Synergistic and concentration-dependent toxicity of multiple heavy metals compared with single heavy metals in Conocarpus lancifolius

Amina Redha,Redha Al-Hasan,Mohammad Afzal,Mohammad Afzal

doi:10.1007/s11356-020-12271-0

Amina Redha, Redha Al-Hasan + Show 2 more

Open Access

https://doi.org/10.1007/s11356-020-12271-0

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Abstract

While heavy metals (HMs) naturally occur in soil, anthropogenic activities can increase the level of these toxic elements. Conocarpus lancifolius Engl. (Combretaceae) was investigated as a potential phytoremediator of soils contaminated with HM containing crude oil. This study assessed the potential of C. lancifolius (CL), a locally available plant species in Kuwait, for resolving local issues of the HM-contaminated soils. The absorption, accumulation, and distribution of three toxic HMs (Cd, Ni, and Pb) and essential metals (Fe, Mg, and metalloid Se) were examined, and their role in plant toxicity and tolerance was evaluated. Conocarpus lancifolius plants were exposed to two different concentrations of single and mixed HMs for 30 days. The accumulation of HMs was determined in the roots, leaves, stems, and the soil using ICP/MS. Biomass, soil pH, proline and protein content, and bioaccumulation, extraction, and translocation factors were measured. The bioaccumulation, extraction, and transcription factors were all >1, indicating CC is a hyperaccumulator of HM. The HM accumulation in CL was concentration-dependent and depended on whether the plants were exposed to individual or mixed HMs. The C.C leaves, stems, and roots showed a significant accumulation of antioxidant constituents, such as proline, protein, Fe, Mg, and Se. There was an insignificant increase in the soil pH, and a decrease in plant biomass and a significant increase in protein, and osmoprotective-proline as a result of the interaction of mixed heavy metals that are more toxic than single heavy metals. This study indicates that C. lancifolius is a good candidate for phytoremediation of multiple HM-contaminated soils. Further studies to establish the phyto-physiological effect of multiple heavy metals are warranted.

Highlights

During the extraction and transport of crude oil, heavy metals (HMs) become an important component of the soil, and because HMs are nondegradable, they persist in the environment and they impose potential human health and ecological risks (Lian et al 2019; Yan et al 2020)
Compared with the control plants, plants exposed to single HMs at 50 μmol L−1 had a significantly higher HMs accumulation than those exposed to single HMs at 25 μmol L−1, revealing the effect of HM concentration on HM accumulation both in the leaves and roots
Plants exposed to the mixed HMs at 25 μmol L−1 showed an different concentrations: Uptake of heavy metals in roots a, b, leaves c, d, and stems e after Conocarpus lancifolius plants were exposed to single (25 or 50 μmol L−1) and mixed heavy metals (HMs) 25 μmol L−1. d The metal enclosed in brackets represents the metal that was measured in the mixture

Summary

Introduction

During the extraction and transport of crude oil, heavy metals (HMs) become an important component of the soil, and because HMs are nondegradable, they persist in the environment and they impose potential human health and ecological risks (Lian et al 2019; Yan et al 2020). In response to oxidative stress (OS), HMs cause a steady rate of the production of reactive oxygen species (ROS) causing extensive cellular damage to the live organisms (Gao. Responsible Editor: Elena Maestri et al 2019; Hasanuzzman et al 2020). The production of ROS reduces the antioxidant defenses, which negatively affects cytoplasmic enzymes and causes a serious impairment of cellular structure, leading to physicochemical changes in the plants (Shahid et al 2014; Nanda and Agrawal 2016; Laxa et al 2019). The damage can be aggravated by altering the morphology and growth dynamics of plants and the damage places reliance on the rate of accumulation of the HMs (Küpper et al 2006). Plants have dissimilar HM-accumulation capacities, and species with higher amassing potentials, such as Brassica juncea (Brassicaceae) subsp. Integrifolia, Var. strumata and B. napus, have been used for the phytoremediation of HM-contaminated ecosystems (Mourato et al 2015)

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