Impact of Metal Nanoparticles on Marine and Freshwater Algae

Abstract

Algae are photosynthetic organisms living in oceans and freshwater lakes and rivers and as primary producers they represent the basic tropical level of the food network in aquatic ecosystems. In addition, they effectively capture atmospheric CO2 and produce about 50% of all oxygen on Earth. On the other hand, marine and freshwater micro- and macro-algae are susceptible to many environmental pollutants, including toxic metals, which adversely affect their physiological and enzymatic activity, resulting in reduced growth and ultimately the death of algae. Metal nanoparticles (MNP) due to their large surface area compared to the volume/size ratio of nanoparticles capable of penetrating algae cells usually exhibit higher biological reactivity compared to their bulk counterparts and therefore increased entry of toxic MNPs from anthropogenic activities into aquatic ecosystems has a negative effect on algal species. This comprehensive review summarizes the findings related to the environmental impact of the most widespread MNPs on freshwater and marine algae, including green algae, diatoms, photosynthetic cyanobacteria, and seaweeds published in the period 2008–2019. Toxic effects of MNP associated with induction of intracellular reactive oxygen species that result in photosynthesis inhibition, lipid peroxidation, membrane destruction, and enhanced accumulation of toxic metals in algae cells causing reduced algal growth and mechanisms of action are discussed and responses of the algae antioxidant defense system to the toxic impact of MNP are analyzed. Emphasis is placed on the effects of particle size, morphology or surface coating of MNPs, environmental factors such as pH or the presence of dissolved natural organic matter, and the possible contribution of dissolved metal ions to the resulting nanotoxicity of MNPs. Green syntheses of MNPs using a wide spectrum of algal species are also presented.