Chemical speciation and distribution of potentially toxic elements in soilless cultivation of cucumber with sewage sludge biochar addition

Summary

This study investigated the efficacy of sewage sludge biochar as a soilless cultivation substrate amendment for immobilising potentially toxic elements and reducing their bioavailability to cucumber plants. Amendment with 10 wt% biochar proved optimal, significantly reducing fruit concentrations and bioavailable fractions of multiple elements whilst meeting Chinese food safety standards (GB 2762-2012), with minimal plant uptake of elements present in the biochar. The findings suggest sewage sludge biochar is a suitable and safe substrate amendment for horticultural production, contingent upon appropriate application rates.

Regional applicability

This study was conducted in China and reflects Chinese food safety standards and soilless cultivation practices. The methodology and findings are relevant to United Kingdom horticulture, particularly as soilless systems are increasingly used in protected cropping; however, UK regulations and substrate standards differ and would require verification of element safety thresholds and local applicability.

Key measures

Chemical speciation of As, Cd, Cr, Ni, Cu, Zn; bioavailable fractions; element concentrations in cucumber tissues (fruit, leaves, roots); plant biomass; bioavailability indices

Outcomes reported

The study examined chemical speciation, bioavailability, and plant uptake of potentially toxic elements (As, Cd, Cr, Ni, Cu, Zn) in cucumber grown in soilless substrate amended with sewage sludge biochar at various concentrations. Results demonstrated that 10 wt% biochar addition optimally reduced element bioavailability and cucumber fruit contamination whilst maintaining plant biomass.

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