Imidacloprid Removal Efficiency with the Use of Rapeseed (Brassica napus L.) at Different Compost Doses

One method for removing neonicotinoids from the environment that is considered safe, eco-friendly, and sustainable is phytoremediation. The aim of this study was to determine the effect of the sewage sludge-based compost rate on substrate activity in the presence of rapeseed (Brassica napus L.) and the effectiveness of the phytoremediation of substrate contaminated with imidacloprid (IM). A pot experiment was conducted using mineral substrate amended with sewage sludge-based compost (4 kg/m2 and 8 kg/m2). IM aqueous solutions (250 ng/L and 500 ng/L) were applied to rapeseed seedlings, alongside compost substrate without IM (control). The following were determined: the content of IM in the substrate/rapeseed shoots, the main substrate properties, the activities of dehydrogenases and β-glucosidase, the number of bacteria, mold fungi and fluorescing Pseudomonas, and the number of ammonia-oxidizing archaea (AOA). It was reported that the application of compost significantly increased rapeseed shoot biomass and substrate enzymatic activity. However, the efficiency of IM uptake by plants decreased (by approximately 40%) with an increase in its dose in the substrate. At the same time, IM had a negative effect on the abundance of AOA (on average, 12% less than in the control), while the compost rate caused an increase in AOA abundance but with a lower IM dose. The obtained results indicate that direct phytoextraction from the shoots was limited, and the low apparent yield may be explained by unmeasured processes including transformation, sorption, retention by the roots or other losses. It should also be noted that an important limitation of these studies was the lack of determination of the IM content in roots and the identification of IM metabolites.