Exfoliating microplastics intensifies heavy metal uptake and physiological stress in wastewater-irrigated chili plants

Microplastics from personal care products and heavy metals (HMs) in wastewater pose significant threats to crop health in peri-urban agricultural areas. This study evaluates the interactive effects of contaminated wastewater with Cd, Hg, Pb and polyethylene microplastics (MPs) from exfoliating personal care products on Capsicum annuum. Plant growth parameters (e.g.,height, biomass, leaf number) were reduced with increasing wastewater and MPs levels, and the observed reduction rates were 71–82%. at SWW (100%) + MPs (5 g/L), accompanied by 51–72% loss in photosynthetic pigments (chlorophyll a, b, and carotenoids) and 74–85% decrease in soluble proteins compared to the control. Oxidative stress markers such as MDA increased by 124–150% and H2O2 by 180–230%, at SWW 100% + MPs (5 g/L) compared to the control. Antioxidant enzyme activities amplified at moderate stress levels (SWW 50%) before declining by 18–20% at higher levels (compared to peak activity), indicating failure to acclimate. Mechanistically, HMs accretion was root-dominant and significantly increased in levels in high stress conditions, with increased HMs uptake facilitated by MPs ranging 11–23% (low MPs: 11–15%, high MPs: 18–23%) at high stress conditions. These findings underscore the need for MPs removal from wastewater to mitigate phytotoxicity and enhance crop safety in contaminated agroecosystems. This study is the first factorial investigation to simultaneously examine exfoliating polyethylene microplastics and multi-metal (Cd, Hg, Pb) wastewater contamination in chili, a key Solanaceae crop frequently irrigated with urban wastewater. Unlike earlier research that treats microplastics or heavy metals in isolation, our work demonstrates how consumer-grade microbeads vector heavy metals into the rhizosphere, intensifying bioavailability, uptake, and oxidative stress. It identifies clear toxicity thresholds where antioxidant defenses fail, redefining the risks of urban irrigation systems contaminated with cosmetic microbeads.