behaviour. In a subsequent investigation at the same site (Kay et al. 2004 ), in which
the soil was tilled, much lower concentrations were observed in the drainflow,
which suggested that tillage may be a useful mitigation strategy in the event when a
veterinary product is found to pose a risk to aquatic systems. While the pig slurry
used in these studies was obtained from a pig farm where tylosin was used as a
prophylactic treatment, this substance was not detected in any drainflow samples,
possibly because it is not persistent in slurry (Loke et al. 2000 ).
3.4 Surface Waters
In the water column, substances may be degraded abiotically via photodegradation
and/or hydrolysis or biotically by aerobic or anaerobic organisms. Highly sorptive
substances may partition to the bed sediment. For example, mesocosm studies using
ivermectin show that when added to water, the compound dissipates quickly from
the water column and that this dissipation is observed as an increase in the
concentration of the compound in the bed sediment (e.g. Sanderson et al. 2007 ).
A significant amount of information is available on the fate and behaviour of
many veterinary medicines in sediment due to their use as aquaculture treatments
(Jacobsen and Berglind 1988 ; Samuelsen 1989 ; Bjo ̈rklund et al. 1990 ; Samuelsen
et al. 1991 ,1992a, 1994 ; Pouliquen et al. 1992 ; Coyne et al. 1994 ; Hektoen et al.
1995 ; Lai et al. 1995 ; Lunestad et al. 1995 ). While many compounds degrade very
quickly (e.g. chloramphenicol, florfenicol, furazolidone and ormethoprim), others
persist in the sediment from months to years (e.g. flumequine, ivermectin, oxolinic
acid, oxytetracycline, sarafloxicin, sulfadiazine and trimethoprim).
3.5 Uptake Into Biota
Veterinary medicines may also be taken up from soil and water into biota (Migliore
et al. 2003 ; Kumar et al. 2005 ; Boxall et al.2006b). The potential uptake of
veterinary medicines into plants is receiving increasing attention. Studies with a
range of veterinary medicines (Boxall et al.2006b) showed that a number of
antibiotics are taken up by plants following exposure to soil at environmentally
realistic concentrations of the compounds whereas other compounds were not
observed to be accumulated. The lack of uptake observed may be due to the
underlying properties of the compound or other factors such as high limits of
detection (LODs) or significant degradation during the study. Data also indicate
that while some compounds are accumulated by some plant species, they may not
be taken up by others. It is generally recognised that chemicals are taken up into
plants via the soil pore water and data for pesticides and neutral organic substances
shows that uptake is typically related to the octanol–water partition coefficient
of the compound (Briggs 1981 ; Burken and Schnoor 1998 ). The available data
indicate that these relationships may not hold true for veterinary medicines (Boxall
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