Nanosized zeolite beta - determining the safety of usage by zebrafish Danio rerio embryos

Zeolites are materials widely used in many fields of human activities. Furthermore, new potential applications constantly emerge, so understanding their possible impact on the environment is necessary. Within this study, the potential toxicity of nanosized particles (140 and 600 nm) of a widely used zeolite beta was evaluated using zebrafish Danio rerio embryos. Embryotoxicity test, with an emphasis on sublethal changes, was performed on three concentrations of each nanosized zeolite sample (calcined and non- calcined). Toxicity of tetraethylammonium species (TEA) present in non- calcined zeolite samples was also investigated using experimental and computational approaches. The data suggest that non-calcined zeolites and tetraethylammonium hydroxide (TEAOH) itself caused hatching failure, but also initiated oxidative stress and apoptosis. Such observation confirmed certain TEA leaching from the zeolite framework, thus impacting embryonic development. Since molecular docking and molecular dynamics simulations did not show TEA inhibition of the hatching enzyme ZHE1 and the ROS formation was detected using fluorescence microscopy, it was concluded that oxidative stress is the major mechanism underlying the toxicity of non- calcined samples and TEAOH. Contrary to that, calcined zeolite nanoparticles, although having a strong interaction with the chorion and subsequently with the embryos, did not show a negative impact on zebrafish survival/development. Such a comprehensive study pinpointed zeolite nanoparticles as safe materials and opened the door for their application.