Factors Influencing Neonicotinoid Insecticide Concentrations in Floodplain Wetland Sediments across Missouri

Widespread use of neonicotinoid insecticides in North America has led to frequent detection of neonicotinoids in surface waters. Despite frequent surface water detection, few studies have evaluated underlying sediments for the presence of neonicotinoids. Thus, we sampled water and sediments for neonicotinoids during a one-year period at 40 floodplain wetlands throughout Missouri. Analyzed for six common neonicotinoids, sediment samples consistently (63% of samples) contained neonicotinoids (e.g., imidacloprid and clothianidin) in all sampling periods. Mean sediment and aqueous neonicotinoid concentrations were 1.19 μg kg–1 (range: 0–17.99 μg kg–1) and 0.03 μg L–1 (0–0.97 μg L–1), respectively. We used boosted regression tree analysis to explain sediment neonicotinoid concentrations and ultimately identified six variables that accounted for 31.6% of concentration variability. Efforts to limit sediment neonicotinoid contamination could include reducing agriculture within a wetland below a threshold of 25% area planted. Also, prolonging periods of overlying water >25 cm deep when water temperatures reach/exceed 18 °C could promote conditions favorable for neonicotinoid degradation. Results of this study can be useful in determining potential routes and levels of neonicotinoid exposure experienced by nontarget benthic aquatic invertebrates as well as potential means to mitigate neonicotinoid concentrations in floodplain wetlands.新烟碱类杀虫剂（neonicotinoid insecticides）在北美地区的广泛使用，导致地表水中频繁检出该类农药成分。尽管地表水中该类农药的检出率颇高，但鲜有研究针对沉积物中的新烟碱类杀虫剂残留情况开展评估。为此，研究团队于密苏里州全境40处泛滥平原湿地（floodplain wetlands）开展为期一年的水样与沉积物采样，以检测其中的新烟碱类杀虫剂残留。本次分析共检测6种常见新烟碱类杀虫剂，结果显示，在所有采样周期中，63%的沉积物样本均检出该类农药（如吡虫啉（imidacloprid）与噻虫胺（clothianidin））。沉积物与水体中新烟碱类杀虫剂的平均浓度分别为1.19 μg·kg⁻¹（范围：0~17.99 μg·kg⁻¹）与0.03 μg·L⁻¹（范围：0~0.97 μg·L⁻¹）。研究采用提升回归树（boosted regression tree）分析法解析沉积物中新烟碱类杀虫剂的浓度分布特征，最终确定6个变量可解释31.6%的浓度变异度。可通过以下措施管控沉积物中新烟碱类杀虫剂污染：将湿地内的农业种植面积占比控制在25%以下。此外，当水体温度达到或超过18℃时，维持水深大于25 cm的时长，可营造利于新烟碱类杀虫剂降解的环境条件。本研究结果可为明确非靶标底栖水生无脊椎动物的新烟碱类杀虫剂暴露途径与暴露水平提供参考，同时可为管控泛滥平原湿地中新烟碱类杀虫剂浓度提供可行方案。