Silver nanoparticles amplify mercury toxicity in rice: Impacts on germination, growth, and cellular integrity

This study investigates the synergistic co-effects of mercury (Hg) and silver nanoparticles (AgNPs) on rice seed germination and early seedling development. Hg were applied at concentrations of 0, 0.33, 1.65, and 8.25 mg kg^-1 while AgNPs were administered at 0, 50, 100, and 500 mg kg^-1. Results demonstrate that single low Hg concentrations enhanced germination rate from 79.63 % to 89.51 %, and stimulated α-amylase activity from 0.26 to 0.34 μg g^-1 FW min^-1. Co-exposure with AgNPs significantly modulated these responses, particularly under 50 and 500 mg kg^-1 AgNPs treatments where α-amylase activity reached from 0.26 to 0.49 and 0.25 μg g^-1 FW min^-1, respectively. The combined treatment with high concentrations of both contaminants further substantially inhibited seedling growth, reducing plant height by 39 % and roots length by 13 %. AgNPs further enhanced Hg accumulation in plant tissues and intensified oxidative stress, as indicated by elevated peroxidase (POD) activity and malondialdehyde (MDA) levels. Ultrastructural and DNA damage analyses confirmed severe cellular disruption and dose-dependent genotoxicity. These findings provide critical insights into the synergistic toxicity mechanisms of Hg and AgNPs co-contamination in rice seedlings, with important implications for agricultural safety under heavy metal and nano-product combined contamination.