Vol.:(0123456789) 1 3 Bulletin of Environmental Contamination and Toxicology https://doi.org/10.1007/s00128-018-2339-z Citrus Epicarp-Derived Biochar Reduced Cd Uptake and Ameliorates Oxidative Stress in Young Abelmoschus esculentus (L.) Moench (okra) Under Low Cd Stress Clement O. Ogunkunle 1  · Mayank Varun 2  · Iyanuoluwa G. Ogundele 1  · Kehinde S. Olorunmaiye 3  · Manoj S. Paul 2 Received: 31 January 2018 / Accepted: 13 April 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Due to the important role of biochar (BC) in reducing metal-toxicity in plants, this study was aimed at assessing the poten- tial of citrus epicarp-derived BC in ameliorating Cd toxicity in young Abelmoschus esculentus (okra) under low Cd toxic- ity. Okra was grown in soil amended with BC at four treatment levels for 49 days as follows: control (A), sole 1.4 mg Cd/ kg-spiked soil (B), 1.4 mg Cd/kg-spiked soil + 1% BC (C) and 1.4 mg Cd/kg-spiked soil + 3% BC (D). The results showed a dose-dependent reduction in shoot accumulation of Cd due to the BC application. In addition, compared to control and sole Cd-amended soil, BC treatments (both at 1% and 3% w/w) decreased the oxidative stress, and enhanced activities of enzymatic and non-enzymatic antioxidants in the young okra. Generally, the application of BC to the soil was efective in ameliorating the Cd-induced oxidative stress in okra with limited shoot bioaccumulation of Cd. Keywords Sweet orange · Biochar · Okra · Heavy metals · Antioxidant enzymes · Metal-induced stress In the last two decades, the concerns for heavy metal con- tamination in environment has increased (Moon et al. 2013) due to their persistence in the pedosphere, even after remov- ing the pollution sources (Imperato et al. 2003). Heavy met- als have signifcant ability to accumulate in soils as well as in food crops and thus can afect human health directly or indirectly via dietary intake (Xu et al. 2015; Yousaf et al. 2016). Among the heavy metals, cadmium (Cd) is a known major contaminant of soil, posing signifcant ecological and human hazards. The normal concentration of Cd in agri- cultural soils is < 1 mg kg −1 (Adriano 2001), but excessive content of Cd in soil matrix can induce toxic symptoms in plants, such as alteration in mineral nutrition, protein and carbohydrate metabolism; and reduction in biomass pro- duction (Figueiredo et al. 2014). At cellular and subcellular levels, the activation and inactivation of enzymes with sev- eral interactions of electron transport chain with nucleic acid can be altered, thereby leading to overproduction of reactive oxygen species (ROS) causing oxidative stress in plants (Chen et al. 2003). To counteract the efects of ROS, plants produce various antioxidant enzymes, such as cata- lases (CAT), superoxide dismutase (SOD), ascorbate per- oxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (POX) and low-molecular weight quenchers such as phenol, favonoid, ascorbic acid, thiols and proline (Ruley et al. 2004; Alvarez et al. 2012; Sarathambal et al. 2017). Malondialdehyde (MDA) is a cytotoxic product of lipid per- oxidation and an indicator of free radical production. The increase level of MDA may result from the overproduction of ROS. The extent of survival and tolerance of plants to stress depends on their ability to make a balance between the production of toxic oxygen derivatives and capacity of antioxidative defence systems. Remediation of metal contaminants in soil is important for safe crop cultivation. Phytoremediation has become a promising technique in soil remediation because it ofers in situ advantages, is cost efective, and is less energy-inten- sive than high-cost traditional cleanup methods (Lim et al. 2013). Heavy metal accumulation in plants can be mini- mized by the addition of organic/inorganic amendments. * Clement O. Ogunkunle seyeogunkunle@gmail.com; ogunkunle.co@unilorin.edu.ng 1 Environmental Biology Unit, Department of Plant Biology, University of Ilorin, Ilorin 240003, Nigeria 2 Department of Botany, St. John’s College, Agra, Uttar Pradesh 282 002, India 3 Plant Physiology and Biochemistry Unit, Department of Plant Biology, University of Ilorin, Ilorin 240003, Nigeria