not, which is most likely due to the high potential for tetracyclines to sorb to the
soil. Carlson and Mabury ( 2006 ) reported that chlortetracycline applied to agricul-
tural soil in manure was detected at soil depths of 25 and 35 cm, but monensin
remained in the upper soil layers. There are only a few reports of veterinary
medicines in groundwater (Hirsch et al. 1999 ; Hamscher et al.2000a). In an
extensive monitoring study conducted in Germany (Hirsch et al. 1999 ), while no
antibiotics were detected in groundwater at most of the sites investigated, residues
of sulfonamide antibiotics were detected at a few of the study sites. Contamination
at two of these sites was attributed to irrigation of agricultural land with domestic
sewage but the other sites were believed to have become contaminated due to the
application of animal manures to the soil surface (Hirsch et al. 1999 ).
3.3.2 Runoff
Transport of veterinary medicines via runoff (i.e. overland flow) has been observed
for tetracycline antibiotics (i.e. oxytetracycline) and sulfonamide antibiotics (sulfa-
diazine, sulfamethazine, sulfathiazole and sulfachloropyridazine) (Kay et al.2005c;
Kreuzig et al. 2005 ). Just like leaching, the transport of these substances is influ-
enced by the sorption behaviour of the compounds, the presence of manure in the
soil matrix and the nature of the land to which the manure is applied. Runoff of
highly sorptive substances, such as tetracyclines, was observed to be significantly
lower than the more mobile sulfonamides (Kay et al.2005c). However, even for the
relatively water soluble sulfonamides, total mass losses to surface are small
(between 0.04% and 0.6% of the mass applied) under actual field conditions
(Stoob et al. 2007 ). Manure and slurry has been shown to increase the transport
of sulfonamides via runoff by 10–40 times in comparison to runoff following direct
application of these medicines to soils (Burkhard et al. 2005 ). Possible explanations
for this observation include physical “sealing” of the soil surface by the slurry and/
or a change in pH as a result of manure addition that alters the speciation and fate of
the medicines (Burkhard et al. 2005 ). It has been shown that overland transport
from ploughed soils is significantly lower than runoff from grasslands (Kreuzig
et al. 2005 ).
3.3.3 Drain Flow
The transport of a range of antibacterial substance (i.e. tetracyclines, macrolides,
sulfonamides and trimethoprim) has been investigated using lysimeter and field-
based studies in tile-drained clay soils (Kay et al. 2004 ; Boxall et al.2006a).
Following application of pig slurry spiked with oxytetracycline and sulfachloro-
pyridazine, the test compounds were detected in drainflow water (Kay et al. 2004 ).
Concentrations of the sulfonamide were an order of a magnitude higher than
tetracycline even though the spiking concentrations for the test compounds were
similar; these differences are again likely to be due to differences in sorption
298 A.B.A. Boxall