Effects of biochar on fate and toxicity of herbicide fenoxaprop-ethyl in soil

The biochar as soil amendment in agriculture has attracted considerable attention. In the study, the fate and toxicity of the herbicide fenoxaprop-ethyl were evaluated in soils with and without 5% rice husk biochar amendment. Fenoxaprop-ethyl and metabolite fenoxaprop degraded followed first-order kinetics in the two soils. Fenoxaprop-ethyl decreased fast with half-lives less than 2 days. Large amounts of fenoxaprop formed and remained in control soil. However, fenoxaprop was much lower in biochar-amended soil with reduction over 85% at the 35th day. The estimated half-lives of fenoxaprop were 56.9 and 1.5 days in control and biochar-amended soils, respectively. Biochar restrained the formation and promoted the dissipation of fenoxaprop. Biological indicator earthworms (Eisenia fetida) were used in a 14-day acute toxicity test. Fenoxaprop-ethyl shown low toxic to earthworms with LC50 value of 322.9 μg/g. Biochar amendment was nontoxic to earthworms and effectively reduced the toxicity. The results suggested that the application of biochar may reduce the risks of fenoxaprop-ethyl in the soil environment.

农业领域中，生物炭（biochar）作为土壤改良剂已受到广泛关注。本研究针对施加5%稻壳生物炭与未施加生物炭的两种土壤，评估了除草剂精噁唑禾草灵（fenoxaprop-ethyl）的归趋与毒性。精噁唑禾草灵及其代谢产物精噁唑（fenoxaprop）在两种土壤中均遵循一级动力学降解规律。精噁唑禾草灵降解速度较快，半衰期均小于2天。对照组土壤中生成并残留了大量精噁唑；而施加生物炭的土壤中，精噁唑含量显著降低，至第35天时降幅超过85%。经估算，精噁唑在对照组与生物炭改良土壤中的半衰期分别为56.9天与1.5天。生物炭可抑制精噁唑的生成，并促进其降解消散。本研究采用模式生物蚯蚓（赤子爱胜蚓，Eisenia fetida）开展了14天急性毒性试验，结果显示精噁唑禾草灵对蚯蚓毒性较低，半数致死浓度（LC50）为322.9 μg/g。生物炭改良剂对蚯蚓无毒性，且可有效降低精噁唑禾草灵的土壤生态毒性。研究结果表明，施加生物炭可降低精噁唑禾草灵在土壤环境中的生态风险。