# Effects of Nanoparticles on Algae: Adsorption, Distribution, Ecotoxicity and Fate
## 6 Fate of NPs in the Aquatic Food Chain  
As a basis for aquatic food chains, algae are the source of food for various aquatic organisms and algae can promote the ingestion of NPs by organisms during feeding, thereby incorporating NPs into food chains (Figure 2) [23; 30; 92]. The transmission or enrichment of NPs through the aquatic food chain may lead to toxic effects on high trophic level organisms in the food chain. Since crustaceans are the major consumer of algae, there have been several studies that reported the transfer of NPs from algae to the crustacean _Daphnia_ through diet. It was reported for the first time that quantum dots can be transported along the food chain from _Pseudokirchenriella subcapitata_ to _Ceriodaphnia dubia_ through fluorescence techniques [93]. When algae were used to feed _Daphnia magna_, _Daphnia magna_ was found to ingest NPs from the test suspension through feeding behaviors [94]. The behavior of gold nanoparticles was studied in a model food chain consisting of a phytoplankton as food (_Ankistradesmus falcatus_) and a zooplankton grazer (_Daphnia magna_), and a significant accumulation of Au NPs in the gut of _Daphnia_ was observed [18]. Using stable isotope labeling techniques, it was revealed that carbon nanomaterials underwent complex aquatic accumulation and transfer from primary producers to secondary consumers (_Scenedesmus obliquus-Daphnia magna_ food chain) [92]. Studies have shown that these NPs could accumulate in the digestive tract of _Daphnia magna_ and  
Figure 2: Fate of NPs in the aquatic food chain. exhibit chronic toxicity upon the growth and reproduction of _Daphnia magna_[32; 95; 96]; even the neonate production from adult daphnids was significantly reduced [97]. Not only can the toxic concentration of NPs cause mortality in _Daphnia_, the selectivity of daphnids to uncontaminated algal cells may also contribute to the reduced growth and reproduction of daphnids due to starvation [98; 99]. It was demonstrated in a study by [PERSON] that the toxicity of TiO\({}_{2}\) NPs to daphnia may be partly due to the starvation of daphnids resulting from their selectivity to algal cells [22]. In this case, daphnids were exposed to TiO\({}_{2}\) NP-treated algal cells at various concentrations for a chronic exposure study. The chronic exposure resulted in a concentration dependent decrease in the body length and reproduction capacity of the daphnids [22]. The toxicity and trophic transfer of metal oxide NPs was assessed from marine microalgae _Cricosphaera elongata_ to the larvae of the sea urchin _Paracentrotus lividus_, where the survival rate of larvae fed with microalgae exposed to SiO\({}_{2}\) and CeO\({}_{2}\) NPs was significantly reduced, and abnormal developments with skeletal degeneration and altered rudiment growth were observed [100]. _Mytilus galloprovincialis_ (Mediterranean mussel) was fed with algae previously exposed to Au NPs, and NPs were found in the gills and digestive glands of the mussels [16]. After zebrafish were fed with _Daphnia magna_ containing TiO\({}_{2}\) NPs, the content of TiO\({}_{2}\) NPs in the fed zebrafish was higher than that of zebrafish exposed to TiO\({}_{2}\) NP aqueous solution alone, which is the first direct evidence for the transfer of TiO\({}_{2}\) NPs from daphnia (_Daphnia magna_) to zebrafish (_Danio rerio_) through dietary intake [101]. The toxic effects of nano-polystyrene on zebrafish delivery along the tertiary aquatic food chain of green algae-_Daphnia magna_-zebrafish were studied by [PERSON] et al., and it was found that nano-polystyrene was transferred from green algae to fish and that it made a great impact on the behavior and lipid metabolism of fish [102]. NPs have toxic effects on zebrafish embryos, such as delayed hatching, reduced larvae body length and tail malformation [103]. These studies suggest that food chain enrichment is likely to be an important pathway for high trophic level bioaccumulation and enrichment of NPs.