Effects of biogenic and commercially available iron-oxide nanoparticles on algal and bacterial growth in freshwater and marine water.

Abstract

We investigated the potential toxic effects of iron oxide magnetic nanoparticles (IOMNPs) of varied size, synthesized through biological and chemical methods on freshwater and marine microalgae and bacterial species. The study provides insights into pollution and ecological impacts of NPs. IOMNPs of two sizes, 20-50 nm (quasi-spherical) synthesized using a cell-free fungal extract (biogenic method), and 104 nm (spherical) obtained from a commercial source (chemical method), were tested for aggregation, bioavailability, and toxicity at multiple concentrations (12.5, 25, 50, 100, and 125 µg mL^-1). Microalgal growth media (Bold's basal media and sea salt media [SSM]) was used for aggregation analysis of IOMNPs using dynamic light scattering (DLS) technique. DLS analysis showed similar aggregation patterns for both type of IOMNPs, with relatively larger aggregate formation in SSM. Toxicity assessments showed that biogenic IOMNPs of smaller size 20-50 nm were non-toxic, while commercial IOMNPs of large size (104 nm) significantly reduced bacterial cell density and microalgal lipid and carotenoid content at higher concentrations. Further, transmission electron microscopy and X-ray fluorescence analysis confirmed IOMNP uptake by microalgae. TEM images showed more pronounced structural damage caused by the uptake of commercial IOMNPs. Our findings provide crucial insights into the differential impacts of IOMNPs based on their size and synthesis methods on key aquatic microorganisms and their potential to mitigate issues related to NP pollution.