Recycling waste, recycling risk: cypermethrin-contaminated poultry litter triggers sublethal toxicity in Folsomia candida at realistic environmental concentrations

This study for the first time investigated the effects of poultry litter containing cypermethrin (740 μg kg^-1 d.w.) and metals on Folsomia candida, assessing lethality, behavior, reproduction, and oxidative stress biomarkers, which were combined into an Integrated Biomarker Response (IBR) assessment. The sublethal effects covered application rates equivalent to those reported for different cropping systems (2.0-25.0 t ha^-1). Compared to control soil, poultry litter showed elevated concentrations in mg kg^-1 of Cu (27.5), Zn (36.6), Mn (37.7), and Cr (0.93). The median lethal concentrations (LC₅₀) were 10.82% at 7 days and decreased to 3.59% at 14 days. Significant avoidance and reproductive effects were detected at poultry litter concentrations of 0.5% (10 t ha^-1) and 0.1% (2 t ha^-1), respectively. The corresponding median effective concentrations (EC₅₀) were 1.38% for avoidance and 0.188% for reproduction. Antioxidant biomarkers, superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), reduced glutathione (GSH), and metallothionein (MT), together with oxidative damage indicators, malondialdehyde (MDA) and protein carbonyls (CARB), revealed a response pattern: at intermediate concentrations (0.75-1.0%), an increase in enzyme activities and antioxidant defenses levels was observed; however, at 0.75% and 1.25%, oxidative damage occurred. Principal Component Analysis and correlation analyses indicate that higher litter concentrations impair antioxidant defenses, increase oxidative damage, and trigger compensatory detoxification in F. candida, while the IBR revealed progressive changes in the antioxidant system in response to increasing poultry litter concentrations. Notably, to the best of our knowledge, this study provides the first evidence of pyrethroid occurrence in poultry litter, revealing a previously unrecognized contamination pathway and underscoring potential risks to soil ecosystems.