The roles of pendimethalin and its nano-form to induce oxidative stress, osmolytes, biochemical alterations and cytotoxic effect in algal cells of Chlorella vulgaris after exposure to sub-lethal concentrations were carried out. The data indicated that, 96-h EC50 values were 20 and 19 ppb for pendimethalin and its nano-form, respectively. Three concentration levels (0.1EC50, 0.025EC50 and EC50) of the examined herbicide decreased the algal pigments (Chlorophyll a and b), but increased carotenoid contents compared with the control group. Biomolecules such as protein, carbohydrates, proline and sucrose of the algal cells significantly increased for the all treatments compared with the control groups. Similarly, malondialdehyde (MDA), some enzymes such as catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) showed significant increases for the all treatments. On the other hand, ultrastructural investigation of the herbicide-treated algal cells showed significant changes in their organelles in comparing with the untreated cells through transmission electron microscope (TEM) images. From all findings, it was obtained that the nano-pendimethalin was more potential toxic than the traditional form to induce adverse effects on the freshwater alga. Thus, biosafety procedures must be followed on non-target species before decision for nano-herbicide practices.

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