Abstract
Heavy metal pollution, manifested by the accumulation, toxicity and persistence in soil, water, air, and living organisms, is a major environmental problem that requires energetic resolution. Mining tailing areas contain metal minerals such as Cu, Zn, Pb, Cr and Cd in high concentrations that pollute the environment and pose threats to human health. Phytoremediation represents a sustainable, long-term, and relatively inexpensive strategy, thus proving to be convenient for stabilizing and improving the environment in former heavy metal-polluted mining sites. This study presents the bioremediation potential of Silphium perfoliatum L. plants, in the vegetative stages of leaf rosette formation, grown on soil polluted with heavy metals from mining dumps in Moldova-Noua, in the Western part of Romania. The bioaccumulation factor (BAF), translocation factor (TF), metal uptake (MU) and removal efficiency (RE) of Cu, Zn, Cr and Pb by S. perfoliatum plants were determined in a potted experiment in controlled environmental conditions. The reference quantities of heavy metals have been determined in the studied soil sample. The experiment followed the dynamics of the translocation and accumulation of heavy metals in the soil, in the various organs of the silphium plants, during the formation of the leaf rosette (13-18 BBCH). The determination of the amount of heavy metals in soil and plants was achieved by the method of digestion with hydrochloric and nitric acid 3/1 (v/v) quantified by atomic absorption spectroscopy (AAS). The obtained experimental results demonstrate that the substrate has a high heavy metal content being at the alert threshold for Zn (260.01 mg kg-1 in substrate compared with alert threshold 300 mg kg-1) and at intervention thresholds for other metals (Cu -234.66 mg kg-1/200 mg kg-1; 299.08 mg kg-1/300 mg kg-1 and Pb-175.18 mg kg-1/100 mg kg-1). The average concentration of the metals determined in dynamics in the dry biomass of plants varied between roots, petioles, and laminas. The root is the main accumulator for Cu and Cr (Cu – 37.32 mg kg-1 -13 BBCH to 43.89 mg kg-1-15 BBCH and 80.71 mg kg-1 – 18 BBCH; Cr – 57.43 mg kg-1 – 13 BBCH to 93.36 mg kg-1 -18 BBCH), and for Zn and Pb the lamina seems to carry the same function. Preliminary results show that Silphium perfoliatum may be a viable alternative in the bioremediation and treatment of heavy metal-contaminated area.
Highlights
Soil pollution with heavy metals is an environmental problem that manifests itself globally
Heavy metals concentration in the experimental substrate Mean concentrations of Cu, Zn, Cr and Pb in the soil collected from the mining area of Moldova Noua, used as a growth substrate for S. perfoliatum during the formation of the rosette of leaves (13-18 BBCH) are relatively high, exceeding normal values, being in alert or intervention thresholds for sensitive soil use types according to Romanian legislation (Order 756/1997, Environmental Pollution Assessment Regulation) (Table 1)
High concentrations of Pb of 175.18 mg kg-1 were encountered, well above the threshold for intervention of 100 mg kg-1 and of Cu 234.66 mg kg-1, over to the intervention threshold (200 mg kg-1), while the Zn concentration is below the alert threshold (300 mg kg-1)
Summary
Soil pollution with heavy metals is an environmental problem that manifests itself globally. The presence of heavy metals in soils is mainly due to anthropogenic activities such as mining, steel casting, medical waste, chaotic application of pesticides and fertilizers, use of wastewater for irrigation, burning of leaded gasoline, coal, etc. Heavy metals have negative effects on the health of humans and animals mainly due to the tendency to bio-accumulate in the food chain and their long-term persistence in the environment (Yoon et al, 2006; Azimi et al, 2017; Shen et al, 2019; Sall et al, 2020). The abandoned mines and accumulated residues are the source of heavy metal pollution, which is washed away and can contaminate all environmental components (Liakopoulos et al, 2010; Li et al, 2014, Yang et al, 2018)
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