不同种植年限红壤果园土壤腐殖质结构变化对吡虫啉吸附的影响

The Effects of Changes in Soil Humus Structure in Red Soil Orchards with Different Cultivation Ages on the Adsorption of Imidacloprid

摘要:

新烟碱类农药是南方丘陵区果园中最常用的杀虫剂之一，长期果园施肥会改变土壤有机质含量及结构，进而影响农药在土壤中的吸附行为。深入了解典型新烟碱类农药（吡虫啉）在果园土壤腐殖质上的吸附行为，有助于提高该类农药在土壤中环境行为的认识，为农药面源污染源头防控提供理论依据。从不同种植年限（10 a、30 a、50 a）柑橘园土壤（0~20 cm）提取得到胡敏酸（HA）馏分（F1~F10）、低碳胡敏素（HuL）和高碳胡敏素（HuH），进行吡虫啉在这些腐殖质组分上的吸附等温线试验。腐殖质组分对吡虫啉的吸附等温线均能很好地拟合Freundlich模型，R2大于0.9。胡敏酸对吡虫啉的吸附亲和力约为胡敏素的100倍，Ce为0.5、2.0、3.0 mg?L-1时，吡虫啉的Kd值分别为523.1~5 276 L?kg-1、543.3~5 717 L?kg-1、520.2~5 980 L?kg-1，随种植年限的延长，Kd值均略有增加；吡虫啉的KOC值与HA馏分（F1~F10）的芳香碳呈正相关关系、与烷基碳呈负相关关系，低碳胡敏素的羰基碳、羧基碳是控制吡虫啉吸附的关键碳官能团，高碳胡敏素的烷基碳是控制吡虫啉吸附的关键碳官能团。因此，长期种植可以在一定程度上提高腐殖质对吡虫啉的吸附，胡敏酸的芳香碳结构是调节吡虫啉吸附的关键结构，胡敏素的脂肪碳结构是调节吡虫啉吸附的关键结构。

Abstract:

【Objective】Neonicotinoid pesticides are one of the most commonly used insecticides in citrus orchards in the hilly areas of southern China. The long-term fertilization of orchards can alter the content and structure of soil organic matter, which in turn affects the adsorption behavior of pesticides in the soil. Therefore, gaining an in-depth understanding of the adsorption behavior of a typical neonicotinoid pesticide (imidacloprid) on soil humus in orchards is crucial for improving our knowledge of the environmental behavior of this class of pesticides in soil. This will provide a theoretical basis for preventing and controlling pesticide surface pollution at its source.【Method】Humic acid (HA) fractions (F1 to F10), low carbon humin (HuL) and high carbon humin (HuH) were extracted from soils (0~20 cm) with different cultivation chronosequences (10, 30 and 50 years). Adsorption isotherm experiments of imidacloprid on these humic fractions were conducted. 【Result】The adsorption isotherms of imidacloprid by humic acid (HA) fractions (F1~F10), and HuL and HuH fractions all fit the Freundlich model well, with R2 greater than 0.9. The adsorption affinity of humic acid for imidacloprid is about 100 times higher than that of HuL and HuH. The Kd values of imidacloprid ranged from 523.1 to 5 276L?kg-1, 543.3 to 5 717 L?kg-1, and 520.2 to 5 980 L?kg-1 at Ce of 0.5, 2.0, and 3.0 mg?L-1, respectively. All of them increased slightly with the increase of planting years. The KOC values of imidacloprid were positively correlated with aromatic C and negatively correlated with alkyl C of HA fractions (F1~F10). Also, the carbonyl C and carboxyl C of HuL were the key carbon functional groups controlling imidacloprid adsorption, while the alkyl C of HuH was the key carbon functional group controlling imidacloprid adsorption. 【Conclusion】Therefore, long-term cultivation can improve the adsorption of imidacloprid by humic substances to a certain extent, and the aromatic carbon structure of humic acid is the key structure regulating the adsorption of imidacloprid while the aliphatic carbon structure of humin is the key structure regulating the adsorption of imidacloprid.