Response of Chara globularis and Hydrodictyon reticulatum to lead pollution: their survival, bioaccumulation, and defense

The responses of the pioneer submerged macroalga (Chara globularis) and the rapidly spreading floating macroalga (Hydrodictyon reticulatum) to high levels of lead (40, 80, and 160 mg L⁻¹) at pH 7.14 were studied. Growth rate, Pb bioaccumulation, and physiological response of plants were measured after 5 and 15 days exposure. Both macroalgae efficiently postponed the deposition process of Pb from water column to soil. The Pb bioaccumulation in C. globularis was concentration- and time-dependent increase during the experiment and the maximum bioaccumulation activity was about 3,650 mg Pb kg⁻¹ DW in 160 mg L⁻¹ Pb at pH 7.14 after 15 days, whereas H. reticulatum showed saturable bioaccumulation in 5 days and the maximum was approximately 4,000 mg Pb kg⁻¹ DW; in addition, H. reticulatum exhibited higher tolerance to Pb pollution than C. globularis. The results also showed that the antioxidant defense systems of both tested macroalgae were overwhelmed under high Pb levels with superoxide radical and malondiadehyde levels increasing significantly. The antioxidant enzymes, superoxide dismutase, catalase, and guaiacol peroxidase activities were inhibited severely increasing Pb levels and exposure time. These results indicate that the pioneer species C. globularis would have difficulty growing in a habitat polluted by Pb >40 mg L⁻¹and the rapidly spreading H. reticulatum may not grow in an environment polluted by >80 mg L⁻¹ Pb. Because Pb levels in most water bodies are lower than 40 mg L⁻¹, both C. globularis and H. reticulatum can be considered for phytoremediation of Pb pollution.