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less than 5 ng/L). Furthermore, the physicochemical properties (lipophilicity) of
such hormones are expected to allow removal via sorption processes in sewage
treatment facilities or adsorption to subsurface soil. However, even the low con-
centrations found in different water bodies (e.g., sewage, surface water, and
groundwater) (Daughton and Ternes 1999 ; Heberer et al. 2002 ) may pose a threat
for ecosystems. For example, exposure of wild male fish to only 0.1 ng/L of
xenoestrogens may provoke feminization in some species.
4.4.3 Antibacterial Drugs
Antibacterial drugs (i.e., antibiotic and bacteriostatic drugs) have received con-
siderable attention because of their heavy use and their potential hazardous effect
on ecosystems. Antibiotics used to treat infections are an invaluable tool, and their
introduction has revolutionized the treatment of infectious diseases. Because of
their widespread use, it is not surprising that antibiotics have been found in liquid
waste at animal feedlots and spread into many surface water and groundwater
supplies. In general, large portions of antibiotics used by humans, as well as for
beef and poultry production, are excreted unchanged in feces and urine. With
increasingly wide use of antibiotics, resistant strains of bacteria are replacing
antibiotic-susceptible bacteria. Furthermore, resistant bacteria in one environment
may not be confined to that specific environment and can be carried over distances
of thousands of kilometers by wind, water, animals, food, or people. And, most
important, antibiotic-resistant organisms that develop in animals, fruits, or vege-
tables can be passed to humans through the food chain and environment. All these
factors have had the effect of changing the balance between antibiotic-susceptible
and antibiotic-resistant bacteria in ecosystems, both locally and globally.
Macrolide antibiotics (clarithromycin, dehydroerythromycin (a metabolite of
erythromycin), roxithromycin, lincomycin, sulfonamides (sulfamethoxazole, sul-
fadimethoxine, sulfamethazine, sulfathiazole), fluoroquinolones (ciprofloxacin,
norfloxacin, enrofloxacin), chloramphenicol, tylosin, and trimethoprim) have been
found up to low lg/L levels in sewage and surface water samples. Sacher et al.
( 2001 ) reported the occurrence of sulfamethoxazole (up to 410 ng/L) and dehy-
droerythromycin (up to 49 ng/L) in groundwater samples in Baden-Wurttemberg,
Germany. Sulfamethoxazole and sulfamethazine have also been detected at low
concentrations in several groundwater samples in the USA and Germany (e.g.
Hartig et al. 1999 ). Holm et al. ( 1995 ) found residues of different sulfonamides at
high concentrations in groundwater samples collected down gradient of a landfill
in Grindsted, Denmark.
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