# The Influence of Silver Nanoparticle Form on the Toxicity in Freshwater Mussels
###### Abstract  
The contribution of the form of silver nanomaterials (nAg) towards toxicity in aquatic organisms is not well understood. The purpose of this study was to examine the toxicity of various structures (sphere, cube and prism) of nAg in _Drissen bugensis_ mussels. Mussels were exposed to increasing concentrations of polyvinyl-coated nAg of the same size for 96 h at 15 \({}^{\circ}\)C. They were then analyzed for biophysical changes in the cytoplasm (viscosity, protein aggregation and lipids), neuro-activity (fractal kinetics of acetylcholinesterase-disinesterase (AChE)), oxidative stress (labile zinc (Zn) and lipid peroxidation) and inflammation (arachidonate cyclooxygenase). Although some decreasing effects in protein aggregation were observed, viscosity was more strongly decreased in mussels exposed to spheric and prismatic nAg. The activity of AChE was significantly decreased in the following form-dependent manner: prismatic > cubic > spheric nAg. The fractal dimension of AChE reactions was reduced by all geometries of nAg, while dissolved Ag had no effects. For nanoparticles with the same coating and relative size, spheric nAg produced more significant changes towards the fractal dimension of AChE, while prismatic nAg increased both protein aggregation and viscosity, whereas cubic nAg decreased protein aggregation in the cytoplasm. It is concluded that the geometries of nanoparticles could influence toxicity in aquatic organisms. v 20  
ity, where triangular prisms are more resilient to oxidation, perhaps due to the reduction of surface area. The shape of Ag oxide nanoparticles influenced the bactericidal toxicity to _Escherichia coli_[8]. Cubic nAgO were more toxic to bacteria than octahedral nAgO. The influence of nAg geometries (cubes, spheres, wires and triangles) towards bacterial toxicity involved the formation of protein corona formation [9]. Triangular and spheric nAg were more toxic to _E coli_ bacteria than wired and cubic nAg. The protein composition of the corona differed according to the geometries of nAg, cubic nAg containing a more diverse array of proteins, such as albumin, ferritin and collagenic chains, than the other forms of nAg. Protein corona thickness was lower in the most toxic forms of nAg, indicating a tenuous protein shell on the nAg exposing Ag more easily at the surface to the surroundings. The toxicity of various shapes of polyvinylpyrrolidone-coated nAg at the same size range was recently examined in freshwater mussels [10]. The study revealed that similarly coated and similar sizes of spheric, cubic and prismatic nAg but not ionic Ag produced different effects. At the level of liquid crystal formation in cells, the following form of nAg produced changes: prismatic > cubic > spherical nAg. A reduction in the fractal diffusion rate of the pyruvate kinase-lactate dehydrogenase complex was observed, leading to decreased specific activity and increased protein damage/denaturation based on protein-ubiquitin patterns. Hence, the increase in viscosity and formation of liquid crystals could initiate protein damage and lead to toxicity. Given the increasing production of nAg forms (wires, octohedra, cubes, spheres, prisms, triangles) essentially for bacteria and fouling prevention of various devices and clothes, further research on their toxicity is warranted. The biophysical changes of protein and lipid status in cells require further examination with respect to protein aggregation and soluble lipids in the cytoplasm. Protein aggregation is involved in aging (lipofuscins) and plaque formation in some degenerative diseases [11; 12]. Neurot toxicological effects of nanomaterials are of concern given the importance of membrane integrity for neurotransmission, namely, choline signaling and acetylcholinesterase-adenosine activity [13]. This enzyme is often used to measure neural activity in aquatic organisms. In fish embryos, a dose-dependent inhibition of AChE activity was observed at concentrations as low as 1 ug/L nAg.