Emerging contaminants in groundwater - NERC Open Research ...

OR/11/013
Parsons et al. (2008) carried out an assessment of risk from pesticide metabolites for both the
US and the UK. For the UK, 54 pesticides were identified as representing 90% of all pesticide
use. The three highest use pesticides without relevant metabolites data were stated to be
chlormequat, MCPP and tri-allate.
A risk index (RI) was used derived from an exposure index, E and the acceptable daily intake
in mg kg -1 body weight day -1 (ADI):
E = A×F×P
where A = amount index (derived from usage and fraction of metabolite formed), F = fraction
of metabolite in the aqueous phase (derived from Kd) and P = persistence index (derived from
DT50)
and RI = E/ADI
Table A1.2, Appendix 1, shows metabolites assessed as having a risk index of >0.5.
Metabolites with insufficient data were assigned a conservative default. Compounds with the
highest risk index were metabolites of cyanazine, followed by those of isoproturon,
flufenacet, tebuconazole and dicamba.
4.4.2 Simple hazard assessment for pesticide metabolites
A simple hazard assessment was made as part of this study. Significant metabolites were
identified from the Footprint website. Key metabolites for pesticides with usage of
>50,000 ha are listed in Table A1.3, Appendix 1. Some properties are also available for
metabolites but these are much less comprehensive than for the parent compounds. The
leaching probability for those metabolites for which data are available is plotted in Figure 4.8
as a possible first pass approach. Here DT50 for soil has been used as this is the most
commonly available parameter for metabolites. Metabolites assessed as vulnerable to leaching
are shown in red in Figure 4.8 and listed in Table 4.5. This approach takes no account of the
activity or toxicity of these metabolites and some of the metabolites may be trivial.
Log DT 50 soil
4
3
2
1
0
‐1
0 1 2 3 4 5 6
Log K oc
Figure 4.8 Leaching classification for key metabolites (red are leachers)
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