The Innovation Team of Soil Health Care of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS), has made significant progress in understanding the immobilization mechanism of cadmium (Cd) in alkaline soils. Their findings, titled "Protaetia brevitarsis larvae produce frass that can be used as an additive to immobilize Cd and improve fertility in alkaline soils," have been published in the "Journal of Hazardous Materials" (IF = 13.6).

The issue of excessive Cd in alkaline farmlands in North China, along with low soil fertility, poses a significant challenge to regional food security production, necessitating the development of multifunctional immobilization materials. Humic substances and other organic materials contain abundant organic functional groups with strong binding capabilities to heavy metal ions. They can also regulate soil physical and chemical properties, enhancing soil fertility, and making them a promising amendment for alkaline soil heavy metal improvement. The biological transformation technology mediated by larvae of Protaetia brevitarsis is a highly promising method for utilizing agricultural waste resources. The frass produced by these larvae is considered a highly humified organic fertilizer that can significantly improve seed germination rates and promote crop growth. However, there has been limited research on the Cd immobilization mechanism of this high-quality soil amendment in alkaline soils.

This study conducted adsorption experiments to investigate the adsorption effects and mechanisms of frass produced by Protaetia brevitarsis larvae feeding on maize straw, rice straw, and sawdust on Cd in alkaline solutions. The frass with the maximum Cd sorption capacity was selected for the pot experiment to evaluate its comprehensive effects on Cd immobilization and fertility enhancement in different alkaline soils through redundancy analysis and path analysis. The adsorption experiment results showed that the maize straw frass had the highest sorption capacity for Cd (176.67-227.27 mg g^-1). X-ray absorption near-edge structure (XANES) and Fourier-transform infrared (FTIR) spectroscopy confirmed that Cd in the maize straw frass primarily existed in an organic-bound form (88-89%), with the abundant C-O, C=O, and O-H bonds capable of binding with Cd. The pot experiment demonstrated that the addition of 0.5% and 1.5% maize straw frass significantly reduced the exchangeable Cd content in different alkaline soils (5.65-18.48%) and increased soil organic matter and available nutrient content.

This research indicates the feasibility of applying frass produced by Protaetia brevitarsis larvae feeding on maize straw for detoxification and fertilization in alkaline Cd-contaminated soils, providing theoretical support for the immobilization technique in alkaline Cd-contaminated soils.

Researcher Yang Jianjun from IARRP, and Professor Wang Xudong from the College of Resources and Environment at Northwest A&F University are the authors of the paper. This work was supported by the National High-Level Talents Special Support Plan for Young Top Talents (2022-2025), the National Modern Agricultural Industry Technology System Special Fund (CARS-03), and the Agricultural Science and Technology Innovation Program of the Chinese Academy of Agricultural Sciences (2021-2025).

Original article link: https://doi.org/10.1016/j.jhazmat.2024.134379