Comparative and Veterinary Pharmacology

test compound on the rate of nitrate mineralisation in soil is also determined
to assess the impacts of the compound on soil microbes. For ecto- and endo-
parasiticides, tests may also be required on dung beetles and dung flies. As a result,
a large body of data is now available in the literature, regulatory assessments and in
many material safety datasheets, on the effects of veterinary products in these
standard studies.
An analysis of the publicly available regulatory data indicates that, in general,
algae are more sensitive to veterinary medicines than fish or invertebrates (Fig. 3 ).
When classes of medicine are considered, antibiotics are found to be particularly
potent to algae (e.g. Halling-Sørenson 1999 ) and the parasiticides (pyrethroids,
macrocyclic lactones and organophosphates) are found to be particularly toxic to
invertebrates. When soil data are considered, many antibiotics are found to show
high potency to plants; this is most likely due to the fact that many plants have
similar biochemical pathways to those that the antibiotic affects, in microbes (Brain
et al. 2008 ).
Obviously, just because a veterinary medicine is highly toxic to a soil or aquatic
organism, it does not mean that it will pose an unacceptable risk to the environment.
In order to assess environmental risks, the current regulatory guidelines for veteri-
nary medicines recommend that the ecotoxicity data are used to estimate predicted
no-effect concentrations (PNECs) and that these PNECs are then compared to
exposure concentrations to establish a risk characterisation ratio. The PNEC is
obtained from the ecotoxicity test endpoint using an assessment factor.
In a study to assess the risks of veterinary medicines in the UK environment,
we measured concentrations of a range of frequently used medicines in areas where
the medicines were known to be used (Boxall et al.2006a). By comparing the

algae

invertebrates

fish

Proportion of tests per taxa (%)

<0.1 0.1 – <1.0 1.0 – <10 10 – 100 >100

EC50 or LC50 (mg/L)

60

50

30

40

20

0

10

Fig. 3Distribution of ecotoxicity test results (median effective concentrations or medial lethal
concentrations) for veterinary medicines tested using algae, invertebrates or fish

Veterinary Medicines and the Environment 303