Prediction models for monitoring selenium and its associated heavy-metal accumulation in four kinds of agro-foods in seleniferous area

DL-alanine promotes the colonization of Pseudomonas aeruginosa and their synergistic enrichment of selenium and decrease of cadmium absorption by Brassica napus

In selenium-rich regions, selenium and cadmium coexist in soil, posing a threat to agricultural product safety. This study explores the influence of Pseudomonas aeruginosa and DL-alanine on selenium and cadmium uptake in Brassica napus. Through pot and medium experiments, along with FTIR and XPS analyses, we found that DL-alanine significantly boosts Pseudomonas aeruginosa biofilm formation and root colonization. Compared with the control group, the combined treatment of DL-alanine and Pseudomonas aeruginosa increased the selenium content in the shoots by 55.8 %, and decreased the cadmium content in the shoots and roots by 66.3 % and 67.9 %, respectively. The direct reason for this result is that the available selenium in the rhizosphere soil increased by 32 % and the available cadmium decreased by 10 %. Further investigation shows that DL-alanine promotes the transformation of Se(0) to Se(-II) and the formation of CdSe nanoparticles by Pseudomonas aeruginosa, which enhances the availability of selenium and reduces that of cadmium. Furthermore, gene expression analysis revealed that the expression levels of selenium-related genes were upregulated, while those of cadmium transport genes were downregulated. This study proposes a new method for improving selenium utilization and reducing cadmium absorption in soils where selenium and cadmium coexist, providing a theoretical basis for safer agricultural practices.

Stabilization mechanism and remediation effectiveness of Pb and cd in agricultural soil using nonmetallic minerals

Soil contaminated by Pb and Cd has aroused worldwide concern due to the environmental hazards they pose. The effects, mechanisms, and evaluation of Pb and Cd contaminated agricultural soil remediation by nonmetallic minerals are still poorly understood. In this study, solidification/stabilization experiments were used to screen nonmetallic mineral materials and optimize their dosages. Stabilization mechanisms of Pb and Cd by nonmetallic mineral materials were investigated by adsorption kinetics, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. The effectiveness of soil remediation was further confirmed through a pot experiment with pak choi (Brassica rapa L. subsp. chinensis), an important non-heading leafy vegetable. Results demonstrated that the SL composite (composed of 2.5% sepiolite and 1.5% limestone, with a total dosage of 4.0%) exhibits the optimal stabilization effect on soil contaminated with Pb and Cd. In soils with low, medium, and high contamination levels, SL reduced the bioavailability of Pb by 97.97%, 96.78%, and 95.82%, and the bioavailability of Cd by 92.96%, 91.76%, and 91.02%, respectively. SL surfaces are rich in hydroxyl (-OH) and carbonate (CO32-) groups, enabling binding with Pb and Cd ions to form hydroxide and carbonate precipitates. Such interactions suggest that chemical adsorption primarily drives Pb and Cd ion stabilization, reducing their bioavailability in soil. Pak choi grown in SL-remediated soil exhibited Pb and Cd contents compliant with China's food safety standards. These findings further validate the bioavailability reduction rate as a suitable metric for evaluating the remediation effectiveness of heavy metal pollution in agricultural soils. This study provides a new strategy for evaluating the remediation efficiency of heavy metal-contaminated agricultural soil.

Selenium and Bacillus proteolyticus SES increased Cu-Cd-Cr uptake by ryegrass: highlighting the significance of key taxa and soil enzyme activity

Many studies have focused their attention on strategies to improve soil phytoremediation efficiency. In this study, a pot experiment was carried out to investigate whether Se and Bacillus proteolyticus SES promote Cu-Cd-Cr uptake by ryegrass. To explore the effect mechanism of Se and Bacillus proteolyticus SES, rhizosphere soil physiochemical properties and rhizosphere soil bacterial properties were determined further. The findings showed that Se and Bacillus proteolyticus SES reduced 23.04% Cu, 36.85% Cd, and 9.85% Cr from the rhizosphere soil of ryegrass. Further analysis revealed that soil pH, organic matter, soil enzyme activities, and soil microbial properties were changed with Se and Bacillus proteolyticus SES application. Notably, rhizosphere key taxa (Bacteroidetes, Actinobacteria, Firmicutes, Patescibacteria, Verrucomicrobia, Chloroflexi, etc.) were significantly enriched in rhizosphere soil of ryegrass, and those taxa abundance were positively correlated with soil heavy metal contents (P < 0.01). Our study also demonstrated that in terms of explaining variations of soil Cu-Cd-Cr content under Se and Bacillus proteolyticus SES treatment, soil enzyme activities (catalase and acid phosphatase) and soil microbe properties showed 42.5% and 12.2% contributions value, respectively. Overall, our study provided solid evidence again that Se and Bacillus proteolyticus SES facilitated phytoextraction of soil Cu-Cd-Cr, and elucidated the effect of soil key microorganism and chemical factor.