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Nanoscale phosphorus (P)-based formulations are being investigated as potentially new fertilizers to overcome the challenges of conventional bulk P fertilizers in agriculture, including low efficacy rates and high application levels. After agricultural applications, the NMs may be released into aquatic environments and transform over time (by aging) or in the presence of abiotic factors such as natural organic matter or sunlight exposure. It is, therefore, important to investigate the physicochemical changes of NMs in environmentally realistic conditions and assess their potential acute and sublethal toxic effects on aquatic organisms. To investigate this, two separate studies were conducted: 1. the effects of 3-months aged P-based NMs on zebrafish embryos, and 2. the influence of humic acid (HA), UV exposure, or a combination of both on P-based NM toxicity in zebrafish embryos. Four different types of nanohydroxyapatites (nHAPs) and a nanophosphorus (nP) were included in the study. These NMs differed in their physicochemical properties, most prominently their shape and size. Environmental transformations were observed for P-based NMs due to aging or interaction with abiotic factors. The aging of the NMs increased the hydrodynamic diameter (HDD) of rod- and needle-shaped NMs and decreased the size of the platelet and spherical NMs, whereas interactions with HA and UV decreased the NMs' HDD. It was observed that no LC 50 (survival) and IC 50 (hatch and heart rates) were obtained when the zebrafish embryos were exposed to the aged NMs or when NMs were added in the presence of HA and UV. Overall, these results suggest that P-based NMs cause no acute toxicity and minimal sub-lethal toxicity to zebrafish embryos in environmentally realistic experimental conditions., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Biogenic phosphorus (P) based - nanomaterials (NMs) are currently being explored as nanofertilizers. In this study, the acute toxic effects and trophic transfer of multiple types of P-based NMs were examined on soil-dwelling nematode, Caenorhabditis elegans. The study involved four variants of nanohydroxyapatites (nHAPs) synthesized either via a biogenic or a chemical route and another NM, nanophosphorus (nP), biosynthesized from bulk rock phosphate (RP). The pristine NMs differed in their physicochemical properties with each possessing different shapes (biogenic nHAP: platelet-shaped, ˜35 nm; biogenic nP, ˜5-10 nm: dots; chemically synthesized nHAPs: spherical, ˜33 nm, rod, ˜80 nm and needle-shaped, ˜64 nm). The toxic effects of NMs' in C. elegans were assessed using survival, hatching and reproductive cycle as the key endpoints in comparison to bulk controls, calcium phosphate and RP. The interactions and potential uptake of fluorescent-tagged nHAP to E. coli OP50 and C. elegans were investigated using confocal microscopy. The transformation of NMs within the nematode gut was also explored using dynamic light scattering and electron microscopy. C. elegans exposed to all of the variants of nHAP and the nP had 88-100% survival and 82-100% hatch rates and insignificant effects on brood size as observed at the tested environmentally relevant concentrations ranging from 5 to 100 μg.mL -1 . Confocal microscopy confirmed the interaction and binding of fluorescent-tagged nHAP with the surface of E. coli OP50 and their trophic transfer and internalization into C. elegans. Interestingly, there was only a small reduction in the hydrodynamic diameter of the nHAP after their uptake into C. elegans and the transformed NMs did not induce any additional toxicity as evident by healthy brood sizes after 72 h. This study provides key information about the environmental safety of agriculturally relevant P-based NMs on non-target species., (Copyright © 2021 Elsevier B.V. All rights reserved.)