Environ. Sci. Technol. 2002, 36, 2387-2394
Anthropogenic Gd in Surface Water, Drainage System, and the Water Supply of the City of Prague, Czech Republic P. MO ¨ L L E R , * ,† T . P A C E S , ‡ P. DULSKI,† AND G. MORTEANI§ Geoforschungszentrum, Projektbereich 4.3, Telegrafenberg, 14473 Potsdam, Germany, Czech Geological Survey, Kla´rov 3, P.O. Box 85, 11821 Praha 1, Czech Republic, and Universita` degli Studi di Trento, Facolta` di Ingegneria, 38050 Trento, Italy
The anthropogenic Gd (Gdant) loads and fluxes of surfaceand groundwaters, and of effluents from sewage treatment plants of Prague and its surroundings, have been determined. While passing Prague the Gdant load of the Vltava river increases from 4.5 to 19.2 nmol/m3, which is caused by the effluents of the central sewage treatment plant with a 6 day average of 250 nmol/m3. The Berounka river with its enhanced content doubles the Gdant flux of the Vltava river before entering Prague. All minor creeks draining Prague add less than 3% of the Gdant load in the Vltava river downstream of Prague. The 11days average of the amount of the administered Gd complexes of the gadopentetic acid (Gd-DTPA), gadobenic acid, and other compounds in Prague’s hospitals (22 g-Gdant/d) exceeds the 6 days average of 15 g-Gdant/d in the effluent of the central sewage treatment plant. This strongly indicates uncontrolled losses of sewage from sewers to the groundwater.
Introduction Since 1988 (1, 2), Gd compounds with organic ligands are used as blood pool contrast agents in magnetic resonance imaging (MRI) in hospitals, private medical clinics, and medical/radiological practices. The commercial Gd compounds are Magnevist (Schering, Germany), Omniscan (Nycomed Pharma, Denmark), Dotarem (Laboratoire Guerbet, France), and MultiHance and ProHance (Byk Gulden, Germany). Theses products represent derivatives of very stable multidentate complexes of the type of the gadopentetic (Gd-DTPA) and gadobenic acids. For instance, the stability of the Gd-DTPA complex, characterized by its formation constant β (logβGd-DTPA ) 23), exceeds that of the well-known Gd-EDTA complex (logβGd-EDTA ) 18) (3). The various Gd compounds are orally or intravenously administered for abdominal, cranial, and spinal MRI checks in doses of about 0.1 mmol Gd-compound per kg body weight, which corresponds roughly to about 1 g of Gd per person (65 kg) and per check. Clinical studies proved that the Gd complex is excreted nonmetabolized by the patients within a few * Corresponding author phone: +49-3312881430; fax: +493312881436; e-mail:
[email protected]. † Geoforschungszentrum. ‡ Czech Geological Survey. § Universita ` degli Studi di Trento. 10.1021/es010235q CCC: $22.00 Published on Web 05/04/2002
2002 American Chemical Society
hours. Most of it enters the hospital sewage and thereafter the public sewage treatment plants. It is supposed a priori that this complex survives for an unknown but long time in the hydrosphere. The effluents of sewage treatment plants of big cities with modern hospitals show low Rare Earth Element (REE) contents with extremely high Gd abundance (4-6). Such anomalous Gd contents are absent in sewage sludges. This is caused by their high contents of clay minerals being important carriers of REE (7). The sewage sludges are higher in REE abundance by a factor of about 105 than the effluents of the sewage plants. Even with an Gd enhancement of a factor of 103 in the sewage, the organically bound, anthropogenic Gd fraction, Gdant, of total Gd, Gdtot, remains undetected in the sewage sludge. In contrast to Gdant, the low geogenic Gd abundance in natural waters, Gdgeo, is leached from soils, sediments, and rocks. The MRI checks are predominantly performed in hospitals from Monday to Friday. The residence time of the sewage in the sewer system and the sewage treatment plants amounts to about 2 days. The Gd-bearing effluents from the sewage plants are, therefore, discharged to nearby rivers with a delay of about 2 days with respect to the day of application of the Gd-bearing compounds to patients. Consequently, the discharge of Gdant into the surface waters is high from Wednesday to Sunday and low on Monday and Tuesday (6). Any sampling scheme and evaluation of the analytical results has to consider this time-dependence of the Gdant abundance in the effluents of sewage-works and consequently in the river water. Very high positive Gd abundance has been found in the surface waters of Berlin (Germany) indicating an anthropogenic enrichment of Gd by factors of nearly 103 compared to the geogenic background (4, 6, 7). Gdant increases systematically downstream the rivers Havel and Spree, when passing Berlin (6). The highest anomalous Gd abundance develops in the Havel river because of (i) the high Gdant load of the effluents from the sewage treatment plants, (ii) the low flow velocity (
