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.

Exploring the influence of concentration fluctuation and matrix effects on a passive sampler of triolein-embedded cellulose acetate membrane measuring polychlorinated biphenyls in water.

A membrane of triolein-embedded cellulose acetate membrane (TECAM), as an integrative passive sampler, was applied to adsorb 28 polychlorinated biphenyls (PCBs) from pure water and sea water in order to probe into the influence of concentration fluctuation and water matrix. The results demonstrated the temporal variations of PCBs concentrations in TECAM followed the first-order kinetics model. The periodic refreshment of solution and matrix effects of sea water significantly prolonged the time that PCBs reached equilibrium stage. The refreshment facilitated the uptake mass in TECAM. On the contrary, the matrix effects of sea water and dissolved organic matter (DOM) declined the PCBs absorption to TECAM. The average logKP values of PCBs in pure water were about 1.2 log unit higher than those in sea water in the experiments that the solution was not refreshed, while the difference of average logKP values narrowed to 0.3 log unit if the PCBs solutions were periodically refreshed. The correlation between logKP and logKOW values fitted the quadratic curve well, which was similar to semi-permeable membrane device (SPMD). The appropriate sampling times (t94%) ranged from 98.8 to 819 h (mean 500 h) for pure water with refreshment, much longer than those in sea water with refreshment (80.1~410 h, mean 189 h). The t94% values in the solution with high DOM content increased significantly, up to 409 h. Furthermore,  comparing the two experiments that the spiked pure water and sea water solution were refreshed frequently, the estimated sampling rates (Rs) in pure water (0.154~2.06 L/day with a mean value of 0.605 L/day) were slightly lower than those in sea water (0.292~3.84 L/day with a mean value of 1.69 L/day). However, the Rs values in sea water with DOM declined sharply to 0.042 L/day. Therefore, concentration fluctuation, matrix effect, and DOM contents of sea water evidently posed significant influence on dynamic parameters of TECAM absorption, which would be screened and probed detailed in future.

Evaluation of the toxicity effects of microplastics and cadmium on earthworms.

Microplastics (MPs) and heavy metal pollution have become research hotspots in recent years. This study focused on the comprehensive evaluation of the toxicity effect on Eisenia fetida under combined exposure to MPs and the heavy metal cadmium (Cd). With Cd concentration, MPs concentration and MPs partical size as stress factors, the TOPSIS model was constructed to explore the toxicity levels of the stress factors. A short-term co-exposure test and a long-term co-exposure test were designed by orthogonal combination tests with equivalent toxicity levels. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione peroxidase (GPX), glutathione S transferase (GST), and acetylcholinesterase (AChE) and the contents of protein (TP), glutathione (GSH), and malondialdehyde (MDA) in earthworms were determined. Integrated biological responses version 2 (IBRv2) was used to evaluate the toxicity of MPs and Cd combined exposure on earthworms. The results showed that the toxicity ratio of Cd concentration, MPs concentration and MPs partical size was 46 to 29 to 25. Combined exposure to MPs and Cd enhanced the activities of SOD, POD, CAT, GPX and GST, MDA and GSH contents also increased, while the AChE activities were inhibited. SOD, GPX and GST play important roles in the resistance of earthworms to pollutant stress. During short-term co-exposure, Cd concentration had antagonistic effects with on MPs concentration and MPs partical size, while they showed synergistic effects during long-term co-exposure.