83
whose receiving water is a tributary of the Seine
estuary (Risle) which fl ows in the mouth of the
Seine estuary. Thus, the aim of the multidisciplinary research program (FLASH) – associating
chemists, hydrologists, and clinical and environmental microbiologists – was to determine to
what extent the hospital effl uent has an ecological impact on the downstream aquatic environment. For this purpose, the fate of Escherichia
coli (antibiotic resistance, gene content integrons;
342 strains) and Enterococci (antibiotic resistance, clonal complex 17, gene content erm B,
mef A; 235 strains) was analyzed in water along a
medical center–WWTP–river–estuary continuum,
during a high epidemiologic period. A multiresidue chemical methodology was developed in
order to detect low levels of 34 antibiotics in
water. To link the occurrence of antibioticresistant bacteria in water and antibiotic prescription, we use the data collection from the hospital
and the antibiotic sales information.
2
Results
2.1
The Fate of Antibiotics:
From the Source
of Contamination
to the Estuary
2.1.1 Antibiotic Contamination
of the Seine Estuary
The concentrations of antibiotics observed in the
Seine estuary well illustrate this quantitative and
qualitative decrease from the sources to the receiving environment (Tabl es 1 and 2 ). Thus, the treated
effl uents from the WTTP and a tributary of the
Seine estuary (Robec) – impacted by effl uents
from a hospital – are the two major sources of
intra-estuary contamination by antibiotics, with
about twenty different molecules and a maximal
concentration of 482 ng.L
−1 observed for clarithromycin (macrolide family) (Table 1 ). Antibiotics
released by WWTP effl uent are rapidly diluted in
the estuary, by at least a factor of 10 depending on
the molecules, as shown in concentrations measured in the dense urban area (Rouen), especially
on the site closest to the WWTP discharge
(Table 2 ). Only nine antibiotics were detected, at
concentrations ranging in ng.L
−1
. With the exception of sulfamethoxazole (sulfonamide family),
this decrease continues for all the antibiotics along
the estuary especially in Caudebec (limit of the
salinity) and then in the mouth of the estuary. The
antibiotics predominantly found are those that are
most stable in the aquatic environment: fl uoroquinolones, sulfonamides, and macrolides.
2.1.2 Relationship Between
Antibiotic Use and Antibiotic
Contamination Along a Medical
Center–WWTP–River
Continuum
However, the multiplicity of intra-estuary supplies
combined with the hydrosedimentary dynamic
does not allow a clear understanding of the fate of
antibiotics in this aquatic environment. A fi ner
scale analysis of the relationship between antibiotic use and the contamination of water by antibiotics has been therefore carried out along a
medical center (hospital of 87 beds and retirement home of 180 beds)–WWTP–river continuum (4 km). The receiving river (Risle) was the
last tributary (Risle) which fl ows in the mouth of
the Seine estuary (Fig. 2 ).
Whereas penicillins (amoxicillin) are the most
prescribed antibiotics in the hospital and in the
town’s pharmacies, the antibiotics mainly found
in the effl uent from the hospital are the molecules
that are most persistent in water: the quinolones/
fl uoroquinolones (ofl oxacin, 68 µg L
−1
; pipemidic acid, 59 µg L
−1 ) and the macrolides, to which
can be added cephalosporins (160 µg L
−1 )
(Tables 3 and 4 ). All the antibiotics prescribed at
the hospital and in the town’s pharmacies are
found in the raw effl uent of the WWTP, but the
concentrations observed are low (in the order
of ng.L
−1
) and decrease further in the receiving
water where only the quinolones, the sulfonamides, and the macrolides are detected at concentrations in the order of ng.L
−1 . These results
highlight that antibiotic contamination of waters
is mainly consecutive to the medical prescriptions (type of molecule and epidemic period), but
also to the stability of antibiotics and/or their
metabolites once released in the water.
