Study on the life maintenance mechanism of Eisenia fetida under low-density polyethylene stress: Based on path analysis and canonical correlation analysis.

The widespread use but low recovery rate of agricultural films has led to microplastic accumulation in farmlands, which poses a serious threat to the health of the soil ecosystem. There is an urgent need for early warning and monitoring of soil microplastics pollution, as well as the performance of bioremediation research. In this study, earthworms were used as test organisms to carry out toxicological tests under low-density polyethylene (LDPE) stress. A canonical correlation analysis model (CCA) was established to analyze the relationship between oxidative stress and microbial community. A path analysis model (PA) was also constructed to examine the detoxification mechanism of earthworms under LDPE stress. The results showed that low concentrations (100 and 500 mg/kg) of LDPE did not cause oxidative damage to earthworms but stimulated their physiological metabolism. Meanwhile, 1000 mg/kg LDPE concentrations caused oxidative damage to earthworms and altered their internal microbial community structure. Furthermore, at 1500 mg/kg LDPE concentrations, the oxidative stress to the earthworms is aggravated, and their physiological responses work in conjunction with the microbial community to cope with the adverse condition. Lastly, treatment with 2000 mg/kg LDPE induced the appearance of LDPE tolerant populations in the microbial community in vivo. Taken together, our results provide a theoretical basis for revealing the physiological response of earthworms when challenged in a polluted environment and provide a model for pollution remediation and ecological security monitoring of soil ecosystems.

A method to study the effects of combined stress of cadmium and microplastics on the acute toxicity of Eisenia fetida.

The compound pollutants formed by microplastics and cadmium present a significant potential threat to the soil-based ecosystem, and it is urgent to carry out relevant ecotoxicological studies. However, the lack of appropriate test methods and scientific mathematical analysis models has restricted the progress of research. Based on an orthogonal test design, a ternary combined stress test was performed to study the effect of microplastics and cadmium on earthworms. This study used the particle size and concentration of microplastics as well as the concentration of cadmium as test factors. Using the improved factor analysis model and the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method, a new model was constructed according to the response surface methodology to analyze the acute toxic effects on earthworms under the combined stress of microplastics and cadmium. In addition, the model was tested in a soil-polluted environment. The results show that the model can perfectly integrate the spatiotemporal cross effects of the concentration and time of the applied stress, and the scientific data analysis process ensures the efficient development of ecotoxicological research in the actual compound pollution environment. Moreover, the results of the filter paper test and soil test showed that the equivalent toxicity ratio of cadmium concentration, microplastic concentration, and microplastic particle size to earthworms as 26:35:39 and 23:36:41, respectively. In terms of the interaction effect, a certain positive interaction was observed between the cadmium concentration and that of the microplastics and their particle size, while a negative interaction was observed between the concentration of microplastics and their particle size. This research provides a test basis and model reference for early monitoring of the health of contaminated soils and assessments of ecological safety and security.