Embryonic exposure to nanoplastics affects the metabolism and locomotor performance of a soil-dwelling, oviparous skink

The contamination of soil with nanoplastic waste has dramatically increased over the past two decades. Nevertheless, we do not yet understand how nanoplastic exposure impacts on embryonic development, hatching physiology and behavior in soil-dwelling animals. To assess the toxicity of polystyrene nanoplastics (PS-NPs), we conducted incubation experiments with the eggs of an oviparous skink, Scincella modesta. Eggs were exposed to environmentally relevant doses of PS-NPs (1 mg/L), and we evaluated multiple physiological traits including embryonic heart rate, post-hatching morphological development, locomotor performance, oxidative stress, and metabolism in comparison to a control sample. We found that PS-NPs penetrated the eggshell barrier and bioaccumulated in the embryos, leading to an increased embryonic heart rate. Exposure to PS-NPs also affected morphological development of hatchlings and significantly reduced their sprint speed. Biochemical analyses revealed complex oxidative stress responses in hatchlings; including upregulated activity of superoxide dismutase and catalase, coupled with elevated glutathione and malondialdehyde. These collectively indicated lipid peroxidation cascades. Endoplasmic reticulum stress was found to activate glycerophospholipid metabolic pathways, leading to dysregulation of lipid homeostasis in S. modesta. Furthermore, perturbations in the cGMP-PKG signaling pathway impaired cardiac contractile functions in S. modesta. Notably, exposure to PS-NPs induced disruptions in energy metabolism, through upregulation of anandamide in the retrograde endocannabinoid signaling pathway. These results demonstrate that embryonic exposure to PS-NPs adversely affects metabolism and locomotor performance in S. modesta. We provide novel insights into the impacts of environmental pollutants, such as nanoplastics, on the physiology and behavior of soil-dwelling oviparous reptiles.