Effects of chlorpyrifos on the growth and ultrastructure of green algae, Ankistrodesmus gracilis

• The exposure of A. gracilis to chlorpyrifos led to effects at cellular and population level.
• Growth of A. gracilis was inhibited after the exposure to chlorpyrifos.
• An increase in A. gracilis biovolume was observed after the exposure to chlorpyrifos.
• Radical changes were observed in the ultrastructure of cells exposed to chlorpyrifos.

The effect of the organophosphorus insecticide chlorpyrifos on the growth, biovolume, and ultrastructure of the green microalga Ankistrodesmus gracilis was evaluated. Concentrations of 9.37, 18.75, 37.5, 75 and 150 mg L−1 of chlorpyrifos were assayed along with a control culture. At the end of the bioassay the ultrastructure of algal cells from control culture and from cultures exposed to 37.5 and 150 mg L−1 was observed under transmission (TEM) and scanning electron microscopy (SEM). After 24 and 48 h, treatments with 75 and 150 mg L−1 inhibited the growth of A. gracilis; whereas after 72 and 96 h, all the treatments except at 9.37 mg L−1 significantly affected the algae growth. The effective concentration 50 (EC50) after 96 h was 22.44 mg L−1 of chlorpyrifos. After the exposure to the insecticide, an increase in the biovolume was observed, with a larger increase in cells exposed to 75 and 150 mg L−1. Radical changes were observed in the ultrastructure of cells exposed to chlorpyrifos. The insecticide affected the cell shape and the distribution of the crests in the wall. At 37.5 mg L−1 electodense bodies were observed along with an increase in the size and number of starch granules. At 150 mg L−1 such bodies occupied almost the whole cytoplasm together with lipids and remains of thylakoids. Autospores formation occurred normally at 37.5 mg L−1 while at 150 mg L−1 karyokinesis occurred, but cell-separation-phase was inhibited. The present study demonstrates that the exposure of phytoplankton to the insecticide chlorpyrifos leads to effects observed at both cellular and population level.