Toxicity assessment of Chlorella vulgaris and Chlorella protothecoides following exposure to Pb(II)

• Pb(II) could inhibit the growth of both algae and dose–response relationships were clear.
• EC50 values indicated that Pb(II) was more harmful to the two algae in long-term exposure.
• Higher level of Pb(II) exposure could significantly inhibit chlorophyll a syntheses of both algae.
• SOD and CAT activities of the two algae were obviously promoted after exposed to medium concentrations of Pb(II).

The short- and long-term toxic effects of Pb(II) exposure on Chlorella vulgaris (C. vulgaris) and Chlorella protothecoides (C. protothecoides) were not well understood. The lab study was performed to observe the Pb(II) exposure induced changes. Results of the observations show: (1) higher level of Pb(II) (50 or 80 mg L−1) could significantly inhibit the growth and chlorophyll a synthesis of both algae in almost all the treatments and dose–response relationships could be clearly observed, (2) the range of EC50 values (24–120 h, 67.73–172.45 mg L−1) indicated that Pb(II) had a relatively limited short-term toxicity to the two algae, while long-term tests (7–28 d, 50.41–63.91 mg L−1) displayed higher toxicity and (3) SOD and CAT activities of both algae after exposed to medium level of Pb(II) were significantly promoted, and their response might be more susceptible in short-term exposure. This research provides a basic understanding of Pb(II) toxicity to aquatic organisms.