Effect of pyrethrins and permethrin insecticides on soil bacterial biodiversity

Soil microorganisms play a key role in maintaining ecosystem stability, yet they are frequently exposed to insecticides used in agriculture and pest control. This study investigated the effects of natural pyrethrins and synthetic permethrin on soil bacterial metabolic activity, functional diversity, community structure, and biodegradation potential. Soil samples collected from a long-term protected, non-agricultural forest area were incubated with commercial formulations containing pyrethrins (Afizol AE) or permethrin (Afanisep® 25 WP) for 7 and 15 days. Microbial metabolic activity was assessed using the Alamar Blue assay and Biolog EcoPlate™ system, while bacterial community composition was analyzed through 16S rRNA gene sequencing. Additionally, the degradation of insecticide active compounds was quantified using UHPLC-QTOF-MS. Permethrin-treated soils exhibited the highest and most sustained microbial metabolic activity, whereas pyrethrin-treated soils showed an initial stimulation followed by a decline over time. Functional diversity indices revealed that permethrin initially promoted metabolic diversity, but prolonged exposure led to a reduction in substrate utilization breadth. Metagenomic analysis demonstrated pronounced shifts in bacterial community composition under both treatments, with strong selection toward Firmicutes-dominated assemblages. Biodegradation assays confirmed substantial degradation of both pyrethrins and permethrin, although incomplete removal and partial accumulation of selected compounds were observed. The obtained results highlight that both natural and synthetic pyrethroids significantly alter soil bacterial communities, emphasizing the need to consider their short-term ecological effects on soil health.