Abstract
Main objective of the present work was to contribute to a detailed understanding of the occurrence and behaviour of iodinated X-ray contrast media (ICM) in waste and drinking water treatment. In particular, the behaviour of five ICM compounds during ozonation for drinking water treatment and the use of activated carbon for the removal of ICM during wastewater treatment was investigated. In addition, the occurrence of the compounds in the raw and drinking waters was studied. The availability of sensitive and accurate analytical methods for the determination of ICM was an indispensable requirement. Therefore, different methods using HPLC-MS instruments including electrospray ionisation were developed. This included a direct detection method using a triple quadrupole mass spectrometer for ICM in water. The limits of detection were below 50 ng.l-1. In addition, it was possible to pre-concentrate the compounds by solid phase extraction. Furthermore, an iodine-specific method in order to screen for unknown oxidation by-products or metabolites of the iodinated compounds was developed. A monitoring programme was carried out in order to study the occurrence of ICM in the ground water of the Danube Reed and the surface water abstracted from the river Danube. Traces of a few ng l-1 of non-ionic ICM were detected in the ground water, whereas the maximum concentration of diatrizoic acid was 45 ng.l-1. In contrast, over 500 ng.l-1 for diatrizoic acid and iopami-dol were found in the Danube. By means of a concentration profile peaks were recorded, whereas the highest concentrations were generally observed on weekdays. Furthermore, it was shown that the elimination rate for the non-ionic ICM was approximately 70% at Langenau waterworks. In particular, intermediate ozonation could remove 33% and granulated activated carbon filtration achieved 50% in average. However, diatrizoic acid was not removed significantly. The maximum concentrations of iomeprol, iopamidol and diatrizoic acid were over 100 ng-1 in the finished drinking water. In addition, it could be demonstrated that 28% to 46% of the ICM compounds were removed during conventional wastewater treatment at sewage treatment plant of Ulm and Neu-Ulm. However, the highest removal rate of 71 % in average was found for iopromide. The average concentrations of ICM in the final effluent ranged between 3.5 μg l-1 for iohexol and 24 μg l-1 for iomeprol. Moreover, the application of powdered activated carbon (PAC) to remove ICM from the effluent proved to be efficient. The removal percentages for iomeprol, iopromide and iohexol were between 77% and 86%, but that for iopamidol was 49% in average for an addition of 10 mg l-1 PAC. In contrast, diatrizoic was only slightly removed by the PAC treatment. Furthermore, the behaviour of ICM during ozonation was investigated in bench-scale studies. Hydroxyl radicals proved to be the major oxidant. It was shown that a complete removal of ICM in pre-treated surface water by ozonation cannot be achieved at moderate ozone concentrations, contact times and realistic pH values. Diatrizoic acid was not eliminated significantly. In general, the compounds should not be mineralised during the ozonation at Langenau waterworks. However, two oxidation by-products of iomeprol could be detected and tentatively identified at Langenau waterworks, which had no significant luminescence inhibition effect towards Vibrio fischeri. In contrast, luminescence inhibition was detected from by-products after UV treatment process of ICM containing wastewater. However, the ICM concentrations in the wastewater were significantly higher than in pre-treated surface water. Therefore, it is reasonable to initiate investigations addressing the toxicological relevance of the by-products.