Diclofenac uptake does not affect the growth and photosynthetic performance of Spirodela polyrhiza (L.) Schleid. fronds under laboratory conditions: Implications for the pharmaceutical compound phytoremoval.

The growing presence of pharmaceutical residues in freshwater ecosystem requires to expand our knowledge of the impact of these pollutants on biota. In this regard, studies on the effects of diclofenac (DCF), one of the most detected pharmaceutical compounds worldwide, on freshwater biota are needed to better understand the mechanisms associated to its toxicity, especially in plants. As model plants for toxicity assay in freshwater environment, duckweeds can be targeted for this scope. In this study, Spirodela polyrhiza L. Schleid. fronds were exposed to 4, 20 and 100 μg L-1 DCF for 7 days under laboratory conditions. At the end of the assay, biometric, spectral reflectance and chlorophyll fluorescence parameters were analysed to investigate the effects of DCF on the growth, pigment content and photosystem performance, revealing a lack of toxic symptoms at any concentration tested. The analysis of DCF concentration in the medium alone, exposed to light, evidenced the photosensitivity of DCF (removal of 22 % and 62 % of the initial DCF content at 4 and 100 µg L-1 DCF, respectively) even in lab conditions. The removal rate of DCF further increased when plants were grown in the medium, reaching the 81 % of the initial DCF content at 4 µg L-1 DCF. Diclofenac was slightly accumulated by S. polyrhiza fronds without a linear relation to its concentration in the medium. The ability of S. polyrhiza plants to remove DCF is discussed, considering the significant reduction in the DCF content of the medium in which the plants were grown, the low DCF accumulation in the plant tissues, the physico-chemical characteristics of the molecule and the experimental conditions used.