PHYTOTOXIC EFFECTS OF TiO2-NPs IN TWO MACROPHYTES FOR CONSTRUCTED WETLANDS

This study aimed to investigate nanometer titania (TiO2-NPs) toxicity in two species of plants commonly used in constructed wetlands: Ceratophyllum demersum and Phragmites australis. The seed germination, plantlet development and physiology were evaluated by exposure experiments. Moreover, Ti distribution and accumulation were determined through TEM-EDX and ICP-MS measurement. Results showed no significant differences in germination rates among plant seeds treated with low-level (<= 500 mg L-1) TiO2-NPs. By contrast, exposure to high-level (>= 1000 mg L-1) TiO2-NPs showed different results, the germination rates and seedling masse for Ceratophyllum demersum or Phragmites australis seeds decreased obviously to 30% and 0.77 g or 31.67% and 0.36 g, respectively, when the seeds were exposed to 2000 mg L-1 TiO2 NPs for 6 d. The growth of Ceratophyllum demersum and Phragmites australis was inhibited during the TiO2-NPs exposure to the plants. TiO2-NPs displayed phytotoxicity with reduced chlorophyll contents increased Superoxide Dismutase (SOD) activity, and Malondialdehyde (MDA) contents in both plant species. TiO2-NPs could enter into the Ceratophyllum demersum and Phragmites australis, and higher concentration could result in more entrance. However, it was difficult for TiO2-NPs to transfer from Phragmites australis roots to stems and leaves. Ti accumulation reached 866 and 829 mu g(-1) d.wt. in Ceratophyllum demersum and Phragmites australis roots, respectively. By contrast, only 28 mu g g(-1) d.wt of Ti was translocated to the Phragmites australis stems, and no Ti was detected in Phragmites australis leaves during 12 d of treatment.