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The Danube: Higher levels of faecal contamination only at a few isolated points in certain countries

(Vienna, 08 August 2019) A microbiological survey (Joint Danube Survey) along a 2,600 km stretch of the Danube and its main tributaries, conducted by a team of scientists made up of experts from MedUni Vienna, MedUni Graz, Vienna University of Technology and Karl Landsteiner University of Health Sciences in Krems, has found that, as in previous years, there are high levels of faecal contamination in Serbia, Romania and Bulgaria. No critical levels were measured in Austria.

Another main finding: "Happily the situation has improved in Hungary downstream of Budapest," says Alexander Kirschner from MedUni Vienna's Institute of Hygiene and Applied Immunology, where the Interuniversity Center for Water and Health (ICC Water & Health, is based.

Determination of faecal origin and antimicrobial-resistant bacteria
The general aim of this largest river survey of the most international river in the world is to record the chemical and biological conditions in the entire Danube and its main tributaries over a length of more than 2,600 river kilometres, from its headwaters in Germany down to its estuary into the Black Sea in Romania. The survey, which is conducted every six years by the ICPDR (International Commission for the Protection of the Danube River) with funding from all countries bordering the Danube, is designed and organised under of the EU Water Framework Directive.

Says Kirschner: "This time the main focus of the microbiological tests was, for the first time, to link the analysis of the extent and origin of faecal contamination along the entire length of the Danube with the occurrence of antimicrobial-resistant, clinically significant bacteria and their resistance genes." For this purpose, a completely new concept was developed to allows quantitative predictions to be made about the dispersion of antimicrobial resistances along the main effluent loads in such a large river. This involved taking water and biofilm samples (from stones and branches) at 30 sampling points along the Danube and in a further eight of its major tributaries and processing and analysing them in six partner laboratories based in Germany, Austria, Hungary, Serbia and Romania. Samples were taken in the middle of the river and along the left and right banks, in collaboration with external fish experts.  

The main results already available for contamination with faecal bacteria (E. coli) – further analyses are ongoing – are as follows: as in the previous surveys, the highest contamination levels in the Danube were found in Serbia, Romania and Bulgaria. "In Serbia, a non-EU country, there are no wastewater treatment plants so that there are critical to extremely high levels of faecal contamination in the Danube downstream of large cities such as Novi Sad and Belgrade," explains project partner Gernot Zarfel from the Diagnostic and Research Institute of Hygiene, Microbiology and Environmental Medicine at MedUni Graz.  

High faecal loads were also found in the tributaries Rusenski Lom (Bulgaria) and Arges (Romania), although there was a significant improvement in the contamination level in the Arges (receiving water for the effluent from the capital of Bucharest) relative to previous years. "This is presumably also due to expansion of the main wastewater treatment plant in this city of over a million inhabitants." The high effluent levels found in the Danube in previous years in Hungary downstream of Budapest was not found this year, which is probably similarly due to expansion of the central wastewater treatment plant in the Hungarian capital, say the experts.

Austrian section of the Danube is quite safe
As far as Austria is concerned, it was assumed that there would be a high level of contamination due to shipping on the Danube but the survey did not back this up: as had already been indicated by a concentrated measurement programme that has been running in Lower Austria since March 2019, faecal contamination levels at the sampling points in the Austrian section of the Danube are – with one exception – in the slight to moderate range. The only value that is slightly above the maximum limit for moderate contamination (1,000 E.coli/100 ml) was found in a sample taken directly downstream of the Abwinden/Asten wastewater treatment plant (1,050 E. coli/100 ml), and, according to Kirschner, "completely within the expected range for a river of this size with state-of-the-art wastewater treatment plants."

Further sampling will be done in 2020. The analyses will be published as scientific publications up until 2022 and, as well as providing basic scientific data, will also give national and regional authorities an important decision-making tool for better management of microbiological water quality in the Danube. In particular, the data that has been gathered also provides important information for the activities defined in the WHO Global Action Plan on Antimicrobial Resistance and the EU Action Plan against Antimicrobial Resistance, which each call for specific surveys into antimicrobial resistance in water bodies.
FWF-financed project

Most of the funding for this survey comes from a project (P32464) recently approved by the Austrian Science Fund (FWF) that is being led by Alexander Kirschner (MedUni Vienna and Karl Landsteiner University), Gernot Zarfel (MedUni Graz) and Andreas Farnleitner (Karl Landsteiner University of Health Sciences and Vienna University of Technology).