Enhancing effect of humic acid on neurodevelopmental impact of cadmium sulfide nanoparticles to zebrafish

Abstract

Metal sulfide nanoparticles (MSNPs) are widespread in aquatic environments, where their stability and toxicity are affected by environmental factors. However, the role of dissolved organic matter (DOM) in modulating oxidative transformation and toxicity of MSNPs remains poorly understood. Here, we investigated the chemical stability and neurodevelopmental toxicity of cadmium sulfide nanoparticles (CdSNPs) in zebrafish, focusing on the effects of humic acid (HA), a representative DOM. Our results demonstrate that light promoted the generation of reactive oxygen species (ROS), thus accelerating CdSNPs dissolution and increasing cadmium uptake. However, the photoinduced release of cadmium ions was significantly decreased by HA, due to the formation of surface coating, thus inhibiting CdSNPs dissolution and decreasing cadmium uptake. Despite these opposing effects on cadmium release and uptake, light and HA did not proportionally influence the neurodevelopmental outcomes in zebrafish, as shown by behavioral response of transgenic line. The nanoparticulate form of CdSNPs and HA themselves also contributed substantially to neurotoxicity. Targeted metabolomic analyses revealed that these effects were mediated by disturbances in dopaminergic, glutamatergic, GABAergic, and glycinergic neurotransmission, with HA further enhancing the disruption of key enzymes and receptors involved in these systems. These findings provide new insights into environmental behavior and neurotoxic potential of MSNPs, informing their ecological risk assessment in natural aquatic systems.

Keywords: Dissolved organic matter; Environmental transformation; Metal sulfides; Neurodevelopmental toxicity; Zebrafish embryos.