Toxicity of PAMAM dendrimers to Chlamydomonas reinhardtii

In recent decades, a new class of polymeric materials, PAMAM dendrimers, has attracted marked interest owing to their unique nanoscopic architecture and their hopeful perspectives in nanomedicine and therapeutics. However, the potential release of dendrimers into the aquatic environment raises the issue about their toxicity on aquatic organisms. Our investigation sought to estimate the toxicity of cationic PAMAM dendrimers on the green alga, Chlamydomonas reinhardtii. Algal cultures were exposed to different concentrations (0.3–10 mg L−1) of low dendrimer generations (G2, G4 and G5) for 72 h. Potential adverse effects on Chlamydomonas were assessed using esterase activity (cell viability), photosynthetic O2 evolution, pigments content and chlorophyll a fluorescence transient. According to the median inhibitory concentration (IC50) appraised from esterase activity, toxicity on cell viability decreased with dendrimer generation number (2, 3 and 5 mg L−1 for G2, G4 and G5 dendrimers, respectively). Moreover, the three generations of dendrimers did not induce the same changes in the photosynthetic metabolism of the green alga. O2 evolution was stimulated in cultures exposed to the lowest generations tested (i.e. G2 and G4) whereas no significant effects were observed with G5. In addition, total chlorophyll content was increased after G2 treatment at 2.5 mg L−1. Finally, G2 and G4 had positive effects on photosystem II (PSII): the amount of active PSII reaction centers, the primary charge separation and the electron transport between QA and QB were all increased inducing activation of the photosynthetic electron transport chain. These changes resulted in stimulation of full photosynthetic performance.