Regulatory FOCUS Surface
Water Models Fail to Predict
Insecticide Concentrations in the Field
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Abstract
The FOrum for the Co-ordination of pesticide fate models
and their
USe (FOCUS) exposure models are used to predict the frequency and
magnitude of pesticide surface water concentrations within the European
regulatory risk assessment. The predictions are based on realistic
worst-case assumptions that result in predicted environmental concentrations
(PEC). Here, we compared for the first time a larger data set of 122
measured field concentrations (MFC) of agricultural insecticides extracted
from 22 field studies to respective PECs by using FOCUS steps 1–4.
While FOCUS step 1 and 2 PECs generally overpredicted the MFCs, 23%
of step 3 and 31% of step 4 standard PECs were exceeded by surface
water MFCs, which questions the protectiveness of the FOCUS exposure
assessment. Using realistic input parameters, step 3 simulations underpredicted
MFCs in surface water and sediment by 43% and 78%, respectively, which
indicate that a higher degree of realism even reduces the protectiveness
of model results. The ratios between PEC and MFC in surface water
were significantly lower for pyrethroids than for organophosphorus
or organochlorine insecticides, which suggests that the FOCUS predictions
are less protective for hydrophobic insecticides. In conclusion, the
FOCUS modeling approach is not protective for insecticide concentrations
in the field