Every year, 5 to 10 million tons of plastic are dumped into the oceans and accumulate in huge ocean gyres. Freshwaters are the main transportation route for plastics to the oceans. This plastic debris undergo very strong physico-chemical stresses under the effect of various biotic and abiotic factors, and thus fragment. The fragmented macroscopic plastics lead to the formation of «microplastics» (between 20 µm and 5 mm), and also «nanoplastics» (between 1 and 1000 nm). These nanoplastics are all the more dangerous as they can penetrate the food chains from the very first links: the primary producers. As part of the TROPHIPLAST project, this study aims to investigate the impact of nanoplastics from the Garonne river on two primary producers: Desmodesmus subspicatus, a freshwater green microalgae, and Thalassiosira weissflogii, a marine diatom. Both species were exposed for up to 96 h to 0.1, 1, 10, 100 µg/L of nanoplastics obtained from plastics samples of Garonne river. The results show that at these concentrations, there is no significant effect of nanoplastics on microalgae growth. However, there are some variations in the expression of photosynthesis genes for Thalassiosira weissflogii.