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 mgL(-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 mgL(-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 mgL(-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 Q(A) and Q(B) were all increased inducing activation of the photosynthetic
electron transport chain. These changes resulted in stimulation of full photosynthetic
performance.