Exposure to biogenic phosphorus nano-agromaterials promotes early hatching and causes no acute toxicity in zebrafish embryos

Abstract

With a growing number of studies now exploring the development of novel phosphorous (P)-based nanomaterials (NMs) for agriculture, there is an increasing concern that these NMs may enter aquatic environments after use and affect aquatic organisms. Little is currently known about the effects of P-based NMs such as nanohydroxyapatite (nHAP) and nanophosphorus (nP) on freshwater fish species. The present study aimed to investigate the role of physicochemical properties of different P-based NMs in their potential toxicity to zebrafish embryos. Four nHAP variants with distinct shapes (platelets, rods, spheres, and needles) were studied along with spherical nP. Zebrafish embryos were exposed to increasing doses (0–500 μg mL⁻¹) of the P-based NMs up to 96 hours post-fertilization (hpf), and both lethal and sub-lethal endpoints were assessed including survival, hatch rate, heart rate, growth parameters, developmental defects, and blood vessel formation. Finally, the effects of NMs on developmental parameters and oxidative stress in zebrafish embryos were further assessed by examining the expression levels of genes zhe1, acvr2a, sod1 and cat. No acute or sub-lethal toxic effects were observed in zebrafish embryos after exposure to each of the nHAPs up to a dose of 500 μg mL⁻¹. At the highest doses, spinal curvature, yolk sac edema and pericardial edema were observed for nP and bulk rock phosphate (RP). Interestingly, several of the nHAPs caused an increase in zebrafish hatch rate at 48 and 54 hpf that appeared to be due to an increase in gene expression of zhe1. Overall, the collective results from this study suggest that biogenic nHAPs cause no acute or sublethal toxic effects whereas nP caused sublethal toxicity at higher doses in zebrafish embryos.