Abstract
In-situ remediation of heavy-metal-contaminated soil in farmland using phytostabilization combined with soil amendments is a low-cost and effective technology for soil pollution remediation. In this study, coconut shell biochar (CB, 0.1% and 0.5%), organic fertilizer (OF, 3.0%), and Fe-Si-Ca material (IS, 3.0%) were used to enhance the phytostabilization effect of ramie (Boehmeria nivea L.) on Cd and Pb in highly polluted soils collected at Dabaoshan (DB) and Yangshuo (YS) mine sites. Results showed that simultaneous application of CB, OF, and IS amendments (0.1% CB + 3.0% OF + 3.0% IS and 0.5% CB + 3.0% OF + 3.0% IS, DB-T5 and DB-T6) could significantly increase soil pH, reduce the concentrations of CaCl2-extractable Cd and Pb, and increase the contents of Ca, P, S, and Si in DB soil. Under these two treatments, the growth of ramie was significantly improved, its photosynthesis was enhanced, and its levels of Cd and Pb were reduced, in comparison with the control (DB-CK). After applying DB-T5 and DB-T6, the concentrations of Cd and Pb in roots were decreased by 97.7–100% and 64.6–77.9%, while in shoots they were decreased by up to 100% and 92.9–100%, respectively. In YS-T4 (0.5% CB + 3.0% OF), the concentrations of Cd and Pb in roots were decreased by 39.5% and 46.0%, and in shoots they were decreased by 44.7% and 88.3%. We posit that phytostabilization using ramie and amendments could reduce the Cd and Pb bioavailability in the soil mainly through rhizosphere immobilization and plant absorption. In summary, this study suggests that the use of tolerant plant ramie and simultaneous application of coconut shell biochar, organic fertilizer, and Fe-Si-Ca materials is an effective stabilization strategy that can reduce Cd and Pb availabilities in soil. Ultimately, this strategy may reduce the exposure risk of crops to heavy metal pollution in farmland.
Highlights
The 2014 National Soil Pollution Status Survey Bulletin of China [1] reported that the national soil over-standard rate for pollutants reached 16.1%, among which heavy metal pollution contributed most significantly (82% of the rate)
A pot experiment was conducted using ramie and a series of amendments to study the phytostabilization effect of Cd- and Pb-polluted farmland soils collected at Dabaoshan (DB) and Yangshuo (YS) mining areas
The shoot Cd and Pb concentrations of DB-T5 and DB-T6 were decreased by up to 100% and by 92.9–100% compared with the DB-CK
Summary
The 2014 National Soil Pollution Status Survey Bulletin of China [1] reported that the national soil over-standard rate for pollutants reached 16.1%, among which heavy metal pollution contributed most significantly (82% of the rate). Chemical immobilization, which involves the use of carbon-, lime-, sepiolite-, bentonite-, clay-mineral-, and silicate-based soil amendments, appears to be the most feasible technology for remediation of heavy-metal-contaminated farmland soil [6,7,8,9]. Addition of organic and inorganic soil amendments can promote the fixation of the metal and can enhance the effect of stable plant restoration [13]. A pot experiment was conducted using ramie and a series of amendments (i.e., coconut shell biochar, organic fertilizer, and Fe-Si-Ca material) to study the phytostabilization effect of Cd- and Pb-polluted farmland soils collected at Dabaoshan (DB) and Yangshuo (YS) mining areas. The results are expected to provide theoretical and practical basis for establishing an effective remediation system for the multi-metal polluted farmland soil
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