Uptake of Chromium by Portulaca Oleracea from Soil: Effects of Organic Content, pH, and Sulphate Concentration

Ayman Alyazouri,Hassan Tayim,Paul Humphreys,Mohammad H Al-Sayah,Roger Jewsbury

doi:10.1155/2020/3620726

Abstract

Phytoextraction is an effective and environment-friendly approach for remediation of soil polluted with toxic metals. Portulaca oleracea is a potential hyperaccumulator of Cr(VI) from polluted soil. In this study, the effect of soil organic content, pH, and sulphate concentration on phytoextraction of Cr(VI) using Portulaca oleracea was investigated. Seedlings of Portulaca oleracea were grown in soils with (i) three organic content compositions, (ii) six levels of pH, and (iii) six concentrations of sulphate salts; all were irrigated with Cr(VI) solutions at 200 ppm concentration. Chromium concentration in different tissues of plants was monitored under the variant conditions. Results indicated that the uptake of Cr(VI) by Portulaca oleracea is favoured at (i) low organic content soil (0.42%), (ii) slightly alkaline pH range (∼8), and (iii) with sulphate concentration in the range of 300–600 ppm.

Highlights

Portulaca oleracea is a succulent plant native to the Mediterranean area, but it grows in several parts of the world from India to Australia and North America. e plant is a self-compatible annual weed that grows fast and can reach up to 40 cm in height
P. oleracea accumulated ∼3,000 mg/kg of chromium in the presence of 0.42% of organic matter, but this concentration decreased to 530 mg/kg at 17.5% and to below 180 mg/ kg at 35% organic matter. is change was concomitant with a decrease in the bioaccumulation factor (Figure 1(c)) of Cr(VI) from 27 to 5.5 and a decrease of the concentration of Cr(VI) available in the soil (Figure 1(b)) from 107 mg/kg to 21 mg/kg
bioaccumulation factor (BAF) of total chromium (Figure 1(c)) followed a parallel trend to that of Cr(VI) but to a lower extent indicating that chromium uptake by the plant is mainly of Cr(VI). e concentration of total chromium (Figure 1(b)) in the soil shows that as the organic content increased, more chromium remained in the soil the concentration of Cr(VI) decreased. is can be attributed mainly to the reduction of Cr(VI) to Cr(III) due to the oxidation of organic compounds

Summary

Introduction

Portulaca oleracea is a succulent plant (family Portulacaceae) native to the Mediterranean area, but it grows in several parts of the world from India to Australia and North America. e plant is a self-compatible annual weed that grows fast and can reach up to 40 cm in height. Ese studies show that the plant has a high tolerance for many metals, including Cd (II), Cu(II), Cr(III), Cr(VI), Fe(III), Mn(II), Ni (II), Pb(II), and Zn(II) ions, and has the ability to extract them to its roots from either soil or aqueous solutions with variant capacities. It was, established that P. oleracea is a hyperaccumulator for Cr(VI); a hyperaccumulator plant can extract the metal at concentrations ten times (at least) higher than their concentrations in the soil or wastewater. BAF is the ratio of the concentration of metal in dry roots (mg/kg dry weight) to the concentration of metal in dry soil or wastewater (mg/kg or ppm)

Methods

Results

Conclusion