# Effects of Nanoparticles on Algae: Adsorption, Distribution, Ecotoxicity and Fate
## 7 Conclusions and Outlook  
As a new kind of material, nanomaterials have been widely used in various fields even though there exists a certain degree of threat to the safety of aquatic organisms. Studies on the toxicity of NPs on algae can not only explore the toxic mechanism of NPs on algae, but also provide a theoretical basis for the safety assessment of biological toxicity of nanomaterials. For this purpose, great efforts have been made in this area and more work will be conducted in future.  
The adsorption of NPs on algal cells was generally tested in the ideal system. Therefore, it is necessary that inhibitors (e.g., NOM) and accelerants (e.g., surfactants) for NPs can be investigated in detail in the adsorption process of algae, and suitable agents would need to be selected to decrease or improve the algal adsorption to NPs. This information can be used in the detoxication procedure of algae to NPs and the treatment of NP-contaminated water by algal cells.  
A few studies have demonstrated the uptake of NPs into algal cells. This research mainly focused on the description of phenomena and provided some deduction about the mechanism of the uptake process. When NPs pass the cell membrane of algae by endocytosis or passive diffusion, the carrier of NPs in the cell membrane may be involved. The study on the structure and act mechanism of NP carriers can be useful for the uptake regulation of NPs by algae.  
After entering the algal cell, NPs were observed on different organelles of cellular structures. Reported studies tended to explain the damage of NPs to organelles. There is still a lack of mechanism exploration for the transportation of NPs in the cytoplasm of an algal cell. Also, the quantitative distribution of NPs on different organelles is important for the evaluation of NPs ecotoxicity to algae.  
The oxidative damage mechanism has been proven to be one of the major possible mechanisms for NP ecotoxicity to algae, which can cause damage to the cell wall, cell membrane and organelles. More information about the change of metabolization in an algal cell is suggested to be investigated by transcriptome analysis and metabolomic analysis. Additionally, the response and repair mechanism of algal cells to the damage done by NPs should be explored and further used to construct new algal strains that are highly resistant to NPs. Currently, high dosages of NPs are often used in NP toxicity tests on algae and the tests are generally characterized by short-term biological effects. However, the exposure dose of NPs in the natural environment is usually low, and exposure time can be much longer. Therefore, a long-term exposure study under a low dosage will provide data that are more useful in evaluating the ecotoxicity of NPs to algae. On the contrary, to relieve the damage caused by the oxidative stress in algae, the expression of an antioxidant enzyme was up-regulated and more antioxidant substrates were produced. Thus, it is possible to use the toxicity mechanism to enhance the production of antioxidant metabolites from algal cells by utilization of NPs at a certain level.  
The concentration of NPs in the water environment is low, and NPs may accumulate in organisms of high trophic level and produce significant toxic effects by the stepwise delivery or enrichment of the food chain. The present research on the transmission and biomagnification of NPs in the food chain of aquatic ecosystem is still limited. It is not clear how the environmental factors would influence the transmission of NPs in the food chain. Therefore, it is necessary to establish a more comprehensive aquatic biological system, including primary producers and consumers at different trophic levels, to investigate the transmission and biological effects of NPs along the food chain.