Options for the Phytoremediation of Polar Pharmaceuticals. Uptake and Removal of Metformin and Iopromide by Typha latifolia L.

The increasing prescription and use of pharmaceuticals and their subsequent release into the environment has raised concerns about the fate of the parent compounds as well as potential residues in the environment since the last decade. Although pharmaca have become an indispensable part of our daily life in health and disease, their uncontrolled occurrence in the environment let them become a very important issue for human health and the integrity of ecosystems. A crucial fact in this respect is the incomplete removal of many pharmaceuticals in traditional wastewater treatment plants (WWTPs), causing their widespread detectability in WWTP effluents and natural water bodies. It is ever so important to prevent that pharmaceuticals and their transformation products become major threats to aquatic ecosystems or even to drinking water quality. In this study, we have investigated the uptake, translocation and transformation of metformin and iopromide in common cattail (Typha latifolia L.). Both polar pharmaceuticals are widely used human medicines. The plants were grown in modified Hoagland nutrient solution under greenhouse conditions. Hydroponic experiments were established to assess the fate of both compounds in T. latifolia over a period of 28 days. After treatment with metformin (50, 150 and 250 μmol·L-1) and iopromide (20 μmol·L-1), nutrient solution and plant samples were collected after 1, 3, 7, 14 and 28 days. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to detected metformin, iopromide and their transformation products in plant tissues. We demonstrated that metformin can be taken up by T. latifolia roots, and the uptake processes were independent of initial concentrations. Inhibitors of organic cation transporters (e.g. quinidine) can significantly affect uptake of metformin by T. latifolia roots. This indicates that organic cation transporters could be one of the important pathways for metformin uptake into the plant. The bioaccumulation level of metformin in roots was much higher than in leaves and rhizomes. Methylbiguanide has been detected as the only transformation product of metformin in plants with a concentration level of nmol·g-1. Iopromide can be removed by T. latifolia and the removal processes followed first order kinetics with a linear regression R2 value of 0.983. The iopromide concentration in roots and rhizomes was higher than in leaves. A total of 8 transformation products (23 isomers) of iopromide have been detected in T. latifolia, especially four of them (13 isomers) were identified for the first time. Four different kinds of transformation products have been shown in plants and could be classified by the type of reaction: 1) aldehyde and ketone transformation products; 2) carboxylic transformation products; 3) decarboxylated transformation products; 4) deiodinated transformation products. All the transformation products in plants have been investigated with the purpose of prediction of the possible transformation pathway in planta at different time periods. The findings of the present study provide a better understanding of the fate of polar pharmaceuticals in plants and will be useful to improve phytoremediation technologies of such kind of compounds