Physiological and microbial alterations induced by pesticides in agricultural systems: A bioassay- and 16S rRNA-based...

The extensive use of pesticides in agricultural production systems has increased interest in understanding their potential impacts on soil environmental dynamics. This study evaluates the effects of pesticide application on Lactuca sativa L. and soil microbiota. An initial field survey identified the main active ingredients commercial pesticides, followed by bioassays assessing germination and early development of Lactuca sativa, as well as soil microbial structure through physiological assessments and metagenomic analyses based on 16S rRNA gene sequencing, during a three-week soil experiment. Thirty active ingredients were identified in 92 agricultural products. Chlorpyrifos was identified as one of the most commercialized insecticides, where insecticides represented 69% of marketed phytosanitary products, mainly organophosphates (18%) and pyrethroids (21%), despite its hazardous classification and ban in several countries. Germination assays showed a hormetic response at low dose (2200 mg/L), reaching 70% germination compared with 51% in the control, while the germination index decreased to 75% at the recommended dose (4400 mg/L). Statistical analyses revealed inhibition of hypocotyl elongation (p = 0.001) and cotyledon development (p = 0.029). Soil microbiome analysis showed that high chlorpyrifos concentrations reduced microbial richness and diversity, while beta diversity analyses explained 99% of the variance among treatments. Proteobacteria, Burkholderiales, and Sphingomonadales increased under pesticide exposure, indicating microbial adaptation and biodegradation potential. Functional prediction using PICRUSt2 revealed enrichment of genes K03381, K00446, K01048, and K01560 associated with potential organophosphate degradation pathways. These findings demonstrate that chlorpyrifos induces ecological and seedling alterations even at agronomically recommended concentrations. highlighting the need to strengthen sustainable pesticide management and environmental monitoring strategies.