Ecotoxic effects of paclitaxel-loaded nanotherapeutics on freshwater algae, Raphidocelis subcapitata and Chlamydomonas reinhardtii

The contamination of water bodies and water pollution with pharmaceuticals are global issues receiving increasing attention, stemming from population growth and the resultant rises in pharmaceutical consumption, disposal, and excretion. However, little is known about how emerging classes of pharmaceuticals, in particular nanopharmaceuticals, influence water bodies and organisms living in them. In this work, we investigate the interactions of paclitaxel-loaded nanomedicine with freshwater algae Raphidocelis subcapitata and Chlamydomonas reinhardtii. For a given paclitaxel concentration, the nanomedicine form of paclitaxel led to a higher localization of paclitaxel on/in algal cell surfaces and inhibited algal growth more than molecular (free) paclitaxel. In addition, while the molecular paclitaxel at the solubility limit in water could not significantly hinder algal growth to reach an IC50 level, the nanomedicine form had a 120 h IC50 value of 1.1 ± 0.1 μg paclitaxel ml−1 for C. reinhardtii and a 72 h IC50 value of 1.6 ± 0.1 μg paclitaxel ml−1 for R. subcapitata. In the case of paclitaxel-loaded nanomedicine, concentrations above 16.2 μg paclitaxel mL−1 for R. subcapitata and above 5.4 μg paclitaxel mL−1 for C. reinhardtii resulted in an algaecidal effect, i.e. algal necrosis and complete stoppage of algal growth. The presence of paclitaxel-loaded nanomedicine also hindered the photosynthetic activity while free-paclitaxel caused no significant effect on it. These findings indicate that nanopharmaceuticals can cause ecotoxic effects on freshwater algae, which is otherwise not possible with traditional pharmaceuticals, owing to their ability to solubilize water-insoluble drug molecules in them.