AFSSE [48], the excess risk of gastroenteritis for the sufficient criteria based on
E. coli in fresh water in Europe is in the range 1.5–2.2% per bath.
The 2006/7/EC directive should soon be reviewed. The WHO [29] made a series
of recommendations to simplify quality criteria and strengthen monitoring. However, it is suggested that FIBs remain the basis for the water quality criteria since data
are still lacking to develop criteria based on pathogens.
7 Present Level of Fecal Bacteria Indicators in the Seine
and Marne Rivers in the Paris Area
Several monitoring networks provide information regarding the amount of FIB in the
Marne and Seine rivers within Greater Paris: drinking water producers, municipalities, and institutions in charge of sanitation. Monitoring was recently intensified to
prepare the bathing objective in 2022 in the Marne River and the organization of the
Olympic Games in Paris in 2024. We selected data provided by the SIAAP, Eau de
Paris, the Paris municipality, and Marne Vive to produce a comprehensive image of
contamination. All data were obtained by the most probable number microplate
methods for E. coli (ISO 9308-3) and intestinal enterococci (ISO 7899-1).
The distribution of E. coli and intestinal enterococci data in the Seine and Marne
rivers shows that 85% of the samples have an EC/IE ratio higher than the ratio
between the EC and IE criteria (900/330). Therefore, E. coli is a more critical
parameter to define the bathing quality of both rivers, and the following sections
will focus on E. coli.
7.1 The Main Factors Explaining the Distribution of E. coli
Long-term data are available at drinking water production intakes in the Seine (Orly
station) and Marne (Joinville station) rivers upstream from Paris. Ten years of data
covering the most recent period, and including about 1,000 data, were selected to
identify the major factors impacting E. coli concentrations. At Orly, a regression
between the log of E. coli concentrations and the log of the river discharge explained
33% of the log E. coli concentration variance (F test p-value <10
À8 ). Adding the
local rain of the previous day improves the explained variance up to 45% ( p-value
<10
À15 ). The addition of rainfall of the second day before sampling did not
significantly improve the regression. Highly similar results were obtained when
summer data only were considered. In the Marne River at Joinville, the effect of
river discharge is not significant, while the rainfall of the previous day explains 26%
and 28% of the variance of log E. coli concentrations ( p-values <10
À5 and 0.003).
The negative influence of rainfall events on water quality was expected since
urban runoff is a known source of fecal contamination; in areas with separate sewers,
Bathing Activities and Microbiological River Water Quality in the Paris. . .
339
E. coli in fresh water in Europe is in the range 1.5–2.2% per bath.
The 2006/7/EC directive should soon be reviewed. The WHO [29] made a series
of recommendations to simplify quality criteria and strengthen monitoring. However, it is suggested that FIBs remain the basis for the water quality criteria since data
are still lacking to develop criteria based on pathogens.
7 Present Level of Fecal Bacteria Indicators in the Seine
and Marne Rivers in the Paris Area
Several monitoring networks provide information regarding the amount of FIB in the
Marne and Seine rivers within Greater Paris: drinking water producers, municipalities, and institutions in charge of sanitation. Monitoring was recently intensified to
prepare the bathing objective in 2022 in the Marne River and the organization of the
Olympic Games in Paris in 2024. We selected data provided by the SIAAP, Eau de
Paris, the Paris municipality, and Marne Vive to produce a comprehensive image of
contamination. All data were obtained by the most probable number microplate
methods for E. coli (ISO 9308-3) and intestinal enterococci (ISO 7899-1).
The distribution of E. coli and intestinal enterococci data in the Seine and Marne
rivers shows that 85% of the samples have an EC/IE ratio higher than the ratio
between the EC and IE criteria (900/330). Therefore, E. coli is a more critical
parameter to define the bathing quality of both rivers, and the following sections
will focus on E. coli.
7.1 The Main Factors Explaining the Distribution of E. coli
Long-term data are available at drinking water production intakes in the Seine (Orly
station) and Marne (Joinville station) rivers upstream from Paris. Ten years of data
covering the most recent period, and including about 1,000 data, were selected to
identify the major factors impacting E. coli concentrations. At Orly, a regression
between the log of E. coli concentrations and the log of the river discharge explained
33% of the log E. coli concentration variance (F test p-value <10
À8 ). Adding the
local rain of the previous day improves the explained variance up to 45% ( p-value
<10
À15 ). The addition of rainfall of the second day before sampling did not
significantly improve the regression. Highly similar results were obtained when
summer data only were considered. In the Marne River at Joinville, the effect of
river discharge is not significant, while the rainfall of the previous day explains 26%
and 28% of the variance of log E. coli concentrations ( p-values <10
À5 and 0.003).
The negative influence of rainfall events on water quality was expected since
urban runoff is a known source of fecal contamination; in areas with separate sewers,
Bathing Activities and Microbiological River Water Quality in the Paris. . .
339