Pre-exposure to chemicals increases springtail vulnerability to high temperatures

Global climate change is increasing the frequency and intensity of heat waves, posing a significant threat to ectothermic organisms. Concurrently, chemical pollution, including heavy metals and pesticides, remains a pervasive environmental stressor. This study investigates the effects of sublethal copper and fluazinam exposure on the thermal tolerance of the soil-dwelling springtail, Folsomia candida. Using a Thermal Death Time (TDT) framework, we assessed how pre-exposure to these toxicants at two acclimation temperatures (20 °C and 24 °C) influenced survival under heat stress. Our findings indicate that toxicant exposure reduced heat tolerance at moderately high temperatures (32.5 °C) but had negligible effects at extreme temperatures (37 °C). Acclimation at 24 °C mitigated the negative effects of both toxicants, suggesting an enhanced capacity for cellular homeostasis under warm conditions. Additionally, soil type influenced thermal tolerance, highlighting the importance of environmental context in multiple stressor interactions. These findings highlight the need to integrate realistic thermal exposure scenarios in ecotoxicological assessments to improve predictions of organismal vulnerability under climate change.