Fate of Antibiotics and Antibiotic-Resistant Fecal Bacteria in Water…
whose receiving water is a tributary of the Seine
estuary (Risle) which fl ows in the mouth of the
Seine estuary. Thus, the aim of the multidisciplinary research program (FLASH) – associating
chemists, hydrologists, and clinical and environmental microbiologists – was to determine to
what extent the hospital effl uent has an ecological impact on the downstream aquatic environment. For this purpose, the fate of Escherichia
coli (antibiotic resistance, gene content integrons;
342 strains) and Enterococci (antibiotic resistance, clonal complex 17, gene content erm B,
mef A; 235 strains) was analyzed in water along a
medical center–WWTP–river–estuary continuum,
during a high epidemiologic period. A multiresidue chemical methodology was developed in
order to detect low levels of 34 antibiotics in
water. To link the occurrence of antibioticresistant bacteria in water and antibiotic prescription, we use the data collection from the hospital
and the antibiotic sales information.
2
Results
2.1
The Fate of Antibiotics:
From the Source
of Contamination
to the Estuary
2.1.1 Antibiotic Contamination
of the Seine Estuary
The concentrations of antibiotics observed in the
Seine estuary well illustrate this quantitative and
qualitative decrease from the sources to the receiving environment (Tabl es 1 and 2 ). Thus, the treated
effl uents from the WTTP and a tributary of the
Seine estuary (Robec) – impacted by effl uents
from a hospital – are the two major sources of
intra-estuary contamination by antibiotics, with
about twenty different molecules and a maximal
concentration of 482 ng.L
−1 observed for clarithromycin (macrolide family) (Table 1 ). Antibiotics
released by WWTP effl uent are rapidly diluted in
the estuary, by at least a factor of 10 depending on
the molecules, as shown in concentrations measured in the dense urban area (Rouen), especially
on the site closest to the WWTP discharge
(Table 2 ). Only nine antibiotics were detected, at
concentrations ranging in ng.L
−1
. With the exception of sulfamethoxazole (sulfonamide family),
this decrease continues for all the antibiotics along
the estuary especially in Caudebec (limit of the
salinity) and then in the mouth of the estuary. The
antibiotics predominantly found are those that are
most stable in the aquatic environment: fl uoroquinolones, sulfonamides, and macrolides.
2.1.2 Relationship Between
Antibiotic Use and Antibiotic
Contamination Along a Medical
Center–WWTP–River
Continuum
However, the multiplicity of intra-estuary supplies
combined with the hydrosedimentary dynamic
does not allow a clear understanding of the fate of
antibiotics in this aquatic environment. A fi ner
scale analysis of the relationship between antibiotic use and the contamination of water by antibiotics has been therefore carried out along a
medical center (hospital of 87 beds and retirement home of 180 beds)–WWTP–river continuum (4 km). The receiving river (Risle) was the
last tributary (Risle) which fl ows in the mouth of
the Seine estuary (Fig. 2 ).
Whereas penicillins (amoxicillin) are the most
prescribed antibiotics in the hospital and in the
town’s pharmacies, the antibiotics mainly found
in the effl uent from the hospital are the molecules
that are most persistent in water: the quinolones/
fl uoroquinolones (ofl oxacin, 68 µg L
−1
; pipemidic acid, 59 µg L
−1 ) and the macrolides, to which
can be added cephalosporins (160 µg L
−1 )
(Tables 3 and 4 ). All the antibiotics prescribed at
the hospital and in the town’s pharmacies are
found in the raw effl uent of the WWTP, but the
concentrations observed are low (in the order
of ng.L
−1
) and decrease further in the receiving
water where only the quinolones, the sulfonamides, and the macrolides are detected at concentrations in the order of ng.L
−1 . These results
highlight that antibiotic contamination of waters
is mainly consecutive to the medical prescriptions (type of molecule and epidemic period), but
also to the stability of antibiotics and/or their
metabolites once released in the water.
Fate of Antibiotics and Antibiotic-Resistant Fecal Bacteria in Water…