Vulnerability and Resilience of Estuaries to Contamination by Antibiotics and Antibiotic-Resistant Bacteria: a Challenge for the Next Decade - Vulnerability of Coastal Ecosystems and Adaptation - page 74

estuary, by a factor of at least 10 depending on the molecules, as shown
in concentrations measured in the urban area around Rouen, especially
on the site closest to the WWTP discharge. With the exception of
sulfamethoxazole (sulfonamide family), this decrease is true 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: fluoroquinolones, sulfonamides and macrolides.
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 finer 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) - the WWTP-river continuum (4 km). The receiving river,
corresponding to the last tributary (Risle), flows in the mouth of the
Seine estuary (the Risle, Figure 2.2).
Contamination in water by antibiotic molecules results directly from
medical prescriptions (type of molecule and epidemic period), and from
the persistence in water of antibiotics and/or their metabolites (Table 2.3).
Even though penicillin and amoxicillin are the most prescribed
antibiotics in hospitals and in the town's pharmacies, the main
antibiotics found in the effluent from the hospitals are the molecules
that are most persistent in water: the quinolones/fluoroquinolones
(ofloxacin: 68 µg L -1 ; pipemidic acid: 59 µg L -1 ) and the macrolides,
to which can be added cephalosporins (160 µg L -1 ) (Table 2.3(a) and
(b)). All the antibiotics prescribed at the hospital and in the town's
pharmacies are found in the raw effluent 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 correlates 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.