| The environmental effects and toxicity risks of organic pollution sites have been a hot topic of concern in the field of environmental science in recent years.Microbial remediation is a commonly used soil remediation technique for organic pollution sites,which has advantages such as being cost-effective,environmentally friendly,having minimal secondary pollution,insitu treatment,and ease of operation.However,during the microbial remediation process of organic pollution sites,stronger secondary metabolites or intermediate products with greater toxicity,persistence,and accumulation than the original pollutants may be produced,leading to a complex composition of pollutants and unclear ecological toxicity effects in the soil.In this study,soil samples were collected from organic pollution sites,and typical higher plants and soil invertebrates(earthworms)were used as biological test subjects to investigate the toxicological effects of the complex system formed during microbial remediation of organic pollution sites.The study also evaluated the rapid response indicators of biological toxicity during the microbial remediation process of organic pollution sites and revealed the patterns of changes in soil characteristics.The aim of this research is to provide a research basis for soil toxicity identification and risk assessment during the microbial remediation process of organic pollution sites.To evaluate the phytotoxicity of organic-polluted soil caused by microbial remediation,buckwheat,radish,and wheat were selected as the tested higher plants to investigate the changes in growth and physiological characteristics during different stages of microbial remediation.The results indicated that the toxicity of organic-polluted soil to plants was significantly enhanced during the 0-20 d microbial remediation period.Among the three plant species,wheat exhibited the best growth indicators to describe the toxicity changes during microbial remediation of organic-polluted soil.Compared with the clean soil,the microbial agent remediation soil significantly inhibited the germination rate of wheat during the first 10 days of remediation,and the germination potential of wheat showed a "U"-shaped change during the40-day remediation period,reaching the lowest value at the 20 th day of microbial remediation.Both the plant height and root length of wheat can well indicate the biological toxicity changes during different stages of microbial remediation.Compared with dry weight,fresh weight of wheat is more sensitive to the microbial remediation soil,and the whole plant fresh weight and aboveground fresh weight of wheat showed the highest inhibition rate at the 10 th day of microbial remediation,decreasing by 14.90% and 10.75% compared with the polluted soil,respectively,while the underground fresh weight showed the maximum inhibition rate at the15 th day of remediation,decreasing by 12.25% compared with the polluted soil.At the 20 th day of microbial remediation,the maximum inhibition rates of chlorophyll a and chlorophyll b contents in wheat leaves were observed in the microbial agent remediation soil,decreasing by15.22% and 35.58%,respectively,compared with the polluted soil,among which chlorophyll b was more sensitive to the biological toxicity changes during soil microbial remediation.The antioxidant enzyme activity of wheat roots was more sensitive to the stress of microbial remediation soil,and the contents of catalase(CAT),superoxide dismutase(SOD),and malondialdehyde(MDA)can well indicate the biological toxicity changes of the polluted soil during microbial remediation.To evaluate the animal toxicity caused by organic pollutants in the soil at a contaminated site during the process of microbial remediation,Eisenia fetida was selected as the test animal to study the changes in behavioral characteristics,growth and physiological traits of earthworms at different stages of microbial remediation.The results showed that the toxicity of organic pollutants in the soil to earthworms was strong during the first 15 days of microbial remediation.Earthworms showed significant avoidance behavior towards the organically polluted soil on the10 th day of microbial remediation,with the highest avoidance rate being 90%.The mortality rate of earthworms was 100% on days 0,5 and 10 of microbial remediation.After 7 days of incubation in soil remediated for 15 days,the maximum attenuation rate of earthworm body weight was 35.53%.The intestinal and epidermal tissues of earthworms were more sensitive to the stress caused by the microbial remediation of contaminated soil.Their MDA content,and POD and SOD activities were good indicators of changes in soil toxicity during remediation,while the enzyme activity of the reproductive system had poor indicating effect.To investigate the changes in soil characteristics and toxicity sources during microbial remediation of organic-polluted sites in the presence of plants or earthworms,the changes in PAHs content,soil p H,and DOC content were analyzed.The variations of soil solution DOM composition and aromaticity were examined using three-dimensional fluorescence spectroscopy and UV-visible absorption spectroscopy.The results indicated that,the content of benzo[a]pyrene in BP soil(coexistence of plants and remediation agents)and BE soil(coexistence of earthworms and remediation agents)decreased significantly after 15 days of microbial remediation,and the metabolites produced during degradation may be the cause of the increased toxicity during the first 15 days.The p H and DOC content of microbial remediation soil BP and BE showed an increasing trend before the 15 th day of microbial remediation.The three-dimensional fluorescence spectra of DOM in microbial remediation soil BP and BE showed an increase in the fluorescence intensity of regions representing polycyclic aromatic hydrocarbons on the 15 th and 5th day of remediation,respectively,and their aromaticity also increased,confirming the production of more toxic metabolites in the first 15 days of microbial remediation.The changes in soil phosphatase activity could better indicate the ecotoxicity of organic-polluted soil during microbial remediation,followed by urease,andβ-glucosidase showed the poorest indication effect.The soil phosphatase activity in microbial remediation soil BP and BE showed a gradual decrease during the initial 20 and 10 days of microbial remediation,respectively,followed by a recovery trend,which was consistent with the observed patterns of changes in biological toxicity. |
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