Atmospheric Lead Deposition under Climate Change: Implications for Lettuce Yield and Dietary Exposure Risks

Recurrent heatwaves (HW) and foliar uptake of fine particulate matter lead (PM2.5-Pb) threaten agriculture and food safety, yet their combined mechanistic impacts remain elusive. Using lettuce (Lactuca sativa L.), we show that HW and PM2.5-Pb coexposure reduces fresh biomass and compromises nutritional quality. This yield collapse is driven by physiological growth-defense trade-offs. Coexposure triggers the accumulation of reactive oxygen species (ROS) (32.3-57.1%), compromising chloroplast integrity, accelerating stomatal closure, and suppressing stomatal conductance (31.8%) and net photosynthesis (48.5%). Metabolomics reveals survival reprogramming driven by altered sulfate, benzylamine, and traumatic acid. This activates an abscisic acid-ROS signaling loop, redirecting carbon from biomass toward glutathione and cell wall biosynthesis for Pb detoxification. In simulated gastrointestinal models, coexposure increases leaf Pb bioavailability by 16.0% and disrupts digestive enzymes, reducing mineral bioaccessibility (7.6-13.2%). These findings elucidate how physiological and metabolic shifts drive agricultural losses, highlighting the compounded threat of atmospheric pollution and climate change.