Biochar Addition Decreases the Mobility, Bioavailability, and Phytotoxicity of Potentially Toxic Elements in an Agricultural Contaminated Soil

ABSTRACT

The implementation of organic amendments, such as biochar and compost, can be an effective and innovative environmental friendly option for the recovery of functionality of soils contaminated by potentially toxic elements (PTE). The aim of this study was therefore to assess the influence of a biochar added at 3% w/w (Bio) and its combination with a municipal solid waste compost (MSWC), on the mobility, bioavailability, and phytotoxicity of several (PTE), As (55 mg·kg⁻¹), Sb (84 mg·kg⁻¹), Ni (176 mg·kg⁻¹) and Cr (214 mg·kg⁻¹) present in a contaminated soil (TS). Sequential extraction procedures showed that biochar and its combination with MSWC decreased soil labile PTE, with biochar increasing remarkably their residual fraction compared to TS-soil (+47, 59, 4, and 9% for As, Sb, Cr, and Ni respectively). Amendment addition also favored an increase of the metabolic potential and catabolic versatility of soil microbial communities, as well as soil functionality. Dehydrogenase, β-glucosidase, and urease activities in TS+Bio showed a significant increase (+45, 16, and 21% respectively) with respect to control. Results from a pot experiment showed that all treatments increased the plant yields significantly in the order: Bio>Bio-MSWC>TS (e.g. the shoot length of green bell pepper and wheat grown on Bio increased, respectively, by a factor of 1.8 and 1.2 compared to TS plants). The amendments addition also reduced PTE transfer from root to shoot. Overall, the results obtained indicated that biochar addition at 3% can be an effective environmental friendly strategy for the in situ stabilization of PTE in polluted soils.

KEYWORDS:

• PTE-polluted soils
• organic amendments
• community level physiological profile
• biomass production
• PTE-uptake

Conclusions

Biochar and its combination with compost showed a significant efficiency at reducing the labile fraction of As, Sb, Cr, and Ni present in a polluted Lebanese soil and increasing their residual fractions. Both treatments increased selected soil enzyme activities, notably DHG, URE, and GLU, and had a strong (positive) influence on the potential catabolic activity of soil microbial communities as highlighted by the Biolog CLPP. This was also accompanied by an enhanced growth of green bell pepper and wheat in the amended soils. PTE uptake by wheat and green bell pepper, and their translocation factor, was reduced for plant grown on amended soils and followed the order: control soil ≥ Bio-MSWC ≥ Bio.

The results obtained suggest that biochar addition can represent a new effective strategy to remediate PTE-contaminated soils, while limiting the contaminants uptake by plants and reducing the possible risks to human health. However, further studies are needed to evaluate the long-term effectiveness of such approach, especially under field conditions, and to assess possible PTE transfer in food and feed.

Acknowledgments

The financial support of the University of Sassari (Fondo di Ateneo per la Ricerca 2020) is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website