Remediation mechanism of “double-resistant” bacteria—Sedum alfredii Hance on Pb- and Cd-contaminated soil

Abstract

Background: Concentrations of heavy metals continue to increase in soil environments as a result of both anthropogenic activities and natural processes. Cadmium (Cd) and lead (Pb) is one of the most toxic heavy metals and pose health risks to both humans and the ecosystem. Therefore, effectively solving the problem of heavy metal pollution is the concern of soil workers. Among the existing remediation techniques, only the combined use of microorganisms and plants for remediation of heavy metal-contaminated soil is the greenest and most developed one. Consequently, based on this background, this study investigates the remediation mechanism of Pb and Cd heavy metals using the combined action of bacteria and Sedum alfredii Hance. Methods: In order to enrich the research theory of combined plant and microorganism remediation of heavy metal-contaminated soil, we constructed a heavy metal composite pollution remediation system by combining Pb and Cd-tolerant bacteria with the Pb and Cd hyperaccumulator plant—Sedum alfredii Hance to investigate its combined remediation effect on Pb and Cd composite contaminated soil. Results: The results showed that resistant bacteria were able to promote enrichment of Pb and Cd in Sedum alfredii Hance and J2 (200 ml of bacterial solution) was significantly (P < 0.05) more effective than J1 (100 ml of bacterial solution). The resistant bacteria were able to alleviate the toxic effects of Pb and Cd heavy metals on Sedum alfredii Hance and promote growth while reducing rhizosphere soil pH. The resistant bacteria were able to significantly reduce the effective state of Pb and Cd in the rhizosphere soil (P < 0.05), with the greatest reduction in the effective state of Pb in treatment A (Cd7Pb100 mg/kg), where J2 was reduced by 9.98% compared to J0, and the greatest reduction in the effective state of Cd in treatment C (Cd28Pb400 mg/kg), where J2 was 43.53% lower than J0. In addition, the resistant bacteria were able to increase the exchangeable state Cd content by 0.97 to 9.85%. The resistant bacteria had a weakly promoting effect and a highly inhibitory effect on the absorption of Pb by Sedum alfredii Hance. Conclusions: The resistant bacteria can change the rhizosphere environment and significantly improve the remediation effect of Sedum alfredii Hance on heavy metal cadmium. The role of “double-resistant” bacteria in promoting the accumulation of Cd was greater than that of Pb.