Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Lead accumulation, growth responses and biochemical changes of three plant species exposed to soil amended with different concentrations of lead nitrate Chandana Chandrasekhar a , Joseph George Ray b, ⁎ a Laboratory of Ecology and Eco-Technology, School of Biosciences, Mahatma Gandhi University, Kottayam, Kerala 686560, India b School of Biosciences, Mahatma Gandhi University, Kottayam, Kerala 686560, India ARTICLE INFO Keywords: Phytoremediation Heavy metal stress Antioxidant enzymes Lead toxicity Eclipta prostrata Abiotic stress response ABSTRACT Lead (Pb) contamination of soil is a serious environmental problem, adversely affecting ecosystems, globally. Phytoremediation is an alternative to conventional methods of soil remediation. The success of phytoremedia- tion depends on the identification of suitable native plant species with high biomass to deal with metal con- tamination. In the present experiment, response of Eclipta prostrata (L.) L., Scoparia dulcis L. and Phyllanthus niruri L. to increase in concentrations of PbNO 3 ·5H 2 O in the soil for a period of 30 days was tested to assess their suitability in phytoremediation. Pb accumulation in all the three plants was in a concentration-dependent manner. Although S. dulcis survived the soil metal concentrations, it exhibited a stunted growth; P. niruri was found susceptible to Pb toxicity; E. prostrata recorded a maximum uptake of 12484 μg/g dry weight in its root and 7229 μg/g dry weight in its shoot, without any adverse impact on growth traits. Bioconcentration factor and translocation factor of the three plants were also calculated, which revealed that E. prostrata has Pb accumu- lation potential. Therefore, enzymatic antioxidant activities and transmission electron microscopic analysis were carried out to determine the physiological adaptation and tolerance of E. prostrata to Pb stress. Overall, E. prostrata is identified as a tolerant plant showing Pb hyperaccumulation tendencies with essential features for phytoextraction. 1. Introduction Lead contamination from geogenic or anthropogenic activities has now become a serious global environmental issue. Technological ad- vancement, industrialisation, urbanization, uncontrolled use of fossil fuel resources, use of pesticides, chemical fertilizers, mining, smelting activities and improper waste management remain the major causes of elevated levels of toxic heavy metals in soil (Lajayer et al., 2017; Padmavathiamma and Li, 2010). Lead is highly toxic and hazardous to humans as well as plants even at low concentrations and has no known biological function (Wang et al., 2016). The conventional methods of removing metals from contaminated environments are not cost effective. A new method known as phytor- emediation for cleaning of metal or organic chemicals from con- taminated environments by using plants has recently emerged as an eco-friendly and economic way of dealing with the issue. It utilizes the ability of specific plants to accumulate or retain or degrade the toxic metal or organic contaminants in soil, water or air. However, the success of phytoremediation depends upon the identification of native high biomass yielding, metal tolerant plants and the exact capacity and mechanism in them for accumulating, detaining or degrading the con- taminant and also the parts of the plant where the same is carried out (Chandrasekhar and Ray, 2017; Gerhardt et al., 2017; Marques et al., 2017). In general, understanding the capability of plants in accumu- lating a metal in its shoots or roots is the clue for identification of metal hyperaccumulator species, which are useful in phytoextraction and phytostabilization. Since Pb is a non-biodegradable inorganic pollutant as well as a non- essential metal, its long-term persistence in soil is a great threat to the environment (Amari et al., 2017; Gerhardt et al., 2017). The excessive amount of lead in soil may cause stress-induced changes in plants in- cluding growth reduction, decreased biomass, leaf chlorosis, many other physiological and biochemical changes (Yongsheng et al., 2011). The toxic Pb is very difficult to be removed from the soil because of its low bioavailability, owing to the formation of strong bonds with or- ganic and inorganic ligands in soil (Chaney et al., 1997; Cunningham https://doi.org/10.1016/j.ecoenv.2018.12.058 Received 13 October 2018; Received in revised form 18 December 2018; Accepted 20 December 2018 ⁎ Corresponding author. E-mail address: jgray@mgu.ac.in (J.G. Ray). Ecotoxicology and Environmental Safety 171 (2019) 26–36 0147-6513/ © 2018 Elsevier Inc. All rights reserved. T