PHARMACEUTICAL RESIDUES IN THE AQUATIC ENVIRONMENT: EFFECT EVALUATION ON PLANTS FOR PHYTOREMEDIATION PURPOSES

Pharmaceuticals residues have been receiving increasing attention as bioactive chemicals in the aquatic environment. They are considered as emerging contaminants being still unregulated or currently undergoing a regularization process. Release of pharmaceutical compounds and their metabolites in the aquatic ecosystem is mostly due to an incomplete removal by conventional wastewater treatment plants (WWTPs). Consequently, they are detected in WWTP effluents, surface water and, less frequently, in groundwater. Among them, a particular attention is paid to ibuprofen (IBU), one of the most diffused drug in surface waters and sediments. Despite the high removal by WWTPs, IBU amount in WWTP effluents is in the range of ?g L-1, whereas in rivers and groundwater generally in the ng L-1 range. Due to their physical-chemical characteristics, IBU and its metabolites represent a potential risk for the aquatic organisms, even if eco-toxicological data are very scarce. Phytoremediation is a technology able to improve the performance of existing WWTPs, including emerging micropollutants. Willows and poplars are proved to remove and degrade organic and inorganic pollutants from contaminated substrates thus they can act as bio-tool to mitigate the impact of micro-contaminants in the riparian ecosystem. Lemna gibba L. is a model aquatic plant species, commonly utilized in water quality biomonitoring and in standardized tests for environmental risk assessment, and thus also proposed as a biological tool for wastewater reclamation. In our studies poplars, willows and L. gibba. plants were used in different experiments to analyse the possible toxic effects of IBU and its metabolites on plants and to evaluate the ability of these plant species in reducing IBU concentration in the growth medium. In separated experiments, callus cultures of P. nigra L. and two clones of Salix alba L. (SS5 and SP3) were exposed for three weeks to different IBU concentrations in agar medium and under hydroponics, respectively. Moreover, L. gibba plants were exposed to 1 mg L-1 IBU (a threshold dose used to evaluate tolerance/sensitive responses in duckweed) in a eight days-test under hydroponics. Results evidenced a notable tolerance of poplar cells to IBU, especially at high concentrations (IBU 30 mg L-1), which even stimulated growth. Furthermore, a complete removal of IBU from the growth medium by poplar cells occurred. The experimental trial on Salix sp. demonstrated that clone SS5 was more tolerant and showed a higher ability to reduce IBU concentration in the solution than clone SP3. The high tolerance to IBU shown by SS5 was likely due to several mechanisms including the capacity to maintain an elevated photosynthetic activity and an efficient antioxidative defence. Finally, a growth stimulation of Lemna gibba L. in response to high level of IBU and the detection of IBU and some metabolites within plant tissues were observed. All these findings represent a valuable contribution to a better evaluation of the biomonitoring and phytoremediation potential of plants used in these trials, and to highlight the fate and the toxic action of IBU and its metabolites in the aquatic ecosystem.