T6 Deiodination of iodinated contrast media (ICMs) in bank filtration of urban waters

Doctoral student: Fatima El-Athman

Supervisors: Dr. Anke Putschew, Prof. Dr. Martin Jekel, Prof. Dr. Lorenz Adrian

Background

The emission of iodinated X-ray contrast media (ICM) via discharge of treated wastewater is typical for larger urban aquatic systems with hospitals and diagnostic centers in their collection area. ICM are tri-iodinated benzoic acid derivatives which are applied as diagnostic pharmaceuticals to enhance the visibility of vessels and organs during computed tomography and conventional radiography scanning. In urban water bodies, they can be found at higher concentrations than any other pharmaceuticals due to their high polarity and their persistentce to deiodination in aerobic environments. At bank filtration sites, a partial deiodination determined by a decreasing concentration of adsorbable organic bound iodine (AOI, part of AOX) has been observed in reducing soil/water environments (anoxic/anaerobic) [1,2].

Aims

The aim of the doctoral thesis is to achieve a comprehensive understanding of the observed deiodination during bank filtration. For that purpose, the redox conditions as well as the abiotic and biotic factors of the deiodination process are investigated. Furthermore, the deiodination degrees of different contrast media are examined and compared to previous field data. Partially and completely deiodinated transformation products of different ICM and iodinated model compounds are identified and characterized for their persistence and polarity.

Methods

The experiments are conducted as batch tests under strictly anaerobic conditions and with defined reactants: pure water including a highly concentrated ICM, a strong reducing agent and different organic substances with redox-mediating properties. Apart from these abiotic tests, microbiological tests with an isolated strain of the bacteria genus Dehalococcoides mccartyi and with dehalogenase enzymes are performed.  

The deiodination is quantified by measuring the AOI and the iodide concentration as well as the concentration of the iodinated substance used. Photometrically measured activity tests are conducted to evaluate deiodination kinetics. Furthermore, ICM transformation products formed under different test conditions will be identified.

In subsequent experiments, the test parameters will be adjusted closer to natural conditions. In this context, saturated laboratory soil columns serving as dynamic models for the simulation of the water flow and transformation processes during bank filtration will be used.

Collaborations

• UWI projects: N1 on the biodegradation of pharmaceuticals, N6 on the AOI decrease in the hyporheic zone
• Common Topics: Interfaces in urban surface waters, Surface water – groundwater interactions, Micropollutant, Biogeochemical processes
• Collaboration: Anaerobic biological dehalogenation
  Helmholtz Centre for Environmental Research – UFZ: PD Dr. Lorenz Adrian, Group of Functional Genomics and Biochemistry
• Research internship: Identification of transformation products
  The German Federal Institute of Hydrology (BfG): Prof. Dr. Thomas Ternes, department of Aquatic Chemistry research internship (identification of transformation products)

References

[1] Jekel, M. et al. (2005). Water Science and Technology: Water Supply 5(5): 57–66

[2] Schittko, S. et al. (2004). Water Science and Technology 50(5): 261–268

Initial project plan