Investigating effects of inorganic engineered nanoparticles on phaeodactylum tricornutum: implications on the eco-biosystems

Abstract

Inorganic engineered nanoparticles (IENs) have garnered much attention lately in regard to their potentially toxic effects should they be introduced unintentionally into the environment. The marine ecosystem is often recognized as the final destination for anthropogenic nanoparticle pollutants and it is likely that the introduction of these engineered nanoparticles will cause several undesirable effects to the biological systems of aquatic creatures due to their poorly understood physical and chemical properties. There is an increasing concern that as autotropic primary producers, the uptake of nanoparticles by diatoms will result in reduced cellular functions and growth. At the very bottom of the food chain, it is not an exaggeration to say that the entire ecosystem may face catastrophic consequences depending on the interactions between nanoparticles and these unicellular microalgae. A select number of inorganic engineered nanoparticles were chosen based on their extensive use in commercial products (silver, zinc oxide and silica nanoparticles). These inorganic nanoparticles were characterized via Dynamic Light Scattering and the toxic effects of metallic and non-metallic nanoparticles were evaluated based on the growth profile and chlorophyll a content in Phaeodactylum tricornutum (P. tricornutum), our diatom of study. Characterization results suggests that the studied nanoparticles tend to flocculate more when suspended in seawater as compared to freshwater, elucidating the behaviour of the studied nanoparticles when they end up in saltwater ecosystems either due to precipitation or surface runoff. Growth trends showed that metallic nanoparticles are more toxic towards the diatom species as compared to non-metallic nanoparticles. In addition, autofluorescence results suggest that the inorganic nanoparticles are capable of inducing cell death by negatively affecting the diatom’s ability to photosynthesize. A greater extent of diatom aggregation was observed for diatoms treated with non-mesoporous silica as compared to mesoporous silica. The presence of a secreted substance by the aggregated diatoms that increases in proportion to the nanoparticle concentration in the culture environment was also detected. It is theorized that the secretions are the microalgae’s extracellular polymeric substances, functioning as a form of algal defence to the inorganic anthropogenic nanoparticles. These findings prove useful as they can be utilized as a future approach to study and understand diatom-nanoparticle interactions. In addition, the difference in autofluorescence intensity of chlorophyll a may be exploited as a potential environmental biosensor to IENs.