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Initial project plan

State of the art and preliminary work

The emission of iodinated X-ray contrast media (ICMs) via discharge of treated wastewater is typical for larger urban aquatic systems which have hospitals and diagnostic centers in their collection area. There are much higher concentrations of the ICMs (a group of about six compounds of similar structure with a triodo-benzene ring and hydrophilic side chain groups) than any other pharmaceutical substance, in the concentration range of major industrial chemicals, such as EDTA (Ternes & Hirsch 2000). The ICMs are highly polar and persistent to deiodination in aerobic environments. Although some of them are metabolised by biological sidechain reactions, the core of the iodinated benzene ring is not changed (Oppel et al. 2004, Batt et al. 2006; Perez et al. 2006, Schulz et al. 2008, Kormos et al. 2011). Therefore, the quantity of adsorbable organic iodine (AOI) representing the sum of all ICMs, is not significantly decreased by aerobic treatment (Drewes et al. 2001). Abiotic dehalogenation can be achieved with using zero-valent iron (Stieber et al., 2008). Our field data from bank filtration transects at Lake Tegel and Wannsee and preliminary laboratory experiments demonstrate deiodination in reducing soil/water environments (anoxic, anerobic), such as bank filtration. About 65 % of the organic iodine (AOI) is removed and split off as iodide (Drewes et al. 2001, Grünheid et al. 2005). This mass balance indicates that 2 of the 3 iodine atoms are removed from the benzene ring, similar to the well-known anaerobic dechlorination processes for trichloro-compounds, such as trichloroethylene or trichlorobenzenes (Hölscher et al. 2010, Marco-Urrea et al. 2011). There is no knowledge of which redox conditions are decisive for deiodination (denitrification, iron/manganese reduction, sulphate reduction), which metabolites are formed, and their impact on the underground environment (adsorption and/or biodegradation). Also unknown are the kinetic factors of deiodination as a function of the driving redox parameters; this lack of knowledge is a serious limitation to the effective modelling of different compartments of the urban water system.

Aims and work steps

The aim of this doctoral thesis is to achieve a comprehensive understanding of the reductive metabolism of ICMs as important organic pollutants in urban surface and bank filtered groundwater. We will study the major influential system parameters (including defined redox conditions, temperature, and co-metabolism via natural organic matter) using saturated laboratory soil columns and with batch tests. Well defined conditions will be established first in artificial model waters (only one ICM with higher concentrations) and later in the doctoral thesis in real surface waters which are polluted with several ICMs and AOI. The DOC and iodide balances, including the AOI as sum parameter, will be established and applied. We will develop the quantitative determination of metabolites using a recent LC-MS-MS (DFG funds) and a high resolution LC-MS (Orbitrap, laboratory of Berliner Wasserbetriebe, BWB). The kinetic biotransformation parameters and their dependencies on major factors will be achieved by column experiments, after successful adaptation of biodegradation. The ICM-metabolites which are partially or fully deiodinated will be analysed and characterised for their persistence, polarity (we expect increases of hydrophobicity by side-chain reduction reactions), adsorptive uptake by soil, and also for their aerobic biodegradability in subsequent drinking water treatment.

Connections to interfaces and other doctoral theses

Connections to interfaces occur where polluted urban surface water and bank filtration are treated. There are close cooperations with N1 on biodegradation of pharmaceuticals (providing analytical instruments), with T1 on soil adsorption properties for deiodinated ICMs (we expect an increase in hydrophobicity), and with N3 and N4 on metabolism. PD Dr. Adrian of UFZ Leipzig is closely involved as a co-advisor and a reputed specialist on anaerobic dehalogenation microbiology and co-speaker of a DFG Research Unit 1530: “Anaerobic biological dehalogenation: organisms, biochemistry and (eco-) physiology”. He will analyse the anaerobic populations in the test systems by 16S rRNA gene analysis via 454- or illumina-sequencing.

 

References

Batt,A.L., Kim,S. & Aga,D.S. (2006): Enhanced biodegradation of iopromide and trimethoprim in nitrifying activated sludge. Environ. Sci. Technol., 40, 7367-7373

Drewes,E.J., Fox,P. & Jekel,M. (2001): Occurrence of iodinated X-ray contrast media in domestic effluents and their fate during indirect potable reuse. J. Environ. Sci. Health, A36 (9), 1633-1645

Grünheid,S., Amy,G. & Jekel,M. (2005): Removal of bulk dissolved organic carbon (DOC) and trace organic compounds by bank filtration and artificial recharge. Wat. Res., 39, 3219-3228

Hölscher,T., Lisec,J., Baani,M., Duan,T.H. & Adrian,L. (2010): Bacterial cultures preferentially removing singly flanked chlorine substituents from chlorobenzenes. Environ. Sci. Technol., 44, 8936-8942

Kormos,J.L., Schulz,M. & Ternes,T. (2011): Occurrence of iodinated X-ray contrast media and their biotransformation products in the urban water cycle. Environ. Sci. Technol., 45(20),8723-8732

Marco-Urrea,E., Nijenhuis,I. & Adrian,L. (2011) Transformation and carbon isotope fractionation of tetra- and trichloroethene to trans-dichloroethene by Dehalococcoides sp. strain CBDB1. Environ. Sci. Technol., 45, 1555-1562

Oppel,J., Broll,G., Löffler,D., Römbke,J. & Ternes,T. (2004): Leaching behaviour of pharmaceuticals in soil-testeing systems: A part of an environmental risk assessment for groundwater protection. Sci. Total Environ., 328, 265-273

Perez,S., Eichhorn,P., Celiz,M.D. & Aga,D.S. (2006) Structural characterization of metabolites of the X-ray contrast agent Iopromide in activated sludge using ion trap mass spectrometry. Anal. Chem., 78, 1866-1871

Schittko,S., Putschew,A. & Jekel,M. (2004): Bank Filtration: a suitable process for the removal of iodinated X-ray contrast media? Water Sci. Technol., 50 (5), 261-268

Schulz,M., Löffler,D., Wagner,M. & Ternes,T. (2008): Transformation of the X-ray contrast medium Iopromide in soil and biological wastewater treatment. Environ. Sci. Technol, 42, 7207-7217

Stieber M., Putschew A., Jekel M. (2008): Reductive dehalogenation of Iopromide by zero-valent iron. Water Sci. Technol., 57(12), 1969-1975

Ternes,T. & Hirsch,R. (2000): Occurrence and behaviour of X-ray contrast media in sewage facilities and the aquatic environment. Environ. Sci. Technol 13, 2741-2478

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