The Impacts Of Nanoparticles On Bioaccumulation Of Heavy Metals By Azolla

With the development of the nanomaterials, the production of nanomaterials is increasing since they have been involved in our life. With the extensive application of these nanomaterials, they release to the surrounded environment, or to be specific, aquatic system and thus impose the damage on aquatic system. For example, these nanoparticles could be directly absorb to the plant species in aquatic system exerting direct nano-toxicity, or, they could be absorbed on the contaminants in aquatic system to change the property of those contaminants. Consequently, could produce impacts on their relationship with plant species. However, it is still unclear. Hence, the study of aquatic ecological toxicity of nanoparticles has attracted the attention, but there are a few reports on nanoparticles impacts on the plant species in aquatic system, as well as their removal of metal ions.In this study, various nanoparticles such as nano-TiO2, nano-ZnO and nano-CNTs was used to impact on the accumulation of heavy metals by Azolla, which is a floating aquatic fern. Firstly, different concentration of nano-TiO2 impacted on the simultaneous accumulation of Cu (Ⅱ) and Cr(Ⅵ) by Azolla was investigated. Results showed that the amount of Cu (Ⅱ) and Cr(Ⅵ) accumulated by Azolla was decreased with increasing of the concentration of nano-TiO2, where indicated that the inhibition of bioaccumulation of Cu (Ⅱ) and Cr(Ⅵ) was observed by the addition of nano-TiO2, however, it was not related with the metal ions valence due to the adsorption of both positive Cu (Ⅱ) and negative Cr(Ⅵ) onto the nano-TiO2 with its amphotericity.In addition, nano -ZnO has a capacity to absorb Cu (Ⅱ) onto its surface. The amount of Cu(Ⅱ) accumulated by Azolla significantly decrease to 0.66 mg/g(DW) with the addition of 50 mg/L nano-ZnO. However, with the increase concentration to 50 mg/L of Cu(Ⅱ), only a slightly increase amount of Cu(Ⅱ) accumulated by the Azolla was observed. When Cu (Ⅱ) concentration increased to 100mg/L, the greater increase in Cu(Ⅱ) accumulated by the Azolla was found. This is resulted from there are much more damage on Azolla membrane with the increase concentration of Cu(Ⅱ).Furthermore, When nano-CNTs (50mg/L) was added into the solutions containing various concentration of Cd (Ⅱ) at 5、15 and 30 mg/L, the accumulation of Cd(Ⅱ) by Azolla was all inhibited, but the inhibitory of nano-CNTs to Azolla decreased while when the concentration of Cd(Ⅱ) reached 30 mg/L, this mainly due to the nano-CNTs with a long strip tubular shape blocked the bioaccumulation of Cd(Ⅱ) by Azolla.,In summary, the different toxicities of nanoparticle to bioaccumulation of metal ions by Azolla were observed in this study, these can be attributed to the differences between nanoparticles, metal ions and Azolla. However, further work will aim to understand the relationship of them.