Impacts of gold nanoparticle exposure on two freshwater species: a phytoplanktonic alga (Scenedesmus subspicatus) and a benthic bivalve (Corbicula fluminea)

For years, nanotechnologies have developed the use of common materials, such as iron or silica, at an extremely small scale because of their new properties (reactivity, conductivity, optical sensitivity). More precisely, gold nanoparticles are used in numerous technologies such as electronics, new paints or research on cancer. But, despite their promising future and expansive utilization, only a few studies deal with their behaviors or impacts on the environment. Thus, we decided to explore the impacts of amine-coated 10nm gold nanoparticle (AuNp) contaminations on two freshwater aquatic models. The green alga Scenedesmus subspicatus was submitted to 24 h-direct exposures at four AuNp concentrations (1.6x10(2), 1.6x10(3), 1.6x10(4) and 1.6x10(5) AuNp/cell) along with a control condition. The process used for the freshwater bivalves Corbicula fluminea was a trophic exposure during 7 days to three AuNp concentrations (1.6x10(3), 1.6x10(4) and 1.6x10(5) AuNp/cell). These conditions were tested in triplicate with controls. For these experiments, OD measurements (lambda = 520nm) were performed to verify AuNp concentrations in the water (stability). Cell numerations of algae were used to determine the growth/mortality effects on this species. Cellular impacts and AuNp distributions in the two species were revealed by transmission electron microscopy (TEM). The bioaccumulation rates were assessed by gold dosages via MS-ICP procedures. Molecular impacts were analyzed by quantifications of metallothionein concentrations (metal detoxification protein) and genetic expressions via real-time RT-PCR. Our study focused on the expression of six genes encoding proteins involved in: metal detoxification (metallothionein), the response to oxidative stress (catalase and superoxide-dismutase), the mitochondrial respiratory chain (subunit 1 of the cytochrome-C-oxidase), the concentration of mitochondria (RNA12s) and the response to xenobiotics (glutathione S transferase); using the beta-actin as reference of the basal rates of gene expressions. The results showed a marked impact on the algae after a 24h-exposure to amine-coated 10nm gold nanoparticles, leading to 20% of mortality for the lowest contamination condition, while the highest one reached 50%. TEM examinations showed that AuNp were strongly adsorbed by the cell wall of algae, leading to progressive intracellular and wall disturbances. The bivalve contaminations revealed the ability of these particles to be bioaccumulated and to penetrate gills and digestive epithelia. Their lysosomial localization leads to the loss of their coating, which brought on an oxidative stress.