# Effects of Nanoparticles on Algae: Adsorption, Distribution, Ecotoxicity and Fate
## 1 Introduction  
With the wide application of nanoparticles (NPs) in different areas, the development of nanotechnology has significantly increased. Nanoparticles are defined as particles with at least one dimension in the range of 1 to 100 nm [1]. NPs can be divided into five categories based on their chemical composition: nano-metal, nano-oxide, carbon nanomaterials, quantum dots and other NPs such as organic polymers [2]. These NPs have many applications in the fields of food packaging, textiles, optoelectronics, biomedicine, cosmetics, energy and catalysis due to their unique capabilities such as their mechanical properties, contact reactivity, optical properties and electrical conductivity [3; 4]. NPs have been used in a variety of common products such as household appliances, cleaning agents, clothes, tableware and children's toys [5]. Currently, the most common nanomaterials include silver, fullerene and carbon nanotubes, zinc oxide, silica and titanium dioxide [6]. For example, Ag NP-based disinfectants have attracted much attention due to their practical applications in daily life [7]. Nanoparticles have been present on Earth from the beginning of its existence, for example, in volcanic dust, water, soil and sediment [8]. With the advent of the industrial revolution, extensiveburning of a large amount of fossil fuels resulted in a significant increase in the number of NPs and has become a potential risk to the environment [9]. Currently, NPs are employed in a wide variety of industries [10]. NPs will enter into the environment during production, transportation, consumption and disposal, and eventually deposit onto bodies of water and soils [11]. In fact, many large-scale chemical manufacturers producing NPs discharge effluent into the ocean or rivers. A large number of NPs are discharged into the water body each year [8]. In a water environment, NPs pose a risk to the aquatic ecosystem and human health through a series of complex processes such as adsorption, desorption, suspension, sedimentation, and acting with minerals, organic matter, biofilm and other complex aspects of the water environment [6; 12]. The use of consumer products containing NPs will expose humans to the risks associated with NPs, especially those that are in contact with the human body, such as sunscreens and cosmetics. Sunscreen contains titanium dioxide (TiO\({}_{2}\)) and zinc oxide (ZnO) nanoparticles, which produce free radicals in the light that not only destroy the formulation of the sunscreen, but also destroy the biomolecules, so as to bring a risk to the consumers [13]. TiO\({}_{2}\) nanoparticles were also used as antibacterial agents and colorants in paints and food packaging [14; 15], which were likely to then migrate into the environment or food sources and cause potential harm to organisms. In addition, nanoparticles in food can penetrate into the digestive tract lymphatic vessels, and compared with other large particles, can be more easily distributed into other tissues and organs [16]. Organisms of different trophic levels are usually selected to assess the ecotoxicity of NPs, including primary producers (algae), consumers (mammals, crustaceans) and decomposers (microbes) [17]. Among them, algae are the most widely used to evaluate the ecotoxicity of NPs. In aquatic ecosystems, algae lie at the lowest trophic level and are the basis of many food webs [18; 19]. Algae play an important role in aquatic ecosystems and are the main producers of aquatic food chains [20]. They do not only provide oxygen and food for other aquatic organisms through their own photosynthesis, but also contribute to the purification of water [21]. Algae have been used as a bio-indicator of pollutants due to their high bioaccumulation ability [20].