Imidazolinones are a group of herbicides with high potential of leaching and long half-lives that are posing a threat to water resources’ quality especially in tropical areas. Biochar, a carbon-rich bio-sorbent, has shown its ability to stabilise organic substances in soils and therefore, potentially is able to reduce their leaching. Biochar is a sustainable and cost-effective material which can be produced from locally available wastes. This work, for the first time, evaluated the biochar’s effects on leaching of two polar members of imidazolinones family namely imazapic and imazapyr, and also Onduty® which is a mixture of these two herbicides, in heavy soil of tropical paddy fields. Leaching columns accompanied with artificial irrigation were used during the laboratory experiment. The herbicides were extracted from both collected leachates and soil columns. Soil amendment with designed biochars significantly reduced the herbicides’ leaching percentages. Oil palm empty fruit bunch (OPEFB) and rice husk (RH) were used as pyrolysis feedstock. About 16% of the applied imazapic was leached out from biochar-free soil. For RH and OPEFB biochar-amended soils, the amounts were 4.3% and 3.6%, respectively. The highest percentage of imazapyr leached out from non-amended soil was (14.2%) followed by RH (4.0%) and OPEFB (2.8%) in biochar-amended soils. Also, 15.2% of the applied Onduty® was leached from non-amended soil. Adding RH and OPEFB biochars could reduce the herbicide leaching to 4.2% and 3.0%, respectively. Soil amended with biochars retained the higher percentages of the herbicides in top 7.5 cm depths. The media sorption capacities were negatively correlated to the amounts of herbicides leached out from soils but positively to the amounts of the herbicides remaining in the soil. Total amount of herbicides adsorbed by biochars-amended soils was more than 95%. Cation/water bridging ion exchange, ligand exchange, electrostatic attraction, and hydrophobic partitioning are the main ways imidazolinones can be adsorbed to soil. It was concluded that biochar application has the potential to reduce polar imidazolinones’ leaching and their environmental pollution. The custom-engineered biochars can specifically control the pesticides transfer and then can certainly enhance the biochars’ commercial values for their applications in the environment.

Graphic abstract

中文翻译：

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碳吸附剂缓解热带土壤中极性除草剂浸出的效率

咪唑啉酮类是一组具有极高的淋洗潜能和较长的半衰期的除草剂，这些农药对水资源的质量构成威胁，特别是在热带地区。Biochar是一种富含碳的生物吸附剂，已显示出能够稳定土壤中有机物的能力，因此有可能减少其浸出。生物炭是一种可持续的，具有成本效益的材料，可以从当地可获得的废物中产生。这项工作首次评估了生物炭对热带稻田重土中咪唑啉酮家族的两个极性成员即咪唑吡和咪唑吡以及这两种除草剂的混合物的浸出的影响。在实验室实验中使用了淋洗柱和人工灌溉。从收集的渗滤液和土壤柱中提取除草剂。使用设计好的生物炭对土壤进行改良可以显着降低除草剂的浸出率。油棕空果束（OPEFB）和稻壳（RH）用作热解原料。从无生物炭的土壤中浸出了约16％的施用的吡虫啉。对于RH和OPEFB生物炭改性的土壤，其含量分别为4.3％和3.6％。在生物炭改良土壤中，从未改良土壤中浸出的吡虫啉的最高百分比为（14.2％），其次是相对湿度（4.0％）和OPEFB（2.8％）。同样，从未改良的土壤中浸出了15.2％的已应用Onduty®。添加RH和OPEFB生物炭可将除草剂的浸出分别减少至4.2％和3.0％。用生物炭改良的土壤在7.5厘米深处保留了较高比例的除草剂。介质的吸附能力与从土壤中浸出的除草剂的数量呈负相关，而与土壤中剩余的除草剂的数量呈正相关。被生物炭改良过的土壤吸附的除草剂总量超过95％。阳离子/水桥离子交换，配体交换，静电吸引和疏水性分配是咪唑啉酮可吸附到土壤的主要方法。结论是生物炭的应用具有减少极性咪唑啉酮的浸出及其对环境污染的潜力。定制工程生物炭可以专门控制农药的转移，然后肯定可以提高其在环境中的应用的商业价值。

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