control and amended soils was assessed using CaCl2 batch leaching experiment and plant performance. In pot experiments, maize plant was grown on the contaminated soil and on soil treated with minimum and optimum doses of the amendments singly and in combination for 6 weeks. Agronomical and chemical parameters of the plants were measured. CaCl2-extractable Pb in the untreated soil was reduced from 60 mg/kg to 0.55 mg/kg in RHB amended soils and non-detectable in other amended soils. RH-biochar/compost increased plant height, number of leaf and leaf area more than the others. Similarly, at minimum rate, it reduced root and shoot Pb by 91% and 86.0% respectively. Compost-modified rice husk biocharstabilised Pb in lead smelting slag contaminated soil reduced Pb plant uptake and improved plant growth. Lead stabilisation through the use of rice husk biochar with compost may be a green method for remediation of lead smelting slag-contaminated soil.
Highlights
A high concentration of lead in soil that is contaminated by lead slag is dangerous to man and the ecosystem
rice husk biochar (RHB) and CNSB have low Pb contents of 1.50, 0.90 and 1.2 mg/kg respectively, suggesting that there is no considerable contribution of Pb level when these materials are applied to the soil
The physico-chemical parameters of compost, rice husk biochar and to an extent cashew nut shell biochar present them as non-toxic, potential soil fertilisers and heavy metal immobilising agents
Summary
A high concentration of lead in soil that is contaminated by lead slag is dangerous to man and the ecosystem. The level of Pb above background concentrations in soil affects soil fertility, plant and animal health. High levels of Pb in soil can alter biomass of soil microbes and their activities in nutrient recycling. They can cause plant physiological disturbances such as oxidative stress and reduction in plant yield [1]. A high concentration of Pb in soil is capable of migrating to other environmental media such as air and water bodies where it becomes poisonous to living organisms. Lead accumulation in human systems has been associated with neurological, reproductive, developmental, metabolic and behavioral changes [2]
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