Compositional changes and ecological characteristics of earthworm mucus under different electrical stimuli

Earthworm mucus is rich in nutrients that can initiate the mineralization and humification of organic matter and is of great importance for contaminated soil remediation and sludge reutilization. In this study, six voltage and current combinations were utilized to promote earthworm mucus production (5 V and 6 V at 10, 20 and 30 mA, respectively), to explore the compositional changes of the mucus produced under different electrical stimuli, and to propose the best electrical stimulation group and mucus fraction applicable to soil heavy metal pollution remediation and sludge reutilization. The results showed that the mucus produced by the six electrical stimuli was mainly composed of proteins, amino acids, carbohydrates, fatty acids, and polysaccharides, with small amounts of alcohol, phenol, and ester organic substances. Under different electrical stimuli, each component changed significantly (P < 0.05). pH and conductivity were higher at 6 V 20 mA, total nitrogen and phosphorus contents reached their maximum at 5 V 30 mA, and total potassium at 6 V 10 mA. Protein, amino acids, and carbohydrates were most abundant in the mucus produced at 5 V 10 mA, while trace metal elements reached their lowest values at 5 V 10 mA. Finally, based on principal component analysis and combined with previous studies, it was concluded that the mucus produced at 5 V 10 mA was weakly alkaline, high in amino acids and nutrients and low in trace metal elements, and most suitable for sludge and straw composting experiments, soil remediation and amendment experiments.